WorldWideScience

Sample records for crater flat pleistocene

  1. SMALL-VOLUME BASALTIC VOLCANOES: ERUPTIVE PRODUCTS AND PROCESSES, AND POST-ERUPTIVE GEOMORPHIC EVOLUTION IN CRATER FLAT (PLEISTOCENE), SOUTHERN NEVADA

    Energy Technology Data Exchange (ETDEWEB)

    G.A. Valentine; F.V. Perry; D. Krier; G.N. Keating; R.E. Kelley; A.H. Cogbill

    2006-04-04

    Five Pleistocene basaltic volcanoes in Crater Flat (southern Nevada) demonstrate the complexity of eruption processes associated with small-volume basalts and the effects of initial emplacement characteristics on post-eruptive geomorphic evolution of the volcanic surfaces. The volcanoes record eruptive processes in their pyroclastic facies ranging from ''classical'' Strombolian mechanisms to, potentially, violent Strombolian mechanisms. Cone growth was accompanied, and sometimes disrupted, by effusion of lavas from the bases of cones. Pyroclastic cones were built upon a gently southward-sloping surface and were prone to failure of their down-slope (southern) flanks. Early lavas flowed primarily southward and, at Red and Black Cone volcanoes, carried abundant rafts of cone material on the tops of the flows. These resulting early lava fields eventually built platforms such that later flows erupted from the eastern (at Red Cone) and northern (at Black Cone) bases of the cones. Three major surface features--scoria cones, lava fields with abundant rafts of pyroclastic material, and lava fields with little or no pyroclastic material--experienced different post-eruptive surficial processes. Contrary to previous interpretations, we argue that the Pleistocene Crater Flat volcanoes are monogenetic, each having formed in a single eruptive episode lasting months to a few years, and with all eruptive products having emanated from the area of the volcanoes main cones rather than from scattered vents. Geochemical variations within the volcanoes must be interpreted within a monogenetic framework, which implies preservation of magma source heterogeneities through ascent and eruption of the magmas.

  2. Late Pleistocene eruptive history of the Mono Craters rhyolites, eastern California, from U-Th dating of explosive and effusive products

    Science.gov (United States)

    Marcaida, M.; Vazquez, J. A.; Calvert, A. T.; Miller, J. S.

    2016-12-01

    During late Pleistocene-Holocene time, repeated explosive and effusive eruptions of high-silica rhyolite magma south of Mono Lake, California, have produced a chain of massive domes known as the Mono Craters and a time-series of tephra deposits preserved in sediments of the Wilson Creek formation of ancestral Mono Lake. The record of late Holocene volcanism at Mono Craters is relatively well constrained by tephrostratigraphy and 14C dating, and the timing of late Pleistocene eruptions is similarly well constrained by tephrochronology and magnetostratigraphy of the Wilson Creek formation. However, the chronology of eruptions for the Mono Craters chain, comprising at least 28 individual domes, has thus far been based on age estimates from hydration rind dating of obsidian that is highly dependent on local calibration. We constrain the timing of late Pleistocene dome emplacement by linking independently dated Wilson Creek tephras to their dome equivalents in the Mono Craters using combined titanomagnetite geochemistry and U-Th geochronology. Ion microprobe 238U-230Th dating of unpolished allanite and zircon rims gives isochron dates of ca. 42 ka, ca. 38 ka, ca. 26 ka, and ca. 20 ka for domes 19, 24, 31 (newly recognized), and 11 of the Mono Craters, respectively. These domes are biotite-bearing rhyolites with titanomagnetites that are compositionally identical to those from several Wilson Creek tephras. Specifically, we correlate Ash 15, Ash 7, and Ash 3 of the Wilson Creek formation to domes 19, 31, and 11 of the Mono Craters, respectively, based on matching titanomagnetite compositions and indistinguishable U-Th ages. 40Ar/39Ar dating of single sanidines from domes 19 and 31 yield mean dates that are 10 k.y. older than their corresponding U-Th dates, likely due to excess argon from melt inclusions and/or incompletely re-equilibrated antecrysts. Based on our new U-Th isochron date of ca. 34 ka for allanite-zircon from Ash 8 pumice and the ca. 26-27 ka age of Ash 7

  3. Lithostratigraphy of the Calico Hills Formation and Prow Pass Tuff (Crater Flat Group) at Yucca Mountain, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Moyer, T.C.; Geslin, J.K. [Science Applications International Corp., Las Vegas, NV (United States)

    1995-07-01

    Lithostratigraphic relations within the Calico Hills Formation and Prow Pass Tuff (Crater Flat Group) were reconstructed from analysis of core samples and observation of outcrop exposures. The Calico Hills Formation is composed of five nonwelded pyroclastic units (each formed of one or more pyroclastic-flow deposits) that overlie an interval of bedded tuff and a basal volcaniclastic sandstone unit. The Prow Pass Tuff is divided into four pyroclastic units and an underlying interval of bedded tuff. The pyroclastic units of the Prow Pass Tuff are distinguished by the sizes and amounts of their pumice and lithic clasts and their degree of welding. Pyroclastic units of the Prow Pass Tuff are distinguished from those of the Calico Hills Formation by their phenocryst assemblage, chemical composition, and ubiquitous siltstone lithic clasts. Downhole resistivity tends to mirror the content of authigenic minerals, primarily zeolites, in both for-mations and may be useful for recognizing the vitric-zeolite boundary in the study area. Maps of zeolite distribution illustrate that the bedded tuff and basal sandstone units of the Calico Hills Formation are altered over a wider area than the pyroclastic units of both the Calico Hills Formation and the upper Prow Pass Tuff.

  4. Barringer Meteor Crater, Arizona

    Science.gov (United States)

    2001-01-01

    Barringer Crater, also known as 'Meteor Crater,' is a 1,300-meter (0.8 mile) diameter, 174-meter (570-feet) deep hole in the flat-lying desert sandstones 30 kilometers (18.6 miles) west of Winslow, Arizona. Since the 1890s geologic studies here played a leading role in developing an understanding of impact processes on the Earth, the moon and elsewhere in the solar system.This view was acquired by the Landsat 4 satellite on December 14, 1982. It shows the crater much as a lunar crater might appear through a telescope. Morning sun illumination is from the southeast (lower right). The prominent gully meandering across the scene is known as Canyon Diablo. It drains northward toward the Little Colorado River and eventually to the Grand Canyon. The Interstate 40 highway crosses and nearly parallels the northern edge of the scene.The ejecta blanket around the crater appears somewhat lighter than the surrounding terrain, perhaps in part due to its altered mineralogic content. However, foot traffic at this interesting site may have scarred and lightened the terrain too. Also, the roughened surface here catches the sunlight on the southerly slopes and protects a highly reflective patchy snow cover in shaded northerly slopes, further lightening the terrain as viewed from space on this date.

  5. Scaling multiblast craters: General approach and application to volcanic craters

    Science.gov (United States)

    Sonder, I.; Graettinger, A. H.; Valentine, G. A.

    2015-09-01

    Most volcanic explosions leave a crater in the surface around the center of the explosions. Such craters differ from products of single events like meteorite impacts or those produced by military testing because they typically result from multiple, rather than single, explosions. Here we analyze the evolution of experimental craters that were created by several detonations of chemical explosives in layered aggregates. An empirical relationship for the scaled crater radius as a function of scaled explosion depth for single blasts in flat test beds is derived from experimental data, which differs from existing relations and has better applicability for deep blasts. A method to calculate an effective explosion depth for nonflat topography (e.g., for explosions below existing craters) is derived, showing how multiblast crater sizes differ from the single-blast case: Sizes of natural caters (radii and volumes) are not characteristic of the number of explosions, nor therefore of the total acting energy, that formed a crater. Also, the crater size is not simply related to the largest explosion in a sequence but depends upon that explosion and the energy of that single blast and on the cumulative energy of all blasts that formed a crater. The two energies can be combined to form an effective number of explosions that is characteristic for the crater evolution. The multiblast crater size evolution has implications on the estimates of volcanic eruption energies, indicating that it is not correct to estimate explosion energy from crater size using previously published relationships that were derived for single-blast cases.

  6. STRAWBERRY CRATER ROADLESS AREAS, ARIZONA.

    Science.gov (United States)

    Wolfe, Edward W.; Light, Thomas D.

    1984-01-01

    The results of a mineral survey conducted in the Strawberry Crater Roadless Areas, Arizona, indicate little promise for the occurrence of metallic mineral or fossil fuel resources in the area. The area contains deposits of cinder, useful for the production of aggregate block, and for deposits of decorative stone; however, similar deposits occur in great abundance throughout the San Francisco volcanic field outside the roadless areas. There is a possibility that the Strawberry Crater Roadless Areas may overlie part of a crustal magma chamber or still warm pluton related to the San Francisco Mountain stratovolcano or to basaltic vents of late Pleistocene or Holocene age. Such a magma chamber or pluton beneath the Strawberry Crater Roadless Areas might be an energy source from which a hot-, dry-rock geothermal energy system could be developed, and a probable geothermal resource potential is therefore assigned to these areas. 9 refs.

  7. Statistical test of reproducibility and operator variance in thin-section modal analysis of textures and phenocrysts in the Topopah Spring member, drill hole USW VH-2, Crater Flat, Nye County, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Moore, L.M.; Byers, F.M. Jr.; Broxton, D.E.

    1989-06-01

    A thin-section operator-variance test was given to the 2 junior authors, petrographers, by the senior author, a statistician, using 16 thin sections cut from core plugs drilled by the US Geological Survey from drill hole USW VH-2 standard (HCQ) drill core. The thin sections are samples of Topopah Spring devitrified rhyolite tuff from four textural zones, in ascending order: (1) lower nonlithophysal, (2) lower lithopysal, (3) middle nonlithophysal, and (4) upper lithophysal. Drill hole USW-VH-2 is near the center of the Crater Flat, about 6 miles WSW of the Yucca Mountain in Exploration Block. The original thin-section labels were opaqued out with removable enamel and renumbered with alpha-numeric labels. The sliders were then given to the petrographer operators for quantitative thin-section modal (point-count) analysis of cryptocrystalline, spherulitic, granophyric, and void textures, as well as phenocryst minerals. Between operator variance was tested by giving the two petrographers the same slide, and within-operator variance was tested by the same operator the same slide to count in a second test set, administered at least three months after the first set. Both operators were unaware that they were receiving the same slide to recount. 14 figs., 6 tabs.

  8. Crater Landslide

    Science.gov (United States)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA06088 Crater Landslide This landslide occurs in an unnamed crater southeast of Millochau Crater. Image information: VIS instrument. Latitude -24.4N, Longitude 87.5E. 17 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  9. Crater Landslide

    Science.gov (United States)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA06088 Crater Landslide This landslide occurs in an unnamed crater southeast of Millochau Crater. Image information: VIS instrument. Latitude -24.4N, Longitude 87.5E. 17 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  10. Crater Copernicus

    Science.gov (United States)

    1999-01-01

    HUBBLE SHOOTS THE MOON in a change of venue from peering at the distant universe, NASA's Hubble Space Telescope has taken a look at Earth's closest neighbor in space, the Moon. Hubble was aimed at one of the Moon's most dramatic and photogenic targets, the 58 mile-wide (93 km) impact crater Copernicus. The image was taken while the Space Telescope Imaging Spectrograph(STIS) was aimed at a different part of the moon to measure the colors of sunlight reflected off the Moon. Hubble cannot look at the Sun directly and so must use reflected light to make measurements of the Sun's spectrum. Once calibrated by measuring the Sun's spectrum, the STIS can be used to study how the planets both absorb and reflect sunlight.(upper left)The Moon is so close to Earth that Hubble would need to take a mosaic of 130 pictures to cover the entire disk. This ground-based picture from Lick Observatory shows the area covered in Hubble's photomosaic with the WideField Planetary Camera 2..(center)Hubble's crisp bird's-eye view clearly shows the ray pattern of bright dust ejected out of the crater over one billion years ago, when an asteroid larger than a mile across slammed into the Moon. Hubble can resolve features as small as 600 feet across in the terraced walls of the crater, and the hummock-like blanket of material blasted out by the meteor impact.(lower right)A close-up view of Copernicus' terraced walls. Hubble can resolve features as small as 280 feet across.

  11. Cutting Craters

    Science.gov (United States)

    2003-01-01

    [figure removed for brevity, see original site] Released 12 November 2003The rims of two old and degraded impact craters are intersected by a graben in this THEMIS image taken near Mangala Fossa. Yardangs and low-albedo wind streaks are observed at the top of the image as well as interesting small grooves on the crater floor. The origin of these enigmatic grooves may be the result of mud or lava and volatile interactions. Variable surface textures observed in the bottom crater floor are the result of different aged lava flows.Image information: VIS instrument. Latitude -15.2, Longitude 219.2 East (140.8 West). 19 meter/pixel resolution.Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  12. Secondary Crater Populations on the Martian South Polar Layered Deposits

    Science.gov (United States)

    Schaller, E. L.; Murray, B.; Rasmussen, J.; Byrne, S.

    2003-12-01

    Understanding the formation and evolution of the Mars South Polar Layered Deposits (SPLD) is an important step toward unraveling Martian climate history. The cratering record on the SPLD suggests that the surface of these deposits has been recently modified. Extremely shallow large (>800 m) impact craters along with a lack of small (material from a primary impact event, are important stratigraphic markers that can shed light on the modification history of the deposits. Using MOC, THEMIS and MOLA data, we examined the broad secondary crater field surrounding McMurdo crater (84.5S, 0W) on the SPLD, the field surrounding a 15 km crater at 80.5S, 284W on the SPLD, and the field surrounding a 43 km crater at 81S, 285W off of the SPLD. These datasets provided us with the opportunity to compare and contrast the morphologies of craters in different secondary crater fields both on and off of the deposits. We measured the depth to diameter (d/D) ratios of secondary craters and compared them with those of other primary craters on the deposits measured by Koutnik et al (2002). Among secondary craters on the SPLD, we found a correlation between crater d/D and the steepness of the slope on which the crater resides. Specifically, craters with extremely low d/D ratios (indicating high modification) are found more often on flat areas. Those with high d/D ratios are often associated with scarps and are on higher slopes. This indicates that there have been different resurfacing rates over areas as small as several hundred square kilometers and that modification occurs more readily on flat areas. We examine different mechanisms that may have led to decreased d/D ratios such as blanketing, ice flow, wind erosion or viscous relaxation. We find that the d/D ratios of secondary craters on flat regions of the SPLD are comparable with the extremely low d/D ratios of the primary craters elsewhere on the deposits measured by Koutnik et al (2002). The d/D ratios of secondary craters on the

  13. Impact cratering experiments in brittle targets with variable thickness: Implications for deep pit craters on Mars

    Science.gov (United States)

    Michikami, T.; Hagermann, A.; Miyamoto, H.; Miura, S.; Haruyama, J.; Lykawka, P. S.

    2014-06-01

    High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1-6 cm, and a bulk density of 1550 kg/m3 by using a mixture of cement, water and sand (0.2 mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2±0.9 MPa. A spherical nylon projectile (diameter 7 mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2 km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead. Craters are formed on the opposite impact side even when no penetration

  14. Formation of complex impact craters - Evidence from Mars and other planets

    Science.gov (United States)

    Pike, R. J.

    1980-01-01

    An analysis of the depth vs diameter data of Arthur (1980), is given along with geomorphic data for 73 Martian craters. The implications for the formation of complex impact craters on solid planets is discussed. The analysis integrates detailed morphological observations on planetary craters with geologic data from terrestrial meteorite and explosion craters. The simple to complex transition for impact craters on Mars appears at diameters in the range of 3 to 8 km. Five features appear sequentially with increasing crater size, flat floors, central peaks and shallower depths, scalloped rims, and terraced walls. This order suggests that a shallow depth of excavation and a rebound mechanism have produced the central peaks, not centripetal collapse and deep sliding. Simple craters are relatively uniform in shape from planet to planet, but complex craters vary considerably. Both the average onset diameter for complex impact craters on Mars and the average depth of complex craters vary inversely with gravitational acceleration on four planets.

  15. Flat semimodules

    Directory of Open Access Journals (Sweden)

    Huda Mohammed J. Al-Thani

    2004-04-01

    Full Text Available We introduce and investigate flat semimodules and k-flat semimodules .We hope these concepts will have the same importance in semimodule theory as in the theory of rings and modules.

  16. Martian Meteor Crater

    Science.gov (United States)

    2004-01-01

    20 February 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a fairly young meteor impact crater on Mars that is about the same size ( 1 kilometer; 0.62 miles) as the famous Meteor Crater in northern Arizona, U.S.A. Like the Arizona crater, boulders of ejected bedrock can be seen on the crater's ejecta blanket and in the crater itself. This crater is located in the Aethiopis region of Mars near 4.7oN, 224.1oW. Sunlight illuminates the scene from the lower left.

  17. Impact craters on Titan

    Science.gov (United States)

    Wood, Charles A.; Lorenz, Ralph; Kirk, Randy; Lopes, Rosaly; Mitchell, Karl; Stofan, Ellen; ,

    2010-01-01

    Five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22% of Titan's surface imaged by Cassini's high-resolution radar through December 2007. The certain craters have morphologies similar to impact craters on rocky planets, as well as two with radar bright, jagged rims. The less certain craters often appear to be eroded versions of the certain ones. Titan's craters are modified by a variety of processes including fluvial erosion, mass wasting, burial by dunes and submergence in seas, but there is no compelling evidence of isostatic adjustments as on other icy moons, nor draping by thick atmospheric deposits. The paucity of craters implies that Titan's surface is quite young, but the modeled age depends on which published crater production rate is assumed. Using the model of Artemieva and Lunine (2005) suggests that craters with diameters smaller than about 35 km are younger than 200 million years old, and larger craters are older. Craters are not distributed uniformly; Xanadu has a crater density 2-9 times greater than the rest of Titan, and the density on equatorial dune areas is much lower than average. There is a small excess of craters on the leading hemisphere, and craters are deficient in the north polar region compared to the rest of the world. The youthful age of Titan overall, and the various erosional states of its likely impact craters, demonstrate that dynamic processes have destroyed most of the early history of the moon, and that multiple processes continue to strongly modify its surface. The existence of 24 possible impact craters with diameters less than 20 km appears consistent with the Ivanov, Basilevsky and Neukum (1997) model of the effectiveness of Titan's atmosphere in destroying most but not all small projectiles.

  18. Impact Crater Collapse

    Science.gov (United States)

    Melosh, H. J.; Ivanov, B. A.

    The detailed morphology of impact craters is now believed to be mainly caused by the collapse of a geometrically simple, bowl-shaped "transient crater." The transient crater forms immediately after the impact. In small craters, those less than approximately 15 km diameter on the Moon, the steepest part of the rim collapses into the crater bowl to produce a lens of broken rock in an otherwise unmodified transient crater. Such craters are called "simple" and have a depth-to-diameter ratio near 1:5. Large craters collapse more spectacularly, giving rise to central peaks, wall terraces, and internal rings in still larger craters. These are called "complex" craters. The transition between simple and complex craters depends on 1/g, suggesting that the collapse occurs when a strength threshold is exceeded. The apparent strength, however, is very low: only a few bars, and with little or no internal friction. This behavior requires a mechanism for temporary strength degradation in the rocks surrounding the impact site. Several models for this process, including acoustic fluidization and shock weakening, have been considered by recent investigations. Acoustic fluidization, in particular, appears to produce results in good agreement with observations, although better understanding is still needed.

  19. Large Crater Clustering tool

    Science.gov (United States)

    Laura, Jason; Skinner, James A.; Hunter, Marc A.

    2017-08-01

    In this paper we present the Large Crater Clustering (LCC) tool set, an ArcGIS plugin that supports the quantitative approximation of a primary impact location from user-identified locations of possible secondary impact craters or the long-axes of clustered secondary craters. The identification of primary impact craters directly supports planetary geologic mapping and topical science studies where the chronostratigraphic age of some geologic units may be known, but more distant features have questionable geologic ages. Previous works (e.g., McEwen et al., 2005; Dundas and McEwen, 2007) have shown that the source of secondary impact craters can be estimated from secondary impact craters. This work adapts those methods into a statistically robust tool set. We describe the four individual tools within the LCC tool set to support: (1) processing individually digitized point observations (craters), (2) estimating the directional distribution of a clustered set of craters, back projecting the potential flight paths (crater clusters or linearly approximated catenae or lineaments), (3) intersecting projected paths, and (4) intersecting back-projected trajectories to approximate the local of potential source primary craters. We present two case studies using secondary impact features mapped in two regions of Mars. We demonstrate that the tool is able to quantitatively identify primary impacts and supports the improved qualitative interpretation of potential secondary crater flight trajectories.

  20. Impact cratering: A geologic process

    Science.gov (United States)

    Melosh, H. J.

    The mechanisms involved in the formation of impact craters are examined theoretically, reviewing the results of recent investigations. Topics addressed include crater morphology, stress waves in solids, the contact and compression stage, the excavation stage, and ejecta deposits. Consideration is given to the scaling of crater dimensions, the crater modification stage, multiring basins, cratered landscapes, atmospheric interactions, and the implications of impact cratering for planetary evolution. Extensive diagrams, graphs, tables, and images of typical craters are provided.

  1. Impact cratering on slopes

    Science.gov (United States)

    Aschauer, Johannes; Kenkmann, Thomas

    2017-07-01

    The majority of impact craters have circular outlines and axially symmetric morphologies. Deviation from crater circularity is caused by either target heterogeneity, a very oblique impact incidence, post-impact deformation, or by topography. Here, we investigate the effect of topography on crater formation and systematically study impact cratering processes on inclined hillsides up to 25° slope utilizing analogue experiments. A spring-driven air gun mounted in a vertical position shoots into three different types of granular bulk solids (two sorts of glass beads, quartz sand) to emulate impact cratering on slopes. In all, 170 experiments were conducted. The transient crater develops roughly symmetrically perpendicular to the slope plane, resulting in higher ejection angles uphill than downhill when measured with respect to a horizontal plane. Craters become increasingly elliptical with increasing slope angle. At slope angles close to angle of repose of the respective bulk solids, aspect ratios of the craters reach ∼1.7. Uphill-downhill cross sections become increasingly asymmetric, the depth-diameter ratio of the craters decreases, and the deepest point shifts downhill with increasing slope angle. Mass wasting is initiated both in the uphill and downhill sectors of the crater rim. For steep slopes the landslides that emanate from the uphill rim can overshoot the crater cavity and superpose the downhill crater rim in a narrow tongue. Mass wasting initiated at the downhill sector forms broader and shallower tongues and is triggered by the deposition of ejecta on the inclined slope. Our experiments help to explain asymmetric crater morphologies observed on asteroids such as Ceres, Vesta, Lutetia, and also on Mars.

  2. Pleistocene Paleoart of Australia

    Directory of Open Access Journals (Sweden)

    Robert G. Bednarik

    2014-02-01

    Full Text Available Pleistocene rock art is abundant in Australia, but has so far received only limited attention. Instead there has been a trend, begun over a century ago, to search for presumed depictions of extinct megafauna and the tracks of such species. All these notions have been discredited, however, and the current evidence suggests that figurative depiction was introduced only during the Holocene, never reaching Tasmania. Nevertheless, some Australian rock art has been attributed to the Pleistocene by direct dating methods, and its nature implies that a significant portion of the surviving corpus of rock art may also be of such age. In particular much of Australian cave art is of the Ice Age, or appears to be so, and any heavily weathered or patinated petroglyphs on particularly hard rocks are good candidates for Pleistocene antiquity. On the other hand, there is very limited evidence of mobiliary paleoart of such age in Australia.

  3. Small simple impact craters

    CERN Document Server

    Sparavigna, Amelia Carolina

    2010-01-01

    The paper discusses some examples of image processing applied to improve optical satellite imagery of small craters (Kamil, Veevers, Haviland). The examples show that image processing can be quite useful for further in-situ researches, because the resultant imagery helps to have a better picture of the crater shape and of the distribution of debris about it. The paper is also disclosing an interesting underwater structure, with shape and size of a small crater, located on the coast-line of Sudan.

  4. The Geomorphology of Lyot crater,Mars

    Science.gov (United States)

    Balme, Matthew; Gallagher, Colman; Conway, Susan

    2013-04-01

    Lyot crater, Mars, is a relatively young (ii) studies of glacial and periglacial environments useful for studying water on Mars throughout its history. Here we present preliminary mapping of the various ice- and water-related landforms found in and around Lyot crater. Of particular interest are polygonal networks of metre-scale clasts (perhaps periglacial in origin?) and a variety of channels, fans and lobate flows that could be interpreted as proglacial fluvial systems [2]. The putative glacial assemblage exists within the crater rim and in high relief areas outside of the crater. Fluvial-like channels and fans are seen both within the crater and on the ejecta blanket. The networks of polygonal clasts occur only on the margins of the continuous ejecta blanket, at a radial distance of about 300 km from the crater's centre. The clastic polygons that compose the networks are found only on the Eastern side of Lyot basin, and extend in a broad swathe from about nor-northwest to southwest of the crater. The polygons are generally one to two hundred metres in diameter and consist of lines of clasts (sometime double lines) with flat, low centre-regions between them. Their spatial distribution strongly indicates that they have a genetic link to the formation of the impact crater. Our working hypothesis is that the glacial/fluvial assemblages are related to climate-controlled deposition of ice, with later flow and probably thaw as well. The polygonal clast network is harder to explain, but could reflect the location of water ice-rich zones of the ejecta blanket. Hence, this could be material excavated from the cryosphere during impacts and then reworked by periglacial processes at a much later time. [1] Harrison, T.N., et al., Impact-induced overland fluid flow and channelized erosion at Lyot Crater, Mars. Geophys. Res. Let., 2010. 37(L21201): doi:10.1029/2010GL045074 [2] Dickson, J.L., et al., Amazonian-aged fluvial valley systems in a climatic microenvironment on Mars

  5. Planetary cratering mechanics

    Science.gov (United States)

    O'Keefe, John D.; Ahrens, Thomas J.

    1993-09-01

    The objective of this study was to obtain a quantitative understanding of the cratering process over a broad range of conditions. Our approach was to numerically compute the evolution of impact induced flow fields and calculate the time histories of the key measures of crater geometry (e.g., depth, diameter, lip height) for variations in planetary gravity (0 to 109 cm/s2), material strength (0 to 2400 kbar), and impactor radius (0.05 to 5000 km). These results were used to establish the values of the open parameters in the scaling laws of Holsapple and Schmidt (1987). We describe the impact process in terms of four regimes: (1) penetration, (2) inertial, (3) terminal, and (4) relaxation. During the penetration regime, the depth of impactor penetration grows linearly for dimensionless times τ=(Ut/a)5.1, the crater grows at a slower rate until it is arrested by either strength or gravitational forces. In this regime, the increase of crater depth, d, and diameter, D, normalized by projectile radius is given by d/a=1.3 (Ut/a)0.36 and D/a=2.0(Ut/a)0.36. For strength-dominated craters, growth stops at the end of the inertial regime, which occurs at τ=0.33 (Yeff/ρU2)-0.78, where Yeff is the effective planetary crustal strength. The effective strength can be reduced from the ambient strength by fracturing and shear band melting (e.g., formation of pseudo-tachylites). In gravity-dominated craters, growth stops when the gravitational forces dominate over the inertial forces, which occurs at τ=0.92 (ga/U2)-0.61. In the strength and gravity regimes, the maximum depth of penetration is dp/a=0.84 (Y/ρ U2)-0.28 and dp/a=1.2 (ga/U2)-0.22, respectively. The transition from simple bowl-shaped craters to complex-shaped craters occurs when gravity starts to dominate over strength in the cratering process. The diameter for this transition to occur is given by Dt=9.0 Y/ρg, and thus scales as g-1 for planetary surfaces when strength is not strain-rate dependent. This scaling result

  6. Experimental impact crater morphology

    Science.gov (United States)

    Dufresne, A.; Poelchau, M. H.; Hoerth, T.; Schaefer, F.; Thoma, K.; Deutsch, A.; Kenkmann, T.

    2012-04-01

    The research group MEMIN (Multidisciplinary Experimental and Impact Modelling Research Network) is conducting impact experiments into porous sandstones, examining, among other parameters, the influence of target pore-space saturation with water, and projectile velocity, density and mass, on the cratering process. The high-velocity (2.5-7.8 km/s) impact experiments were carried out at the two-stage light-gas gun facilities of the Fraunhofer Institute EMI (Germany) using steel, iron meteorite (Campo del Cielo IAB), and aluminium projectiles with Seeberg Sandstone as targets. The primary objectives of this study within MEMIN are to provide detailed morphometric data of the experimental craters, and to identify trends and characteristics specific to a given impact parameter. Generally, all craters, regardless of impact conditions, have an inner depression within a highly fragile, white-coloured centre, an outer spallation (i.e. tensile failure) zone, and areas of arrested spallation (i.e. spall fragments that were not completely dislodged from the target) at the crater rim. Within this general morphological framework, distinct trends and differences in crater dimensions and morphological characteristics are identified. With increasing impact velocity, the volume of craters in dry targets increases by a factor of ~4 when doubling velocity. At identical impact conditions (steel projectiles, ~5km/s), craters in dry and wet sandstone targets differ significantly in that "wet" craters are up to 76% larger in volume, have depth-diameter ratios generally below 0.19 (whereas dry craters are almost consistently above this value) at significantly larger diameters, and their spallation zone morphologies show very different characteristics. In dry craters, the spall zone surfaces dip evenly at 10-20° towards the crater centre. In wet craters, on the other hand, they consist of slightly convex slopes of 10-35° adjacent to the inner depression, and of sub-horizontal tensile

  7. Automatical identification of secondary craters with crater spatial distribution

    Science.gov (United States)

    Kinoshita, T.; Honda, C.; Hirata, N.; Morota, T.

    2013-12-01

    We can estimate relative and absolute ages of geological units on the lunar surface with crater counting. This method is called as crater chronology and based on an assumption that each impact cratering occurs randomly to the surface. In contrast to these primary craters, secondary craters are impact craters formed by ejecta blocks and constitute clustering craters. As a result of the clustering, the secondary craters show a biased spatial distribution of craters. For the crater chronology, researchers have to exclude secondary craters and their regions from the surface image including primary and secondary craters based on his or her subjective views. We can identify most of secondary craters with unique shape and spatial distribution of craters. However, the secondary craters produced by high-velocity ejecta fragments are more circular and may be less clustered than the adjacent secondary craters, and it can therefor be difficult to distinguish from primary craters. So, it has been suggested that individual differences in the recognition of secondary craters exist. We propose an algorithm for evaluating spatial distribution of craters on the lunar images. We have developed two procedures. In these procedures, we evaluated the spatial distribution of craters by using the group average method in one of the hierarchical clustering, or by using the Voronoi diagram. In these procedures, we compare the result of evaluation for observed spatial distribution of craters with the result of evaluation for ideal random spatial distribution of craters. We demonstrated for some regions on the lunar surface. As a result, almost of clustered secondary craters are identified quantitatively by our algorithm.

  8. Evaluation of Recharge Potential at Crater U5a (WISHBONE)

    Energy Technology Data Exchange (ETDEWEB)

    Richard H. French; Samuel L. Hokett

    1998-11-01

    Radionuclides are present both below and above the water table at the Nevada Test Site (NTS), as the result of underground nuclear testing. Mobilization and transport of radionuclides from the vadose zone is a complex process that is influenced by the solubility and sorption characteristics of the individual radionuclides, as well as the soil water flux. On the NTS, subsidence craters resulting from testing underground nuclear weapons are numerous, and many intercept surface water flows. Because craters collect surface water above the sub-surface point of device detonation, these craters may provide a mechanism for surface water to recharge the groundwater aquifer system underlying the NTS. Given this situation, there is a potential for the captured water to introduce contaminants into the groundwater system. Crater U5a (WISHBONE), located in Frenchman Flat, was selected for study because of its potentially large drainage area, and significant erosional features, which suggested that it has captured more runoff than other craters in the Frenchman Flat area. Recharge conditions were studied in subsidence crater U5a by first drilling boreholes and analyzing the collected soil cores to determine the soil properties and moisture conditions. This information, coupled with a 32-year precipitation record, was used to conduct surface and vaodse zone modeling. Surface water modeling predicted that approximately 13 ponding events had occurred during the life of the crater. Vadose zone modeling indicated that since the crater's formation approximately 5,900 m3 of water were captured by the crater. Of this total, approximately 5,200 m3 of potential recahrge may have occurred, and the best estimates of annual average potential recharge rates lie between 36 and 188 cm of water per year. The term potential is used here to indicate that the water is not technically recharged because it has not yet reached the water table.

  9. What Dominates a Craters Size, the Largest Single Explosion of the Formation Process or the Cumulative Energy of Many? Results of Multiblast Crater Evolution Experiments

    Science.gov (United States)

    Sonder, I.; Graettinger, A. H.; Valentine, G. A.

    2015-12-01

    Craters of explosive volcanic eruptions are products of many explosions. Such craters are different than products of single events such as meteorite impacts or those produced by military testing because they typically result from multiple, rather than single, explosions. We analyzed the evolution of experimental craters that were created by several detonations of chemical explosives in layered aggregates. A method to calculate an effective explosion depth for non-flat topography (e.g. for explosions below existing craters) is derived, showing how multi-blast crater sizes differ from the single blast case. It is shown that sizes of natural caters (radii, volumes) are not characteristic of the number of explosions, and therefore not characteristic for the total acting energy, that formed a crater. Also the crater size is not simply related to the largest explosion in a sequence, but depends upon that explosion and the energy of that single blast and on the cumulative energy of all blasts that formed the crater. The two energies can be combined to form an effective number of explosions that is characteristic for the crater evolution. The multi-blast crater size evolution implies that it is not correct to estimate explosion energy of volcanic events from crater size using previously published relationships that were derived for single blast cases.

  10. Buried Craters of Utopia

    Science.gov (United States)

    2003-01-01

    MGS MOC Release No. MOC2-365, 19 May 2003Beneath the northern plains of Mars are numerous buried meteor impact craters. One of the most heavily-cratered areas, although buried, occurs in Utopia Planitia, as shown in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image. The history of Mars is complex; impact craters provide a tool by which to understand some of that history. In this case, a very ancient, cratered surface was thinly-buried by younger material that is not cratered at all. This area is near 48.1oN, 228.2oW; less than 180 km (112 mi) west of the Viking 2 lander site. Sunlight illuminates the scene from the lower left.

  11. Investigating target versus impactor influences on Martian crater morphology at the simple-complex transition

    Science.gov (United States)

    Herrick, Robert R.; Hynek, Brian M.

    2017-08-01

    Comparing craters of identical diameter on a planet is an empirical method of studying the effects of different target and impactor properties while holding total impact energy nearly constant. We have analyzed the Martian crater population within a narrow diameter range (7 km crater diameter crater transition using three approaches. We looked for correlations of morphology with surface geology using a global crater database and global geologic map. We examined selected regions in detail with high-resolution images to further understand the relationship between crater morphology and bulk target properties. Finally, we examined craters in close proximity to each other in order to hold target properties constant, so that we could isolate impactor effects on crater morphology. We found a strong correlation between target properties and interior crater morphology, and we found little evidence that impactor properties (other than impact angle) affect crater appearance. Central uplift and wall slumping are enhanced for less consolidated targets. Layered targets affected both the excavation and modification stages of complex crater formation; the resulting craters have pseudoterraces, flat floors, and central pits.

  12. Impact Crater with Peak

    Science.gov (United States)

    2002-01-01

    (Released 14 June 2002) The Science This THEMIS visible image shows a classic example of a martian impact crater with a central peak. Central peaks are common in large, fresh craters on both Mars and the Moon. This peak formed during the extremely high-energy impact cratering event. In many martian craters the central peak has been either eroded or buried by later sedimentary processes, so the presence of a peak in this crater indicates that the crater is relatively young and has experienced little degradation. Observations of large craters on the Earth and the Moon, as well as computer modeling of the impact process, show that the central peak contains material brought from deep beneath the surface. The material exposed in these peaks will provide an excellent opportunity to study the composition of the martian interior using THEMIS multi-spectral infrared observations. The ejecta material around the crater can is well preserved, again indicating relatively little modification of this landform since its initial creation. The inner walls of this approximately 18 km diameter crater show complex slumping that likely occurred during the impact event. Since that time there has been some downslope movement of material to form the small chutes and gullies that can be seen on the inner crater wall. Small (50-100 m) mega-ripples composed of mobile material can be seen on the floor of the crater. Much of this material may have come from the walls of the crater itself, or may have been blown into the crater by the wind. The Story When a meteor smacked into the surface of Mars with extremely high energy, pow! Not only did it punch an 11-mile-wide crater in the smoother terrain, it created a central peak in the middle of the crater. This peak forms kind of on the 'rebound.' You can see this same effect if you drop a single drop of milk into a glass of milk. With craters, in the heat and fury of the impact, some of the land material can even liquefy. Central peaks like the one

  13. Venus - Impact Crater 'Jeanne

    Science.gov (United States)

    1991-01-01

    This Magellan full-resolution image shows Jeanne crater, a 19.5 kilometer (12 mile) diameter impact crater. Jeanne crater is located at 40.0 degrees north latitude and 331.4 degrees longitude. The distinctive triangular shape of the ejecta indicates that the impacting body probably hit obliquely, traveling from southwest to northeast. The crater is surrounded by dark material of two types. The dark area on the southwest side of the crater is covered by smooth (radar-dark) lava flows which have a strongly digitate contact with surrounding brighter flows. The very dark area on the northeast side of the crater is probably covered by smooth material such as fine-grained sediment. This dark halo is asymmetric, mimicking the asymmetric shape of the ejecta blanket. The dark halo may have been caused by an atmospheric shock or pressure wave produced by the incoming body. Jeanne crater also displays several outflow lobes on the northwest side. These flow-like features may have formed by fine-grained ejecta transported by a hot, turbulent flow created by the arrival of the impacting object. Alternatively, they may have formed by flow of impact melt.

  14. Lunar secondary craters, part K

    Science.gov (United States)

    Overbeck, V. R.; Morrison, R. H.; Wedekind, J.

    1972-01-01

    Formation of V-shaped structures surrounding the fresh Copernicus Crater and its secondary craters are reviewed, and preliminary observations of the more extensively eroded secondary crater field of Theophilus are presented. Results of laboratory simulation of secondary lunar craters to examine their effects on V-shaped ridges are also described.

  15. Flat pyramid

    OpenAIRE

    Doherty, Kevin Andrew

    2017-01-01

    'Flat pyramid' is a multi-channel video installation. The project employs appropriated promotional and instructional video from a defunct pyramid scheme as the source material for fictionalized reenactment. The footage primarily consists of presentation documentation, testimonial interviews, and product photography—throughout all of which cutting rarely occurs between takes. Perpetrators and victims are seen moving in and out of their promotional personas, inadvertently making their disquieti...

  16. Venus - Crater Aurelia

    Science.gov (United States)

    1990-01-01

    This Magellan image shows a complex crater, 31.9 kilometers (20 miles) in diameter with a circular rim, terraced walls, and central peaks, located at 20.3 degrees north latitude and 331.8 degrees east longitude. Several unusual features are evidenced in this image: large dark surface up range from the crater; lobate flows emanating from crater ejecta, and very radar-bright ejecta and floor. Aurelia has been proposed to the International Astronomical Union, Subcommittee of Planetary Nomenclature as a candidate name. Aurelia is the mother of Julius Caesar.

  17. Crater in Utopia

    Science.gov (United States)

    2004-01-01

    23 March 2004 Craters of the martian northern plains tend to be somewhat shallow because material has filled them in. Their ejecta blankets, too, are often covered by younger materials. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example--a crater in Utopia Planitia near 43.7oN, 227.3oW. Erosion has roughened some of the surfaces of the material that filled the crater and covered its ejecta deposit. The picture covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.

  18. Venus Crater Database

    Data.gov (United States)

    National Aeronautics and Space Administration — This web page leads to a database of images and information about the 900 or so impact craters on the surface of Venus by diameter, latitude, and name.

  19. Zhamanshin meteor crater

    Science.gov (United States)

    Florenskiy, P. V.; Dabizha, A. I.

    1987-01-01

    A historical survey and geographic, geologic and geophysical characteristics, the results of many years of study of the Zhamanshin meteor crater in the Northern Aral region, are reported. From this data the likely initial configuration and cause of formation of the crater are reconstructed. Petrographic and mineralogical analyses are given of the brecciated and remelted rocks, of the zhamanshinites and irgizite tektites in particular. The impact melting, dispersion and quenching processes resulting in tektite formation are discussed.

  20. High Resolution Digital Elevation Models of Pristine Explosion Craters

    Science.gov (United States)

    Farr, T. G.; Krabill, W.; Garvin, J. B.

    2004-01-01

    In order to effectively capture a realistic terrain applicable to studies of cratering processes and landing hazards on Mars, we have obtained high resolution digital elevation models of several pristine explosion craters at the Nevada Test Site. We used the Airborne Terrain Mapper (ATM), operated by NASA's Wallops Flight Facility to obtain DEMs with 1 m spacing and 10 cm vertical errors of 4 main craters and many other craters and collapse pits. The main craters that were mapped are Sedan, Scooter, Schooner, and Danny Boy. The 370 m diameter Sedan crater, located on Yucca Flat, is the largest and freshest explosion crater on Earth that was formed under conditions similar to hypervelocity impact cratering. As such, it is effectively pristine, having been formed in 1962 as a result of a controlled detonation of a 100 kiloton thermonuclear device, buried at the appropriate equivalent depth of burst required to make a simple crater. Sedan was formed in alluvium of mixed lithology and subsequently studied using a variety of field-based methods. Nearby secondary craters were also formed at the time and were also mapped by ATM. Adjacent to Sedan and also in alluvium is Scooter, about 90 m in diameter and formed by a high-explosive event. Schooner (240 m) and Danny Boy (80 m) craters were also important targets for ATM as they were excavated in hard basalt and therefore have much rougher ejecta. This will allow study of ejecta patterns in hard rock as well as engineering tests of crater and rock avoidance and rover trafficability. In addition to the high resolution DEMs, crater geometric characteristics, RMS roughness maps, and other higher-order derived data products will be generated using these data. These will provide constraints for models of landing hazards on Mars and for rover trafficability. Other planned studies will include ejecta size-frequency distribution at the resolution of the DEM and at finer resolution through air photography and field measurements

  1. On the Flow and Fluidization of Granular Materials: Applications to Large Lunar Craters, Cliff Collapses and Asteroid Shapes

    Science.gov (United States)

    Holsapple, K. A.

    2011-03-01

    About flows of granular materials and assumptions about fluidization mechanisms to explain large flat craters and landslide run outs. No such mechanisms are needed, the reasons and examples are given.

  2. Craters! A Multi-Science Approach to Cratering and Impacts.

    Science.gov (United States)

    Hartmann, William K.; Cain, Joe

    This book provides a complete Scope Sequence and Coordination teaching module. First, craters are introduced as a generally observable phenomena. Then, by making craters and by investigating the results, students gain close-up, hands-on experience with impact events and their products. Real crater examples from the Moon and elsewhere are included…

  3. Impact cratering calculations

    Science.gov (United States)

    Ahrens, Thomas J.; Okeefe, J. D.; Smither, C.; Takata, T.

    1991-01-01

    In the course of carrying out finite difference calculations, it was discovered that for large craters, a previously unrecognized type of crater (diameter) growth occurred which was called lip wave propagation. This type of growth is illustrated for an impact of a 1000 km (2a) silicate bolide at 12 km/sec (U) onto a silicate half-space at earth gravity (1 g). The von Misses crustal strength is 2.4 kbar. The motion at the crater lip associated with this wave type phenomena is up, outward, and then down, similar to the particle motion of a surface wave. It is shown that the crater diameter has grown d/a of approximately 25 to d/a of approximately 4 via lip propagation from Ut/a = 5.56 to 17.0 during the time when rebound occurs. A new code is being used to study partitioning of energy and momentum and cratering efficiency with self gravity for finite-sized objects rather than the previously discussed planetary half-space problems. These are important and fundamental subjects which can be addressed with smoothed particle hydrodynamic (SPH) codes. The SPH method was used to model various problems in astrophysics and planetary physics. The initial work demonstrates that the energy budget for normal and oblique impacts are distinctly different than earlier calculations for silicate projectile impact on a silicate half space. Motivated by the first striking radar images of Venus obtained by Magellan, the effect of the atmosphere on impact cratering was studied. In order the further quantify the processes of meteor break-up and trajectory scattering upon break-up, the reentry physics of meteors striking Venus' atmosphere versus that of the Earth were studied.

  4. Secondary Craters and the Size-Velocity Distribution of Ejected Fragments around Lunar Craters Measured Using LROC Images

    Science.gov (United States)

    Singer, K. N.; Jolliff, B. L.; McKinnon, W. B.

    2013-12-01

    [1986, Icarus 67, and 1987], who compared secondary crater SVDs for craters on the Moon, Mercury, and Mars. Additionally, meter-scale NAC images enable characterization of secondary crater morphologies and fields around much smaller primary craters than were previously investigated. Combined results from all previous studies of ejecta fragment SVDs from secondary crater fields show that β ranges between approximately 1 and 3. First-order spallation theory predicts a β of 1 [Melosh 1989, Impact Cratering, Oxford Univ. Press]. Results in Vickery [1987] for the Moon exhibit a generally decreasing β with increasing primary crater size (5 secondary fields mapped). In the same paper, however, this trend is flat for Mercury (3 fields mapped) and opposite for Mars (4 fields mapped). SVDs for craters on large icy satellites (Ganymede and Europa), with gravities not too dissimilar to lunar gravity, show generally low velocity exponents (β between 1 and 1.5), except for the very largest impactor measured: the 585-km-diameter Gilgamesh basin on Ganymede (β = 2.6 × 0.4) [Singer et al., 2013, Icarus 226]. The present work, focusing initially on lunar craters using LROC data, will attempt to confirm or clarify these trends, and expand the number of examples under a variety of impact conditions and surface materials to evaluate possible causes of variations.

  5. Secrets of the Wabar craters

    Science.gov (United States)

    Wynn, Jeffrey C.; Shoemaker, Eugene M.

    1997-01-01

    Focuses on the existence of craters in the Empty Quarter of Saudi Arabia created by the impact of meteors in early times. Mars Pathfinder and Mars Global Surveyor's encounter with impact craters; Elimination of craters in the Earth's surface by the action of natural elements; Impact sites' demand for careful scientific inspections; Location of the impact sites.

  6. Quaternary Eruptions of the Mono-Inyo Craters, California

    Science.gov (United States)

    Bursik, M. I.; Pouget, S.; Mangan, M.; Marcaida, M.; Vazquez, J. A.

    2013-12-01

    The eruptive products of the Mono-Inyo Craters volcanic chain include the tephra and associated volcanic rocks of Black Point, islands of Mono Lake, Mono Craters, Inyo Craters, late eruptions of Mammoth Mountain and Red Cones. Most of the eruptions were explosive, and generated numerous pyroclastic flows, surges and falls as well as the prominent domes and lava flows that now cover vents. The eruptions range in age from several hundred years to at least 60,000 yr BP. The Mono-Inyo tephras are dispersed throughout the Sierra Nevada and Basin and Range, providing key time-stratigraphic marker layers. Recent work has not only resulted in high-precision radiometric dating of many of the tephras, but also detailed geochemical data that for the first time provides fingerprinting sufficiently precise to discriminate among the tephras. Lithostratigraphy of many of the layers is herein described for the first time, based on careful sampling and description in the field, and laboratory grain size, grain shape and componentry analyses of the late Pleistocene tephras of the Wilson Creek Formation. Most of the Wilson Creek volcanic layers are fall deposits accumulated within paleolake Russell, which were generated by eruptions of variable intensity and influenced by paleowinds of different orientation. Prevailing winds were generally to the North and East, but often the Pleistocene layers less than 25 ka were dispersed to the West. Many of the fall layers show evidence of wave reworking, generally near the top, although in some cases it is pervasive. Only near the vent do some layers of apparent debris flow origin occur. Maximum pumice sizes range up to nearly 3 cm, and lithics range up to 1 cm in the rhyolitic fall beds, while thicknesses range up to c. 30 cm. These data are consistent with relatively low volume, subplinian style eruptive behavior for most of the life of the Mono-Inyo Craters.

  7. Field experiment for blasting crater

    Institute of Scientific and Technical Information of China (English)

    YE Tu-qiang

    2008-01-01

    A series of single hole blasting crater experiments and a variable distance multi-hole simultaneous blasting experiment was carded in the Yunfu Troilite Mine, according to the Livingston blasting crater theory. We introduce in detail, our methodology of data collection and processing from our experiments. Based on the burying depth of the explosives, the blasting crater volume was fitted by the method of least squares and the characteristic curve of the blasting crater was obtained using the MATLAB software. From this third degree polynomial, we have derived the optimal burying depth, the critical burying depth and the optimal explosive specific charge of the blasting crater.

  8. Heavy Cratering near Callisto's South Pole

    Science.gov (United States)

    1997-01-01

    Images from NASA's Galileo spacecraft provide new insights into this region near Callisto's south pole. This two frame mosaic shows a heavily cratered surface with smooth plains in the areas between craters. North is to the top of the image. The smoothness of the plains appears to increase toward the south pole, approximately 480 kilometers (293 miles) south of the bottom of the image. This smoothness of Callisto's surface was not evident in images taken during the 1979 flyby of NASA's Voyager spacecraft because the resolution was insufficient to show the effect. This smooth surface, and the process(es) that cause it, are among the most intriguing aspects of Callisto. Although not fully understood, the process(es) responsible for this smoothing could include erosion by tiny meteorites and energetic ions. Some craters, such as Keelut, the 47 kilometer (29 mile) crater in the lower right corner, have sharp, well defined rims. Keelut contains an inner ring surrounding a central depression about 17 kilometers (11 miles) in diameter. Keelut, and the more irregularly shaped, degraded Reginleif, the 32 kilometer (19.5 mile) crater in the top center of the image, are very shallow and have flat floors. Crater forms can be seen down to less than 2 kilometers (1.2 miles) in diameter in the image. Each picture element (pixel) in this image is approximately 0.68 kilometers (0.41 miles) across.This image which was taken by the Galileo spacecraft's solid state imaging (CCD) system during its eighth orbit around Jupiter, on May 6th, 1997. The center of the image is located at 71.3 degrees south latitude, 97.6 degrees west longitude, and was taken when the spacecraft was approximately 35,470 kilometers (21,637 miles) from Callisto.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http

  9. Pleistocene Paleoart of Europe

    Directory of Open Access Journals (Sweden)

    Robert G. Bednarik

    2014-06-01

    Full Text Available As in Australia, Pleistocene rock art is relatively abundant in Europe, but it has so far received much more attention than the combined Ice Age paleoart of the rest of the world. Since archaeology initially rejected its authenticity for several decades, the cave art of France and Spain and the portable paleoart from various regions of Europe have been the subjects of thousands of studies. It is shown, however, that much of the published information is unreliable and subjective, and that fundamental trends in the evidence have been misunderstood. In particular, the data implies that the paleoart of the Early Upper Paleolithic, the work of robust humans such as Neanderthals, is considerably more sophisticated and developed that that of more recent times. Thus, the European paleoart demonstrates that the teleological model of cultural “evolution” is false, which is to be expected because evolution is purely dysteleological. This is confirmed by the extensive record of pre-Upper Paleolithic European paleoart, which is comprehensively reviewed in this paper.

  10. Formation of Craters in Sand

    Directory of Open Access Journals (Sweden)

    Vanissra Boonyaleepun

    2007-06-01

    Full Text Available The diameter of craters formed by spheres of varying mass dropped into sand at low speed was studied. The relationship between the diameter of the crater formed and the kinetic energy of the projectile at impact was found to be of the same general form as that for planetary meteor craters. The relationship is shown to be a power law with exponent 0.17.

  11. Formation of Craters in Sand

    Directory of Open Access Journals (Sweden)

    Vanissra Boonyaleepun

    2007-06-01

    Full Text Available The diameter of craters formed by spheres of varying mass dropped into sand at low speed was studied. The relationship between the diameter of the crater formed and the kinetic energy of the projectile at impact was found to be of the same general form as that for planetary meteor craters. The relationship is shown to be a power law with exponent 0.17

  12. Identification of craters on Moon using Crater Density Parameter

    Science.gov (United States)

    Vandana, Vandana

    2016-07-01

    Lunar craters are the most noticeable features on the face of the moon. They take up 40.96% of the lunar surface and, their accumulated area is approximately three times as much as the lunar surface area. There are many myths about the moon. Some says moon is made of cheese. The moon and the sun chase each other across the sky etc. but scientifically the moon are closest and are only natural satellite of earth. The orbit plane of the moon is tilted by 5° and orbit period around the earth is 27-3 days. There are two eclipse i.e. lunar eclipse and solar eclipse which always comes in pair. Moon surface has 3 parts i.e. highland, Maria, and crater. For crater diagnostic crater density parameter is one of the means for measuring distance can be easily identity the density between two craters. Crater size frequency distribution (CSFD) is being computed for lunar surface using TMC and MiniSAR image data and hence, also the age for the selected test sites of mars is also determined. The GIS-based program uses the density and orientation of individual craters within LCCs (as vector points) to identify potential source craters through a series of cluster identification and ejection modeling analyses. JMars software is also recommended and operated only the time when connected with server but work can be done in Arc GIS with the help of Arc Objects and Model Builder. The study plays a vital role to determine the lunar surface based on crater (shape, size and density) and exploring affected craters on the basis of height, weight and velocity. Keywords: Moon; Crater; MiniSAR.

  13. The temporal bones from Sima de los Huesos Middle Pleistocene site (Sierra de Atapuerca, Spain). A phylogenetic approach.

    Science.gov (United States)

    Martínez, I; Arsuaga, J L

    1997-01-01

    Three well-preserved crania and 22 temporal bones were recovered from the Sima de los Huesos Middle Pleistocene site up to and including the 1994 field season. This is the largest sample of hominid temporal bones known from a single Middle Pleistocene site and it offers the chance to characterize the temporal bone morphology of an European Middle Pleistocene population and to study the phylogenetic relationships of the SH sample with other Upper and Middle Pleistocene hominids. We have carried out a cladistic analysis based on nine traits commonly used in phylogenetic analysis of Middle and Late Pleistocene hominids: shape of the temporal squama superior border, articular eminence morphology, contribution of the sphenoid bone to the median glenoid wall, postglenoid process projection, tympanic plate orientation, presence of the styloid process, mastoid process projection, digastric groove morphology and anterior mastoid tubercle. We have found two autapomorphies on the Home erectus temporal bone: strong reduction of the postglenoid process and absence of the styloid process. Modern humans, Neandertals and the Middle Pleistocene fossils from Europe and Africa constitute a clade characterized by a convex superior border of the temporal squama. The European Middle Pleistocene fossils from Sima de los Huesos, Petralona, Steinheim, Bilzingsleben and Castel di Guido share a Neandertal apomorphy: a relatively flat articular eminence. The fossils from Ehringsdorf, La Chaise Suardi and Biache-Saint-Vaast also display another Neandertal derived trait: an anteriorly obliterated digastric groove. Modern humans and the African Middle Pleistocene fossils share a synapomorphy: a sagittally orientated tympanic plate.

  14. Dunes in Darwin Crater

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03039 Dunes in Darwin Crater The dunes and sand deposits in this image are located on the floor of Darwin Crater. Image information: VIS instrument. Latitude 57.4S, Longitude 340.2E. 17 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  15. Landslide in a Crater

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] The landslide in this VIS image is located inside an impact crater in the Elysium region of Mars. The unnamed crater is located at the margin of the volcanic flows from the Elysium Mons complex. Image information: VIS instrument. Latitude 1.2, Longitude 134 East (226 West). 19 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  16. Landslide in a Crater

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] The landslide in this VIS image is located inside an impact crater in the Elysium region of Mars. The unnamed crater is located at the margin of the volcanic flows from the Elysium Mons complex. Image information: VIS instrument. Latitude 1.2, Longitude 134 East (226 West). 19 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  17. Crater density differences: Exploring regional resurfacing, secondary crater populations, and crater saturation equilibrium on the moon

    Science.gov (United States)

    Povilaitis, R Z; Robinson, M S; van der Bogert, C H; Hiesinger, Harald; Meyer, H M; Ostrach, Lillian

    2017-01-01

    The global population of lunar craters >20 km in diameter was analyzed by Head et al., (2010) to correlate crater distribution with resurfacing events and multiple impactor populations. The work presented here extends the global crater distribution analysis to smaller craters (5–20 km diameters, n = 22,746). Smaller craters form at a higher rate than larger craters and thus add granularity to age estimates of larger units and can reveal smaller and younger areas of resurfacing. An areal density difference map generated by comparing the new dataset with that of Head et al., (2010) shows local deficiencies of 5–20 km diameter craters, which we interpret to be caused by a combination of resurfacing by the Orientale basin, infilling of intercrater plains within the nearside highlands, and partial mare flooding of the Australe region. Chains of 5–30 km diameter secondaries northwest of Orientale and possible 8–22 km diameter basin secondaries within the farside highlands are also distinguishable. Analysis of the new database indicates that craters 57–160 km in diameter across much of the lunar highlands are at or exceed relative crater densities of R = 0.3 or 10% geometric saturation, but nonetheless appear to fit the lunar production function. Combined with the observation that small craters on old surfaces can reach saturation equilibrium at 1% geometric saturation (Xiao and Werner, 2015), this suggests that saturation equilibrium is a size-dependent process, where large craters persist because of their resistance to destruction, degradation, and resurfacing.

  18. Meteor Crater, AZ

    Science.gov (United States)

    2002-01-01

    The Barringer Meteorite Crater (also known as 'Meteor Crater') is a gigantic hole in the middle of the arid sandstone of the Arizona desert. A rim of smashed and jumbled boulders, some of them the size of small houses, rises 50 m above the level of the surrounding plain. The crater itself is nearly a 1500 m wide, and 180 m deep. When Europeans first discovered the crater, the plain around it was covered with chunks of meteoritic iron - over 30 tons of it, scattered over an area 12 to 15 km in diameter. Scientists now believe that the crater was created approximately 50,000 years ago. The meteorite which made it was composed almost entirely of nickel-iron, suggesting that it may have originated in the interior of a small planet. It was 50 m across, weighed roughly 300,000 tons, and was traveling at a speed of 65,000 km per hour. This ASTER 3-D perspective view was created by draping an ASTER bands 3-2-1image over a digital elevation model from the US Geological Survey National Elevation Dataset.This image was acquired on May 17, 2001 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next 6 years to map and monitor the changing surface of our planet.ASTER is one of five Earth-observing instruments launched December 18,1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. Science team leader; Bjorn Eng of JPL is the project manager. ASTER is the only high resolution imaging sensor on Terra. The Terra mission is part of NASA's Earth Science Enterprise, along

  19. An Olivine-Rich Crater in Tyrrhena Terra

    Science.gov (United States)

    2008-01-01

    This image of the ejecta of a crater in the Tyrrhena Terra region was taken by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at 0328 UTC on February 23, 2007 (10:28 p.m. EST on February 22, 2007), near 13 degrees south latitude, 67 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 18 meters (60 feet) across. The region covered is roughly 9 kilometers (5.6 miles) wide at its narrowest point. Named for a classic albedo feature, Tyrrhena Terra is an extensive, heavily-cratered part of Mars' southern highlands, some 2,300 kilometers (1,430 miles) at its broadest extent. It is located to the northeast of the Hellas basin. The region imaged by CRISM is to the north of Hellas Planitia and just east of the crater Huygens in Tyrrhena Terra's western end. The uppermost image in the montage above reveals the location of the CRISM image on a mosaic taken by the Mars Odyssey spacecraft's Thermal Emission Imaging System (THEMIS). The CRISM image is located inside a large, flat-floored crater measuring about 52 kilometers (32 miles) across. The image includes a small crater and its ejecta blanket, an apron of material thrown out during a crater's formation, both located inside the larger crater. The lower left image is an infrared false-color image that reveals the extent of the ejecta blanket. It also includes ejecta from another small crater located just east of the CRISM image. The lower right image shows the strengths of mineral absorptions, and reveals the composition of the ejecta and surrounding material. The ejecta surrounding the small impact crater is thickest at the crater's rim, and becomes thinner to discontinuous at the blanket's outer edge. This small crater's ejecta blanket shows an enhanced spectral signature of the mineral olivine, as does the ejecta from the small crater just out of view to the east. In contrast the surrounding material is rich in the volcanic mineral

  20. Flat for Free Flow

    Institute of Scientific and Technical Information of China (English)

    Yan Manman

    2010-01-01

    @@ Just as Thomas Fried man's famous book,The World Is Flat,if not completely flat,it is anyway tending to be shaped flat.January 1,2010 saw the formation of the China-ASEAN Free Trade Agreement(CAFTA),which was another historical event flattening majority of Asia continent for international trade.

  1. The origin of lunar concentric craters

    Science.gov (United States)

    Trang, David; Gillis-Davis, Jeffrey J.; Hawke, B. Ray

    2016-11-01

    Lunar concentric craters are a unique class of impact craters because the interior of the craters contains a concentric ridge, but their formation mechanism is unknown. In order to determine the origin of concentric craters, we examined multiple working hypotheses, which include eight impact-related and endogenic processes. We analyzed data sets that originated from instruments onboard Clementine, Kaguya, and the Lunar Reconnaissance Orbiter to characterize the morphology, spatial distribution, composition, and absolute model ages of 114 concentric craters. Concentric craters contain five key properties: (1) a concentric ridge, (2) anomalously shallow floors, (3) their occurrence is concentrated near mare margins and in mare pond regions (4) the concentric ridge composition is similar to the surrounding area and (5) concentric crater ages are Eratosthenian and older. These five key properties served as constraints for testing impact-related and endogenic mechanisms of formation. We find that most impact-related hypotheses cannot explain the spatial and age distribution of concentric craters. As for endogenic hypotheses, we deduce that igneous intrusions are the likely mechanism that formed concentric craters because of the close relationship between concentric craters and floor-fractured craters and the concentration of both features near mare-highland boundaries and in mare ponds. Furthermore, we observe that floor-fractured craters are common at crater diameters > 15 km, whereas concentric craters are common at crater diameters 15 km) produce floor-fractured craters.

  2. Geographical Distribution of Crater Depths on Mars

    Science.gov (United States)

    Stepinski, T. F.

    2010-03-01

    Global maps of crater depths on Mars are constructed using a new dataset that lists depths of >75,000 craters. Distribution of crater depths is interpreted in terms of cryosphere extent, and the locations of deepest craters on Mars are identified.

  3. Chesapeake Bay impact structure: Morphology, crater fill, and relevance for impact structures on Mars

    Science.gov (United States)

    Horton, J.W.; Ormo, J.; Powars, D.S.; Gohn, G.S.

    2006-01-01

    The late Eocene Chesapeake Bay impact structure (CBIS) on the Atlantic margin of Virginia is one of the largest and best-preserved "wet-target" craters on Earth. It provides an accessible analog for studying impact processes in layered and wet targets on volatile-rich planets. The CBIS formed in a layered target of water, weak clastic sediments, and hard crystalline rock. The buried structure consists of a deep, filled central crater, 38 km in width, surrounded by a shallower brim known as the annular trough. The annular trough formed partly by collapse of weak sediments, which expanded the structure to ???85 km in diameter. Such extensive collapse, in addition to excavation processes, can explain the "inverted sombrero" morphology observed at some craters in layered targets. The distribution of crater-fill materials i n the CBIS is related to the morphology. Suevitic breccia, including pre-resurge fallback deposits, is found in the central crater. Impact-modified sediments, formed by fluidization and collapse of water-saturated sand and silt-clay, occur in the annular trough. Allogenic sediment-clast breccia, interpreted as ocean-resurge deposits, overlies the other impactites and covers the entire crater beneath a blanket of postimpact sediments. The formation of chaotic terrains on Mars is attributed to collapse due to the release of volatiles from thick layered deposits. Some flat-floored rimless depressions with chaotic infill in these terrains are impact craters that expanded by collapse farther than expected for similar-sized complex craters in solid targets. Studies of crater materials in the CBIS provide insights into processes of crater expansion on Mars and their links to volatiles. ?? The Meteoritical Society, 2006.

  4. McLaughlin Crater as a Candidate Landing Site for Humans on Mars

    Science.gov (United States)

    Michalski, J. R.; Niles, P. B.; Sutter, B.; Bell, M. S.

    2015-01-01

    McLaughlin Crater is an ancient (Noachian) Martian impact crater located at 337.6 East, 21.9 North, just south of the dichotomy boundary. This site should be considered for future landed exploration because: a) it is located at the boundary of three types of scientifically important terrain that will yield key results about the geological evolution and habitability of Mars; b) it contains surfaces where radiometric dating can be related to age dates estimated from crater counting, c) it contains volatile-rich rocks that will not only yield interesting results regarding ancient atmospheric chemistry, but will also be high quality, accessible targets for in-situ resource utilization (ISRU), and d) the site within the crater provides a flat, low-risk and low-elevation landing zone, which will facilitate landing large payloads on Mars.

  5. How old is Autolycus crater?

    Science.gov (United States)

    Hiesinger, Harald; Pasckert, Jan Henrik; van der Bogert, Carolyn H.; Robinson, Mark S.

    2016-04-01

    Accurately determining the lunar cratering chronology is prerequisite for deriving absolute model ages (AMAs) across the lunar surface and throughout the Solar System [e.g., 1]. However, the lunar chronology is only constrained by a few data points over the last 1 Ga and there are no calibration data available between 1 and 3 Ga and beyond 3.9 Ga [2]. Rays from Autolycus and Aristillus cross the Apollo 15 landing site and presumably transported material to this location [3]. [4] proposed that at the Apollo 15 landing site about 32% of any exotic material would come from Autolycus crater and 25% would come from Aristillus crater. [5,6] proposed that the 39Ar-40Ar age of 2.1 Ga derived from three petrologically distinct, shocked Apollo 15 KREEP basalt samples, date Autolycus crater. Grier et al. [7] reported that the optical maturity (OMAT) characteristics of these craters are indistinguishable from the background values despite the fact that both craters exhibit rays that were used to infer relatively young, i.e., Copernican ages [8,9]. Thus, both OMAT characteristics and radiometric ages of 2.1 Ga and 1.29 Ga for Autolycus and Aristillus, respectively, suggest that these two craters are not Copernican in age. [10] interpreted newer U-Pb ages of 1.4 and 1.9 Ga from sample 15405 as the formation ages of Aristillus and Autolycus. If Autolycus is indeed the source of the dated exotic material collected at the Apollo 15 landing site, than performing crater size frequency distribution (CSFD) measurements for Autolycus offers the possibility to add a new calibration point to the lunar chronology, particularly in an age range that was previously unconstrained. We used calibrated and map-projected LRO NAC images to perform CSFD measurements within ArcGIS, using CraterTools [11]. CSFDs were then plotted with CraterStats [12], using the production and chronology functions of [13]. We determined ages of 3.72 and 3.85 Ga for the interior (Ai1) and ejecta area Ae3, which we

  6. Degradation of Victoria Crater, Mars

    Science.gov (United States)

    Wilson, Sharon A.; Grant, John A.; Cohen, Barbara A.; Golombek, Mathew P.; Geissler, Paul E.; Sullivan, Robert J.; Kirk, Randolph L.; Parker, Timothy J.

    2008-01-01

    The $\\sim$750 m diameter and $\\sim$75 m deep Victoria crater in Meridiani Planum, Mars, presents evidence for significant degradation including a low, serrated, raised rim characterized by alternating alcoves and promontories, a surrounding low relief annulus, and a floor partially covered by dunes. The amount and processes of degradation responsible for the modified appearance of Victoria crater were evaluated using images obtained in situ by the Mars Exploration Rover Opportunity in concert with a digital elevation model created using orbital HiRISE images. Opportunity traversed along the north and northwest rim and annulus, but sufficiently characterized features visible in the DEM to enable detailed measurements of rim relief, ejecta thickness, and wall slopes around the entire degraded, primary impact structure. Victoria retains a 5 m raised rim consisting of 1-2 m of uplifted rocks overlain by 3 m of ejecta at the rim crest. The rim is $\\sim$120 to 220 m wide and is surrounded by a dark annulus reaching an average of 590 m beyond the raised rim. Comparison between observed morphology and that expected for pristine craters 500 to 750 m across indicate the original, pristine crater was close to 600 m in diameter. Hence, the crater has been erosionally widened by approximately 150 m and infilled by about 50 m of sediments. Eolian processes are responsible for modification at Victoria, but lesser contributions from mass wasting or other processes cannot be ruled out. Erosion by prevailing winds is most significant along the exposed rim and upper walls and accounts for $\\sim$50 m widening across a WNW-ESE diameter. The volume of material eroded from the crater walls and rim is $\\sim$20% less than the volume of sediments partially filling the crater, indicating eolian infilling from sources outside the crater over time. The annulus formed when $\\sim$1 m deflation of the ejecta created a lag of more resistant hematite spherules that trapped darker, regional

  7. Limb of Copernicus Impact Crater

    Science.gov (United States)

    1991-01-01

    Copernicus is 93 km wide and is located within the Mare Imbrium Basin, northern nearside of the Moon (10 degrees N., 20 degrees W.). Image shows crater floor, floor mounds, rim, and rayed ejecta. Rays from the ejecta are superposed on all other surrounding terrains which places the crater in its namesake age group: the Copernican system, established as the youngest assemblage of rocks on the Moon (Shoemaker and Hackman, 1962, The Moon: London, Academic Press, p.289- 300).

  8. Geology of Lofn Crater, Callisto

    Science.gov (United States)

    Greeley, Ronald; Heiner, Sarah; Klemaszewski, James E.

    2001-01-01

    Lofn crater is a 180-km-diameter impact structure in the southern cratered plains of Callisto and is among the youngest features seen on the surface. The Lofn area was imaged by the Galileo spacecraft at regional-scale resolutions (875 m/pixel), which enable the general geology to be investigated. The morphology of Lofn crater suggests that (1) it is a class of impact structure intermediate between complex craters and palimpsests or (2) it formed by the impact of a projectile which fragmented before reaching the surface, resulting in a shallow crater (even for Callisto). The asymmetric pattern of the rim and ejecta deposits suggests that the impactor entered at a low angle from the northwest. The albedo and other characteristics of the ejecta deposits from Lofn also provide insight into the properties of the icy lithosphere and subsurface configuration at the time of impact. The "target" for the Lofn impact is inferred to have included layered materials associated with the Adlinda multiring structure northwest of Loh and ejecta deposits from the Heimdall crater area to the southeast. The Lofn impact might have penetrated through these materials into a viscous substrate of ductile ice or possibly liquid water. This interpretation is consistent with models of the current interior of Callisto based on geophysical information obtained from the Galileo spacecraft.

  9. Pleistocene and pre-Pleistocene Begonia speciation in Africa.

    Science.gov (United States)

    Plana, Vanessa; Gascoigne, Angus; Forrest, Laura L; Harris, David; Pennington, R Toby

    2004-05-01

    This paper presents a historical biogeographic analysis of African Begonia based on combined internal transcribed spacer (ITS) and trnL intron sequences. Age range estimates for Begonia in Africa ranged from only 1.5 Ma for some terminal nodes to 27 Ma for basal nodes when the ages of Réunion (2 Ma) andMayotte (5.4 Ma) were used to date the split between Begonia salaziensis and Begonia comorensis. Assuming a more recent origin age for Begonia salaziensis (2 Ma) provided age estimates in other parts of the phylogeny which agreed with patterns observed in other African organisms. A large proportion of the Begonia diversity seen today in Africa is of pre-Pleistocene origin. Species of Pleistocene origin are concentrated in species-rich groups such as sections Loasibegonia, Scutobegonia, and Tetraphila, which have their centre of diversity in western Central Africa. Phylogenetically isolated taxa such as Begonia longipetiolata, Begonia iucunda, and Begonia thomeana date to the late Miocene, a period of extended aridification on the African continent that had severe effects on African rain forest species. A general pattern is identified where phylogenetically isolated species occur outside the main identified rain forest refuges. Endemic species on the island of São Tomé such as Begonia baccata, Begonia molleri, and Begonia subalpestris appear to be palaeoendemics. Of these species, the most recent age estimate is for B. baccata, which is dated at ca. 3 Ma. Therefore, São Tomé appears to have functioned as an important (if previously unrecognised) pre-Pleistocene refuge. On the mainland, areas such as the Massif of Chaillu in Gabon, southern Congo (Brazzaville), and far western areas of Congo (Kinshasa) have played similar roles to São Tomé.

  10. Relatively Flat Envelopes

    Institute of Scientific and Technical Information of China (English)

    丁南庆

    1994-01-01

    The aim of this paper is to investigate relatively flat envelopes. A necessary and sufficient condition is given for a relatively-finitely presented module to have a (mono-morphic or epic) relatively flat envelope. Then those rings are characterized whose every relatively-finitely presented module has a relatively flat envelope which coincides with its in-jective envelope. Some known results are obtained as corollaries.

  11. Creating flat design websites

    CERN Document Server

    Pratas, Antonio

    2014-01-01

    This book contains practical, step-by-step tutorials along with plenty of explanation about designing your flat website. Each section is introduced sequentially, building up your web design skills and completing your website.Creating Flat Design Websites is ideal for you if you are starting on your web development journey, but this book will also benefit seasoned developers wanting to start developing in flat.

  12. Strongly Gorenstein Flat Dimensions

    Institute of Scientific and Technical Information of China (English)

    Chun Xia ZHANG; Li Min WANG

    2011-01-01

    This article is concerned with the strongly Gorenstein flat dimensions of modules and rings.We show this dimension has nice properties when the ring is coherent,and extend the well-known Hilbert's syzygy theorem to the strongly Gorenstein flat dimensions of rings.Also,we investigate the strongly Gorenstein flat dimensions of direct products of rings and (almost)excellent extensions of rings.

  13. Reuyl Crater Dust Avalanches

    Science.gov (United States)

    2002-01-01

    (Released 13 May 2002) The Science The rugged, arcuate rim of the 90 km crater Reuyl dominates this THEMIS image. Reuyl crater is at the southern edge of a region known to be blanketed in thick dust based on its high albedo (brightness) and low thermal inertia values. This thick mantle of dust creates the appearance of snow covered mountains in the image. Like snow accumulation on Earth, Martian dust can become so thick that it eventually slides down the face of steep slopes, creating runaway avalanches of dust. In the center of this image about 1/3 of the way down is evidence of this phenomenon. A few dozen dark streaks can be seen on the bright, sunlit slopes of the crater rim. The narrow streaks extend downslope following the local topography in a manner very similar to snow avalanches on Earth. But unlike their terrestrial counterparts, no accumulation occurs at the bottom. The dust particles are so small that they are easily launched into the thin atmosphere where they remain suspended and ultimately blow away. The apparent darkness of the avalanche scars is due to the presence of relatively dark underlying material that becomes exposed following the passage of the avalanche. Over time, new dust deposition occurs, brightening the scars until they fade into the background. Although dark slope streaks had been observed in Viking mission images, a clear understanding of this dynamic phenomenon wasn't possible until the much higher resolution images from the Mars Global Surveyor MOC camera revealed the details. MOC images also showed that new avalanches have occurred during the time MGS has been in orbit. THEMIS images will allow additional mapping of their distribution and frequency, contributing new insights about Martian dust avalanches. The Story The stiff peaks in this image might remind you of the Alps here on Earth, but they really outline the choppy edge of a large Martian crater over 50 miles wide (seen in the context image at right). While these aren

  14. Shape of impact craters in granular media.

    Science.gov (United States)

    de Vet, Simon J; de Bruyn, John R

    2007-10-01

    We present the results of experiments studying the shape of craters formed by the normal impact of a solid spherical projectile into a deep noncohesive granular bed at low energies. The resultant impact crater surfaces are accurately digitized using laser profilometry, allowing for the detailed investigation of the crater shape. We find that these impact craters are very nearly hyperbolic in profile. Crater radii and depths are dependent on impact energy, as well as the projectile density and size. The precise crater shape is a function of the crater aspect ratio. While the dimensions of the crater are highly dependent on the impact energy, we show that the energy required to excavate the crater is only a tiny fraction (0.1%-0.5%) of the kinetic energy of the projectile.

  15. Martian parent craters for the SNC meteorites

    Science.gov (United States)

    Mouginis-Mark, P. J.; Mccoy, T. J.; Taylor, G. J.; Keil, K.

    1992-01-01

    Information on the petrology and ages of the SNC meteorites, together with geological data derived from Viking Orbiter images, are used to identify 25 candidate impact craters in the Tharsis region of Mars that could possibly be the source craters for these meteorites. The craters chosen as candidate source craters had diameters greater than 10 km, morphologies indicative of young craters, and satisfied both the petrological criteria of the SNCs and the proposed 1.3 Ga crystallization ages. On the basis of the constraints implied by the identification of the candidate source craters, interpretations of the absolute chronology of Mars are proposed.

  16. Size variation in Middle Pleistocene humans.

    Science.gov (United States)

    Arsuaga, J L; Carretero, J M; Lorenzo, C; Gracia, A; Martínez, I; Bermúdez de Castro, J M; Carbonell, E

    1997-08-22

    It has been suggested that European Middle Pleistocene humans, Neandertals, and prehistoric modern humans had a greater sexual dimorphism than modern humans. Analysis of body size variation and cranial capacity variation in the large sample from the Sima de los Huesos site in Spain showed instead that the sexual dimorphism is comparable in Middle Pleistocene and modern populations.

  17. Spatial distribution of impact craters on Deimos

    Science.gov (United States)

    Hirata, Naoyuki

    2017-05-01

    Deimos, one of the Martian moons, has numerous impact craters. However, it is unclear whether crater saturation has been reached on this satellite. To address this issue, we apply a statistical test known as nearest-neighbor analysis to analyze the crater distribution of Deimos. When a planetary surface such as the Moon is saturated with impact craters, the spatial distribution of craters is generally changed from random to more ordered. We measured impact craters on Deimos from Viking and HiRISE images and found (1) that the power law of the size-frequency distribution of the craters is approximately -1.7, which is significantly shallower than those of potential impactors, and (2) that the spatial distribution of craters over 30 m in diameter cannot be statistically distinguished from completely random distribution, which indicates that the surface of Deimos is inconsistent with a surface saturated with impact craters. Although a crater size-frequency distribution curve with a slope of -2 is generally interpreted as indicating saturation equilibrium, it is here proposed that two competing mechanisms, seismic shaking and ejecta emplacement, have played a major role in erasing craters on Deimos and are therefore responsible for the shallow slope of this curve. The observed crater density may have reached steady state owing to the obliterations induced by the two competing mechanisms. Such an occurrence indicates that the surface is saturated with impact craters despite the random distribution of craters on Deimos. Therefore, this work proposes that the age determined by the current craters on Deimos reflects neither the age of Deimos itself nor that of the formation of the large concavity centered at its south pole because craters should be removed by later impacts. However, a few of the largest craters on Deimos may be indicative of the age of the south pole event.

  18. Terrace Zone Structure in the Chicxulub Impact Crater Based on 2-D Seismic Reflection Profiles: Preliminary Results From EW#0501

    Science.gov (United States)

    McDonald, M. A.; Gulick, S. P.; Gorney, D. L.; Christeson, G. L.; Barton, P. J.; Morgan, J. V.; Warner, M. R.; Urrutia-Fucugauchi, J.; Melosh, H. J.; Vermeesch, P. M.; Surendra, A. T.; Goldin, T.; Mendoza, K.

    2005-05-01

    Terrace zones, central peaks, and flat floors characterize complex craters like the Chicxulub impact crater located near the northeast coast of the Yucatan Peninsula. The subsurface crater structure was studied using seismic reflection surveying in Jan/Feb 2005 by the R/V Maurice Ewing. We present 2-D seismic profiles including constant radius, regional, and grid profiles encompassing the 195 km width of the crater. These diversely oriented lines clearly show the terrace zones and aid in the search for crater ejecta as we investigate the formation of the crater including the incidence angle and direction of the extraterrestrial object that struck the Yucatan Peninsula 65 million years ago (K-T boundary). Terrace zones form in complex craters after the modification stage as a result of the gravitational collapse of overextended sediment back into the crater cavity. The terrace zone is clearly imaged on seismic profiles confirming the complex structure of the Chixculub crater. Recent work on reprocessed 1996 profiles found different sizes and spacing of the terraces and concluded that the variations in radial structure are a result of an oblique impact. A SW-NE profile from this study was the only line to show a concentration of deformation near the crater rim hinting that the northeast was the downrange direction of impact. We confirm this narrowing in terrace spacing using a profile with a similar orientation in the 2005 images. Through integration of the new dense grid of profiles and radial lines from the 1996 and 2005 surveys we map the 3-D variability of the terrace zones to further constrain impact direction and examine the formative processes of the Chixculub and other large impact craters.

  19. Robust Automated Identification of Martian Impact Craters

    Science.gov (United States)

    Stepinski, T. F.; Mendenhall, M. P.; Bue, B. D.

    2007-03-01

    Robust automatic identification of martian craters is achieved by a computer algorithm acting on topographic data. The algorithm outperforms manual counts; derived crater sizes and depths are comparable to those measured manually.

  20. Moon - 'Ghost' craters formed during Mare filling.

    Science.gov (United States)

    Cruikshank, D. P.; Hartmann, W. K.; Wood, C. A.

    1973-01-01

    This paper discusses formation of 'pathological' cases of crater morphology due to interaction of craters with molten lavas. Terrestrial observations of such a process are discussed. In lunar maria, a number of small impact craters (D less than 10 km) may have been covered by thin layers of fluid lavas, or formed in molten lava. Some specific lunar examples are discussed, including unusual shallow rings resembling experimental craters deformed by isostatic filling.

  1. MAPPING OF PLANETARY SURFACE AGE BASED ON CRATER STATISTICS OBTAINED BY AN AUTOMATIC DETECTION ALGORITHM

    Directory of Open Access Journals (Sweden)

    A. L. Salih

    2016-06-01

    Full Text Available The analysis of the impact crater size-frequency distribution (CSFD is a well-established approach to the determination of the age of planetary surfaces. Classically, estimation of the CSFD is achieved by manual crater counting and size determination in spacecraft images, which, however, becomes very time-consuming for large surface areas and/or high image resolution. With increasing availability of high-resolution (nearly global image mosaics of planetary surfaces, a variety of automated methods for the detection of craters based on image data and/or topographic data have been developed. In this contribution a template-based crater detection algorithm is used which analyses image data acquired under known illumination conditions. Its results are used to establish the CSFD for the examined area, which is then used to estimate the absolute model age of the surface. The detection threshold of the automatic crater detection algorithm is calibrated based on a region with available manually determined CSFD such that the age inferred from the manual crater counts corresponds to the age inferred from the automatic crater detection results. With this detection threshold, the automatic crater detection algorithm can be applied to a much larger surface region around the calibration area. The proposed age estimation method is demonstrated for a Kaguya Terrain Camera image mosaic of 7.4 m per pixel resolution of the floor region of the lunar crater Tsiolkovsky, which consists of dark and flat mare basalt and has an area of nearly 10,000 km2. The region used for calibration, for which manual crater counts are available, has an area of 100 km2. In order to obtain a spatially resolved age map, CSFDs and surface ages are computed for overlapping quadratic regions of about 4.4 x 4.4 km2 size offset by a step width of 74 m. Our constructed surface age map of the floor of Tsiolkovsky shows age values of typically 3.2-3.3 Ga, while for small regions lower (down to

  2. Mapping of Planetary Surface Age Based on Crater Statistics Obtained by AN Automatic Detection Algorithm

    Science.gov (United States)

    Salih, A. L.; Mühlbauer, M.; Grumpe, A.; Pasckert, J. H.; Wöhler, C.; Hiesinger, H.

    2016-06-01

    The analysis of the impact crater size-frequency distribution (CSFD) is a well-established approach to the determination of the age of planetary surfaces. Classically, estimation of the CSFD is achieved by manual crater counting and size determination in spacecraft images, which, however, becomes very time-consuming for large surface areas and/or high image resolution. With increasing availability of high-resolution (nearly) global image mosaics of planetary surfaces, a variety of automated methods for the detection of craters based on image data and/or topographic data have been developed. In this contribution a template-based crater detection algorithm is used which analyses image data acquired under known illumination conditions. Its results are used to establish the CSFD for the examined area, which is then used to estimate the absolute model age of the surface. The detection threshold of the automatic crater detection algorithm is calibrated based on a region with available manually determined CSFD such that the age inferred from the manual crater counts corresponds to the age inferred from the automatic crater detection results. With this detection threshold, the automatic crater detection algorithm can be applied to a much larger surface region around the calibration area. The proposed age estimation method is demonstrated for a Kaguya Terrain Camera image mosaic of 7.4 m per pixel resolution of the floor region of the lunar crater Tsiolkovsky, which consists of dark and flat mare basalt and has an area of nearly 10,000 km2. The region used for calibration, for which manual crater counts are available, has an area of 100 km2. In order to obtain a spatially resolved age map, CSFDs and surface ages are computed for overlapping quadratic regions of about 4.4 x 4.4 km2 size offset by a step width of 74 m. Our constructed surface age map of the floor of Tsiolkovsky shows age values of typically 3.2-3.3 Ga, while for small regions lower (down to 2.9 Ga) and higher

  3. Impact Melt in Small Lunar Highlands Craters

    Science.gov (United States)

    Plescia, J. B.; Cintala, M. J.; Robinson, M. S.; Barnouin, O.; Hawke, B. R.

    2011-01-01

    Impact-melt deposits are a typical characteristic of complex impact craters, occurring as thick pools on the crater floor, ponds on wall terraces, veneers on the walls, and flows outside and inside the rim. Studies of the distribution of impact melt suggested that such deposits are rare to absent in and around small (km to sub-km), simple impact craters. noted that the smallest lunar crater observed with impact melt was approximately 750 m in diameter. Similarly, theoretical models suggest that the amount of melt formed is a tiny fraction (crater volume and thus significant deposits would not be expected for small lunar craters. LRO LROC images show that impact-melt deposits can be recognized associated with many simple craters to diameters down to approximately 200 m. The melt forms pools on the crater floor, veneer on the crater walls or ejecta outside the crater. Such melt deposits are relatively rare, and can be recognized only in some fresh craters. These observations indicate that identifiable quantities of impact melt can be produced in small impacts and the presence of such deposits shows that the material can be aggregated into recognizable deposits. Further, the present of such melt indicates that small craters could be reliably radiometrically dated helping to constrain the recent impact flux.

  4. Flat-port connectors

    KAUST Repository

    Alrashed, Mohammed

    2017-05-26

    Disclosed are various embodiments for connectors used with electronic devices, such as input and/or output ports to connect peripheral equipment or accessories. More specifically, various flat-port are provided that can be used in place of standard connectors including, but not limited to, audio jacks and Universal Serial Bus (USB) ports. The flat-port connectors are an alternate connection design to replace the traditional receptacle port (female-port), making the device more sealed creation more dust and water resistant. It is unique in the way of using the outer surfaces of the device for the electrical connection between the ports. Flat-port design can allow the manufacture of extremely thin devices by eliminating the side ports slots that take a lot of space and contribute to the increase thickness of the device. The flat-port receptacle improves the overall appearance of the device and makes it more resistant to dust and water.

  5. Stratigraphy of the crater Copernicus

    Science.gov (United States)

    Paquette, R.

    1984-01-01

    The stratigraphy of copernicus based on its olivine absorption bands is presented. Earth based spectral data are used to develop models that also employ cratering mechanics to devise theories for Copernican geomorphology. General geologic information, spectral information, upper and lower stratigraphic units and a chart for model comparison are included in the stratigraphic analysis.

  6. Small crater populations on Vesta

    CERN Document Server

    Marchi, S; O'Brien, D P; Schenk, P; Mottola, S; De Sanctis, M C; Kring, D A; Williams, D A; Raymond, C A; Russell, C T

    2013-01-01

    The NASA Dawn mission has extensively examined the surface of asteroid Vesta, the second most massive body in the main belt. The high quality of the gathered data provides us with an unique opportunity to determine the surface and internal properties of one of the most important and intriguing main belt asteroids (MBAs). In this paper, we focus on the size frequency distributions (SFDs) of sub-kilometer impact craters observed at high spatial resolution on several selected young terrains on Vesta. These small crater populations offer an excellent opportunity to determine the nature of their asteroidal precursors (namely MBAs) at sizes that are not directly observable from ground-based telescopes (i.e., below ~100 m diameter). Moreover, unlike many other MBA surfaces observed by spacecraft thus far, the young terrains examined had crater spatial densities that were far from empirical saturation. Overall, we find that the cumulative power-law index (slope) of small crater SFDs on Vesta is fairly consistent with...

  7. Low-emissivity impact craters on Venus

    Science.gov (United States)

    Weitz, C. M.; Elachi, C.; Moore, H. J.; Basilevsky, A. T.; Ivanov, B. A.; Schaber, G. G.

    1992-01-01

    An analysis of 144 impact craters on Venus has shown that 11 of these have floors with average emissivities lower than 0.8. The remaining craters have emissivities between 0.8 and 0.9, independent of the specific backscatter cross section of the crater floors. These 144 impact craters were chosen from a possible 164 craters with diameters greater than 30 km as identified by researchers for 89 percent of the surface of Venus. We have only looked at craters below 6053.5 km altitude because a mineralogical change causes high reflectivity/low emissivity above the altitude. We have also excluded all craters with diameters smaller than 30 km because the emissivity footprint at periapsis is 16 x 24 km and becomes larger at the poles.

  8. PyCraters: A Python framework for crater function analysis

    CERN Document Server

    Norris, Scott A

    2014-01-01

    We introduce a Python framework designed to automate the most common tasks associated with the extraction and upscaling of the statistics of single-impact crater functions to inform coefficients of continuum equations describing surface morphology evolution. Designed with ease-of-use in mind, the framework allows users to extract meaningful statistical estimates with very short Python programs. Wrappers to interface with specific simulation packages, routines for statistical extraction of output, and fitting and differentiation libraries are all hidden behind simple, high-level user-facing functions. In addition, the framework is extensible, allowing advanced users to specify the collection of specialized statistics or the creation of customized plots. The framework is hosted on the BitBucket service under an open-source license, with the aim of helping non-specialists easily extract preliminary estimates of relevant crater function results associated with a particular experimental system.

  9. Lethal Interpersonal Violence in the Middle Pleistocene

    OpenAIRE

    Nohemi Sala; Juan Luis Arsuaga; Ana Pantoja-Pérez; Adrián Pablos; Ignacio Martínez; Quam, Rolf M.; Asier Gómez-Olivencia; José María Bermúdez de Castro; Eudald Carbonell

    2015-01-01

    Evidence of interpersonal violence has been documented previously in Pleistocene members of the genus Homo, but only very rarely has this been posited as the possible manner of death. Here we report the earliest evidence of lethal interpersonal violence in the hominin fossil record. Cranium 17 recovered from the Sima de los Huesos Middle Pleistocene site shows two clear perimortem depression fractures on the frontal bone, interpreted as being produced by two episodes of localized blunt force ...

  10. Evolution of the Pleistocene Climate Continuum

    Science.gov (United States)

    Meyers, S. R.; Hinnov, L. A.

    2008-12-01

    Orbital-climate theory provides a powerful deterministic framework for the analysis of Pleistocene climate change, and has become a cornerstone of modern Paleoclimatology. The stochastic component of Pleistocene climate has received considerably less attention, although some studies have argued for the dominance of stochastic climate processes. Undoubtedly, a complete understanding of the controls on Pleistocene climate change necessitates an assessment of both deterministic and stochastic processes, as well as potential linkages between the two. In this study, we investigate changes in the dominance of deterministic versus stochastic climate processes associated with evolution of the Pleistocene climate system. Achievement of this objective requires: (1) careful selection and analysis of paleoclimate data series, to isolate true climate noise from other proxy noise sources (e.g., proxy fidelity, time-scale distortion, diagenesis, analytical error), and (2) application of quantitative methods capable of separating deterministic periodic signals (the spectral "lines") from the stochastic component of climate (the spectral "continuum"). This study focuses on an analysis of published benthic foraminifera oxygen isotopic records using a number of techniques rooted in Thomson's multi-taper method, which is specifically designed to separate deterministic "line" energy from stochastic "continuum" energy. Our analysis indicates large, and sometimes abrupt, changes in the relative dominance of stochastic versus deterministic energy. These changes in energy distribution parallel the evolution of the Pleistocene climate system. This analysis also demonstrates linkages between stochastic and deterministic climate processes, and yields insight into the mechanisms of Pleistocene climate change.

  11. An analytical model of crater count equilibrium

    Science.gov (United States)

    Hirabayashi, Masatoshi; Minton, David A.; Fassett, Caleb I.

    2017-06-01

    Crater count equilibrium occurs when new craters form at the same rate that old craters are erased, such that the total number of observable impacts remains constant. Despite substantial efforts to understand this process, there remain many unsolved problems. Here, we propose an analytical model that describes how a heavily cratered surface reaches a state of crater count equilibrium. The proposed model formulates three physical processes contributing to crater count equilibrium: cookie-cutting (simple, geometric overlap), ejecta-blanketing, and sandblasting (diffusive erosion). These three processes are modeled using a degradation parameter that describes the efficiency for a new crater to erase old craters. The flexibility of our newly developed model allows us to represent the processes that underlie crater count equilibrium problems. The results show that when the slope of the production function is steeper than that of the equilibrium state, the power law of the equilibrium slope is independent of that of the production function slope. We apply our model to the cratering conditions in the Sinus Medii region and at the Apollo 15 landing site on the Moon and demonstrate that a consistent degradation parameterization can successfully be determined based on the empirical results of these regions. Further developments of this model will enable us to better understand the surface evolution of airless bodies due to impact bombardment.

  12. Locating the LCROSS Impact Craters

    CERN Document Server

    Marshall, William; Moratto, Zachary; Colaprete, Anthony; Neumann, Gregory; Smith, David; Hensley, Scott; Wilson, Barbara; Slade, Martin; Kennedy, Brian; Gurrola, Eric; Harcke, Leif; 10.1007/s11214-011-9765-0

    2011-01-01

    The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket stage into a permanently shadowed region near the lunar south pole. The Sheperding Spacecraft (SSC) separated \\sim9 hours before impact and performed a small braking maneuver in order to observe the Centaur impact plume, looking for evidence of water and other volatiles, before impacting itself. This paper describes the registration of imagery of the LCROSS impact region from the mid- and near-infrared cameras onboard the SSC, as well as from the Goldstone radar. We compare the Centaur impact features, positively identified in the first two, and with a consistent feature in the third, which are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta region. The images are registered to Lunar Reconnaisance Orbiter (LRO) topographical data which allows determination of the impact location. This location is compared with the impact location derived from ground-based tracking and propagation of...

  13. Boulders Ejected From Small Impact Craters

    Science.gov (United States)

    Bart, Gwendolyn D.; Melosh, H. J.

    2006-09-01

    We investigate the distribution of boulders ejected from lunar craters by analyzing high resolution Lunar Orbiter images. Our previous study (DPS 2004) of four small craters indicated that larger boulders are more frequently found close to the crater rim rather than far away, and that the size of the ejecta drops off as a power law with distance from the crater. Our current study adds more than ten new bouldery craters that range in size from 200 m to several kilometers and are found on a variety of terrain (mare, highlands, and the Copernicus ejecta blanket.) For each crater we plot the boulder diameter as a function of the ejection velocity of the boulder. We compare this size-velocity distribution with the size-velocity distribution of ejecta from large craters (Vickery 1986, 1987) to ascertain the mechanism of fracture of the substrate in the impact. We also make cumulative plots of the boulders, indicating the number of boulders of each size present around the crater. The cumulative plots allow us to compare our boulder distributions with the distributions of secondary craters from large impacts. Material thrown from a several-hundred-meter diameter crater may land intact as boulders, but material thrown from a tens-of-kilometers diameter crater will travel at a significantly higher velocity, and will form a secondary crater when it impacts the surface. Our data helps elucidate whether the upturn, at small diameters, of the cratering curve of the terrestrial planets is due to secondary impacts or to the primary population. This work is funded by NASA PGG grant NNG05GK40G.

  14. Discovering Research Value in Small Meteorite Craters

    Science.gov (United States)

    Cassidy, W. A.

    1995-09-01

    The Campo del Cielo meteorite crater field in Argentina contains at least 20 small meteorite craters, but a recent review of the field data and a remote sensing study suggest there may be many more. The fall occurred about 4000 y ago into a uniform loessy soil, and the craters are well enough preserved so that some of their parameters of impact can be determined by excavation. The craters were formed by multi-ton fragments of a type IA meteoroid with abundant silicate inclusions. Relative to the horizontal, the angle of infall was around 10 degrees. Reflecting the low angle of infall, the crater field is elongated with apparent dimensions of 3 x 18.5 km. The largest craters are near the center of this ellipse. This suggests that when the parent meteoroid broke apart the resulting fragments diverged from the original trajectory in inverse relation to their masses and did not undergo size sorting due to atmospheric deceleration. The major axis of the crater field as we know it extends along N58 degrees E, but the azimuths of infall determined by excavation of Craters 9 and 10 are N84 degrees E and N77 degrees E, respectively, suggesting that the major axis of the crater field is not yet well determined. This is supported by the elongation of magnetic anomalies over 4 other craters, all of which trend significantly more easterly than the major axis of the crater field. The 3 or 4 largest craters appear to be explosion craters and the others are shock-wave excavations extended by penetration funnels with multi-ton masses preserved within them. There are two ways in which field research on the Campo del Cielo craterfield is found to be useful. (1)This occurrence of a swarm of projectiles impacting at known angles and similar velocities into a uniform target material provides an excellent field site at which to test the applicability of various existing studies directed toward the interpretation of impact craters on planetary surfaces other than the earth. Given certain

  15. Individual energy savings for individual flats in blocks of flats

    DEFF Research Database (Denmark)

    Nielsen, Anker; Rose, Jørgen

    2014-01-01

    It is well known that similar flats in a block do not have the same energy demand. Part of the explanation for this is the location of the flat in the building, e.g. on the top floor, at the house end or in the middle of the building. It is possible to take this into account when the heating bill...... is distributed on the individual flats. Today, most blocks of flats have individual heat meters to save energy and to ensure a fair distribution of the cost. If all flats have the same indoor temperature, the distribution is correct. In practice, the inhabitants of the different flats maintain different indoor...

  16. Crater formation during raindrop impact on sand

    Science.gov (United States)

    de Jong, Rianne; Zhao, Song-Chuan; van der Meer, Devaraj

    2017-04-01

    After a raindrop impacts on a granular bed, a crater is formed as both drop and target deform. After an initial, transient, phase in which the maximum crater depth is reached, the crater broadens outwards until a final steady shape is attained. By varying the impact velocity of the drop and the packing density of the bed, we find that avalanches of grains are important in the second phase and hence affect the final crater shape. In a previous paper, we introduced an estimate of the impact energy going solely into sand deformation and here we show that both the transient and final crater diameter collapse with this quantity for various packing densities. The aspect ratio of the transient crater is however altered by changes in the packing fraction.

  17. Clustered impacts - Experiments and implications. [cratering mechanics

    Science.gov (United States)

    Schultz, P. H.; Gault, D. E.

    1985-01-01

    The characteristics of impact by clusters of projectiles are experimentally studied by launching grouped projectiles of aluminum shot, steel shot, iron filings, and sand. Cratering efficiency is considered as a function of a dimensionless parameter related to projectile size and impact velocity. The effects of different target and projectile densities on cratering efficiency are examined. Crater morphology is addressed by considering a typical example, reviewing the systematics between cluster dispersion and crater morphology for vertical impacts, and examining oblique angle impacts which have relevance for planetary secondary cratering processes. These results are compared with impacts by single bodies with different strengths. The evolution of the ejecta plume for clustered impacts is compared to that for single-body impacts for vertical and oblique impacts from 1.3 to 1.8 km/s. The experimental results are discussed in the context of planetary surface processes, emphasizing processes in an atmosphere-free environment and secondary impact cratering.

  18. The Cratering History of Asteroid (21) Lutetia

    CERN Document Server

    Marchi, S; Vincent, J -B; Morbidelli, A; Mottola, S; Marzari, F; Kueppers, M; Besse, S; Thomas, N; Barbieri, C; Naletto, G; Sierks, H

    2011-01-01

    The European Space Agency's Rosetta spacecraft passed by the main belt asteroid (21) Lutetia the 10th July 2010. With its ~100km size, Lutetia is one of the largest asteroids ever imaged by a spacecraft. During the flyby, the on-board OSIRIS imaging system acquired spectacular images of Lutetia's northern hemisphere revealing a complex surface scarred by numerous impact craters, reaching the maximum dimension of about 55km. In this paper, we assess the cratering history of the asteroid. For this purpose, we apply current models describing the formation and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models, coupled with appropriate crater scaling laws, allow us to interpret the observed crater size-frequency distribution (SFD) and constrain the cratering history. Thanks to this approach, we derive the crater retention age of several regions on Lutetia, namely the time lapsed since their formation or global surface reset. We also investigate the influe...

  19. Defrosting of Russell Crater Dunes

    Science.gov (United States)

    2007-01-01

    These two images (at right) were acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) 39 days apart at 19:10 UTC (2:10 PM EST) on December 28, 2006 (upper right) and at 20:06 UTC (3:06 PM EST) on February 5, 2007 (lower right). These CRISM data were acquired in 544 colors covering the wavelength range from 0.36-3.92 micrometers, and show features as small as 20 meters (about 65 feet) across. Both images are false color composites of bands at 2.5, 1.5, and 1.25 micrometers, and are nearly centered at the same location, 54.875oS, 12.919oE (upper right) and 54.895oS, 12.943oE (lower right). Each image is approximately 11 kilometers (7 miles) across at its narrowest. These are part of a series of images capturing the evolution of carbon dioxide frost on the surface of the dunes in Russell Crater. Russell Crater is one of many craters in the southern highland region of Mars that contain large areas of sand dunes. The sand in these dunes has accumulated over a very long time period -- perhaps millions of years -- as wind blows over the highland terrain, picking up sand in some places and depositing in others. The topography of the craters forces the wind to blow up and over the crater rims, and the wind often isn't strong enough to keep the tiny grains suspended. This makes the sand fall to the ground and gradually pile up, and over time the surface breezes shape the sand into ripples and dunes. A similar process is at work at the Great Sand Dunes National Park and Preserve in Colorado, USA. The above left image shows a THEMIS daytime infrared mosaic of Russell Crater and the location of its (approximately) 30-kilometer wide dune field in the northeastern quadrant of the crater floor. Superposed on this view and shown enlarged at the upper right is CRISM image FRT000039DF. This CRISM image was acquired during the late Martian southern winter (solar longitude = 157.7o), and the bright blue in this false color composite indicates the presence of

  20. A meteorite crater on Mt. Ararat?

    CERN Document Server

    Gurzadyan, V G

    2010-01-01

    We briefly report on a crater on the western slope of Mt.Ararat . It is located in an area closed to foreigners at an altitude around 2100m with geographic coordinates 39\\deg 47' 30"N, 44\\deg 14' 40"E. The diameter of the crater is around 60-70m, the depth is up to 15m. The origin of the crater, either of meteorite impact or volcanic, including the evaluation of its age, will need detailed studies.

  1. Central Remnant Craters on Mars - Localization of Hydrothermal Alteration at the Edge of Crater Floors?

    Science.gov (United States)

    Newsom, H. E.

    2001-01-01

    Localized erosion at the edge of crater floors may be caused by hydrothermal alteration due to focusing of fluid flow around an impact melt sheet following crater formation, coupled with hydrothermal self-sealing under the center of the crater. Additional information is contained in the original extended abstract.

  2. Experimental study of impact-cratering damage on brittle cylindrical column model as a fundamental component of space architecture

    Science.gov (United States)

    Fujiwara, Akira; Onose, Naomi; Setoh, Masato; Nakamura, Akiko M.; Hiraoka, Kensuke; Hasegawa, Sunao; Okudaira, Kyoko

    2014-10-01

    The cylindrical column of brittle material processed from soil and rock is a fundamental component of architectures on the surface of solid bodies in the solar system. One of the most hazardous events for the structure is damaging by hypervelocity impacts by meteoroids and debris. In such a background, cylindrical columns made of plaster of Paris and glass-bead-sintered ceramic were impacted by spherical projectiles of nylon, glass, and steel at velocity of about 1-4.5 km/s. Measured crater radii, depth, and excavated mass expressed by a function of the cylinder radius are similar irrespective of the target material, if those parameters are normalized by appropriate parameters of the crater produced on the flat-surface target. The empirical scaling relations of the normalized crater radii and depth are provided. Using them, crater dimensions and excavated mass of crater on cylindrical surface of any radius can be predicted from the existing knowledge of those for flat surface. Recommendation for the minimum diameter of a cylinder so as to resist against a given impact is provided.

  3. Using quantitative topographic analysis to understand the role of water on transport and deposition processes on crater walls

    Science.gov (United States)

    Palucis, Marisa Christina

    The amount of water runoff need to evolve landscapes is rarely assessed. Empirical studies correlate erosion rate to runoff or mean annual precipitation, but rarely is the full history of a landscape known such that it is possible to assess how much water was required to produce it. While this may not seem to be of primary importance on Earth where water is commonly plentiful, on Mars the amount of water to drive landscape evolution is a key question. Here we tackle this question through a series of five chapters, one devoted to field work at Meteor Crater, another to laboratory experiments about controlling processes, and then two chapters on analysis of landforms and implications of water runoff on Mars (associated with the Mars Science Laboratory mission to Gale Crater), and then we complete this effort with a consideration of how we can reliably assign relative timing between events resulting in small depositional features. What follows below is a summary of what is found in each chapter. Meteor Crater, a 4.5 km2 impact crater that formed ˜50,000 years ago in northern Arizona, has prominent gully features on its steep walls that appear similar to some gullies found on Mars. At the crater bottom, there are over 30 meters of lake sediments from a lake that disappeared ˜10,000 to 11,000 years ago, indicating the transition from the Pleistocene to the current, drier climate. A combination of fieldwork, cosmogenic dating, and topographic analysis of LiDAR data show that debris flows, not seepage erosion and fluvial processes as previously suggested in the literature, drove gully incision during their formation period of ˜40,000 years before the onset of the Holocene. Runoff from bare bedrock source areas high on the crater wall cut into lower debris mantled slopes, where the runoff bulked up and transformed into debris flows that carried boulders down to ˜5 to 8 degree slopes, leaving distinct boulder lined levees and lobate tongues of terminal debris deposits

  4. Synchronous extinction of North America's Pleistocene mammals

    Science.gov (United States)

    Faith, J. Tyler; Surovell, Todd A.

    2009-12-01

    The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago (≈13,800-11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000-10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant.

  5. Late Pleistocene potential distribution of the North African sengi or ...

    African Journals Online (AJOL)

    Late Pleistocene potential distribution of the North African sengi or ... origin for an extant species, predating the dramatic climatic fluctuations of the Pleistocene. ... occurrence points to develop models of present-day potential distributions of E.

  6. Machine cataloging of impact craters on Mars

    Science.gov (United States)

    Stepinski, Tomasz F.; Mendenhall, Michael P.; Bue, Brian D.

    2009-09-01

    This study presents an automated system for cataloging impact craters using the MOLA 128 pixels/degree digital elevation model of Mars. Craters are detected by a two-step algorithm that first identifies round and symmetric topographic depressions as crater candidates and then selects craters using a machine-learning technique. The system is robust with respect to surface types; craters are identified with similar accuracy from all different types of martian surfaces without adjusting input parameters. By using a large training set in its final selection step, the system produces virtually no false detections. Finally, the system provides a seamless integration of crater detection with its characterization. Of particular interest is the ability of our algorithm to calculate crater depths. The system is described and its application is demonstrated on eight large sites representing all major types of martian surfaces. An evaluation of its performance and prospects for its utilization for global surveys are given by means of detailed comparison of obtained results to the manually-derived Catalog of Large Martian Impact Craters. We use the results from the test sites to construct local depth-diameter relationships based on a large number of craters. In general, obtained relationships are in agreement with what was inferred on the basis of manual measurements. However, we have found that, in Terra Cimmeria, the depth/diameter ratio has an abrupt decrease at ˜38°S regardless of crater size. If shallowing of craters is attributed to presence of sub-surface ice, a sudden change in its spatial distribution is suggested by our findings.

  7. Flat covers of modules

    CERN Document Server

    Xu, Jinzhong

    1996-01-01

    Since the injective envelope and projective cover were defined by Eckmann and Bas in the 1960s, they have had great influence on the development of homological algebra, ring theory and module theory. In the 1980s, Enochs introduced the flat cover and conjectured that every module has such a cover over any ring. This book provides the uniform methods and systematic treatment to study general envelopes and covers with the emphasis on the existence of flat cover. It shows that Enochs' conjecture is true for a large variety of interesting rings, and then presents the applications of the results. Readers with reasonable knowledge in rings and modules will not have difficulty in reading this book. It is suitable as a reference book and textbook for researchers and graduate students who have an interest in this field.

  8. Impact craters in South America

    CERN Document Server

    Acevedo, Rogelio Daniel; Ponce, Juan Federico; Stinco, Sergio G

    2015-01-01

    A complete and updated catalogue of impact craters and structures in South America from 2014 is presented here. Approximately eighty proven, suspected and disproven structures have been identified by several sources in this continent. All the impact sites of this large continent have been exhaustively reviewed: the proved ones, the possible ones and some very doubtful. Many sites remain without a clear geological ""in situ"" confirmation and some of them could be even rejected. Argentina and Brazil are leading the list containing almost everything detected. In Bolivia, Chile, Colombia, Guyana,

  9. Flat Earth图片

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    欢迎来到这期的光盘介绍。本月的附刊光盘中,除了每月的精彩教程外,您可在光盘中找到15张由Flat Earth友情提供的库存图片。当然还有Twixtor和最新的Acrobat Reader 7。

  10. Hydrothermal Alteration at Lonar Crater, India and Elemental Variations in Impact Crater Clays

    Science.gov (United States)

    Newsom, H. E.; Nelson, M. J.; Shearer, C. K.; Misra, S.; Narasimham, V.

    2005-01-01

    The role of hydrothermal alteration and chemical transport involving impact craters could have occurred on Mars, the poles of Mercury and the Moon, and other small bodies. We are studying terrestrial craters of various sizes in different environments to better understand aqueous alteration and chemical transport processes. The Lonar crater in India (1.8 km diameter) is particularly interesting being the only impact crater in basalt. In January of 2004, during fieldwork in the ejecta blanket around the rim of the Lonar crater we discovered alteration zones not previously described at this crater. The alteration of the ejecta blanket could represent evidence of localized hydrothermal activity. Such activity is consistent with the presence of large amounts of impact melt in the ejecta blanket. Map of one area on the north rim of the crater containing highly altered zones at least 3 m deep is shown.

  11. The variability of crater identification among expert and community crater analysts

    CERN Document Server

    Robbins, Stuart J; Kirchoff, Michelle R; Chapman, Clark R; Fassett, Caleb I; Herrick, Robert R; Singer, Kelsi; Zanetti, Michael; Lehan, Cory; Huang, Di; Gay, Pamela L

    2014-01-01

    The identification of impact craters on planetary surfaces provides important information about their geological history. Most studies have relied on individual analysts who map and identify craters and interpret crater statistics. However, little work has been done to determine how the counts vary as a function of technique, terrain, or between researchers. Furthermore, several novel internet-based projects ask volunteers with little to no training to identify craters, and it was unclear how their results compare against the typical professional researcher. To better understand the variation among experts and to compare with volunteers, eight professional researchers have identified impact features in two separate regions of the moon. Small craters (diameters ranging from 10 m to 500 m) were measured on a lunar mare region and larger craters (100s m to a few km in diameter) were measured on both lunar highlands and maria. Volunteer data were collected for the small craters on the mare. Our comparison shows t...

  12. Chronology of heavily cratered terrains on Mercury

    Science.gov (United States)

    Marchi, S.; Chapman, C. R.

    2012-12-01

    Imaging of Mercury by Mariner 10 revealed a planet with more extensive plains units than on the Moon. Even in heavily cratered terrain, there is a lack of craters Morbidelli et al., [1] in order to interpret new crater counts on these terrains. We find that these craters are probably not saturated but may have been in equilibrium with a rapid resurfacing process, presumably volcanism that formed the earliest recognized intercrater plains. The crater retention age for this terrain, which contains the oldest large craters on Mercury, is surprisingly young, perhaps hundreds of millions of years younger than the heavily cratered pre-Nectarian terrains on the Moon [2]. These results are important for understanding the early geological and geophysical evolution of Mercury. References: [1] Morbidelli A., Marchi S., Bottke W.F., and Kring D.A. 2012. A sawtooth timeline for the first billion years of the lunar bombardment. Earth and Planetary Science Letters, in press. [2] Marchi S., Bottke W.F., Kring D.A., and Morbidelli A. 2012. The onset of the lunar cataclysm as recorded in its ancient crater populations. Earth and Planetary Science Letters 325, 27-38.

  13. Projectile Velocity and Crater Formation in Water

    Directory of Open Access Journals (Sweden)

    Pravitra Chaikulngamdee

    2010-01-01

    Full Text Available The relationship between the velocity of impact and maximum crater diameter was found for two steel balls dropped into water using 300 fps video. The maximum diameter of the crater was found to be proportional to the impact velocity and independent of the diameter of the ball.

  14. Processes Modifying Cratered Terrains on Pluto

    Science.gov (United States)

    Moore, J. M.

    2015-01-01

    The July encounter with Pluto by the New Horizons spacecraft permitted imaging of its cratered terrains with scales as high as approximately 100 m/pixel, and in stereo. In the initial download of images, acquired at 2.2 km/pixel, widely distributed impact craters up to 260 km diameter are seen in the near-encounter hemisphere. Many of the craters appear to be significantly degraded or infilled. Some craters appear partially destroyed, perhaps by erosion such as associated with the retreat of scarps. Bright ice-rich deposits highlight some crater rims and/or floors. While the cratered terrains identified in the initial downloaded images are generally seen on high-to-intermediate albedo surfaces, the dark equatorial terrain informally known as Cthulhu Regio is also densely cratered. We will explore the range of possible processes that might have operated (or still be operating) to modify the landscape from that of an ancient pristinely cratered state to the present terrains revealed in New Horizons images. The sequence, intensity, and type of processes that have modified ancient landscapes are, among other things, the record of climate and volatile evolution throughout much of the Pluto's existence. The deciphering of this record will be discussed. This work was supported by NASA's New Horizons project.

  15. Surface expression of the Chicxulub crater

    Science.gov (United States)

    Pope, K O; Ocampo, A C; Kinsland, G L; Smith, R

    1996-06-01

    Analyses of geomorphic, soil, and topographic data from the northern Yucatan Peninsula, Mexico, confirm that the buried Chicxulub impact crater has a distinct surface expression and that carbonate sedimentation throughout the Cenozoic has been influenced by the crater. Late Tertiary sedimentation was mostly restricted to the region within the buried crater, and a semicircular moat existed until at least Pliocene time. The topographic expression of the crater is a series of features concentric with the crater. The most prominent is an approximately 83-km-radius trough or moat containing sinkholes (the Cenote ring). Early Tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km, respectively. Two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km. The low ridge between the inner troughs corresponds to the buried peak ring. The moat corresponds to the outer edge of the crater floor demarcated by a major ring fault. The outer trough and the approximately 62-km-radius inner trough also mark buried ring faults. The ridge crest corresponds to the topographic rim of the crater as modified by postimpact processes. These interpretations support previous findings that the principal impact basin has a diameter of approximately 180 km, but concentric, low-relief slumping extends well beyond this diameter and the eroded crater rim may extend to a diameter of approximately 260 km.

  16. Cratering Rates in the Outer Solar System

    Science.gov (United States)

    Zahnle, K.; Levison, H.; Dones, L.; Schenk, P.

    1999-09-01

    We use numerical simulations of the orbital evolution of stray Kuiper Belt objects to relate the number of comets striking the planets to the number of Jupiter-family comets observed in the inner solar system. Cratering rates are obtained by accounting for gravitational focusing, cratering efficiency, and an intuitive average of the various available calibrations of cometary mass. The most telling craters are those of Triton, a retrograde moon in a prograde system. It is well-known that much of Triton's surface is relatively young. Less well-known is that Triton features the most startling hemispheric cratering asymmetry in the solar system: fresh impact craters are almost exclusively limited to the leading hemisphere. It would seem that Triton has been colliding almost exclusively with planetocentric debris. If so, then we conclude that Triton's trailing hemisphere is less than 10 million years old. Recent too must be the event that cratered the leading hemisphere. Once admitted we must consider planetocentric cratering of other, prograde satellites. In particular, the lack of a strong apex-antapex asymmetry on Ganymede is not as good an argument for nonsynchronous rotation as we once thought. Rather, many or most of Ganymede's craters might prove to be secondaries, most likely made by ejecta launched into orbit about Jupiter, only to return not too much later, like the insatiable shards of Texas in Armageddon II: The New Millenium.

  17. Cascading Crater Detection with Active Learning

    Science.gov (United States)

    Miller, W. I.; Stepinski, T. F.; Mu, Y.; Ding, W.

    2011-03-01

    Our strategy for automatic crater detection consists of employing a cascading AdaBoost classifier for identification of craters in images, and using the SOM as an active learning tool to minimize the number of image examples that need to be labeled by an analyst.

  18. Constraining the Cratering Chronology of Vesta

    CERN Document Server

    O'Brien, David P; Morbidelli, Alessandro; Bottke, William F; Schenk, Paul M; Russell, Christopher T; Raymond, Carol A

    2014-01-01

    Vesta has a complex cratering history, with ancient terrains as well as recent large impacts that have led to regional resurfacing. Crater counts can help constrain the relative ages of different units on Vesta's surface, but converting those crater counts to absolute ages requires a chronology function. We present a cratering chronology based on the best current models for the dynamical evolution of asteroid belt, and calibrate it to Vesta using the record of large craters on its surface. While uncertainties remain, our chronology function is broadly consistent with an ancient surface of Vesta as well as other constraints such as the bombardment history of the rest of the inner Solar System and the Ar-Ar age distribution of howardite, eucrite and diogenite (HED) meteorites from Vesta.

  19. International Assistance in Naming Craters on Mercury

    Science.gov (United States)

    Weir, H. M.; Edmonds, J.; Hallau, K.; Hirshon, B.; Goldstein, J.; Hamel, J.; Hamel, S.; Solomon, S. C.

    2015-12-01

    NASA's robotic MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft made history in March 2011 by becoming the first to orbit Mercury. During the mission, MESSENGER acquired more than 250,000 images and made many other kinds of measurements. Names are often given to surface features that are of special scientific interest, such as craters. To draw international attention to the achievements of the spacecraft and engineers and scientists who made the MESSENGER mission a success, the MESSENGER Education and Public Outreach (EPO) Team initiated a Name a Crater on Mercury Competition.Five craters of particular geological interest were chosen by the science team. In accordance with International Astronomical Union (IAU) rules for Mercury, impact craters are named in honor of those who have made outstanding or fundamental contributions to the arts and humanities. He or she must have been recognized as a historically significant figure in the arts for at least 50 years and deceased for the last three years. We were particularly interested in entries honoring people from nations and cultural groups underrepresented in the current list of crater names. From more than 3600 entries received from around the world, the EPO team was able to reduce the number of entries to about 1200 names of 583 different artists who met the contest eligibility criteria. Next, the proposed individuals were divided into five artistic field groups and distributed to experts in that respective field. Each expert reviewed approximately100 artists with their biographical information. They narrowed down their list to a top ten, then to a top five by applying a rubric. The final selection was based on the reviewer lists and scores, with at least three finalist names selected from each artistic field. Of the 17 finalists provided to the IAU, the following names were selected: Carolan crater, Enheduanna crater, Karsh crater, Kulthum crater, and Rivera crater. For more

  20. Flow Fields at Tooting Crater, Mars

    Science.gov (United States)

    Mouginis-Mark, P. J.; Garbeil, H.

    2007-12-01

    HiRISE images of the impact crater Tooting (~29 km dia., located at 23.4°N, 207.5°E) on Mars have revealed a remarkable series of lobate flows on the southern rim, wall and floor of the crater. The origin of these flows has not yet been determined, but their spatial distribution and morphology could indicate that they are flows of impact melt, mudflows, or lava flows. Tooting crater shows numerous signs of being very young (very few superposed impact craters, very high depth/diameter ratio, high thermal inertia ejecta, and a well preserved set of secondary craters), and so allows detailed analysis of these unusual flows, which appear to be almost pristine. We have developed a 2-meter digital elevation model of Tooting using stereo HiRISE images to characterize the flows, which in general are relief close to the crater rim crest. Five discrete segments of this flow exist, including a 1.3 km segment with a discrete 15 m wide central channel and three lobate distal margins. (3) A set of 7 lobes ~700 m long on the inner S wall. These lobes have very well defined central channels ~25 m wide and levees 30 m thick and 300 m wide. These flows no doubt formed in an unusual environment, probably including extensive amounts of impact melt, volatiles released from the substrate, and highly unstable slopes on the crater rim. Tooting crater therefore displays a novel planetary flow field; the correct identification of the origin of these flows holds significance for understanding the role of volatiles in the impact cratering process, the potential of thermal anomalies existing within the crater cavity for extended period of time, and the emplacement of the ejecta. We are therefore developing numerical models, based on the rheology of lava flows, in order to help to resolve the origin of this flow field.

  1. Flat conductor cable commercialization project

    Science.gov (United States)

    Hogarth, P.; Wadsworth, E.

    1977-01-01

    An undercarpet flat conductor cable and a baseboard flat conductor cable system were studied for commercialization. The undercarpet system is designed for use in office and commercial buildings. It employs a flat power cable, protected by a grounded metal shield, that terminates in receptacles mounted on the floor. It is designed to interface with a flat conductor cable telephone system. The baseboard system consists of a flat power cable mounted in a plastic raceway; both the raceway and the receptacles are mounted on the surface of the baseboard. It is designed primarily for use in residential buildings, particularly for renovation and concrete and masonry construction.

  2. Late Pleistocene glaciation of the Changbai Mountains in northeastern China

    Institute of Scientific and Technical Information of China (English)

    ZHANG Wei; NIU YunBo; YAN Ling; CUI ZhiJiu; LI ChuanChuan; MU KeHua

    2008-01-01

    The Changbai Mountains (2749 m a.s.l.) in northeastern China are one of the typical mountain regions with glaciation since late Pleistocene as evidenced by well-preserved erosive and accumulative land-forms at elevations above 2000 m a.s.l. Formed by glaciers around the crater lake, Tianchi Lake. Cirque glaciers developed on both the inner and outer sides of the volcanic cone. Well-preserved cirques, glacial trough valleys, glacial threholds, polished surfaces of the glacial erratics and the moraine ridges indicate that several glaciation processes took place during the last glacial period in this region. Re-sults of optically stimulated luminescence (OSL) dating on the moraine sediments, and the K/Ar, ther-mal ionization mass spectrometry (TIMS), electronic spinning resonance (ESR) dating on the volcanic rocks suggest two periods of glacier advances. One is named the Black Wind Mouth glacier advance taking place on the west and north slopes of the volcanic cone at an elevation of 2000-2100 m a.s.l.,which is dated to about 20 ka, being the result of the Last Glacial Maximum (LGM). The other is named the Meteorological Station glacier advance at the elevation of 2400--2600 m a.s.l., dated to 11 ka during the late glacial period, and is tentatively correlated to the Younger Dryas stage. The scope of the former glacier advance is larger than that of the latter. Regional comparisons showed that the glacial se-quences in the Changbai Mountains are similar to other glaciated areas in eastern Asia during the later part of the last glacial cycle.

  3. Lunar polar craters - Icy, rough or just sloping?

    Science.gov (United States)

    Eke, Vincent R.; Bartram, Sarah A.; Lane, David A.; Smith, David; Teodoro, Luis F. A.

    2014-10-01

    Circular Polarisation Ratio (CPR) mosaics from Mini-SAR on Chandrayaan-1 and Mini-RF on LRO are used to study craters near to the lunar north pole. The look direction of the detectors strongly affects the appearance of the crater CPR maps. Rectifying the mosaics to account for parallax also significantly changes the CPR maps of the crater interiors. It is shown that the CPRs of crater interiors in unrectified maps are biased to larger values than crater exteriors, because of a combination of the effects of parallax and incidence angle. Using the LOLA Digital Elevation Map (DEM), the variation of CPR with angle of incidence has been studied. For fresh craters, CPR ∼0.7 with only a weak dependence on angle of incidence or position interior or just exterior to the crater, consistent with dihedral scattering from blocky surface roughness. For anomalous craters, the CPR interior to the crater increases with both incidence angle and distance from the crater centre. Central crater CPRs are similar to those in the crater exteriors. CPR does not appear to correlate with temperature within craters. Furthermore, the anomalous polar craters have diameter-to-depth ratios that are lower than those of typical polar craters. These results strongly suggest that the high CPR values in anomalous polar craters are not providing evidence of significant volumes of water ice. Rather, anomalous craters are of intermediate age, and maintain sufficiently steep sides that sufficient regolith does not cover all rough surfaces.

  4. Piecewise flat gravitational waves

    Energy Technology Data Exchange (ETDEWEB)

    Van de Meent, Maarten, E-mail: M.vandeMeent@uu.nl [Institute for Theoretical Physics and Spinoza Institute, Utrecht University, PO Box 80.195, 3508 TD Utrecht (Netherlands)

    2011-04-07

    We examine the continuum limit of the piecewise flat locally finite gravity model introduced by 't Hooft. In the linear weak field limit, we find the energy-momentum tensor and metric perturbation of an arbitrary configuration of defects. The energy-momentum turns out to be restricted to satisfy certain conditions. The metric perturbation is mostly fixed by the energy-momentum except for its lightlike modes which reproduce linear gravitational waves, despite no such waves being present at the microscopic level.

  5. Flat feet in children

    Directory of Open Access Journals (Sweden)

    Vukašinović Zoran

    2009-01-01

    Full Text Available The authors describe flatfoot, as one of very frequent deformities in everyday medical practice. A special condition of the deformity associated with a calcaneal valgus position and complicated by a knee valgus position (as a consequence of non-treatment is described. Also, the precise anatomy of the longitudinal foot arches (medial and lateral, definition and classification of the deformity, clinical findings and therapeutic protocols are proposed. The authors especially emphasise that the need for having extensive knowledge on the differences between a flexible and rigid flatfoot, having in mind that the treatment of flexible flat foot is usually not necessary, while the treatment of rigid flatfoot is usually unavoidable.

  6. Evaluation of Cavity Collapse and Surface Crater Formation for Selected Lawrence Livermore National Laboratory Underground Nuclear Tests - 2007

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, S K; Pawloski, G A; Raschke, K

    2007-04-26

    statements describe collapse evolution and crater stability in response to the 2007 request to review 20 LLNL test locations in areas 2, 9 and 10 of Yucca Flat listed in Table 1.

  7. Ancient DNA analysis of the extinct North American flat-headed peccary (Platygonus compressus).

    Science.gov (United States)

    Perry, Tahlia; van Loenen, Ayla L; Heiniger, Holly; Lee, Carol; Gongora, Jaime; Cooper, Alan; Mitchell, Kieren J

    2017-03-28

    The geographical range of extant peccaries extends from the southwestern United States through Central America and into northern Argentina. However, from the Miocene until the Pleistocene now-extinct peccary species inhabited the entirety of North America. Relationships among the living and extinct species have long been contentious. Similarly, how and when peccaries moved from North to South America is unclear. The North American flat-headed peccary (Platygonus compressus) became extinct at the end of the Pleistocene and is one of the most abundant subfossil taxa found in North America, yet despite this extensive fossil record its phylogenetic position has not been resolved. This study is the first to present DNA data from the flat-headed peccary and full mitochondrial genome sequences of all the extant peccary species. We performed a molecular phylogenetic analysis to determine the relationships among ancient and extant peccary species. Our results suggested that the flat-headed peccary is sister-taxon to a clade comprising the extant peccary species. Divergence date estimates from our molecular dating analyses suggest that if extant peccary diversification occurred in South America then their common ancestor must have dispersed from North America to South America well before the establishment of the Isthmus of Panama. We also investigated the genetic diversity of the flat-headed peccary by performing a preliminary population study on specimens from Sheriden Cave, Ohio. Flat-headed peccaries from Sheriden Cave appear to be genetically diverse and show no signature of population decline prior to extinction. Including additional extinct Pleistocene peccary species in future phylogenetic analyses will further clarify peccary evolution.

  8. Evidence for rapid topographic evolution and crater degradation on Mercury from simple crater morphometry

    Science.gov (United States)

    Fassett, Caleb I.; Crowley, Malinda C.; Leight, Clarissa; Dyar, M. Darby; Minton, David A.; Hirabayashi, Masatoshi; Thomson, Bradley J.; Watters, Wesley A.

    2017-06-01

    Examining the topography of impact craters and their evolution with time is useful for assessing how fast planetary surfaces evolve. Here, new measurements of depth/diameter (d/D) ratios for 204 craters of 2.5 to 5 km in diameter superposed on Mercury's smooth plains are reported. The median d/D is 0.13, much lower than expected for newly formed simple craters ( 0.21). In comparison, lunar craters that postdate the maria are much less modified, and the median crater in the same size range has a d/D ratio that is nearly indistinguishable from the fresh value. This difference in crater degradation is remarkable given that Mercury's smooth plains and the lunar maria likely have ages that are comparable, if not identical. Applying a topographic diffusion model, these results imply that crater degradation is faster by a factor of approximately two on Mercury than on the Moon, suggesting more rapid landform evolution on Mercury at all scales.Plain Language SummaryMercury and the Moon are both airless bodies that have experienced numerous impact events over billions of years. These impacts form craters in a geologic instant. The question examined in this manuscript is how fast these craters erode after their formation. To simplify the problem, we examined craters of a particular size (2.5 to 5 km in diameter) on a particular geologic terrain type (volcanic smooth plains) on both the Moon and Mercury. We then measured the topography of hundreds of craters on both bodies that met these criteria. Our results suggest that craters on Mercury become shallower much more quickly than craters on the Moon. We estimate that Mercury's topography erodes at a rate at least a factor of two faster than the Moon's.

  9. SMALL CRATERS AND THEIR DIAGNOSTIC POTENTIAL

    Directory of Open Access Journals (Sweden)

    R. Bugiolacchi

    2017-07-01

    Full Text Available I analysed and compared the size-frequency distributions of craters in the Apollo 17 landing region, comprising of six mare terrains with varying morphologies and cratering characteristics, along with three other regions allegedly affected by the same secondary event (Tycho secondary surge. I propose that for the smaller crater sizes (in this work 9–30 m, a] an exponential curve of power −0.18D can approximate Nkm−2 crater densities in a regime of equilibrium, while b] a power function D−3 closely describes the factorised representation of craters by size (1 m. The saturation level within the Central Area suggests that c] either the modelled rates of crater erosion on the Moon should be revised, or that the Tycho event occurred much earlier in time than the current estimate. We propose that d] the size-frequency distribution of small secondary craters may bear the signature (in terms of size-frequency distribution of debris/surge of the source impact and that this observation should be tested further.

  10. Processing Images of Craters for Spacecraft Navigation

    Science.gov (United States)

    Cheng, Yang; Johnson, Andrew E.; Matthies, Larry H.

    2009-01-01

    A crater-detection algorithm has been conceived to enable automation of what, heretofore, have been manual processes for utilizing images of craters on a celestial body as landmarks for navigating a spacecraft flying near or landing on that body. The images are acquired by an electronic camera aboard the spacecraft, then digitized, then processed by the algorithm, which consists mainly of the following steps: 1. Edges in an image detected and placed in a database. 2. Crater rim edges are selected from the edge database. 3. Edges that belong to the same crater are grouped together. 4. An ellipse is fitted to each group of crater edges. 5. Ellipses are refined directly in the image domain to reduce errors introduced in the detection of edges and fitting of ellipses. 6. The quality of each detected crater is evaluated. It is planned to utilize this algorithm as the basis of a computer program for automated, real-time, onboard processing of crater-image data. Experimental studies have led to the conclusion that this algorithm is capable of a detection rate >93 percent, a false-alarm rate <5 percent, a geometric error <0.5 pixel, and a position error <0.3 pixel.

  11. The Cratering History of Asteroid (2867) Steins

    CERN Document Server

    Marchi, S; Kueppers, M; Marzari, F; Davidsson, B; Keller, H U; Besse, S; Lamy, P; Mottola, S; Massironi, M; Cremonese, G

    2010-01-01

    The cratering history of main belt asteroid (2867) Steins has been investigated using OSIRIS imagery acquired during the Rosetta flyby that took place on the 5th of September 2008. For this purpose, we applied current models describing the formation and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models coupled with appropriate crater scaling laws, allow the cratering history to be estimated. Hence, we derive Steins' cratering retention age, namely the time lapsed since its formation or global surface reset. We also investigate the influence of various factors -like bulk structure and crater erasing- on the estimated age, which spans from a few hundred Myrs to more than 1Gyr, depending on the adopted scaling law and asteroid physical parameters. Moreover, a marked lack of craters smaller than about 0.6km has been found and interpreted as a result of a peculiar evolution of Steins cratering record, possibly related either to the formation of the 2.1km ...

  12. Locating the LCROSS Impact Craters

    Science.gov (United States)

    Marshall, William; Shirley, Mark; Moratto, Zachary; Colaprete, Anthony; Neumann, Gregory A.; Smith, David E.; Hensley, Scott; Wilson, Barbara; Slade, Martin; Kennedy, Brian; hide

    2012-01-01

    The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket stage into a permanently shadowed region near the lunar south pole. The Sheperding Spacecraft (SSC) separated approx. 9 hours before impact and performed a small braking maneuver in order to observe the Centaur impact plume, looking for evidence of water and other volatiles, before impacting itself. This paper describes the registration of imagery of the LCROSS impact region from the mid- and near-infrared cameras onboard the SSC, as well as from the Goldstone radar. We compare the Centaur impact features, positively identified in the first two, and with a consistent feature in the third, which are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta region. The images are registered to Lunar Reconnaisance Orbiter (LRO) topographical data which allows determination of the impact location. This location is compared with the impact location derived from ground-based tracking and propagation of the spacecraft's trajectory and with locations derived from two hybrid imagery/trajectory methods. The four methods give a weighted average Centaur impact location of -84.6796 deg, -48.7093 deg, with a 1s uncertainty of 115 m along latitude, and 44 m along longitude, just 146 m from the target impact site. Meanwhile, the trajectory-derived SSC impact location is -84.719 deg, -49.61 deg, with a 1 alpha uncertainty of 3 m along the Earth vector and 75 m orthogonal to that, 766 m from the target location and 2.803 km south-west of the Centaur impact. We also detail the Centaur impact angle and SSC instrument pointing errors. Six high-level LCROSS mission requirements are shown to be met by wide margins. We hope that these results facilitate further analyses of the LCROSS experiment data and follow-up observations of the impact region

  13. Sands at Gusev Crater, Mars

    Science.gov (United States)

    Cabrol, Nathalie A.; Herkenhoff, Kenneth E.; Knoll, Andrew H.; Farmer, Jack D.; Arvidson, Raymond E.; Grin, E.A.; Li, Ron; Fenton, Lori; Cohen, B.; Bell, J.F.; Yingst, R. Aileen

    2014-01-01

    Processes, environments, and the energy associated with the transport and deposition of sand at Gusev Crater are characterized at the microscopic scale through the comparison of statistical moments for particle size and shape distributions. Bivariate and factor analyses define distinct textural groups at 51 sites along the traverse completed by the Spirit rover as it crossed the plains and went into the Columbia Hills. Fine-to-medium sand is ubiquitous in ripples and wind drifts. Most distributions show excess fine material, consistent with a predominance of wind erosion over the last 3.8 billion years. Negative skewness at West Valley is explained by the removal of fine sand during active erosion, or alternatively, by excess accumulation of coarse sand from a local source. The coarse to very coarse sand particles of ripple armors in the basaltic plains have a unique combination of size and shape. Their distribution display significant changes in their statistical moments within the ~400 m that separate the Columbia Memorial Station from Bonneville Crater. Results are consistent with aeolian and/or impact deposition, while the elongated and rounded shape of the grains forming the ripples, as well as their direction of origin, could point to Ma'adim Vallis as a possible source. For smaller particles on the traverse, our findings confirm that aeolian processes have dominated over impact and other processes to produce sands with the observed size and shape patterns across a spectrum of geologic (e.g., ripples and plains soils) and aerographic settings (e.g., wind shadows).

  14. Craters of the Pluto-Charon system

    Science.gov (United States)

    Robbins, Stuart J.; Singer, Kelsi N.; Bray, Veronica J.; Schenk, Paul; Lauer, Tod R.; Weaver, Harold A.; Runyon, Kirby; McKinnon, William B.; Beyer, Ross A.; Porter, Simon; White, Oliver L.; Hofgartner, Jason D.; Zangari, Amanda M.; Moore, Jeffrey M.; Young, Leslie A.; Spencer, John R.; Binzel, Richard P.; Buie, Marc W.; Buratti, Bonnie J.; Cheng, Andrew F.; Grundy, William M.; Linscott, Ivan R.; Reitsema, Harold J.; Reuter, Dennis C.; Showalter, Mark R.; Tyler, G. Len; Olkin, Catherine B.; Ennico, Kimberly S.; Stern, S. Alan; New Horizons Lorri, Mvic Instrument Teams

    2017-05-01

    NASA's New Horizons flyby mission of the Pluto-Charon binary system and its four moons provided humanity with its first spacecraft-based look at a large Kuiper Belt Object beyond Triton. Excluding this system, multiple Kuiper Belt Objects (KBOs) have been observed for only 20 years from Earth, and the KBO size distribution is unconstrained except among the largest objects. Because small KBOs will remain beyond the capabilities of ground-based observatories for the foreseeable future, one of the best ways to constrain the small KBO population is to examine the craters they have made on the Pluto-Charon system. The first step to understanding the crater population is to map it. In this work, we describe the steps undertaken to produce a robust crater database of impact features on Pluto, Charon, and their two largest moons, Nix and Hydra. These include an examination of different types of images and image processing, and we present an analysis of variability among the crater mapping team, where crater diameters were found to average ± 10% uncertainty across all sizes measured (∼0.5-300 km). We also present a few basic analyses of the crater databases, finding that Pluto's craters' differential size-frequency distribution across the encounter hemisphere has a power-law slope of approximately -3.1 ± 0.1 over diameters D ≈ 15-200 km, and Charon's has a slope of -3.0 ± 0.2 over diameters D ≈ 10-120 km; it is significantly shallower on both bodies at smaller diameters. We also better quantify evidence of resurfacing evidenced by Pluto's craters in contrast with Charon's. With this work, we are also releasing our database of potential and probable impact craters: 5287 on Pluto, 2287 on Charon, 35 on Nix, and 6 on Hydra.

  15. Craters of the Pluto-Charon System

    Science.gov (United States)

    Robbins, Stuart J.; Singer, Kelsi N.; Bray, Veronica J.; Schenk, Paul; Lauer, Todd R.; Weaver, Harold A.; Runyon, Kirby; Mckinnon, William B.; Beyer, Ross A.; Porter, Simon; hide

    2016-01-01

    NASA's New Horizons flyby mission of the Pluto-Charon binary system and its four moons provided humanity with its first spacecraft-based look at a large Kuiper Belt Object beyond Triton. Excluding this system, multiple Kuiper Belt Objects (KBOs) have been observed for only 20 years from Earth, and the KBO size distribution is unconstrained except among the largest objects. Because small KBOs will remain beyond the capabilities of ground-based observatories for the foreseeable future, one of the best ways to constrain the small KBO population is to examine the craters they have made on the Pluto-Charon system. The first step to understanding the crater population is to map it. In this work, we describe the steps undertaken to produce a robust crater database of impact features on Pluto, Charon, and their two largest moons, Nix and Hydra. These include an examination of different types of images and image processing, and we present an analysis of variability among the crater mapping team, where crater diameters were found to average +/-10% uncertainty across all sizes measured (approx.0.5-300 km). We also present a few basic analyses of the crater databases, finding that Pluto's craters' differential size-frequency distribution across the encounter hemisphere has a power-law slope of approximately -3.1 +/- 0.1 over diameters D approx. = 15-200 km, and Charon's has a slope of -3.0 +/- 0.2 over diameters D approx. = 10-120 km; it is significantly shallower on both bodies at smaller diameters. We also better quantify evidence of resurfacing evidenced by Pluto's craters in contrast with Charon's. With this work, we are also releasing our database of potential and probable impact craters: 5287 on Pluto, 2287 on Charon, 35 on Nix, and 6 on Hydra.

  16. Why Landers Should Explore Fresh, Small Craters on Mars

    Science.gov (United States)

    Kirkland, L. E.; Herr, K. C.; Adams, P. M.

    2008-03-01

    Small, fresh craters at the Nevada Test Site are unique, high quality test beds to develop exploration techniques for new craters spotted on Mars by Malin et al. The NTS craters provide data to determine the optimum crater size for exploration.

  17. Aboriginal Oral Traditions of Australian Impact Craters

    CERN Document Server

    Hamacher, Duane W

    2013-01-01

    We explore Aboriginal oral traditions that relate to Australian meteorite craters. Using the literature, first-hand ethnographic records, and fieldtrip data, we identify oral traditions and artworks associated with four impact sites: Gosses Bluff, Henbury, Liverpool, and Wolfe Creek. Oral traditions describe impact origins for Gosses Bluff and Wolfe Creek craters and non-impact origins of Liverpool and Henbury craters, with Wolfe Creek stories having both impact and non-impact origins. Three impact sites that are believed to have formed during human habitation of Australia - Dalgaranga, Veevers, and Boxhole - do not have associated oral traditions that are reported in the literature.

  18. Degradation of Victoria Crater, Meridiani Planum, Mars

    Science.gov (United States)

    Grant, J. A.; Wilson, S. A.; Cohen, B. A.; Golombek, M. P.; Geissler, P. E.; Sullivan, R. J.

    2007-12-01

    Victoria crater (2.05N, 354.51E) is ~750 m in diameter and the largest crater on Mars observed in situ. The Mars Exploration Rover Opportunity traversed NW to SE across a broad annulus dominated by dark sand that at least partially surrounds the crater before navigating the northern crater rim. Rover observations of the crater and ejecta deposits are complemented by images with 26-52 cm/pixel scales from the High Resolution Imaging Science Experiment (HiRISE) on Mars Reconnaissance Orbiter and enable assessment of degradation state. The present depth/diameter ratio for Victoria is 0.1, less than the 0.2 expected for a pristine primary impact structure. Together with the eroded, serrated rim, this implies an originally smaller crater diameter and/or considerable infilling consistent with occurrence of a large dune field and few exposed rocks on the crater floor. The height and width of the raised rim is generally 4-5 m and 150-225 m, respectively, less than the 30 m and 500-600 m, respectively, expected for a pristine 750 m diameter crater. Ejecta thicknesses around the rim were derived using rover-based and HiRISE images and yield consistent estimates averaging ~3 m. The serrated rim plan creates a series of promontories extending up to 50 m into the crater and generally fronted by 30-60 degree slopes that are locally vertical and are separated by bays whose floors typically slope 15-25 degrees. A crater originally on order of 600-650 m in diameter and subsequently enlarged by mass wasting and aeolian erosion may yield a structure resembling Victoria today. The steep expression of the promontories and local outcroppings of rocks in the ejecta blanket points to some ongoing mass wasting, but the relative paucity of associated flanking talus indicates derived blocks of sulfate sandstone are not resistant to saltating sand and are rapidly broken down by the wind or are completely covered/filled in by aeolian drift. At Cape St. Vincent, the promontory appears undercut

  19. IS THE WORLD FLAT?

    Directory of Open Access Journals (Sweden)

    Cristian Încalţărău

    2010-06-01

    Full Text Available Globalization became more and more prominent during the last decades. There is no way to argue that globalization led to more interconnected economies, facilitating the communication and the collaboration around the world. But where is this going? Doesglobalization mean uniformity or diversity? As the world begins to resemble more, the people are trying to distinguish between them more, which can exacerbate nationalistic feeling. Friedman argues that globalization made the world smaller and flatter, allowing all countries to take chance of the available opportunities equally. But is this really true? Although politic and cultural factors can stand in front of a really flat world, what is the key for Chinese and Indian success and which are theirs perspectives?

  20. Flat Helical Nanosieves

    CERN Document Server

    Mei, Shengtao; Hussain, Sajid; Huang, Kun; Ling, Xiaohui; Siew, Shawn Yohanes; Liu, Hong; Teng, Jinghua; Danner, Aaron; Qiu, Cheng-Wei

    2016-01-01

    Compact and miniaturized devices with flexible functionalities are always highly demanded in optical integrated systems. Plasmonic nanosieve has been successfully harnessed as an ultrathin flat platform for complex manipulation of light, including holography, vortex generation and non-linear processes. Compared with most of reported single-functional devices, multi-functional nanosieves might find more complex and novel applications across nano-photonics, optics and nanotechnology. Here, we experimentally demonstrate a promising roadmap for nanosieve-based helical devices, which achieves full manipulations of optical vortices, including its generation, hybridization, spatial multiplexing, focusing and non-diffraction propagation etc., by controlling the geometric phase of spin light via over 121 thousands of spatially-rotated nano-sieves. Thanks to such spin-conversion nanosieve helical elements, it is no longer necessary to employ the conventional two-beam interferometric measurement to characterize optical ...

  1. Determining proportions of lunar crater populations by fitting crater size distribution

    CERN Document Server

    Wang, Nan

    2016-01-01

    We determine the proportions of two mixed crater populations distinguishable by size distributions on the Moon. A "multiple power-law" model is built to formulate crater size distribution $N(D) \\propto D^{-\\alpha}$ whose slope $\\alpha$ varies with crater diameter $D$. Fitted size distribution of lunar highland craters characterized by $\\alpha = 1.17 \\pm 0.04$, $1.88 \\pm 0.07$, $3.17 \\pm 0.10$ and $1.40 \\pm 0.15$ for consecutive $D$ intervals divided by 49, 120 and 251 km and that of lunar Class 1 craters with a single slope $\\alpha = 1.96 \\pm 0.14$, are taken as Population 1 and 2 crater size distribution respectively, whose sum is then fitted to the size distribution of global lunar craters with $D$ between 10 and 100 km. Estimated crater densities of Population 1 and 2 are $44 \\times 10^{-5}$ and $5 \\times 10^{-5}$ km$^{-2}$ respectively, leading to the proportion of the latter $10 \\%$. The results underlines the need for considering the Population 1 craters and the relevant impactors, the primordial main-b...

  2. More Ricci-flat branes

    CERN Document Server

    Figueroa-O'Farrill, J M

    1999-01-01

    Certain supergravity solutions (including domain walls and the magnetic fivebrane) have recently been generalised by Brecher and Perry by relaxing the condition that the brane worldvolume be flat. In this way they obtain examples in which the brane worldvolume is a static spacetime admitting parallel spinors. In this note we simply point out that the restriction to static spacetimes is unnecessary, and in this way exhibit solutions where the brane worldvolume is an indecomposable Ricci-flat lorentzian manifold admitting parallel spinors. We discuss more Ricci-flat fivebranes and domain walls, as well as new Ricci-flat D3-branes.

  3. Ponded Impact Melt Dynamics and its Effects on Pond Surface Morphology - Insights from King Crater

    Science.gov (United States)

    Ashley, J. W.; DiCarlo, N.; Enns, A. C.; Hawke, B. R.; Hiesinger, H.; Robinson, M. S.; Sato, H.; Speyerer, E.; van der Bogert, C.; Wagner, R.; Young, K. E.; LROC Science Team

    2011-12-01

    King crater is a 77-km diameter impact feature located at 5.0°N and 120.5°E on the lunar farside. Previous work delimited King crater with an asymmetric distribution of ejecta that includes a large impact melt pond (~385 square kilometer surface area), located in nearby Al-Tusi crater. The pond provides an opportunity to study the behavior of a large impact melt deposit. The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) and Narrow Angle Cameras (NAC) [1] imaged King crater from a nominal 50 km altitude at pixel scales of 100 meters and up to 0.5 meters, respectively providing the means to create geologic maps for the region. Digital terrain/elevation models (DTMs) were derived [2] from both WAC and NAC images for the area, and supplemented the mapping effort. The high-resolution (50 cm/p) NAC images show fine details within the Al-Tusi melt pond that raise questions about melt pond dynamics and evolution. These include both positive- and negative-relief features, anomalous crater morphologies, and flow features that show variable degrees of melt viscosity. WAC DTM processing reveals a horizontal and relatively flat (at the 20 m contour interval) pond, demonstrating that an equipotential surface was achieved during initial melt accumulation. The NAC DTM shows kilometer-scale zones of topographic down-warping within the 20 m contour interval. The perimeters of these depressed areas show moderate to high spatial correlation with the occurrence of negative relief features (~10 to 100 m in length). Such sagging may have occurred as the result of contraction and/or compaction within the melt both during and following cooling, with the negative relief features resulting from consequent structural failure and separation of the thickening surface crust. The variability in the degree of contraction/compaction may be explained by the presence of underlying hummocky ejecta deposits (which probably also explains the positive relief features) emplaced by

  4. Stratigraphy, mineralogy, and origin of layered deposits inside Terby crater, Mars

    Science.gov (United States)

    Ansan, V.; Loizeau, D.; Mangold, N.; Le Mouélic, S.; Carter, J.; Poulet, F.; Dromart, G.; Lucas, A.; Bibring, J.-P.; Gendrin, A.; Gondet, B.; Langevin, Y.; Masson, Ph.; Murchie, S.; Mustard, J. F.; Neukum, G.

    2011-01-01

    The 174 km diameter Terby impact crater (28.0°S-74.1°E) located on the northern rim of the Hellas basin displays anomalous inner morphology, including a flat floor and light-toned layered deposits. An analysis of these deposits was performed using multiple datasets from Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter missions, with visible images for interpretation, near-infrared data for mineralogical mapping, and topography for geometry. The geometry of layered deposits was consistent with that of sediments that settled mainly in a sub-aqueous environment, during the Noachian period as determined by crater counts. To the north, the thickest sediments displayed sequences for fan deltas, as identified by 100 m to 1 km long clinoforms, as defined by horizontal beds passing to foreset beds dipping by 6-10° toward the center of the Terby crater. The identification of distinct sub-aqueous fan sequences, separated by unconformities and local wedges, showed the accumulation of sediments from prograding/onlapping depositional sequences, due to lake level and sediment supply variations. The mineralogy of several layers with hydrated minerals, including Fe/Mg phyllosilicates, supports this type of sedimentary environment. The volume of fan sediments was estimated as >5000 km 3 (a large amount considering classical martian fan deltas such as Eberswalde (6 km 3)) and requires sustained liquid water activity. Such a large sedimentary deposition in Terby crater is characteristic of the Noachian/Phyllosian period during which the environment favored the formation of phyllosilicates. The latter were detected by spectral data in the layered deposits of Terby crater in three distinct layer sequences. During the Hesperian period, the sediments experienced strong erosion, possibly enhanced by more acidic conditions, forming the current morphology with three mesas and closed depressions. Small fluvial valleys and alluvial fans formed subsequently

  5. Impacts do not initiate volcanic eruptions: Eruptions close to the crater

    Science.gov (United States)

    Ivanov, B. A.; Melosh, H. J.

    2003-10-01

    Many papers on meteorite impact suggest that large impacts can induce volcanic eruptions through decompression melting of the underlying rocks. We perform numerical simulations of the impact of an asteroid with a diameter of 20 km striking at 15 km·s-1 into a target with a near-surface temperature gradient of 13 K·km-1 (“cold” case) or 30 K·km-1 (“hot” case). The impact creates a 250 300-km-diameter crater with ˜10,000 km3 of impact melt. However, the crater collapses almost flat, and the pressure field returns almost to the initial lithostat. Even an impact this large cannot raise mantle material above the peridotite solidus by decompression. Statistical considerations also suggest that impacts cannot be the common initiator of large igneous provinces any time in post heavy bombardment Earth history.

  6. Topography of the Martian Impact Crater Tooting

    Science.gov (United States)

    Mouginis-Mark, P. J.; Garbeil, H.; Boyce, J. M.

    2009-01-01

    Tooting crater is approx.29 km in diameter, is located at 23.4degN, 207.5degE, and is classified as a multi-layered ejecta crater [1]. Our mapping last year identified several challenges that can now be addressed with HiRISE and CTX images, but specifically the third dimension of units. To address the distribution of ponded sediments, lobate flows, and volatile-bearing units within the crater cavity, we have focused this year on creating digital elevation models (DEMs) for the crater and ejecta blanket from stereo CTX and HiRISE images. These DEMs have a spatial resolution of approx.50 m for CTX data, and 2 m for HiRISE data. Each DEM is referenced to all of the available individual MOLA data points within an image, which number approx.5,000 and 800 respectively for the two data types

  7. Exposure histories of Bench Crater rocks

    Science.gov (United States)

    Burnett, D. S.; Drozd, R. J.; Morgan, C. J.; Podosek, F. A.

    1975-01-01

    A description is presented of the results of mass spectrometric analyses of the noble gases krypton and xenon, in eight Apollo 12 basaltic rocks. The significance of the results is evaluated. It is concluded that the Bench Crater rocks are not what they appear to be in their field relationships. They are not fragments ejected from bedrock by the Bench impact. Most, if not all, have had a previous history of regolith residence prior to the Bench impact. In retrospect, sampling of fresh ejecta from lunar craters during the Apollo missions turned out to be surprisingly difficult. Sampling was successful for Cone and North Ray craters where large boulders were available, but fresh South Ray ejecta was surprisingly elusive. The reported investigation shows that fresh ejecta was not obtained from Bench, and moreover, that the concept of 'radial sampling', in which the rocks sampled from a crater rim are supposed to represent the deepest material excavated, fails very badly for Bench.

  8. Impact Structures: What Does Crater Diameter Mean?

    Science.gov (United States)

    Turtle, E. P.; Pierazzo, E.; Collins, G. S.; Osinski, G. R.; Melosh, H. J.; Morgan, J. V.; Reimold, W. U.; Spray, J. G.

    2004-03-01

    Crater diameter is an important parameter in energy scaling and impact simulations. However, disparate types of data make the use of consistent metrics difficult. We suggest a consistent terminology and discuss it in the context of several examples.

  9. On the Clustering of Europa's Small Craters

    Science.gov (United States)

    Bierhaus, E. B.; Chapman, C. R.; Merline, W. J.

    2001-01-01

    We analyze the spatial distribution of Europa's small craters and find that many are too tightly clustered to result from random, primary impacts. Additional information is contained in the original extended abstract.

  10. The source crater of martian shergottite meteorites.

    Science.gov (United States)

    Werner, Stephanie C; Ody, Anouck; Poulet, François

    2014-03-21

    Absolute ages for planetary surfaces are often inferred by crater densities and only indirectly constrained by the ages of meteorites. We show that the meteorites classified as shergottites. Shergottites and this crater are linked by their coinciding meteorite ejection ages and the crater formation age and by mineralogical constraints. Because Mojave formed on 4.3 billion-year-old terrain, the original crystallization ages of shergottites are old, as inferred by Pb-Pb isotope ratios, and the much-quoted shergottite ages of <600 million years are due to resetting. Thus, the cratering-based age determination method for Mars is now calibrated in situ, and it shifts the absolute age of the oldest terrains on Mars backward by 200 million years.

  11. The Chicxulub Impact Crater and Oblique Impact

    Science.gov (United States)

    McDonald, M.; Gulick, S.; Melosh, H.; Christeson, G.

    2007-05-01

    Determining whether or not the Chicxulub impact was oblique (<45 degrees) will aid in our understanding of the environmental consequences 65 Ma. Planetary impact events, and impact simulations in the laboratory, show that oblique impacts have clear asymmetric ejecta distributions. However, the subsurface structures of the resultant craters are not well understood. In 2005, we acquired 1822 km of seismic reflection data onboard the R/V Maurice Ewing imaging the massive (200+ km) Chicxulub impact crater. The seismic profiles show that pre- crater stratigraphy outside the central basin of the Chicxulub impact crater is offset downward into the crater marking the post-impact slumping and formation of the terrace zone. The inward collapse of the Chicxulub terrace zone coincides with the outward collapse of the central uplift to form the peak ring. Chicxulub's peak ring is offset to the southeast, away from the deepest terrace zone mapped in the seismic data, suggesting that its peak ring was offset toward a more gradual wall of the transient cavity. Peak ring offsets, relative to crater center, of Venusian craters from radar images in the Magellan data set allow us to determine whether there are systematic variations in peak ring offset due to oblique impact. Ten pristine Venusian peak ring craters formed by oblique impact show that peak rings are offset both uprange and downrange, suggesting that peak ring position, and related subsurface asymmetries in the terrace zone, do not provide information about impact obliquity. This analysis supports the idea that Chicxulub's peak ring offset is a consequence of target properties and pre-impact structure and independent of impact trajectory.

  12. Pleistocene vertebrates of the Yukon Territory

    Science.gov (United States)

    Harington, C. R.

    2011-08-01

    Unglaciated parts of the Yukon constitute one of the most important areas in North America for yielding Pleistocene vertebrate fossils. Nearly 30 vertebrate faunal localities are reviewed spanning a period of about 1.6 Ma (million years ago) to the close of the Pleistocene some 10 000 BP (radiocarbon years before present, taken as 1950). The vertebrate fossils represent at least 8 species of fishes, 1 amphibian, 41 species of birds and 83 species of mammals. Dominant among the large mammals are: steppe bison ( Bison priscus), horse ( Equus sp.), woolly mammoth ( Mammuthus primigenius), and caribou ( Rangifer tarandus) - signature species of the Mammoth Steppe fauna ( Fig. 1), which was widespread from the British Isles, through northern Europe, and Siberia to Alaska, Yukon and adjacent Northwest Territories. The Yukon faunas extend from Herschel Island in the north to Revenue Creek in the south and from the Alaskan border in the west to Ketza River in the east. The Yukon holds evidence of the earliest-known people in North America. Artifacts made from bison, mammoth and caribou bones from Bluefish Caves, Old Crow Basin and Dawson City areas show that people had a substantial knowledge of making and using bone tools at least by 25 000 BP, and possibly as early as 40 000 BP. A suggested chronological sequence of Yukon Pleistocene vertebrates ( Table 1) facilitates comparison of selected faunas and indicates the known duration of various taxa.

  13. Oblique impact cratering experiments in brittle targets: Implications for elliptical craters on the Moon

    Science.gov (United States)

    Michikami, Tatsuhiro; Hagermann, Axel; Morota, Tomokatsu; Haruyama, Junichi; Hasegawa, Sunao

    2017-01-01

    Most impact craters observed on planetary bodies are the results of oblique impacts of meteoroids. To date, however, there have only been very few laboratory oblique impact experiments for analogue targets relevant to the surfaces of extraterrestrial bodies. In particular, there is a lack of laboratory oblique impact experiments into brittle targets with a material strength on the order of 1 MPa, with the exception of ice. A strength on the order of 1 MPa is considered to be the corresponding material strength for the formation of craters in the 100 m size range on the Moon. Impact craters are elliptical if the meteoroid's trajectory is below a certain threshold angle of incidence, and it is known that the threshold angle depends largely on the material strength. Therefore, we examined the threshold angle required to produce elliptical craters in laboratory impact experiments into brittle targets. This work aims to constrain current interpretations of lunar elliptical craters and pit craters with sizes below a hundred meters. We produced mortar targets with compressive strength of 3.2 MPa. A spherical nylon projectile (diameter 7.14 mm) was shot into the target surface at a nominal velocity of 2.3 km/s, with an impact angle of 5°-90° from horizontal. The threshold angle of this experiment ranges from 15° to 20°. We confirmed that our experimental data agree with previous empirical equations in terms of the cratering efficiency and the threshold impact angle. In addition, in order to simulate the relatively large lunar pit craters related to underground cavities, we conducted a second series of experiments under similar impact conditions using targets with an underground rectangular cavity. Size and outline of craters that created a hole are similar to those of craters without a hole. Moreover, when observed from an oblique angle, a crater with a hole has a topography that resembles the lunar pit craters. The relation between the impact velocity of meteoroids on

  14. Pollen analyses of Pleistocene hyaena coprolites from Montenegro and Serbia

    Directory of Open Access Journals (Sweden)

    Argant Jacqueline

    2007-01-01

    Full Text Available The results of pollen analyses of hyaena coprolites from the Early Pleistocene cave of Trlica in northern Montenegro and the Late Pleistocene cave of Baranica in southeast Serbia are described. The Early Pleistocene Pachycrocuta brevirostris, and the Late Pleistocene Crocuta spelaea are coprolite-producing species. Although the pollen concentration was rather low, the presented analyses add considerably to the much-needed knowledge of the vegetation of the central Balkans during the Pleistocene. Pollen extracted from a coprolite from the Baranica cave indicates an open landscape with the presence of steppe taxa, which is in accordance with the recorded conditions and faunal remains. Pollen analysis of the Early Pleistocene samples from Trlica indicate fresh and temperate humid climatic conditions, as well as the co-existence of several biotopes which formed a mosaic landscape in the vicinity of the cave.

  15. The Degradational History of Endeavour Crater, Mars

    Science.gov (United States)

    Grant, J. A.; Parker, T. J.; Crumpler, L. S.; Wilson, S. A.; Golombek, M. P.; Mittlefehldt, D. W.

    2015-01-01

    Endeavour crater (2.28 deg S, 354.77 deg E) is a Noachian-aged 22 km-diameter impact structure of complex morphology in Meridiani Planum. The degradation state of the crater has been studied using Mars Reconnaissance Orbiter and Opportunity rover data. Exposed rim segments rise approximately 10 m to approximately 100 m above the level of the embaying Burns Formation and the crater is 200-500 m deep with the southern interior wall exposing over approximately 300 m relief. Both pre-impact rocks (Matijevic Formation) and Endeavour impact ejecta (Shoemaker Formation) are present at Cape York, but only the Shoemaker crops out (up to approximately 140 m) along the rim segment from Murray Ridge to Cape Tribulation. Study of pristine complex craters Bopolu and Tooting, and morphometry of other martian complex craters, enables us to approximate Endeavour's pristine form. The original rim likely averaged 410 m (+/-)200 m in elevation and a 250-275 m section of ejecta ((+/-)50-60 m) would have composed a significant fraction of the rim height. The original crater depth was likely between 1.5 km and 2.2 km. Comparison between the predicted original and current form of Endeavour suggests approximately 100-200 m rim lowering that removed most ejecta in some locales (e.g., Cape York) while thick sections remain elsewhere (e.g., Cape Tribulation). Almost complete removal of ejecta at Cape York and minimal observable offset across fractures indicates current differences in rim relief are not solely due to original rim relief. Rim segments are embayed by approximately 100-200 m thickness of plains rocks outside the crater, but thicker deposits lie inside the crater. Ventifact textures confirm ongoing eolian erosion with the overall extent difficult to estimate. Analogy with degraded Noachian-aged craters south of Endeavour, however, suggests fluvial erosion dominated rim degradation in the Noachian and was likely followed by approximately 10s of meters modification by alternate

  16. Palaeogeography of the Caspian Sea marine Pleistocene

    Science.gov (United States)

    Yanina, Tamara; Svitoch, Aleksander; Makshaev, Radik; Khomchenko, Denis

    2016-04-01

    Vertical succession of the fossil molluscs of Didacna genus along the Pleistocene sequence of the Caspian Sea area allows for detailed subdivision of the sediments. Zone, i.e. the Caspian Sea Pleistocene, is the highest stratigraphical unit of the regional Quaternary stratigraphic scale. It corresponds to the biozone of Didacna Eichwald subgenus. Based on the fossil groups of Didacna molluscs, the deposits are subdivided into the Baku, Urundzhik-Singil', lower and upper Khazarian, Khvalinian, and post-Khvalinian horizons. Further subdision is based on the changes in Didacna assemblages. Three big transgressive epochs are distinguished in the Pleistocene history of the Caspian Sea that were separated by deep and long regressions. These are the Baku, early Khazarian and Khvalinian transgressions. In transgressive sea basins, the sea level reached the height of 40-50 m and was regulated by the outflow of the Caspian waters into the Black Sea via the Manych depression. The areas of transgressive basins were similar. At the Caucasian coast, the extent of the Baku and early Khazarian transgressions exceeded that of the Khvalinian transgression, while in the Northern Caspian Sea Region the latter was slightly more extensive than the preceding ones. The Urundzhik, late Khazarian and New Caspian transgressions represented sea-level rise of lower rank. All of them were recorded within big regressive epochs being usually related to warm (interglacial) climatic conditions: Singil' (Likhvin), Mikulino and Holocene, respectively. Like at present, the Pleistocene Caspian Sea represented a self-regulating system. Maximal extent of ancient sea basins was dependent upon the height of the Manych sill (that was the main regulating factor), the amount of precipitation, river runoff, and decrease in evaporation. Minimal extent of the sea basin was dependent upon the area and capacity of its southern and middle depressions. At the same time, the rest states (extents) of the Caspian Sea

  17. Dynamics of impact cratering in shallow sand layers.

    Science.gov (United States)

    Boudet, J F; Amarouchene, Y; Kellay, H

    2006-04-21

    When a solid sphere impacts a shallow layer of sand deposited on a solid surface, a crater can be obtained. The dynamics of the opening of the crater can be followed accurately. During this opening, the radius of the crater can be conveniently modeled by an exponential saturation with a well-defined time constant. The crater then closes up partially once the opening phase is over as the sand avalanches down the slope of the crater. We here present a detailed study of the full dynamics of the crater formation as well as the dynamics of the corrola formed during this process. A simple model accounts for most of our observations.

  18. Dune Activity in Proctor Crater

    Science.gov (United States)

    1999-01-01

    Observation of dune activity--whether the movement of whole dunes or the movement of sediment on a dune--is the result of a direct link between the martian surface and its atmosphere. Observation of dune activity can be used to determine the rate at which wind moves sediment. It can also help to estimate how long it takes for windblown sand to abrade surfaces--including rocks and Mars landers. One of the first sand dune fields ever recognized on Mars is shown here. Located on the floor of Proctor Crater (at 48oS, 330oW), this dune field was seen in Mariner 9images more than 27 years ago. In fact, the photomosaic base map in MOC2-170a (above, left) is constructed from Mariner 9 images taken in February and March of 1972. The thin strip overlain on the Mariner 9 mosaic is a Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image taken in June 1999. The new MOC image shows evidence that the Proctor Crater dunes are active today. The picture on the right is an expanded view of a portion of the MOC image (its location is indicated by the white box in the picture on the left). In this view (right), the sand dunes are dark and patches of southern winter frost are bright. The sun illuminates the scene from the upper left. Dark streaks can be seen on frost-covered slopes, particularly just left of the center of the picture. Thesestreaks result from recent avalanching of sand on the steep (up to 35o), down-wind side of the dune, otherwise known as the slip face. Because the dark sand streaks are superposed upon the bright frost, these streaks can only be as old as the frost. This frost cannot be more than 11 months old, and was probably only a few months old at the time the picture was taken. Thus, the dunes must be active today in order to show such streaks. The placement of dunes in the MOC image was also compared with their positions in the earlier Mariner 9 image (above, left). No evidence that entire dunes have moved since March 1972 has been found. While the period

  19. Irritated Method for Flat warts

    Institute of Scientific and Technical Information of China (English)

    LiBingxu

    2004-01-01

    Summary Background The relation between spontaneous regression of Flat warts and T cells depended immunity was confirmed. Cells immunity against HPV was induced by presenting of HPV related antigens, and thrived by cytokine and some chemistry agent. So how to make HPV which incubated in keratinocyte to present PHV antigens and keratinocyte to secret cytokine or chemistry agents should be a pursuance for dermatologist who are looking for a efficient method to deal with flat warts. Present research had exhibited inflammable agents can induce dermatitis when apply to the skin surface, so it might bring flat warts to spontaneous regression. Objective To observe the effectiveness of irritant drugs on flat warts, and at same time to understand more on the mechanism of the regression. Methods Compared with Control we treat 88 case of flat warts with retinoid gel or 3% hydrogen peroxide solution plus 5 % salicylic acid cream (HPSC). Results Both retinoid gel and HPSC reveal significant effect on flat warts. Conclusion Retinoid gel or SPHC was effective on the treatment of flat warts. The possible explanation for this is the drugs when put on the skin will induce dermatitis and dissolve or denude keratin.

  20. Geological Study of Gale Crater on Mars

    Science.gov (United States)

    Le Deit, L.; Hauber, E.; Fueten, F.; Pondrelli, M.; Rossi, A.; Mangold, N.; Jaumann, R.

    2011-12-01

    Gale is an impact crater of 150 km in diameter, formed at Late Noachian/Early Hesperian located close to the dichotomy boundary and to the Medusae Fossae Formation. This crater is partially filled by a crescent-shaped mound of layered deposits up to 5 km thick and 6000 km2 in area, for which several origins have been proposed including volcanic, eolian, and fluviatile and lacustrine processes, precipitation as spring deposits, and a combination of several origins. The past presence of water is attested by the occurrence of many channels carved into the deposits and the crater rim, and of phyllosilicates and sulfates located in the lowest part of the deposits. Hence, Gale crater is a site of high interest to understand the evolution of the geochemical and climatic environment of the region through time, and may have had favorable conditions for supporting life in the past. This will be studied in situ by Curiosity (Mars Science Laboratory) from August 2012. In order to better constrain the history of Gale and the origin of its deposits, a geologic map of Gale crater based on the analysis of the orbital data CTX (~ 6 m/pixel) and HiRISE (25-32 cm/pixel) was produced. The geometry of the layered deposits was measured from HiRISE DEM. The geological units and landforms were defined according to their location, physical characteristics, albedo, erosion patterns, and mineralogical composition. Five main units were identified within the mound of layered deposits, which are interpreted as mainly airfall deposits including aeolian dunes. North of the mound, linear lobate features and a fan-shaped feature might have resulted from mass-wasting processes (i.e., landslides, debris flows, or viscous flows). The crater fill units correspond to deposits located on the rims and on the floor of the crater. They are incised by many valleys and superposed by sinuous ridges, interpreted as fluvial channels and inverted channels respectively. These crater fill units are interpreted as

  1. The Crater Ejecta Distribution on Ceres

    Science.gov (United States)

    Schmedemann, Nico; Neesemann, Adrian; Schulzeck, Franziska; Krohn, Katrin; Gathen, Isabel; Otto, Katharina; Jaumann, Ralf; Michael, Gregory; Raymond, Carol; Russell, Christopher

    2017-04-01

    Since March 6 2015 the Dawn spacecraft [1] has been in orbit around the dwarf planet Ceres. At small crater diameters Ceres appears to be peppered with secondary craters that often align in chains or form clusters. Some of such possible crater chains follow curved geometries and are not in a radial orientation with respect to possible source craters [2]. Ceres is a fast rotating body ( 9 h per revolution) with comparatively low surface gravity ( 0.27 m/s2). A substantial fraction of impact ejecta may be launched with velocities similar to Ceres' escape velocity (510 m/s), which implies that many ejected particles follow high and long trajectories. Thus, due to Ceres' fast rotation the distribution pattern of the reimpacting ejected material is heavily affected by Coriolis forces that results in a highly asymmetrical and curved pattern of secondary crater chains. In order to simulate flight trajectories and distribution of impact ejected material for individual craters on Ceres we used the scaling laws by [3] adjusted to the Cerean impact conditions [4] and the impact ejecta model by [5]. These models provide the starting conditions for tracer particles in the simulation. The trajectories of the particles are computed as n-body simulation. The simulation calculates the positions and impact velocities of each impacting tracer particle with respect to the rotating surface of Ceres, which is approximated by a two-axis ellipsoid. Initial results show a number of interesting features in the simulated deposition geometries of specific crater ejecta. These features are roughly in agreement with features that can be observed in Dawn imaging data of the Cerean surface. For example: ray systems of fresh impact craters, non-radial crater chains and global scale border lines of higher and lower color ratio areas. Acknowledgment: This work has been supported by the German Space Agency (DLR) on behalf of the Federal Ministry for Economic Affairs and Energy, Germany, grants 50 OW

  2. Crater and cavity depth in hypervelocity impact

    Science.gov (United States)

    Kadono, T.; Fujiwara, A.

    2003-04-01

    Hypervelocity impact experiments with low-density mediums (e.g., foams) have been so far carried out to develop the instruments for intact capture of interplanetary dust particles. The results show that the impact leads a "cavity", a cylindrical or carrot (spindle) shaped vestige. Its shape depends on the condition of projectiles; when impact velocity is so low that projectiles are intact, the depth increases with impact velocity, while it decreases or is constant with impact velocity when the impact velocity is so high that projectiles are broken (e.g., Kadono, Planet. Space Sci. 47, 305--318, 1999). On the other hand, as described by Summers (NASA TN D-94, 1959), crater shape with high density targets (comparable to projectile density) also changes with impact velocity. At low velocities, the strength of projectile's materials is greater than the dynamic impact pressure and the projectile penetrates the target intact. The crater produced is deep and narrow. With increase in impact velocity, a point is reached at which the impact pressure is sufficient to cause the projectile to fragment into a few large pieces at impact. Then as the impact velocity is increased further, the projectile shatters into numerous small pieces and the penetration actually decreases. Finally a velocity is reached at which the typical fluid impact occurs, the crater formed is nearly hemispherical in shape. It appears that the situation in cavity formation with low density targets is quite similar to that in cratering with high density targets at low impact velocity. This similarity allows us to discuss cavity formation and cratering in a unified view. As described above, the previous experiments clearly suggest that the condition of projectiles plays important roles in both cratering and cavity formation. Hence here, by introducing a parameter that characterizes the condition of projectiles at the instance of impact, cratering processes such as projectile penetration and shock wave

  3. The missing large impact craters on Ceres

    Science.gov (United States)

    Marchi, S.; Ermakov, A.; Raymond, C.A.; Fu, R.R.; O'Brien, D.P.; Bland, Michael; Ammannito, E.; De Sanctis, M.C.; Bowling, Tim; Schenk, P.; Scully, J.E.C.; Buczkowski, D.L.; Williams, D.A.; Hiesinger, H.; Russell, C.T.

    2016-01-01

    Asteroids provide fundamental clues to the formation and evolution of planetesimals. Collisional models based on the depletion of the primordial main belt of asteroids predict 10–15 craters >400 km should have formed on Ceres, the largest object between Mars and Jupiter, over the last 4.55 Gyr. Likewise, an extrapolation from the asteroid Vesta would require at least 6–7 such basins. However, Ceres’ surface appears devoid of impact craters >~280 km. Here, we show a significant depletion of cerean craters down to 100–150 km in diameter. The overall scarcity of recognizable large craters is incompatible with collisional models, even in the case of a late implantation of Ceres in the main belt, a possibility raised by the presence of ammoniated phyllosilicates. Our results indicate that a significant population of large craters has been obliterated, implying that long-wavelength topography viscously relaxed or that Ceres experienced protracted widespread resurfacing.

  4. Flats: Preliminary WFC Data and Plans for Flight Flats

    Science.gov (United States)

    Bohlin, R. C.; Hartig, G.; Tsvetanov, Z.

    2000-10-01

    The ACS WFC pixel-to-pixel P-flats with the build-3 detector repeat over a three month time span to a precision of better than 0.1% rms. The shape of the low frequency Lflat field varies with wavelength, where the ratio of the F435W/F814W L-flats differs from unity by - 10% in two patches near opposite corners of the field of view. At ~0.5%, the high frequency pixel-to-pixel structure in the WFC P-flats is about half that of the HRC build-2 and does not increase as much toward shorter wavelengths as the HRC build-2 with the Lesser coating. The amplitude of the fringes for continuum illumination is less than 1%, even in the narrow band ramp filters, while the fringing in monochromatic light is - 10% at 9300 Å. The goals of the laboratory WFC and HRC flat field program are to obtain the set of external flats that fully populates the pipeline database and to archive a baseline of high S/N internal flats for tracking post-launch changes.

  5. Is classical flat Kasner spacetime flat in quantum gravity?

    CERN Document Server

    Singh, Parampreet

    2016-01-01

    Quantum nature of classical flat Kasner spacetime is studied using effective spacetime description in loop quantum cosmology. We find that even though the spacetime curvature vanishes at the classical level, non-trivial quantum gravitational effects can arise. For the standard loop quantization of Bianchi-I spacetime, which uniquely yields universal bounds on expansion and shear scalars and results in a generic resolution of strong singularities, we find that a flat Kasner metric is not a physical solution of the effective spacetime description, except in a limit. The lack of a flat Kasner metric at the quantum level results from a novel feature of the loop quantum Bianchi-I spacetime: quantum geometry induces non-vanishing spacetime curvature components, making it not Ricci flat even when no matter is present. The non-curvature singularity of the classical flat Kasner spacetime is avoided, and the effective spacetime transits from a flat Kasner spacetime in asymptotic future, to a Minkowski spacetime in asym...

  6. Characterization of Boulders Ejected from Small Impact Craters

    Science.gov (United States)

    Bart, G. D.; Melosh, H. J.; Strom, R. G.

    2004-11-01

    When an asteroid or comet impacts the surface of a solid body, some of the surface material is often ejected from the crater in the form of blocks. We are characterizing the size and location of such blocks around craters on the Moon and Mars. The lunar craters were observed in Lunar Orbiter III images from P-12 and S-18. The Mars crater was observed in Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Release No. MOC2-712. The craters range in size from 300 m to 3 km diameter. We measured the diameters of boulders observed around the craters, and also measured the distance between the boulder and the crater center. We then calculate the ejection velocity of each boulder based on how far the block was from the crater. The data indicate that larger boulders are more frequently found close to the crater rim rather than far away. The size of the ejecta drops off as a power law with distance from the crater. Our results are consistent with studies by Vickery (1986, 1987), which indirectly found the distribution of ejecta sizes from large craters by analyzing the size and distribution of their secondary craters. Our work characterizes the other end of the ejecta spectrum --- low velocity boulders ejected from small craters. We have also constructed R-plots of the boulder diameters for each crater. We found that the R-plot for the boulders has a dependence remarkably similar to an R-plot of the diameters of secondary craters. This similarity supports the already accepted idea that the impactors that produce secondaries are blocks ejected from larger craters. It is also consistent with the interpretation that the upturn of the cratering curve at small diameters on the terrestrial planets is due to secondary impacts rather than a primary population as some have proposed.

  7. Pleistocene glaciation of the Biokovo Massif

    Directory of Open Access Journals (Sweden)

    Manja Žebre

    2013-12-01

    Full Text Available Biokovo massif is situated in the coastal part of the Dinaric Mountains in Croatia. Detailed morphographic and morphometric analysis of the highest parts of the massif were used to determine the extent and characteristics of Late Pleistocene glaciation. The reconstruction of glaciers and calculations of equilibrium line altitude (ELA were carried out. Our research revealed that on the north-eastern side of the highest peak Sveti Jure two cirque glaciers with an overall area of 1 km2 were formed and their ELA was 1515 m a.s.l.

  8. Two-dimensional computer simulation of hypervelocity impact cratering: some preliminary results for Meteor Crater, Arizona

    Energy Technology Data Exchange (ETDEWEB)

    Bryan, J.B.; Burton, D.E.; Cunningham, M.E.; Lettis, L.A. Jr.

    1978-06-01

    A computational approach used for subsurface explosion cratering was extended to hypervelocity impact cratering. Meteor (Barringer) Crater, Arizona, was selected for the first computer simulation because it is one of the most thoroughly studied craters. It is also an excellent example of a simple, bowl-shaped crater and is one of the youngest terrestrial impact craters. Initial conditions for this calculation included a meteorite impact velocity of 15 km/s, meteorite mass of 1.67 x 10/sup 8/ kg, with a corresponding kinetic energy of 1.88 x 10/sup 16/ J (4.5 megatons). A two-dimensional Eulerian finite difference code called SOIL was used for this simulation of a cylindrical iron projectile impacting at normal incidence into a limestone target. For this initial calculation, a Tillotson equation-of-state description for iron and limestone was used with no shear strength. Results obtained for this preliminary calculation of the formation of Meteor Crater are in good agreement with field measurements. A color movie based on this calculation was produced using computer-generated graphics. 19 figures, 5 tables, 63 references.

  9. Physics of soft impact and cratering

    CERN Document Server

    Katsuragi, Hiroaki

    2016-01-01

    This book focuses on the impact dynamics and cratering of soft matter to describe its importance, difficulty, and wide applicability to planetary-related problems. A comprehensive introduction to the dimensional analysis and constitutive laws that are necessary to discuss impact mechanics and cratering is first provided. Then, particular coverage is given to the impact of granular matter, which is one of the most crucial constituents for geophysics. While granular matter shows both solid-like and fluid-like behaviors, neither solid nor fluid dynamics is sufficient to fully understand the physics of granular matter. In order to reveal its fundamental properties, extensive impact tests have been carried out recently. The author reveals the findings of these recent studies as well as what remains unsolved in terms of impact dynamics. Impact crater morphology with various soft matter impacts also is discussed intensively. Various experimental and observational results up to the recent Itokawa asteroid’s terrain...

  10. Fossil brachiopods from the Pleistocene of the Antilles

    NARCIS (Netherlands)

    Harper, D.A.T.; Donovan, S.K.

    2007-01-01

    Pleistocene brachiopods are poorly known from the Antillean region, but are locally common in forereef deposits of Jamaica (lower Pleistocene Manchioneal Formation) and Barbados (Coral Rock). Of the four species known, two are new. Lacazella sp. cf. L. caribbeanensis Cooper, an encrusting thecideide

  11. Titan's Impact Cratering Record: Erosion of Ganymedean (and other) Craters on a Wet Icy Landscape

    Science.gov (United States)

    Schenk, P.; Moore, J.; Howard, A.

    2012-04-01

    We examine the cratering record of Titan from the perspective of icy satellites undergoing persistent landscape erosion. First we evaluate whether Ganymede (and Callisto) or the smaller low-gravity neighboring icy satellites of Saturn are the proper reference standard for evaluating Titan’s impact crater morphologies, using topographic and morphometric measurements (Schenk, 2002; Schenk et al. (2004) and unpublished data). The special case of Titan’s largest crater, Minrva, is addressed through analysis of large impact basins such as Gilgamesh, Lofn, Odysseus and Turgis. Second, we employ a sophisticated landscape evolution and modification model developed for study of martian and other planetary landforms (e.g., Howard, 2007). This technique applies mass redistribution principles due to erosion by impact, fluvial and hydrological processes to a planetary landscape. The primary advantage of our technique is the possession of a limited but crucial body of areal digital elevation models (DEMs) of Ganymede (and Callisto) impact craters as well as global DEM mapping of Saturn’s midsize icy satellites, in combination with the ability to simulate rainfall and redeposition of granular material to determine whether Ganymede craters can be eroded to resemble Titan craters and the degree of erosion required. References: Howard, A. D., “Simulating the development of martian highland landscapes through the interaction of impact cratering, fluvial erosion, and variable hydrologic forcing”, Geomorphology, 91, 332-363, 2007. Schenk, P. "Thickness constraints on the icy shells of the galilean satellites from impact crater shapes". Nature, 417, 419-421, 2002. Schenk, P.M., et al. "Ages and interiors: the cratering record of the Galilean satellites". In: Jupiter: The Planet, Satellites, and Magnetosphere, Cambridge University Press, Cambridge, UK, pp. 427-456, 2004.

  12. Ronchi test for flat mirrors

    Energy Technology Data Exchange (ETDEWEB)

    Estrada, N. [Instituto de Fisica, Universidad Autonoma de San Luis Potosi (Mexico); Engelfried, J. [Instituto de Fisica, Universidad Autonoma de San Luis Potosi (Mexico)]. E-mail: jurgen@ifisica.uaslp.mx; Morelos, A. [Instituto de Fisica, Universidad Autonoma de San Luis Potosi (Mexico)

    2005-11-11

    One of the RICHes in the velocity spectrometers of the proposed CKM experiment requires a flat mirror, situated in the high intensity kaon beam. To reduce the interaction background for the experiment, this mirror has to be as thin as possible. First glass prototypes were produced in Mexico. To test the surface quality of these prototypes, we extended the Ronchi method so flat mirrors can also be tested. We present the methods and report on results of our measurements.

  13. Crater lakes of the Pali Aike Volcanic Field as key sites for paleoclimatic and paleoecological reconstructions in southern Patagonia, Argentina

    Science.gov (United States)

    Zolitschka, Bernd; Schäbitz, Frank; Lücke, Andreas; Corbella, Hugo; Ercolano, Bettina; Fey, Michael; Haberzettl, Torsten; Janssen, Stephanie; Maidana, Nora; Mayr, Christoph; Ohlendorf, Christian; Oliva, Gabriel; Paez, Marta M.; Schleser, Gerhard H.; Soto, Julio; Tiberi, Pedro; Wille, Michael

    2006-07-01

    Sedimentary records from crater lakes are of major scientific interest because they provide continuous high-resolution climatic and environmental archives. From a limnogeological survey of crater lakes performed in the Pali Aike Volcanic Field (52°S, southeastern Patagonia, Santa Cruz, Argentina), two deep crater lakes have been recognized: Laguna Potrok Aike (100 m water depth) and Laguna Azul (56 m water depth). Physico-chemical analyses of these closed lake systems demonstrate that Laguna Azul has a dimictic and thermally stratified freshwater body, whereas Laguna Potrok Aike is a subsaline polymictic lake. Both have an oxygen-rich water column from top to bottom. Laguna Potrok Aike in particular is enriched in Na, P, and Cl. The morphometry suggests that Laguna Azul is of Holocene age, whereas the potential sediment infill of Laguna Potrok Aike may comprise 250 m to a mid-Pleistocene age (770 ka). Several aerial and subaquatic lake level terraces at Laguna Potrok Aike point to lake level fluctuations triggered by prior hydrological changes. Although fine-grained sediments of both lakes are not varied, they may eventually provide a detailed terrestrial record of past environmental and climatic variations for this southern mid-latitude region.

  14. Impact Craters as Habitats for Life on Early Mars

    Science.gov (United States)

    Osinski, G. R.; Tornabene, L. L.; Banerjee, N. R.; Cockell, C. S.; Flemming, R.; Izawa, M. R. M.; McCutcheon, J.; Pontefract, A.; Parnell, J.; Sapers, H.; Southam, G.

    2012-05-01

    In this contribution we present a case that impact craters on Early Mars would have represented prime habitats for life, and potentially for its origin, and that impact craters, therefore, should be prime exploration targets for future missions.

  15. Does crater 'saturation equilibrium' occur in the solar system?

    Science.gov (United States)

    Hartmann, W. K.

    1984-01-01

    The similarity in crater densities on the most heavily cratered surfaces throughout the solar system is statistically examined and discussed in terms of a 'saturation equilibrium' being achieved by cratering processes. This hypothesis accounts for (1) the similarity in maximum relative crater density, below certain theoretically predicted values, on all heavily cratered surfaces; (2) a levelling off at this same relative density among 100-m scale craters in populations on lunar maria and other sparsely cratered lunar surfaces; and (3) the approximate uniformity of maximum relative densities on Saturn satellites. The lunar frontside upland crater population, sometimes described as a well-preserved production function useful for interpreting other planetary surfaces, is found not to be a production function. It was modified by intercrater plains at least partly formed by early upland basaltic lava flooding.

  16. Novel approach of crater detection by crater candidate region selection and matrix-pattern-oriented least squares support vector machine

    Institute of Scientific and Technical Information of China (English)

    Ding Meng; Cao Yunfeng; Wu Qingxian

    2013-01-01

    Impacted craters are commonly found on the surface of planets,satellites,asteroids and other solar system bodies.In order to speed up the rate of constructing the database of craters,it is important to develop crater detection algorithms.This paper presents a novel approach to automatically detect craters on planetary surfaces.The approach contains two parts:crater candidate region selection and crater detection.In the first part,crater candidate region selection is achieved by Kanade-Lucas-Tomasi (KLT) detector.Matrix-pattern-oriented least squares support vector machine (MatLSSVM),as the matrixization version of least square support vector machine (SVM),inherits the advantages of least squares support vector machine (LSSVM),reduces storage space greatly and reserves spatial redundancies within each image matrix compared with general LSSVM.The second part of the approach employs MatLSSVM to design classifier for crater detection.Experimental results on the dataset which comprises 160 preprocessed image patches from Google Mars demonstrate that the accuracy rate of crater detection can be up to 88%.In addition,the outstanding feature of the approach introduced in this paper is that it takes resized crater candidate region as input pattern directly to finish crater detection.The results of the last experiment demonstrate that MatLSSVM-based classifier can detect crater regions effectively on the basis of KLT-based crater candidate region selection.

  17. Late Pleistocene dune activity in the central Great Plains, USA

    Science.gov (United States)

    Mason, J.A.; Swinehart, J.B.; Hanson, P.R.; Loope, D.B.; Goble, R.J.; Miao, X.; Schmeisser, R.L.

    2011-01-01

    Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated luminescence (OSL) ages from drill cores and outcrops provide evidence of Late Pleistocene dune activity at sites distributed across the central Great Plains. In addition, Late Pleistocene eolian sands deposited at 20-25 ka are interbedded with loess south of the Sand Hills. Several of the large dunes sampled in the Sand Hills clearly contain a substantial core of Late Pleistocene sand; thus, they had developed by the Late Pleistocene and were fully mobile at that time, although substantial sand deposition and extensive longitudinal dune construction occurred during the Holocene. Many of the Late Pleistocene OSL ages fall between 17 and 14 ka, but it is likely that these ages represent only the later part of a longer period of dune construction and migration. At several sites, significant Late Pleistocene or Holocene large-dune migration also probably occurred after the time represented by the Pleistocene OSL ages. Sedimentary structures in Late Pleistocene eolian sand and the forms of large dunes potentially constructed in the Late Pleistocene both indicate sand transport dominated by northerly to westerly winds, consistent with Late Pleistocene loess transport directions. Numerical modeling of the climate of the Last Glacial Maximum has often yielded mean monthly surface winds southwest of the Laurentide Ice Sheet that are consistent with this geologic evidence, despite strengthened anticyclonic circulation over the ice sheet. Mobility of large dunes during the Late Pleistocene on the central Great Plains may have been the result of

  18. 'Sharks Teeth' -- Sand Dunes in Proctor Crater

    Science.gov (United States)

    2001-01-01

    Sometimes, pictures received from Mars Global Surveyor's Mars Orbiter Camera (MOC) are 'just plain pretty.' This image, taken in early September 2000, shows a group of sand dunes at the edge of a much larger field of dark-toned dunes in Proctor Crater. Located at 47.9oS, 330.4oW, in the 170 km (106 mile) diameter crater named for 19th Century British astronomer Richard A. Proctor (1837-1888), the dunes shown here are created by winds blowing largely from the east/northeast. A plethora of smaller, brighter ripples covers the substrate between the dunes. Sunlight illuminates them from the upper left.

  19. Lethal interpersonal violence in the Middle Pleistocene.

    Science.gov (United States)

    Sala, Nohemi; Arsuaga, Juan Luis; Pantoja-Pérez, Ana; Pablos, Adrián; Martínez, Ignacio; Quam, Rolf M; Gómez-Olivencia, Asier; Bermúdez de Castro, José María; Carbonell, Eudald

    2015-01-01

    Evidence of interpersonal violence has been documented previously in Pleistocene members of the genus Homo, but only very rarely has this been posited as the possible manner of death. Here we report the earliest evidence of lethal interpersonal violence in the hominin fossil record. Cranium 17 recovered from the Sima de los Huesos Middle Pleistocene site shows two clear perimortem depression fractures on the frontal bone, interpreted as being produced by two episodes of localized blunt force trauma. The type of injuries, their location, the strong similarity of the fractures in shape and size, and the different orientations and implied trajectories of the two fractures suggest they were produced with the same object in face-to-face interpersonal conflict. Given that either of the two traumatic events was likely lethal, the presence of multiple blows implies an intention to kill. This finding shows that the lethal interpersonal violence is an ancient human behavior and has important implications for the accumulation of bodies at the site, supporting an anthropic origin.

  20. Lethal interpersonal violence in the Middle Pleistocene.

    Directory of Open Access Journals (Sweden)

    Nohemi Sala

    Full Text Available Evidence of interpersonal violence has been documented previously in Pleistocene members of the genus Homo, but only very rarely has this been posited as the possible manner of death. Here we report the earliest evidence of lethal interpersonal violence in the hominin fossil record. Cranium 17 recovered from the Sima de los Huesos Middle Pleistocene site shows two clear perimortem depression fractures on the frontal bone, interpreted as being produced by two episodes of localized blunt force trauma. The type of injuries, their location, the strong similarity of the fractures in shape and size, and the different orientations and implied trajectories of the two fractures suggest they were produced with the same object in face-to-face interpersonal conflict. Given that either of the two traumatic events was likely lethal, the presence of multiple blows implies an intention to kill. This finding shows that the lethal interpersonal violence is an ancient human behavior and has important implications for the accumulation of bodies at the site, supporting an anthropic origin.

  1. The Middle Pleistocene human tibia from Boxgrove.

    Science.gov (United States)

    Stringer, C B; Trinkaus, E; Roberts, M B; Parfitt, S A; Macphail, R I

    1998-05-01

    The Boxgrove tibia was discovered in 1993, associated with Middle Pleistocene fauna, and Lower Palaeolithic archaeology. The sediments at Boxgrove were deposited during a temperate interglacial episode and ensuing cold stage. They thus represent a wide range of modes and environments of deposition. Archaeological remains have been excavated from all the major stratigraphic units, giving a continuity of occupation for this part of southern England over a 10(4) year timescale, through markedly changing climatic regimes. The stratigraphic, archaeological and sedimentological contexts of the tibia are described, as well as its preservation and morphology. Measurements are given, with discussion of reconstructed bone length, and stature estimates. Comparative measurements are provided for fossil and recent human samples: the large dimensions of its diaphysis place the Boxgrove tibia near or beyond the upper size limits of the comparative samples, but its reconstructed length and estimated stature are less exceptional. The elevated robusticity of the specimen indicates exceptional diaphyseal strength and/or cold adapted body proportions paralleling those of the Neanderthals. Disagreement about the taxonomy of Middle Pleistocene hominids and lack of comparable fossil material make a specific assignment for the Boxgrove tibia problematic. The tibia can only definitely be assigned to non-modern Homo sp., with possible further reference to Homo cf. heidelbergensis (Schoetensack, 1908) on temporal and geographic grounds, if the validity of that species is accepted.

  2. The two Suvasvesi impact structures, Finland: Argon isotopic evidence for a "false" impact crater doublet

    Science.gov (United States)

    Schmieder, Martin; Schwarz, Winfried H.; Trieloff, Mario; Buchner, Elmar; Hopp, Jens; Tohver, Eric; Pesonen, Lauri J.; Lehtinen, Martti; Moilanen, Jarmo; Werner, Stephanie C.; Öhman, Teemu

    2016-05-01

    The two neighboring Suvasvesi North and South impact structures in central-east Finland have been discussed as a possible impact crater doublet produced by the impact of a binary asteroid. This study presents 40Ar/39Ar geochronologic data for impact melt rocks recovered from the drilling into the center of the Suvasvesi North impact structure and melt rock from glacially transported boulders linked to Suvasvesi South. 40Ar/39Ar step-heating analysis yielded two essentially flat age spectra indicating a Late Cretaceous age of ~85 Ma for the Suvasvesi North melt rock, whereas the Suvasvesi South melt sample gave a Neoproterozoic minimum (alteration) age of ~710 Ma. Although the statistical likelihood for two independent meteorite strikes in close proximity to each other is rather low, the remarkable difference in 40Ar/39Ar ages of >600 Myr for the two Suvasvesi impact melt samples is interpreted as evidence for two temporally separate, but geographically closely spaced, impacts into the Fennoscandian Shield. The Suvasvesi North and South impact structures are, thus, interpreted as a "false" crater doublet, similar to the larger East and West Clearwater Lake impact structures in Québec, Canada, recently shown to be unrelated. Our findings have implications for the reliable recognition of impact crater doublets and the apparent rate of binary asteroid impacts on Earth and other planetary bodies in the inner solar system.

  3. Impact and cratering rates onto Pluto

    Science.gov (United States)

    Greenstreet, Sarah; Gladman, Brett; McKinnon, William B.

    2015-09-01

    The New Horizons spacecraft fly-through of the Pluto system in July 2015 will provide humanity's first data for the crater populations on Pluto and its binary companion, Charon. In principle, these surfaces could be dated in an absolute sense, using the observed surface crater density (# craters/km2 larger than some threshold crater diameter D). Success, however, requires an understanding of both the cratering physics and absolute impactor flux. The Canada-France Ecliptic Plane Survey (CFEPS) L7 synthetic model of classical and resonant Kuiper belt populations (Petit, J.M. et al. [2011]. Astron. J. 142, 131-155; Gladman, B. et al. [2012]. Astron. J. 144, 23-47) and the scattering object model of Kaib et al. (Kaib, N., Roškar, R., Quinn, T. [2011]. Icarus 215, 491-507) calibrated by Shankman et al. (Shankman, C. et al. [2013]. Astrophys. J. 764, L2-L5) provide such impact fluxes and thus current primary cratering rates for each dynamical sub-population. We find that four sub-populations (the q 100km) connects to smaller projectiles, we compute cratering rates using five model impactor size distributions: a single power-law, a power-law with a knee, a power-law with a divot, as well as the "wavy" size distributions described in Minton et al. (Minton, D.A. et al. [2012]. Asteroids Comets Meteors Conf. 1667, 6348) and Schlichting et al. (Schlichting, H.E., Fuentes, C.I., Trilling, D.E. [2013]. Astron. J. 146, 36-42). We find that there is only a small chance that Pluto has been hit in the past 4 Gyr by even one impactor with a diameter larger than the known break in the projectile size distribution (d ≈ 100km) which would create a basin on Pluto (D ⩾ 400km in diameter). We show that due to present uncertainties in the impactor size distribution between d = 1- 100km , computing absolute ages for the surface of Pluto is entirely dependent on the extrapolation to small sizes and thus fraught with uncertainty. We show, however, what the ages would be for several cases

  4. Characterization of Boulders Ejected from Small Impact Craters

    NARCIS (Netherlands)

    Bart, G.D.; Melosh, H.J.; Strom, R.G.

    2004-01-01

    When an asteroid or comet impacts the surface of a solid body, some of the surface material is often ejected from the crater in the form of blocks. We are characterizing the size and location of such blocks around craters on the Moon and Mars. The lunar craters were observed in Lunar Orbiter III ima

  5. Characterization of Boulders Ejected from Small Impact Craters

    NARCIS (Netherlands)

    Bart, G.D.; Melosh, H.J.; Strom, R.G.

    2004-01-01

    When an asteroid or comet impacts the surface of a solid body, some of the surface material is often ejected from the crater in the form of blocks. We are characterizing the size and location of such blocks around craters on the Moon and Mars. The lunar craters were observed in Lunar Orbiter III ima

  6. Recharge from a subsidence crater at the Nevada test site

    Science.gov (United States)

    Wilson, G. V.; Ely, D.M.; Hokett, S. L.; Gillespie, D. R.

    2000-01-01

    Current recharge through the alluvial fans of the Nevada Test Site (NTS) is considered to be negligible, but the impact of more than 400 nuclear subsidence craters on recharge is uncertain. Many of the craters contain a playa region, but the impact of these playas has not been addressed. It was hypothesized that a crater playa would focus infiltration through the surrounding coarser-grained material, thereby increasing recharge. Crater U5a was selected because it represented a worst case for runoff into craters. A borehole was instrumented for neutron logging beneath the playa center and immediately outside the crater. Physical and hydraulic properties were measured along a transect in the crater and outside the crater. Particle-size analysis of the 14.6 m of sediment in the crater and morphological features of the crater suggest that a large ponding event of ≈63000 m3 had occurred since crater formation. Water flow simulations with HYDRUS-2D, which were corroborated by the measured water contents, suggest that the wetting front advanced initially by as much as 30 m yr−1 with a recharge rate 32 yr after the event of 2.5 m yr−1Simulations based on the measured properties of the sediments suggest that infiltration will occur preferentially around the playa perimeter. However, these sediments were shown to effectively restrict future recharge by storing water until removal by evapotranspiration (ET). This work demonstrated that subsidence craters may be self-healing.

  7. Seismic Stratigraphy of Pleistocene Deltaic Deposits in Bahía Blanca Estuary, Argentina

    Directory of Open Access Journals (Sweden)

    SALVADOR ALIOTTA

    2014-06-01

    Full Text Available The Bahía Blanca estuary (Argentina has a morphological configuration resulting from hydrological and sedimentary processes related to Late Quaternary sea level changes. This estuarine system occupies a large coastal plain with a dense net of tidal channels, low-altitude islands and large intertidal flats. Little is known about the sedimentary units of the marine subbottom. Therefore, a stratigraphical analysis of the northern coast of Bahía Blanca estuary was carried out using high resolution seismic (3.5 kHz in order to: i define Quaternary sequences, ii describe sedimentary structures, and iii determine the paleoenvironmental conditions of sedimentation. The seismic stratigraphic data collected and their correlation with drilling lithological data show five seismic sequences (S1, S2, S3, S4 and S5, of which S1-S2 were found to be associated with a continental paleoenvironment of Miocene-Pleistocene age. Sequences S3 and S4, whose lithology and seismic facies (paleochannel structures and prograding reflection configurations, were defined on these materials, to evidence the development of an ancient deltaic environment which was part of a large Pleistocene drainage system. The S5 sequence was formed during the Holocene transgressive-regressive process and complete the seismostratigraphic column defined in the present study.

  8. Mineral resources of the Devil's Garden Lava Bed, Squaw Ridge Lava Bed, and Four Craters Lava Bed Wilderness Study Areas, Lake County, Oregon

    Energy Technology Data Exchange (ETDEWEB)

    Keith, W.J.; King, H.D.; Gettings, M.E. (Geological Survey, Reston, VA (USA)); Johnson, F.L. (US Bureau of Mines (US))

    1988-01-01

    The Devel's Garden lava Bed, Squaw Ridge Lava Bed, and Four Craters Lava Bed Wilderness Study Areas include approximately 70,940 acres and are underlain entirely by Pleistocene or Holocene lava flows and associated sediments. There is no evidence of hydrothermal alteration in the study areas. No resources were identified in the study areas, but there is low potential for perlite resources in the southern part of the Devil's Garden Lava Bed and the northern half of the Squaw Ridge Lava Bed areas. All three study areas have low potential for geothermal resources and for oil and gas resources.

  9. Volcano/Ice Interaction Origin of Thermally Distinct Craters in Hrad Vallis, Elysium Planitia, Mars

    Science.gov (United States)

    Morris, A. R.

    2009-12-01

    Evidence of volcano-ground ice interactions on Mars can provide important constraints on the timing and distribution of Martian volcanic processes and climate characteristics. We seek to constrain the presence of volatiles in close association with volcanic activity in the Elysium region of Mars. Northwest of the Elysium Rise is Hrad Vallis, a ~370 m deep, 800 km long sinuous valley that begins in a source region at 34oN, 218 oW. Flanking both sides of the source region is a lobate deposit that extends ~50 km perpendicular from the source and is an average of ~40 m thick. Within the lobate deposit 12 craters have been identified by thermal infrared signatures and morphologies that are distinct from any other craters or depressions in the region. The thermally distinct craters (TDCs) are 1100-1800 m in diameter, 30-40 m deep and are typically circular with central depressions surrounded by ~1 to >6 concentric fracture sets. In order to investigate the origin of the thermal anomalies, as well as scrutinize previous observations made using THEMIS and MOC data, the meter-scale morphology of the TDCs and the surrounding terrain was characterized using images from the CTX (~6 m/pix) and HiRISE (0.25-0.30 m/pix) cameras. Patches of the terrain appear smooth at the meter scale, while fields of cones populate other regions of the surface. The cones are ~30-50 m across at the summit, and ~60-80 m across at the base. Many of the cones have flat summits, while some have a summit crater. The larger cones exhibit channels extending radially away from the summit and decameter-scale pits are observed at the base of many of the cones. The cone morphology suggests they may be the result of the explosive interaction between hot material (lava? mudflow?) and volatiles (either frozen ground or ground ice). Morris and Mouginis-Mark (2006) noted the ejecta surrounding Crater 11 appeared to have a slight “rayed” appearance. HiRISE views of the proposed rays reveal that these are

  10. Late Pleistocene-Holocene cataclysmic eruptions at Nevado de Toluca and Jocotitlan volcanoes, central Mexico

    Science.gov (United States)

    Macias, J.L.; Garcia, P.A.; Arce, J.L.; Siebe, C.; Espindola, J.M.; Komorowski, J.C.; Scott, K.

    1997-01-01

    This field guide describes a five day trip to examine deposits of Late Pleistocene-Holocene cataclysmic eruptions at Nevado de Toluca and Jocotitlan volcanoes in central Mexico. We will discuss the stratigraphy, petrology, and sedimentological characteristics of these deposits which provide insights into the eruptive history, type of volcanic activity, and transport and emplacement mechanisms of pyroclastic materials. These parameters will allow us to discuss the kinds of hazards and the risk that they pose to populations around these volcanoes. The area to be visited is tectonically complex thus we will also discuss the location of the volcanoes with respect to the tectonic environment. The first four days of the field trip will be dedicated to Nevado de Toluca Volcano (19 degrees 09'N; 99 degrees 45'W) located at 23 km. southwest of the City of Toluca, and is the fourth highest peak in the country, reaching an elevation of 4,680 meters above sea level (m.a.s.l.). Nevado de Toluca is an andesitic-dacitic stratovolcano, composed of a central vent excavated upon the remains of older craters destroyed by former events. Bloomfield and Valastro, (1974, 1977) concluded that the last cycle of activity occurred nearly equal 11,600 yr. ago. For this reason Nevado de Toluca has been considered an extinct volcano. Our studies, however, indicate that Nevado de Toluca has had at least two episodes of cone destruction by sector collapse as well as several explosive episodes including plinian eruptions and dome-destruction events. These eruptions occurred during the Pleistocene but a very young eruption characterized by surge and ash flows occurred ca. 3,300 yr. BP. This new knowledge of the volcano's eruptive history makes the evaluation of its present state of activity and the geological hazards necessary. This is important because the area is densely populated and large cities such as Toluca and Mexico are located in its proximity.

  11. Martian fluvial conglomerates at gale crater

    NARCIS (Netherlands)

    Williams, R.M.E.; Grotzinger, J.P.; Dietrich, W.E.; Gupta, S.; Sumner, D.Y.; Wiens, R.C.; Mangold, N.; Malin, M.C.; Edgett, K.S.; Maurice, S.; Forni, O.; Gasnault, O.; Ollila, A.; Newsom, H.E.; Dromart, G.; Palucis, M.C.; Yingst, R.A.; Anderson, R.B.; Herkenhoff, K.E.; Le Mouélic, S.; Goetz, W.; Madsen, M.B.; Koefoed, A.; Jensen, J.K.; Bridges, J.C.; Schwenzer, S.P.; Lewis, K.W.; Stack, K.M.; Rubin, D.; Kah, L.C.; Bell III, J.F.; Farmer, J.D.; Sullivan, R.; Van Beek, T.; Blaney, D.L.; Pariser, O.; Deen, R.G.; MSL Science Team, the

    2013-01-01

    Observations by the Mars Science Laboratory Mast Camera (Mastcam) in Gale crater reveal isolated outcrops of cemented pebbles (2 to 40 millimeters in diameter) and sand grains with textures typical of fluvial sedimentary conglomerates. Rounded pebbles in the conglomerates indicate substantial fluvia

  12. Erosion of ejecta at Meteor Crater, Arizona

    Science.gov (United States)

    Grant, John A.; Schultz, Peter H.

    1993-01-01

    New methods for estimating erosion at Meteor Crater, Arizona, indicate that continuous ejecta deposits beyond 1/4-1/2 crater radii from the rim have been lowered less than 1 m on the average. This conclusion is based on the results of two approaches: coarsening of unweathered ejecta into surface lag deposits and calculation of the sediment budget within a drainage basin on the ejecta. Preserved ejecta morphologies beneath thin alluvium revealed by ground-penetrating radar provide qualitative support for the derived estimates. Although slightly greater erosion of less resistant ejecta locally has occurred, such deposits were limited in extent, particularly beyond 0.25R-0.5R from the present rim. Subtle but preserved primary ejecta features further support our estimate of minimal erosion of ejecta since the crater formed about 50,000 years ago. Unconsolidated deposits formed during other sudden extreme events exhibit similarly low erosion over the same time frame; the common factor is the presence of large fragments or large fragments in a matrix of finer debris. At Meteor Crater, fluvial and eolian processes remove surrounding fines leaving behind a surface lag of coarse-grained ejecta fragments that armor surfaces and slow vertical lowering.

  13. Molecular depth profiling by wedged crater beveling.

    Science.gov (United States)

    Mao, Dan; Lu, Caiyan; Winograd, Nicholas; Wucher, Andreas

    2011-08-15

    Time-of-flight secondary ion mass spectrometry and atomic force microscopy are employed to characterize a wedge-shaped crater eroded by a 40-keV C(60)(+) cluster ion beam on an organic film of Irganox 1010 doped with Irganox 3114 delta layers. From an examination of the resulting surface, the information about depth resolution, topography, and erosion rate can be obtained as a function of crater depth for every depth in a single experiment. It is shown that when measurements are performed at liquid nitrogen temperature, a constant erosion rate and reduced bombardment induced surface roughness is observed. At room temperature, however, the erosion rate drops by ∼(1)/(3) during the removal of the 400 nm Irganox film and the roughness gradually increased to from 1 nm to ∼4 nm. From SIMS lateral images of the beveled crater and AFM topography results, depth resolution was further improved by employing glancing angles of incidence and lower primary ion beam energy. Sub-10 nm depth resolution was observed under the optimized conditions on a routine basis. In general, we show that the wedge-crater beveling is an important tool for elucidating the factors that are important for molecular depth profiling experiments.

  14. Material Handling Equipment Evaluation for Crater Repair

    Science.gov (United States)

    2016-11-01

    material handling equipment with a reduced logistical footprint for use by crater repair teams in airfield damage repair (ADR) scenarios. A market ...compared to currently utilized material handling equipment. This report presents the results of the market survey and equipment evaluations. Results...1 1.2 Objective and scope

  15. Styles of crater gradation in Southern Ismenius Lacus, Mars: Clues from Meteor Crater, Arizona

    Science.gov (United States)

    Grant, J. A.; Schultz, P. H.

    1992-01-01

    Impact craters on the Earth and Mars provide a unique opportunity to quantify the gradational evolution of instantaneously created landforms in a variety of geologic settings. Unlike most landforms, the initial morphology associated with impact craters on both planets is uncomplicated by competition between construction and degradation during formation. Furthermore, pristine morphologies are both well-constrained and similar to a first order. The present study compares styles of graduation at Meteor Crater with those around selected craters (greater than 1-2 km in diameter) in southern Ismenius Lacus. Emphasis is placed on features visible in images near LANDSAT TM resolution (30-50 m/pixel) which is available for both areas. In contrast to Mars, vegetation on the Earth can modify gradation, but appears to influence overall rates and styles by 2X-3X rather than orders of magnitude. Further studies of additional craters in differing settings will refine the effects of this and other factors (e.g., substrate). Finally, by analogy with results from other terrestrial gradational surfaces this study should help provide constraints on climate over crater histories.

  16. IS THE LARGE CRATER ON THE ASTEROID (2867) STEINS REALLY AN IMPACT CRATER?

    Energy Technology Data Exchange (ETDEWEB)

    Morris, A. J. W.; Price, M. C.; Burchell, M. J., E-mail: m.j.burchell@kent.ac.uk [Centre for Astrophysics and Planetary Science, School of Physical Science, University of Kent, Canterbury, Kent CT2 7NH (United Kingdom)

    2013-09-01

    The large crater on the asteroid (2867) Steins attracted much attention when it was first observed by the Rosetta spacecraft in 2008. Initially, it was widely thought to be unusually large compared to the size of the asteroid. It was quickly realized that this was not the case and there are other examples of similar (or larger) craters on small bodies in the same size range; however, it is still widely accepted that it is a crater arising from an impact onto the body which occurred after its formation. The asteroid (2867) Steins also has an equatorial bulge, usually considered to have arisen from redistribution of mass due to spin-up of the body caused by the YORP effect. Conversely, it is shown here that, based on catastrophic disruption experiments in laboratory impact studies, a similarly shaped body to the asteroid Steins can arise from the break-up of a parent in a catastrophic disruption event; this includes the presence of a large crater-like feature and equatorial bulge. This suggests that the large crater-like feature on Steins may not be a crater from a subsequent impact, but may have arisen directly from the fragmentation process of a larger, catastrophically disrupted parent.

  17. Impact-derived features of the Xiuyan meteorite crater

    Institute of Scientific and Technical Information of China (English)

    CHEN Ming

    2008-01-01

    Up to now, 176 meteorite impact craters have been found on the Earth. Among these craters, none of them lies in China. The Xiuyan crater is located in the Liaodong Peninsula of China. This bowl-shaped crater has a diameter of 1.8 km and depth of about 150 m. The impact-derived features include planar deformation features (PDFs) in quartz, shatter cones, impact breccia, and radial valleys on the wall of rim. It is the first confirmed meteorite impact crater in China.

  18. Exploration of Victoria crater by the mars rover opportunity

    Science.gov (United States)

    Squyres, S. W.; Knoll, A.H.; Arvidson, R. E.; Ashley, James W.; Bell, J.F.; Calvin, W.M.; Christensen, P.R.; Clark, B. C.; Cohen, B. A.; De Souza, P.A.; Edgar, L.; Farrand, W. H.; Fleischer, I.; Gellert, Ralf; Golombek, M.P.; Grant, J.; Grotzinger, J.; Hayes, A.; Herkenhoff, K. E.; Johnson, J. R.; Jolliff, B.; Klingelhofer, G.; Knudson, A.; Li, R.; McCoy, T.J.; McLennan, S.M.; Ming, D. W.; Mittlefehldt, D. W.; Morris, R.V.; Rice, J. W.; Schroder, C.; Sullivan, R.J.; Yen, A.; Yingst, R.A.

    2009-01-01

    The Mars rover Opportunity has explored Victoria crater, a ???750-meter eroded impact crater formed in sulfate-rich sedimentary rocks. Impact-related stratigraphy is preserved in the crater walls, and meteoritic debris is present near the crater rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the crater walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those ???6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope.

  19. The Wabar impact craters, Saudi Arabia, revisited

    Science.gov (United States)

    Gnos, E.; Hofmann, B. A.; Halawani, M. A.; Tarabulsi, Y.; Hakeem, M.; Al Shanti, M.; Greber, N. D.; Holm, S.; Alwmark, C.; Greenwood, R. C.; Ramseyer, K.

    2013-10-01

    The very young Wabar craters formed by impact of an iron meteorite and are known to the scientific community since 1933. We describe field observations made during a visit to the Wabar impact site, provide analytical data on the material collected, and combine these data with poorly known information discovered during the recovery of the largest meteorites. During our visit in March 2008, only two craters (Philby-B and 11 m) were visible; Philby-A was completely covered by sand. Mapping of the ejecta field showed that the outcrops are strongly changing over time. Combining information from different visitors with our own and satellite images, we estimate that the large seif dunes over the impact site migrate by approximately 1.0-2.0 m yr-1 southward. Shock lithification took place even at the smallest, 11 m crater, but planar fractures (PFs) and undecorated planar deformation features (PDFs), as well as coesite and stishovite, have only been found in shock-lithified material from the two larger craters. Shock-lithified dune sand material shows perfectly preserved sedimentary structures including cross-bedding and animal burrows as well as postimpact structures such as open fractures perpendicular to the bedding, slickensides, and radiating striation resembling shatter cones. The composition of all impact melt glasses can be explained as mixtures of aeolian sand and iron meteorite. We observed a partial decoupling of Fe and Ni in the black impact glass, probably due to partitioning of Ni into unoxidized metal droplets. The absence of a Ca-enriched component demonstrates that the craters did not penetrate the bedrock below the sand sheet, which has an estimated thickness of 20-30 m.

  20. The Role of Nonlocal Sediment Transport in Shaping Impact Crater Walls on Earth and Mars

    Science.gov (United States)

    Abbott, A. M.; Furbish, D. J.

    2013-12-01

    With increasing interest in the concept of ';nonlocal' sediment transport on steep, regolith covered hillslopes, clearer connections between theoretical formulations of nonlocal transport and natural landforms are needed. Scree slopes that form within impact craters provide useful, interesting study sites, due in part to their reasonably well-known initial morphologies. Recent research also suggests that the surface of Mars may be more erosionally active than previously thought. By using elevations derived from LiDAR data for Earth and HiRISE images for Mars together with a probabilistic description of nonlocal transport that includes entrainment and disentrainment rates, comparisons are made between Barringer Meteorite Crater in Arizona and Martian craters of various ages. This enables commentary on whether nonlocal transport produces similar slopes, despite the differing transport processes and acceleration due to gravity for the two planets. Physical insight is obtained through laboratory experiments where gravel particles are dropped on a loose granular slope composed of similar sized gravel inclined at different slopes, including the angle of repose and a flat layer of gravel. Total travel distances were obtained for approximately 500 particles dropped from three different heights for each slope angle. The resulting distributions of travel distances are exponential-like, but for steeper slopes these distributions may decay less rapidly than an exponential function, indicating a decreasing likelihood of disentrainment with increasing travel distance. These approximately dynamically scaled experiments will help clarify the relationship between drop height, slope, surface roughness, and mean travel distance. A description of the disentrainment rate based partly on these findings will to be incorporated in a numerical model that simulates impact crater erosion for Earth and Mars. This will test the theoretical similarity of two locations that are physically very

  1. The Formation of Widespread Volcanically Filled Crater Floors on Mars: Insights from Modeling and Observations

    Science.gov (United States)

    Edwards, C. S.; Asimow, P. D.; Stewart, S. T.; Ehlmann, B. L.

    2014-12-01

    The identification and mapping of compositionally (olivine-/pyroxene-enriched), thermophysically (rocky), and morphologically (flat floors with lobate margins, no visible ejecta/central peak) distinct infilled craters over the majority of the martian cratered southern highlands coupled with the ancient formation age of floor materials (~3.5-4Ga) recently resulted in the interpretation that volcanic infilling was the likely responsible process. However, the source of this material is enigmatic, as no vents are observed and these deposits do not occur in association with any specific volcanic or geographic provinces, leading to the proposal that impact excavation-induced decompression melting of a mantle source may be responsible for the intra-crater materials. The conditions under which impact-induced decompression melting occurs, if at all, are not well constrained. In this work, we present the quantitative modeling of this process by coupling the pMELTS thermodynamic model for silicate magmas to a CTH shock physics impact model with realistic rock rheology. Initial conditions are established for early to modern Mars with mantle potential temperatures (1250-1550˚C), surface heat fluxes (20-80 mW/m2) and radiogenic crustal heat production (1x10-10-1.0x10-12 W/kg) with a crustal composition of Adirondack class basalts and mantle composition following Dreibus and Wanke. Early results (~80km lithosphere, 1350˚C mantle potential temperature) show ~5-7% excess melt generated at the lithosphere-asthenosphere boundary for large craters (e.g. 180 km). These impact events also create zones of high shear strain/fracture systems that propagate through the entire brittle lithosphere. In general the thinner lithosphere and higher mantle potential temperature conditions on early planetary bodies should produce more melt at a given crater size and allow for the translation of this process to smaller crater sizes like those observed on Mars. If pre-existing melt is trapped below

  2. Lunar polar craters -- icy, rough or just sloping?

    CERN Document Server

    Eke, Vincent R; Lane, David A; Smith, David; Teodoro, Luis F A

    2013-01-01

    Circular Polarisation Ratio (CPR) mosaics from Mini-SAR on Chandrayaan-1 and Mini-RF on LRO are used to study craters near to the lunar north pole. The look direction of the detectors strongly affects the appearance of the crater CPR maps. Rectifying the mosaics to account for parallax also significantly changes the CPR maps of the crater interiors. It is shown that the CPRs of crater interiors in unrectified maps are biased to larger values than crater exteriors, because of a combination of the effects of parallax and incidence angle. Using the LOLA Digital Elevation Map (DEM), the variation of CPR with angle of incidence has been studied. For fresh craters, CPR~0.7 with only a weak dependence on angle of incidence or position interior or just exterior to the crater, consistent with dihedral scattering from blocky surface roughness. For anomalous craters, the CPR interior to the crater increases with both incidence angle and distance from the crater centre. Central crater CPRs are similar to those in the cra...

  3. LAMPADENA IONICA: A NEW TELEOST FROM THE MEDITERRANEAN PLEISTOCENE

    Directory of Open Access Journals (Sweden)

    ANGELA GIRONE

    2002-11-01

    Full Text Available The new species Lampadena ionica (Myctophidae, Teleostei is described from lower and middle Pleistocene deposits of Southern Italy. In particular, L. ionica is known from the "large Gephyrocapsa" up to the Pseudoemiliania lacunosa biozone. Apparently the species became extinct before the end of the Pleistocene. Although the genus Lampadena lives only outside the Mediterranean today, it is known from the Mediterranean realm since the early Miocene. L. ionica seems to be the only species of the genus Lampadena existing in Pleistocene deposits of the Mediterranean area.   

  4. The Fallacies of Flatness: Thomas Friedman's "The World Is Flat"

    Science.gov (United States)

    Abowitz, Kathleen Knight; Roberts, Jay

    2007-01-01

    Thomas Friedman's best-selling "The World is Flat" has exerted much influence in the west by providing both an accessible analysis of globalization and its economic and social effects, and a powerful cultural metaphor for globalization. In this review, we more closely examine Friedman's notion of the social contract, the moral center of his…

  5. Nonlocal gravity: Conformally flat spacetimes

    CERN Document Server

    Bini, Donato

    2016-01-01

    The field equations of the recent nonlocal generalization of Einstein's theory of gravitation are presented in a form that is reminiscent of general relativity. The implications of the nonlocal field equations are studied in the case of conformally flat spacetimes. Even in this simple case, the field equations are intractable. Therefore, to gain insight into the nature of these equations, we investigate the structure of nonlocal gravity in two-dimensional spacetimes. While any smooth 2D spacetime is conformally flat and satisfies Einstein's field equations, only a subset containing either a Killing vector or a homothetic Killing vector can satisfy the field equations of nonlocal gravity.

  6. Using lunar boulders to distinguish primary from distant secondary impact craters

    Science.gov (United States)

    Bart, Gwendolyn D.; Melosh, H. J.

    2007-04-01

    A high-resolution study of 18 lunar craters, including both primary and distant secondary craters, shows that the secondary craters produce larger ejecta fragments at a given crater size than do the primary craters. The maximum boulder diameter (B) increases with crater size (D) according to the power law B = KD 2/3; for primary craters, when B and D are in meters, K is 0.29, whereas for secondary craters, we find that K is 0.46 (60% larger). Next we show that impact fracture theory predicts that secondary craters, because of their lower impact velocity, will produce larger ejecta fragments than primary craters. This result provides an opportunity for distinguishing between primary and secondary craters in high resolution planetary images. The ability to identify distant secondary craters will help constrain primary production rates of small craters and improve surface age determination of small areas based on small crater counts.

  7. Development of ramp-flat structures during Aegean extension

    Science.gov (United States)

    Brun, Jean-Pierre; Sokoutis, Dimitrios

    2014-05-01

    Low-angle extensional shear is frequently observed in the Aegean metamorphic rocks. This deformation is commonly interpreted as being related to detachment at crustal scale, yet it often corresponds to ramp-flat extensional systems that, at many places, control the deposition of Neogene sedimentary basins. From a mechanical point of view, the development of a ramp-flat structure requires the presence of weak layers that can be activated as décollement between stronger rocks units. In the Aegean, the décollement generally develops within the upper brittle crust (i.e. with temperatures lower than about 400°C) that consists in recently exhumed metamorphic rocks. The process by which, these layers become weak enough to form efficient décollements in extension is somewhat intriguing and not well understood. In this contribution we examine the particular case of ramp-flat structures of the Southern Rhodope Core Complex that controlled the deposition of late Miocene to Pleistocene sediments in continental and marine basins. Field evidence is used to argue that the décollement corresponds to marble layers that separate orthogneisses at 2-3 km depth within an upper brittle crust whose thickness is around 5 km. Field observation and stable isotope measurements suggest that the ramp-flat structure observed on the island of Thassos occurred in a marble unit rich in fluids at a temperature of around 200°C. Using laboratory experiments, we explore the geometry of extensional structures (fault systems, rollovers, piggy-back basins…) that can develop at crustal-scale as a function of: i) décollement depth and dip, ii) number of décollements, and iii) strength contrast, between the décollement and overlying strong units. The results are compared with the situation observed in the Southern Rhodope Core Complex. We are convinced that the principles of ramp-flat extension discussed here have a strong potential of application in many other orogenic domains affected by large

  8. Paleomagnetism of Lonar Crater Impact Glass

    Science.gov (United States)

    Garrick-Bethell, I.; Weiss, B. P.; Maloof, A. C.; Stewart, S. T.; Louzada, K. L.; Soule, S. A.; Swanson-Hysell, N.

    2006-12-01

    The source of magnetic fields on extraterrestrial bodies is largely unknown. There is particularly little information about magnetic fields on asteroids and the Moon for the last 3 billion years because most samples from these bodies predate this time. An exception is the small amount of impact-melt which has been continuously created by hypervelocity impactors over most of solar system history. Impact melt can be used to test the controversial hypothesis that magnetic fields on extraterrestrial bodies were predominantly the product of impact-produced plasmas rather than of core dynamos. However, to date only a small amount of impact melt has been analyzed paleomagnetically. To assess the quality of impact melts as recorders of magnetic fields, in January 2004 and January 2005 we collected thousands of samples of basaltic glass from the perimeter of Lonar Crater, a 1.8 km diameter impact crater which formed approximately 50,000 years ago in the Deccan Traps in Maharashtra, India. Lonar crater is a unique extraterrestrial analog because it is the only fresh impact crater on the Earth in a basaltic target. Most glass samples have rounded features and are between 0.01 and 1 cm in size, indicating that they are fladen and impact spherules (microtektites) formed from molten ejecta that cooled in mid-air while subject to rotational and aerodynamic forces. We have found that both types of glasses are strongly magnetic (saturation remanence of ~2 A m-1), contain ferromagnetic crystals that are predominantly single domain in size, and have no significant remanence anisotropy. The glasses also carry a natural remanent magnetization (NRM) presumably acquired just after the impact. However, alternating field demagnetization results in large directional changes of the magnetic moment, with little decrease in moment intensity. We interpret this unusual behavior as progressive removal of different coercivity components that cooled while the orientation of the spinning glasses

  9. Lidar Mapping Documents Post-glacial Faulting West of the High Cascades Axis at Crater Lake National Park, Oregon

    Science.gov (United States)

    Bacon, C. R.; Robinson, J. E.

    2014-12-01

    The Cascades magmatic arc lies mainly within the High Cascades graben system in the state of Oregon. Normal faults of the Klamath graben trend north into Mount Mazama, the volcano whose catastrophic eruption ~7700 cal y BP resulted in collapse of 8x10 km Crater Lake caldera. Geologic mapping of Mount Mazama (Bacon, USGS SIM 2832, 2008) delineated faults of the West Klamath Lake fault zone (WKLFZ) and their northern extensions through Crater Lake National Park west of the caldera. Outcrop patterns implied presence of normal faults farther west but dense conifer forest made discovery of subtle scarps impractical. Closer to the Cascades axis, successively decreasing offsets of mapped Mazama lava flows with decreasing age yielded a long-term vertical slip rate of ~0.3 mm/y on the principal fault segments of the WKLFZ near Crater Lake, where the youngest offset lavas are 35 ka in age. Other workers have found offset lateral moraine crests where Last Glacial Maximum (LGM) valley glaciers crossed the WKLFZ south of Crater Lake. A lidar survey of Crater Lake National Park in 2010 supported by the Oregon Lidar Consortium (Robinson, USGS Data Series 716, 2012) revealed meter-scale, dominantly N-S trending fault scarps with down-to-the-east displacement west of most previously mapped faults at the latitude of Crater Lake, increasing the known width of the fault zone there to as much as 11 km. Fault segments as long as 7-16 km form a semi-continuous system for virtually the entire 32 km N-S extent of lidar coverage. Along the western part of the fault zone, scarp height is as great as ~20 m. Scarp length and height imply that several M>6-7 earthquakes have occurred in late Pleistocene-Holocene time. Field observations show that the ignimbrite of the Mazama climactic eruption banks against or covers scarps. One fault vertically displaces a lateral moraine ~3 m. The moraine contains clasts of ~50 ka andesite and therefore likely dates from the LGM so that the most recent

  10. Flat space physics from holography

    CERN Document Server

    Bousso, R

    2004-01-01

    We point out that aspects of quantum mechanics can be derived from the holographic principle, using only a perturbative limit of classical general relativity. In flat space, the covariant entropy bound reduces to the Bekenstein bound. The latter does not contain Newton's constant and cannot operate via gravitational backreaction. Instead, it is protected by - and in this sense, predicts - the Heisenberg uncertainty principle

  11. The complexity of flat origami

    Energy Technology Data Exchange (ETDEWEB)

    Bern, M. [Xerox, Palo Alto, CA (United States); Hayes, B. [ParcPlace-Digitalk, Inc., Sunnyvale, CA (United States)

    1996-12-31

    We study a basic problem in mathematical origami: determine if a given crease pattern can be folded to a flat origami. We show that assigning mountain and valley folds is NP-hard. We also show that determining a suitable overlap order for flaps is NP-hard, even assuming a valid mountain and valley assignment.

  12. Line bundles and flat connections

    Indian Academy of Sciences (India)

    INDRANIL BISWAS; GEORG SCHUMACHER

    2017-06-01

    We prove that there are cocompact lattices $\\Gamma$ in $\\rm SL(2,\\mathbb C)$ with the property that there are holomorphic line bundles $L$ on $\\rm SL(2,\\mathbb C)/ \\Gamma$ with $c_{1}(L) = 0$ such that $L$ does not admit any unitary flat connection.

  13. A phase-space model for Pleistocene ice volume

    CERN Document Server

    Imbrie, John Z; Lisiecki, Lorraine E

    2011-01-01

    We present a phase-space model that simulates Pleistocene ice volume changes based on Earth's orbital parameters. Terminations in the model are triggered by a combination of ice volume and orbital forcing and agree well with age estimates for Late Pleistocene terminations. The average phase at which model terminations begin is approximately 90 +/- 90 degrees before the maxima in all three orbital cycles. The large variability in phase is likely caused by interactions between the three cycles and ice volume. Unlike previous ice volume models, this model produces an orbitally driven increase in 100-kyr power during the mid-Pleistocene transition without any change in model parameters. This supports the hypothesis that Pleistocene variations in the 100-kyr power of glacial cycles could be caused, at least in part, by changes in Earth's orbital parameters, such as amplitude modulation of the 100-kyr eccentricity cycle, rather than changes within the climate system.

  14. Zonation of uplifted pleistocene coral reefs on barbados, west indies.

    Science.gov (United States)

    Mesolella, K J

    1967-05-05

    The coral species composition of uplifted Pleistocene reefs on Barbados is very similar to Recent West Indian reefs. Acropora palmata, Acropora cervicornis, and Montastrea annularis are qtuantitatively the most important of the coral species.

  15. Pleistocene horses (genus Equus in the central Balkans

    Directory of Open Access Journals (Sweden)

    Forsten Ann

    2003-01-01

    Full Text Available A review of the fossil horses of the genus Equus from the central Balkans, a mountainous area comprising Serbia and Montenegro, is presented in this paper. The time period covered by the finds is from the late Early to and including the Late Pleistocene, but the record is not complete: the dated finds are Late Pleistocene in age, while Early and Middle Pleistocene are poorly represented. The horses found resemble those from neighbouring countries from the same time period, probably showing the importance of river valleys as migration routes. The Morava River valley runs in a roughly south-to-north direction, connecting, via the Danube and Tisa River valleys the Hungarian Pannonian Plain in the north with northern Greece in the south, via the Vardar River valley in Macedonia. In Pleistocene, large mammals, including horses, probably used this route for dispersal.

  16. Automatic Flatness Control of Cold Rolling Mill

    Science.gov (United States)

    Anbe, Yoshiharu; Sekiguchi, Kunio

    One of the subjects of cold rolling is a flatness of the rolled strip. Conventionally, measured strip flatness was approximated by polynomial (2th, 4th, 6th) equation across the entire strip width. This made it difficult to deal with desired loose edge or any desired flatness across the entire strip width. Also conventional flatness control was done for the entire strip width, so if there is a different flatness error among drive side and work side, conventional flatness control can not control properly. We propose independent strip flatness control among drive side and work side, and also automatic flatness control (AFC) system with arbitrary desired strip flatness. Also some applied results to cold mill are shown.

  17. Morphology, volcanism, and mass wasting in Crater Lake, Oregon

    Science.gov (United States)

    Bacon, C.R.; Gardner, J.V.; Mayer, L.A.; Buktenica, M.W.; Dartnell, P.; Ramsey, D.W.; Robinson, J.E.

    2002-01-01

    Crater Lake was surveyed nearly to its shoreline by high-resolution multibeam echo sounding in order to define its geologic history and provide an accurate base map for research and monitoring surveys. The bathymetry and acoustic backscatter reveal the character of landforms and lead to a chronology for the concurrent filling of the lake and volcanism within the ca. 7700 calibrated yr B.P. caldera. The andesitic Wizard Island and central-plattform volcanoes are composed of sequences of lava deltas that record former lake levels and demonstrate simultaneous activity at the two vents. Wizard Island eruptions ceased when the lake was ~80 m lower than at present. Lava streams from prominent channels on the surface of the central platform descended to feed extensive subaqueous flow fields on the caldera floor. The Wizard Island and central-platform volcanoes, andesitic Merriam Cone, and a newly discovered probable lava flow on the eastern floor of the lake apparently date from within a few hundred years of caldera collapse, whereas a small rhydacite dome was emplaced on the flank of Wizard Island at ca. 4800 cal. yr B.P. Bedrock outcrops on the submerged caldera walls are shown in detail and, in some cases, can be correlated with exposed geologic units of Mount Mazama. Fragmental debris making up the walls elsewhere consists of narrow talus cones forming a dendritic pattern that leads to fewer, wider ridges downslope. Hummocky topography and scattered blocks up to ~280 m long below many of the embayments in the caldera wall mark debris-avalanche deposits that probably formed in single events and commonly are affected by secondary failures. The flat-floored, deep basins contain relatively fine-grained sediment transported from the debris aprons by sheet-flow turbidity currents. Crater Lake apparently filled rapidly (ca. 400-750 yr) until reaching a permeable layer above glaciated lava identified by the new survey in the northeast caldera wall at ~1845 m elevation

  18. GEOLOGICAL MAPPING OF LUNAR CRATER LALANDE: TOPOGRAPHIC CONFIGURATION, MORPHOLOGY AND CRATERING PROCESS

    Directory of Open Access Journals (Sweden)

    B. Li

    2017-07-01

    Full Text Available Highland crater Lalande (4.45° S, 8.63° W; D = 23.4 km is located on the PKT area of the lunar near side, southeast of Mare Insularum. It is a complex crater in Copernican era and has three distinguishing features: high silicic anomaly, highest Th abundance and special landforms on its floor. There are some low-relief bulges on the left of crater floor with regular circle or ellipse shapes. They are ~ 250 to 680 m wide and ~ 30 to 91 m high with maximum flank slopes > 20°. There are two possible scenarios for the formation of these low-relief bulges which are impact melt products or young silicic volcanic eruptions. According to the absolute model ages of ejecta, melt ponds and hummocky floor, the ratio of diameter and depth, similar bugle features within other Copernican-aged craters and lack of volcanic source vents, we hypothesized that these low-relief bulges were most consistent with an origin of impact melts during the crater formation instead of small and young volcanic activities occurring on the crater floor. Based on Kaguya TC ortho-mosaic and DTM data produced by TC imagery in stereo, geological units and some linear features on the floor and wall of Lalande have been mapped. Eight geological units are organized by crater floor units: hummocky floor, central peak and low-relief bulges; and crater wall units: terraced walls, channeled and veneered walls, interior walls, mass wasting areas, blocky areas, and melt ponds. These geological units and linear features at Lalande provided us a chance to understand some details of the cratering process and elevation differences on the floor. We evaluated several possibilities to understand the potential causes for the observed elevation differences on the Lalande's floor. We proposed that late-stage wall collapse and subsidence due to melt cooling could be the possible causes of observed elevation differences on the floor.

  19. Searching for the Source Crater of Nakhlite Meteorites.

    Science.gov (United States)

    Kereszturi, A; Chatzitheodoridis, E

    2016-11-01

    We surveyed the Martian surface in order to identify possible source craters of the nakhlite Martian meteorites. We investigated rayed craters that are assumed to be younger than 11 Ma, on lava surfaces with a solidification age around 1.2 Ga. An area of 17.3 million km(2) Amazonian lava plains was surveyed and 53 rayed craters were identified. Although most of them are smaller than the threshold limit that is estimated as minimum of launching fragments to possible Earth crossing trajectories, their observed size frequency distribution agrees with the expected areal density from cratering models characteristic for craters that are less than few tens of Ma old. We identified 6 craters larger than 3 km diameter constituting the potentially best source craters for nakhlites. These larger candidates are located mostly on a smooth lava surface, and in some cases, on the earlier fluvial-like channels. In three cases they are associated with fluidized ejecta lobes and rays - although the rays are faint in these craters, thus might be older than the other craters with more obvious rays. More work is therefore required to accurately estimate ages based on ray system for this purpose. A more detailed search should further link remote sensing Martian data with the in-situ laboratory analyses of Martian meteorites, especially in case of high altitude, steep terrains, where the crater rays seems to rarely survive several Ma.

  20. Treatment of non-sparse cratering in planetary surface dating

    Science.gov (United States)

    Kneissl, T.; Michael, G. G.; Schmedemann, N.

    2016-10-01

    We here propose a new technique to derive crater size-frequency distributions (CSFDs) from non-sparsely cratered surfaces, by accounting for the loss of craters due to subsequent crater/ejecta coverage. This approach, which we refer to as the buffered non-sparseness correction (BNSC), relates each crater to a measurement area found by excluding regions in the study area that have been resurfaced by larger craters and their ejecta blankets. The approach includes the well-known buffered crater counting (BCC) technique in order to consider the potential identification of craters whose centers are located outside the counting area. We demonstrate the new approach at two test sites on the Moon, one on the ancient lunar highlands outside the South Pole Aitken basin and the other on the much younger surface of lunar Mare Serenitatis. As expected, the correction has a much stronger effect on ancient, densely cratered surfaces than on younger, sparsely cratered surfaces. Furthermore, these first results indicate that the shapes of CSFDs on ancient terrains are actually very similar to the shapes of CSFDs on younger terrains.

  1. Searching for the Source Crater of Nakhlite Meteorites

    Science.gov (United States)

    Kereszturi, A.; Chatzitheodoridis, E.

    2016-11-01

    We surveyed the Martian surface in order to identify possible source craters of the nakhlite Martian meteorites. We investigated rayed craters that are assumed to be younger than 11 Ma, on lava surfaces with a solidification age around 1.2 Ga. An area of 17.3 million km2 Amazonian lava plains was surveyed and 53 rayed craters were identified. Although most of them are smaller than the threshold limit that is estimated as minimum of launching fragments to possible Earth crossing trajectories, their observed size frequency distribution agrees with the expected areal density from cratering models characteristic for craters that are less than few tens of Ma old. We identified 6 craters larger than 3 km diameter constituting the potentially best source craters for nakhlites. These larger candidates are located mostly on a smooth lava surface, and in some cases, on the earlier fluvial-like channels. In three cases they are associated with fluidized ejecta lobes and rays - although the rays are faint in these craters, thus might be older than the other craters with more obvious rays. More work is therefore required to accurately estimate ages based on ray system for this purpose. A more detailed search should further link remote sensing Martian data with the in-situ laboratory analyses of Martian meteorites, especially in case of high altitude, steep terrains, where the crater rays seems to rarely survive several Ma.

  2. Late pleistocene history of coniferous woodland in the mohave desert.

    Science.gov (United States)

    Wells, P V; Berger, R

    1967-03-31

    Seventeen ancient wood-rat middens, ranging in radiocarbon age from 7400 to 19,500 years and to older than 40,000 years, have been uncovered in the northeastern, north-central, southeastern, and southwestern sectors of the Mohave Desert. Excellent preservation of macroscopic plant materials (including stems, buds, leaves, fruits, and seeds) enables identification of many plant species growing within the limited foraging range of the sedentary wood rat. An approximately synchronous zonal differentiation of vegetation in response to a gradient of elevation on limestone in the northeastern Mohave Desert is apparent from the macrofossil evidence, preserved in wood-rat middens and ground-sloth coprolites, covering a time span bracketed by radiocarbon ages of about 9000 and 10,000 years. XerophilQus juniper woodlands descended to an elevation of 1100 meters, some 600 meters below the present lower limit of woodland (1700 meters) in the latitude of Frenchman Flat. But desert or semidesert shrubs coexisted with the woodland trees throughout much of the span of elevation corresponding to the pluvial lowering of the woodland zone, and the more mesophytic phase of pinyonjuniper woodland was evidently confined to montane habitats at elevations above 1500 meters. Joshua trees, accompanied by desert shrubs, prevailed down to about 600 meters at Gypsum Cave, Nevada, but only the shrubs of the existing warm-desert vegetation occurred at 530 meters near Rampart Cave, Arizona. Pleistocene middens from the southeastern Mohave Desert record a relatively large downward shift of the pinyon-juniper woodland zone, paralleling the remarkably low minimum elevation of the existing woodland zone in that area. The macrofossil evidence speaks for former continuity of the many disjunct stands of woodland vegetation in the Mohave Desert region, at least along the higher divides connecting most of the ranges. However, there is no macrofossil evidence of pluvial continuity of range for the more

  3. Impact cratering and the Oort cloud

    CERN Document Server

    Wickramasinghe, J T

    2008-01-01

    We calculate the expected flux profile of comets into the planetary system from the Oort cloud arising from Galactic tides and encounters with molecular clouds. We find that both periodic and sporadic bombardment episodes, with amplitudes an order of magnitude above background, occur on characteristic timescales ~25-35 Myr. Bombardment episodes occurring preferentially during spiral arm crossings may be responsible both for mass extinctions of life and the transfer of viable microorganisms from the bombarded Earth into the disturbing nebulae. Good agreement is found between the theoretical expectations and the age distribution of large, well-dated terrestrial impact craters of the past 250 million years. A weak periodicity of ~36 Myr in the cratering record is consistent with the Sun's recent passage through the Galactic plane, and implies a central plane density ~0.15 M_Sun pc^(-3). This leaves little room for a significant dark matter component in the disc.

  4. Coral associations of the Pleistocene Ironshore Formation, Grand Cayman

    Science.gov (United States)

    Hunter, I. G.; Jones, B.

    1996-11-01

    The 125-ka sea level, which was approximately 6 m above present-day sea level, led to the partial flooding of many Caribbean islands. On Grand. Cayman, this event led to the formation of the large Ironshore Lagoon that covered most of the western half of the island and numerous, small embayments along the south, east, and north coasts. At that time, at least 33 coral species grew in waters around Grand Cayman. This fauna, like the modern coral fauna of Grand Cayman, was dominated by Montastrea annularis, Porites porites, Acropora polmata, and A. cervicornis. Scolymia cubensis and Mycetophyllia ferox, not previously identified from the Late Pleistocene, are found in the Pleistocene patch reefs. Madracis mirabilis, Colpophyllia breviserialis, Agaricia tenuifolia, A. lamarcki, A. undata, Millepora spp., Mycetophyllia reesi, M. aliciae, and M. danaana, found on modern reefs, have not been identified from the Late Pleistocene reefs. Conversely, Pocillopora sp. cf. P. palmata, which is found in Late Pleistocene reefs, is absent on the modern reefs around Grand Cayman. The corals in the Ironshore Formation of Grand Cayman have been divided into 10 associations according to their dominant species, overall composition, and faunal diversity. Many of these associations are similar to the modern associations around Grand Cayman. Each of the Pleistocene coral associations, which can be accurately located on the known Late Pleistocene paleogeography of Grand Cayman, developed in distinct environmental settings. Overall trends identified in the modern settings are also apparent in the Late Pleistocene faunas. Thus, the diversity of the coral faunas increased from the interior of the Ironshore Lagoon to the reef crest. Similarly, the coral diversity in the Pleistocene patch reefs was related to the size of the reefs and their position relative to breaks in the barrier reef. The barrier reef included corals that are incapable of sediment rejection; whereas the patch reefs lacked

  5. Low-velocity impact cratering experiments in granular slopes

    Science.gov (United States)

    Hayashi, Kosuke; Sumita, Ikuro

    2017-07-01

    Low-velocity impact cratering experiments are conducted in sloped granular targets to study the effect of the slope angle θ on the crater shape and its scales. We use two types of granular matter, sand and glass beads, former of which has a larger friction coefficient μs = tanθr , where θr is the angle of repose. Experiments show that as θ increases, the crater becomes shallower and elongated in the direction of the slope. Furthermore the crater floor steepens in the upslope side and a thick rim forms in the downslope side, thus forming an asymmetric profile. High-speed images show that these features are results of ejecta being dispersed farther towards the downslope side and the subsequent avalanche which buries much of the crater floor. Such asymmetric ejecta dispersal can be explained by combining the Z-model and a ballistic model. Using the topographic maps of the craters, we classify crater shape regimes I-III, which transition with increasing θ : a full-rim crater (I), a broken-rim crater (II), and a depression (III). The critical θ for the regime transitions are larger for sand compared to glass beads, but collapse to close values when we use a normalized slope θ^ = tanθ / tanθr . Similarly we derive θ^-dependences of the scaled crater depth, length, width and their ratios which collapse the results for different targets and impact energies. We compare the crater profiles formed in our experiments with deep craters on asteroid Vesta and find that some of the scaled profiles nearly overlap and many have similar depth / length ratios. This suggests that these Vestan craters may also have formed in the gravity regime and that the formation process can be approximated by a granular flow with a similar effective friction coefficient.

  6. Robust System for Automated Identification of Martian Impact Craters

    Science.gov (United States)

    Stepinski, T. F.; Mendenhall, M. P.

    2006-12-01

    Detailed analysis of the number and morphology of impact craters on Mars provides the worth of information about the geologic history of its surface. Global catalogs of Martian craters have been compiled (for example, the Barlow catalog) but they are not comprehensive, especially for small craters. Existing methods for machine detection of craters from images suffer from low efficiency and are not practical for global surveys. We have developed a robust two-stage system for an automated cataloging of craters from digital topography data (DEM). In the first stage an innovative crater-finding transform is performed on a DEM to identify centers of potential craters, their extents, and their basic characteristics. This stage produces a preliminary catalog. In the second stage a machine learning methods are employed to eliminate false positives. Using the MOLA derived DEMs with resolution of 1/128 degrees/pixel, we have applied our system to six ~ 106 km2 sites. The system has identified 3217 craters, 43% more than are present in the Barlow catalog. The extra finds are predominantly small craters that are most difficult to account for in manual surveys. Because our automated survey is DEM-based, the resulting catalog lists craters' depths in addition to their positions, sizes, and measures of shape. This feature significantly increases the scientific utility of any catalog generated using our system. Our initial calculations yield a training set that will be used to identify craters over the entire Martian surface with estimated accuracy of 95%. Moreover, because our method is pixel-based and scale- independent, the present training set may be used to identify craters in higher resolution DEMs derived from Mars Express HRSC images. It also can be applied to future topography data from Mars and other planets. For example, it may be utilized to catalog craters on Mercury and the Moon using altimetry data to be gathered by Messenger and Lunar Reconnaissance Orbiter

  7. Martian cratering 11. Utilizing decameter scale crater populations to study Martian history

    Science.gov (United States)

    Hartmann, W. K.; Daubar, I. J.

    2017-03-01

    New information has been obtained in recent years regarding formation rates and the production size-frequency distribution (PSFD) of decameter-scale primary Martian craters formed during recent orbiter missions. Here we compare the PSFD of the currently forming small primaries (P) with new data on the PSFD of the total small crater population that includes primaries and field secondaries (P + fS), which represents an average over longer time periods. The two data sets, if used in a combined manner, have extraordinary potential for clarifying not only the evolutionary history and resurfacing episodes of small Martian geological formations (as small as one or few km2) but also possible episodes of recent climatic change. In response to recent discussions of statistical methodologies, we point out that crater counts do not produce idealized statistics, and that inherent uncertainties limit improvements that can be made by more sophisticated statistical analyses. We propose three mutually supportive procedures for interpreting crater counts of small craters in this context. Applications of these procedures support suggestions that topographic features in upper meters of mid-latitude ice-rich areas date only from the last few periods of extreme Martian obliquity, and associated predicted climate excursions.

  8. Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater, Egypt

    Science.gov (United States)

    Fazio, Agnese; Folco, Luigi; D'Orazio, Massimo; Frezzotti, Maria Luce; Cordier, Carole

    2014-12-01

    Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz-rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high-pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s-1. The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.

  9. Analytical formulation of lunar cratering asymmetries

    CERN Document Server

    Wang, Nan

    2016-01-01

    We formulate the lunar cratering distribution and verify the cratering asymmetries generated by the main-belt asteroids (MBAs) as well as the near-Earth objects (NEOs). Based on a planar model that excludes the terrestrial and lunar gravitations on the impactors and assuming the impactor encounter speed with Earth $v_{\\rm{enc}}$ is higher than the lunar orbital speed $v_{\\rm{M}}$, we rigorously integrated the lunar cratering distribution, and derived its approximation to the first order of $v_{\\rm{M}}/v_{\\rm{enc}}$. Numerical simulations of lunar bombardment by the MBAs during the late heavy bombardment were performed with an Earth-Moon distance $a_{\\rm{M}}$ = 20--60 Earth radii in five cases. The analytical model directly proves the existence of a leading/trailing asymmetry and the absence of near/far asymmetry. The approximate form of the leading/trailing asymmetry is $(1 + A_1 \\cos\\beta)$, which decreases as the apex distance $\\beta$ increases. The numerical simulations show evidence of a pole/equator asym...

  10. Crater-and-split technique for phacoemulsification: modification of the crater-and-chop technique.

    Science.gov (United States)

    Aslan, Bekir Sıtkı; Müftüoglu, Orkun; Gayretli, Deniz

    2012-09-01

    We describe a modification of the crater-and-chop technique for removing cataracts of all densities. Following creation of a central crater approximately 3.0 mm in diameter at the geometric center of the endonucleus, a nucleus splitter is inserted under the capsule and the phaco tip is inserted in the crater. Simultaneously, the splitter is moved from the nucleus periphery toward the phaco tip horizontally to split the nucleus and both the phaco tip and nucleus splitter are pushed aside as they come very close without vacuum at any point. The nucleus is rotated and splitting is repeated in the same manner until the nucleus is divided into pieces that are small enough to be emulsified easily. With this technique, the soft nucleus is split without vacuum and a very hard nucleus can be split through the posterior plate with minimal stress to zonular fibers. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  11. Origin of the anomalously rocky appearance of Tsiolkovskiy crater

    Science.gov (United States)

    Greenhagen, B. T.; Neish, C.; Williams, J. P.; Cahill, J. T.; Ghent, R. R.; Hayne, P. O.; Lawrence, S. J.; Petro, N. E.; Bandfield, J.

    2016-12-01

    In this study, we analyzed the rock population and distribution around Tsiolkovskiy crater, an approximately 180 km diameter, mare-filled crater on the lunar farside. This study was enabled by new datasets from the Lunar Reconnaissance Orbiter (LRO) that provide information on the surface and near-subsurface rock populations at a variety of spatial scales and wavelengths. We found that Tsiolkovskiy has an external deposit where (1) Diviner Lunar Radiometer (Diviner) rock abundance is anomalously high, similar to Copernican-aged craters, (2) Diviner estimates of rock-free regolith thickness are anomalously low, consistent with antipodal impacts. The source of this disruption is unknown, but Tsiolkovskiy crater is located antipodal to the Copernican-aged Aristarchus crater. Future modeling of the seismic effects of this impact may help to determine whether this was a likely source for the recent surface modification at Tsiolkovskiy crater.

  12. The nature of crater rays - The Copernicus example

    Science.gov (United States)

    Pieters, C. M.; Adams, J. B.; Smith, M. O.; Mouginis-Mark, P. J.; Zisk, S. H.

    1985-01-01

    It is pointed out that crater rays are filamentous, generally high-albedo features which emanate nearly radially from young impact structures. An investigation has been conducted of the physical and chemical properties of a single lunar ray system for Copernicus crater with the objective to achieve a better understanding of the nature of crater rays, taking into account questions regarding the local or foreign origin of ray material. A combination of data is considered, giving attention to spectral reflectance (for composition), radar (for physical properties), and images (for photogeologic context). The crater Copernicus was selected because of its well-developed ray system, the crater's relative youth, and the compositional contrast between the target material of Copernicus crater and the material on which many rays were emplaced.

  13. Lucy's flat feet: the relationship between the ankle and rearfoot arching in early hominins.

    Directory of Open Access Journals (Sweden)

    Jeremy M DeSilva

    Full Text Available BACKGROUND: In the Plio-Pleistocene, the hominin foot evolved from a grasping appendage to a stiff, propulsive lever. Central to this transition was the development of the longitudinal arch, a structure that helps store elastic energy and stiffen the foot during bipedal locomotion. Direct evidence for arch evolution, however, has been somewhat elusive given the failure of soft-tissue to fossilize. Paleoanthropologists have relied on footprints and bony correlates of arch development, though little consensus has emerged as to when the arch evolved. METHODOLOGY/PRINCIPAL FINDINGS: Here, we present evidence from radiographs of modern humans (n = 261 that the set of the distal tibia in the sagittal plane, henceforth referred to as the tibial arch angle, is related to rearfoot arching. Non-human primates have a posteriorly directed tibial arch angle, while most humans have an anteriorly directed tibial arch angle. Those humans with a posteriorly directed tibial arch angle (8% have significantly lower talocalcaneal and talar declination angles, both measures of an asymptomatic flatfoot. Application of these results to the hominin fossil record reveals that a well developed rearfoot arch had evolved in Australopithecus afarensis. However, as in humans today, Australopithecus populations exhibited individual variation in foot morphology and arch development, and "Lucy" (A.L. 288-1, a 3.18 Myr-old female Australopithecus, likely possessed asymptomatic flat feet. Additional distal tibiae from the Plio-Pleistocene show variation in tibial arch angles, including two early Homo tibiae that also have slightly posteriorly directed tibial arch angles. CONCLUSIONS/SIGNIFICANCE: This study finds that the rearfoot arch was present in the genus Australopithecus. However, the female Australopithecus afarensis "Lucy" has an ankle morphology consistent with non-pathological flat-footedness. This study suggests that, as in humans today, there was variation in arch

  14. PLEISTOCENE BATHYAL MOLLUSCAN ASSEMBLAGES FROM SOUTHERN ITALY

    Directory of Open Access Journals (Sweden)

    ITALO DI GERONIMO

    1997-11-01

    Full Text Available Four Pleistocene bathyal molluscan assemblages from southern Italy (Calabria and Messina area were studied. One hundred and thirty-six species were recorded. Twenty-four were classified and described in detail and thirty-five were illustrated. The following new combinations are pro posed: Solariella marginulata (Philippi, 1844, Iphitus tenuisculptus (Seguenza, 1876, Benthomangelia tenuicostata (Seguenza, 1879, Chrysallida microscalaria (Seguenza, 1876, Ennucula corbuloides (Seguenza, 1877, Ennucula rotundata (Seguenza, 1877, Thestyleda cuspidata (Philippi, 1844, Katadesmia confusa (Seguenza, 1877, Austrotindaria pusio (Philippi, 1844, Austrotindaria salicensis (Seguenza, 1877. Comments concerning the taxonomy of Fissurisepta Seguenza, 1862, Solariella Wood, 1842, Ennucula Iredale, 1931, Thestyleda Iredale, 1929, Ledella Verrill & Bush, 1897, Yoldiella Verrill & Bush, 1897, Bathyspinula Filatova, 1958, Katadesmia Dall, 1908, Austrotindaria Fleming, 1948 and Cadulus Philippi, 1844 are included. The assemblages are dominated by nuculoids and fit the general compositional pattern of the deep-sea molluscan communities. A paleodepth of 500-600 m is inferred for two assemblages, whereas a greater depth, pro bably not exceeding 1,000 m, is suggested for the other two. Taxonomic affinities with northeast Atlantic and more generally with World Ocean deep-sea molluscan faunas are remarkable. The Plio-Quaternary evolution of the deep Mediterranean benthos is discussed.    

  15. Flat

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    菲亚特选在柏林举行的“面包与黄油(Bread&Butter)”青年时尚秀中发布了500柴油版车型。这款车型首先推出的是黑色和绿色车身颜色,共限量1万辆,目前已有6000辆被售出。现在,它又追加了1款车身颜色“午夜蓝”,菲亚特选择这款颜色,是因为它很接近牛仔裤的颜色,更容易吸引年轻的消费者。

  16. Laser illuminated flat panel display

    Energy Technology Data Exchange (ETDEWEB)

    Veligdan, J.T.

    1995-12-31

    A 10 inch laser illuminated flat panel Planar Optic Display (POD) screen has been constructed and tested. This POD screen technology is an entirely new concept in display technology. Although the initial display is flat and made of glass, this technology lends itself to applications where a plastic display might be wrapped around the viewer. The display screen is comprised of hundreds of planar optical waveguides where each glass waveguide represents a vertical line of resolution. A black cladding layer, having a lower index of refraction, is placed between each waveguide layer. Since the cladding makes the screen surface black, the contrast is high. The prototype display is 9 inches wide by 5 inches high and approximately I inch thick. A 3 milliwatt HeNe laser is used as the illumination source and a vector scanning technique is employed.

  17. Parallel spinors on flat manifolds

    Science.gov (United States)

    Sadowski, Michał

    2006-05-01

    Let p(M) be the dimension of the vector space of parallel spinors on a closed spin manifold M. We prove that every finite group G is the holonomy group of a closed flat spin manifold M(G) such that p(M(G))>0. If the holonomy group Hol(M) of M is cyclic, then we give an explicit formula for p(M) another than that given in [R.J. Miatello, R.A. Podesta, The spectrum of twisted Dirac operators on compact flat manifolds, Trans. Am. Math. Soc., in press]. We answer the question when p(M)>0 if Hol(M) is a cyclic group of prime order or dim⁡M≤4.

  18. Graphene folding on flat substrates

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xiaoming; Zhao, Yadong; Ke, Changhong, E-mail: cke@binghamton.edu [Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, New York 13902 (United States); Zhang, Liuyang; Wang, Xianqiao [College of Engineering, University of Georgia, Athens, Georgia 30602 (United States)

    2014-10-28

    We present a combined experimental-theoretical study of graphene folding on flat substrates. The structure and deformation of the folded graphene sheet are experimentally characterized by atomic force microscopy. The local graphene folding behaviors are interpreted based on nonlinear continuum mechanics modeling and molecular dynamics simulations. Our study on self-folding of a trilayer graphene sheet reports a bending stiffness of about 6.57 eV, which is about four times the reported values for monolayer graphene. Our results reveal that an intriguing free sliding phenomenon occurs at the interlayer van der Waals interfaces during the graphene folding process. This work demonstrates that it is a plausible venue to quantify the bending stiffness of graphene based on its self-folding conformation on flat substrates. The findings reported in this work are useful to a better understanding of the mechanical properties of graphene and in the pursuit of its applications.

  19. Flat heat pipe design, construction, and analysis

    Energy Technology Data Exchange (ETDEWEB)

    Voegler, G.; Boughey, B.; Cerza, M.; Lindler, K.W.

    1999-08-02

    This paper details the design, construction and partial analysis of a low temperature flat heat pipe in order to determine the feasibility of implementing flat heat pipes into thermophotovoltaic (TPV) energy conversion systems.

  20. The role of strength defects in shaping impact crater planforms

    Science.gov (United States)

    Watters, W. A.; Geiger, L. M.; Fendrock, M.; Gibson, R.; Hundal, C. B.

    2017-04-01

    High-resolution imagery and digital elevation models (DEMs) were used to measure the planimetric shapes of well-preserved impact craters. These measurements were used to characterize the size-dependent scaling of the departure from circular symmetry, which provides useful insights into the processes of crater growth and modification. For example, we characterized the dependence of the standard deviation of radius (σR) on crater diameter (D) as σR ∼ Dm. For complex craters on the Moon and Mars, m ranges from 0.9 to 1.2 among strong and weak target materials. For the martian simple craters in our data set, m varies from 0.5 to 0.8. The value of m tends toward larger values in weak materials and modified craters, and toward smaller values in relatively unmodified craters as well as craters in high-strength targets, such as young lava plains. We hypothesize that m ≈ 1 for planforms shaped by modification processes (slumping and collapse), whereas m tends toward ∼ 1/2 for planforms shaped by an excavation flow that was influenced by strength anisotropies. Additional morphometric parameters were computed to characterize the following planform properties: the planform aspect ratio or ellipticity, the deviation from a fitted ellipse, and the deviation from a convex shape. We also measured the distribution of crater shapes using Fourier decomposition of the planform, finding a similar distribution for simple and complex craters. By comparing the strength of small and large circular harmonics, we confirmed that lunar and martian complex craters are more polygonal at small sizes. Finally, we have used physical and geometrical principles to motivate scaling arguments and simple Monte Carlo models for generating synthetic planforms, which depend on a characteristic length scale of target strength defects. One of these models can be used to generate populations of synthetic planforms which are very similar to the measured population of well-preserved simple craters on

  1. Detection and analysis of rock cracks in meteor crater

    OpenAIRE

    Wang, Min

    2010-01-01

    In 2000, a geologist Fridtjof Riis discovered a meteor crater in Ritland, Hjelmelan municipality in Rogland. This crater was formed by meteorite impact. The crater has areas with a lot of cracks in the rocks, and geologists think these cracks are very valuable information for them. By making photos with an ordinary camera, they want to get binary pictures where the cracks are shown as white lines on a black background. They can measure and quantify the length and direction of t...

  2. Machine Identification of Martian Craters Using Digital Elevation Data

    Science.gov (United States)

    Bue, B.; Stepinski, T. F.

    2005-12-01

    Impact craters are among the most studied features on Martian surface. Their importance stems from the worth of information that a detailed analysis of their number and morphology can bring forth. Because building manually a comprehensive dataset of craters is a laborious process, there have been many previous attempts to develop an automatic, image-based crater identifier. The resulting identifiers suffer from low efficiency and remain in an experimental stage. We have developed a DEM-based, fully autonomous crater identifier that takes an arbitrarily large Martian site as an input and produces a catalog of craters as an output. Using the topography data we calculate a topographic profile curvature that is thresholded to produce a binary image, pixels having maximum negative curvature are labeled black, the remaining pixels are labeled white. The black pixels outline craters because crater rims are the most convex feature in the Martian landscape. The Hough Transform (HT) is used for an actual recognition of craters in the binary image. The image is first segmented (without cutting the craters) into a large number of smaller images using the ``flood" algorithm that identifies basins. This segmentation makes possible the application of highly inefficient HT to large sites. The identifier is applied to a 106 km2 site located around the Herschel crater. According to the Barlow catalog, this site contains 485 craters >5 km. Our identifier finds 1099 segments, 628 of them are classified as craters >5 km. Overall, there is an excellent agreement between the two catalogs, although the specific statistics are still pending due to the difficulties in recalculating the MDIM 1 coordinate system used in the Barlow catalog to the MDIM 2.1 coordinate system used by our identifier.

  3. Zumba crater, Daedalia Planum, Mars: Geologic investigation of a young, rayed impact crater and its secondary field

    Science.gov (United States)

    Chuang, Frank C.; Crown, David A.; Tornabene, Livio L.

    2016-05-01

    Zumba is a ∼2.9 km diameter rayed crater on Mars located on extensive lava plains in Daedalia Planum to the southwest of Arsia Mons. It is a well-preserved young crater with large ejecta rays that extend for hundreds of kilometers from the impact site. The rays are thermally distinct from the background lava flows in THEMIS daytime and nighttime thermal infrared data, a unique characteristic among martian rayed craters. Concentrated within the rays are solitary or dense clusters of secondary craters with associated diffuse dark-toned deposits along with fewer secondary craters lacking dark-toned deposits. Using CTX images, we have mapped secondary craters with dark-toned deposits, collectively termed "secondary fields", to investigate their distribution as a function of distance from the impact site. The mapped secondary field was then used to investigate various aspects of the crater-forming event such as the surface angle and direction of the projectile, the effect of secondary craters on surface age estimates, and the number of secondary craters produced by the impact event. From our mapping, a total of 13,064 secondary fields were documented out to a 200 km radial distance beyond a 15 km-wide non-secondary zone around Zumba crater. Results show that the highest areal coverage of secondary fields occurs within 100 km of Zumba and within its rays, decreasing radially with distance to a background scattering of small secondary fields that are moderately oblique impact projectile coming from the south. Using primary craters in a ∼101 km2 sample region and all craters (primaries and secondaries) from 43 select secondary fields in two map sectors in the study area, we obtain ages of ∼580 ± 100 Ma and ∼650 ± 70 Ma, respectively, for the lava flows into which Zumba impacted. These ages are consistent with and intermediate to 0.1-1 Ga volcanic flow units within and near Daedalia Planum. For craters within the secondary fields, a log differential plot of the

  4. Half-flat Quantum Hair

    CERN Document Server

    García-Compeán, Hugo; Martínez-Merino, Aldo; Santos-Silva, Roberto

    2013-01-01

    By wrapping D3-branes over 3-cycles on a Half-flat manifold we construct an effective supersymmetric Black Hole in the N=2 low-energy theory in four-dimensions. Specifically we find that the torsion cycles present in a half-flat compactification, corresponding to the mirror symmetric image of electric NS flux on a Calabi-Yau manifold, manifest in the black hole physics as quantum hair. We compute the electric and magnetic charges related to the quantum hair, and also the mass contribution to the effective black hole. We find that by wrapping a number of D3-branes equal to the order of the discrete group associated to the torsional part of the half-flat homology, the effective charge and mass terms vanishes. We compute the variation of entropy and the corresponding temperature associated with the lost of the quantum hair. We also comment on the equivalence between canceling Freed-Witten anomalies and the assumption of self-duality for the five-form field strength. Finally from a K-theoretical perspective, we c...

  5. Flat colon polyps: what should radiologists know?

    Energy Technology Data Exchange (ETDEWEB)

    Ignjatovic, A. [Intestinal Imaging Centre, St Mark' s Hospital, Harrow, Middlesex (United Kingdom); Burling, D., E-mail: burlingdavid@yahoo.co.u [Intestinal Imaging Centre, St Mark' s Hospital, Harrow, Middlesex (United Kingdom); Ilangovan, R.; Clark, S.K.; Taylor, S.A.; East, J.E.; Saunders, B.P. [Intestinal Imaging Centre, St Mark' s Hospital, Harrow, Middlesex (United Kingdom)

    2010-12-15

    With the recent publication of international computed tomography (CT) colonography standards, which aim to improve quality of examinations, this review informs radiologists about the significance of flat polyps (adenomas and hyperplastic polyps) in colorectal cancer pathways. We describe flat polyp classification systems and propose how flat polyps should be reported to ensure patient management strategies are based on polyp morphology as well as size. Indeed, consistency when describing flat polyps is of increasing importance given the strengthening links between CT colonography and endoscopy.

  6. IODP/ICDP Expedition 364-Drilling the Cretaceous-Paleogene Chicxulub impact crater: Insights into large craters formation and their effect on life.

    Science.gov (United States)

    Gulick, S. P. S.; Morgan, J. V.; Fucugauchi, J. U.; Bralower, T. J.; Chenot, É.; Christeson, G. L.; Claeys, P.; Cockell, C. S.; Collins, G. S.; Coolen, M.; Gebhardt, C.; Goto, K.; Kring, D. A.; Xiao, L.; Lowery, C.; Mellett, C.; Ocampo-Torres, R.; Osinski, G. R.; Perez-Cruz, L. L.; Pickersgill, A.; Poelchau, M.; Rae, A.; Rasmussen, C.; Rebolledo-Vieyra, M.; Riller, U. P.; Sato, H.; Schmitt, D. R.; Smit, J.; Tikoo, S.; Tomioka, N.; Whalen, M. T.; Zylberman, W.; Jones, H.; Gareth, C.; Wittmann, A.; Lofi, J.; Yamaguchi, K. E.; Ferrière, L.

    2016-12-01

    An international project to drill the Chicxulub impact crater was conducted in April and May, 2016 as Expedition 364 of the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Project (ICDP). Site M0077 is located offshore Yucatan in the southern Gulf of Mexico. The target was to core the only pristine terrestrial peak ring and to measure physical properties of the entire borehole. Specific questions included: What rocks comprise a topographic peak ring? How are peak rings formed? How are rocks weakened during large impacts to allow them to collapse and form relatively wide, flat craters? What insights arise from biologic recovery in the Paleogene within a potentially "toxic" ocean basin? Are impact craters (including peak rings) habitats for life? Coring occurred from 503 - 1334.7 mbsf with nearly 100% recovery. Wireline logs were collected from ultra slimline tools to total depth including gamma ray, magnetic susceptibility, sonic, borehole fluid temperature and conductivity, resistivity data, borehole images, and a finely spaced vertical seismic profile. Stratigraphy cored included 110 m of Eocene and Paleocene carbonates, 130 m of allochthonous impactites, and 590 m of crustal basement with dikes. All cores were measured using a shipboard core logger (density, gamma ray, magnetic susceptibility and resistivity) and shorebased dual energy, 0.3 mm resolution CT scanner. These data allow us to: 1) refine numerical models of the formation of the Chicxulub impact structure; 2) place constraints on environmental perturbations that led to the K-Pg mass extinction; 3) improve simulations of impact craters on other planetary bodies; 4) examine deformation mechanisms for insights into how rocks weaken during impacts; 5) study impact generated hydrothermal systems and 6) understand the effects of impacts on the deep biosphere including as a habitat for microbial life with implications for evolution on Earth and astrobiology. Key

  7. Secondary crater-initiated debris flow on the Moon

    Science.gov (United States)

    Martin-Wells, K. S.; Campbell, D. B.; Campbell, B. A.; Carter, L. M.; Fox, Q.

    2017-07-01

    In recent work, radar circular polarization echo properties have been used to identify secondary craters without distinctive ;secondary; morphologies. Because of the potential for this method to improve our knowledge of secondary crater populations-in particular the effect of secondary populations on crater-derived ages based on small craters-it is important to understand the origin of radar polarization signatures associated with secondary impacts. In this paper, we utilize Lunar Reconnaissance Orbiter Camera photographs to examine the geomorphology of secondary craters with radar circular polarization ratio enhancements. Our investigation reveals evidence of dry debris flow with an impact melt component at such secondary craters. We hypothesize that these debris flows were initiated by the secondary impacts themselves, and that they have entrained blocky material ejected from the secondaries. By transporting this blocky material downrange, we propose that these debris flows (rather than solely ballistic emplacement) are responsible for the tail-like geometries of enhanced radar circular polarization ratio associated with the secondary craters investigated in this work. Evidence of debris flow was observed at both clustered and isolated secondary craters, suggesting that such flow may be a widespread occurrence, with important implications for the mixing of primary and local material in crater rays.

  8. Ancient impact and aqueous processes at Endeavour Crater, Mars.

    Science.gov (United States)

    Squyres, S W; Arvidson, R E; Bell, J F; Calef, F; Clark, B C; Cohen, B A; Crumpler, L A; de Souza, P A; Farrand, W H; Gellert, R; Grant, J; Herkenhoff, K E; Hurowitz, J A; Johnson, J R; Jolliff, B L; Knoll, A H; Li, R; McLennan, S M; Ming, D W; Mittlefehldt, D W; Parker, T J; Paulsen, G; Rice, M S; Ruff, S W; Schröder, C; Yen, A S; Zacny, K

    2012-05-04

    The rover Opportunity has investigated the rim of Endeavour Crater, a large ancient impact crater on Mars. Basaltic breccias produced by the impact form the rim deposits, with stratigraphy similar to that observed at similar-sized craters on Earth. Highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits. Gypsum-rich veins cut sedimentary rocks adjacent to the crater rim. The gypsum was precipitated from low-temperature aqueous fluids flowing upward from the ancient materials of the rim, leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate-rich sandstones of the Meridiani region.

  9. The geology of Darwin Crater, western Tasmania, Australia

    Science.gov (United States)

    Howard, Kieren T.; Haines, Peter W.

    2007-08-01

    Darwin glass is a siliceous impact glass found in a 400 km 2 strewn field near Mt Darwin, western Tasmania, Australia. It has been dated by Ar-Ar methods at 816 ± 7 ka. A 1.2 km diameter circular depression, named Darwin Crater (42°18.39'S, 145°39.41'E), is the assumed source crater for the glass. Darwin Crater is situated in a remote rain forested valley developed within Siluro-Devonian quartzite and slate (Eldon Group). Earlier geophysical investigations demonstrated that the structure is an almost circular bowl-shaped sediment-filled basin. This paper provides the first detailed description of the geology of Darwin Crater. The centre of the crater has been penetrated by two drill cores, the deeper to a maximum depth of ˜ 230 m. The drill cores intersected fine-grained lacustrine sediments (˜ 60 m thick) overlying poorly sorted coarser crater-fill deposits. The pre-lacustrine crater-fill stratigraphy comprises an uppermost polymict breccia (˜ 40 m thick) of angular quartz and country rock, which contains very rare (≪ 1%) fresh glass fragments (Crater-fill Facies A). Beneath the polymict breccia facies, the drill core intersected monomict sandy breccias of angular quartz (Crater-fill Facies B), and a complicated package of deformed slate clasts (Crater-fill Facies C). Quartz grains in the crater-fill samples contain abundant irregular fractures. In some of the most deformed quartz grains, sub-planar fractures define zones of alternating extinction that superficially resemble twinning. Kinked micas are also present. While the deformation observed in clasts of the crater-fill facies is far greater than in rocks cropping out around the crater, no diagnostic shock indicators, such as planar deformation features (PDF's) in quartz, were observed. If the crater is of impact origin, as seems likely due to the close association with Darwin glass, this is another example of a simple crater where diagnostic shock indicators appear to be absent, preventing

  10. Impact crater and basin control of igneous processes on Mars

    Science.gov (United States)

    Schultz, P. H.; Glicken, H.

    1979-01-01

    The possible role of impact craters in controlling local Martian endogenic activity is reviewed. Martian impact craters exhibiting evidence for endogenic modification are considered, including the style of modification. In addition, the cooling history of a mafic body intruded beneath impact craters of different sizes which contain water-ice deposits are examined, and results are related to modified Martian craters. This analysis is extended to basin-sized structures, and evidence for impact basin control of major volcanic and tectonic provinces is considered.

  11. Modification of premare impact craters by volcanism and tectonism

    Science.gov (United States)

    Brennan, W. J.

    1975-01-01

    Many lunar craters greater than 10 km in diameter exhibit a variety of morphological characteristics which are not produced by meteorite impact or meteorite erosion. Most such craters are located in or near the margins of the maria. Although some could have resulted from processes such as cauldron resurgence, caldera formation, or ring dike emplacement, most have formed by modification of impact craters by endogenic processes including erosion by flowing lava, fissure volcanism, plutonism, and uplift of crater floors along ring fractures of impact origin.

  12. Characteristics of ejecta and alluvial deposits at Meteor Crater, Arizona and Odessa Craters, Texas: Results from ground penetrating radar

    Science.gov (United States)

    Grant, J. A.; Schultz, P. H.

    1991-01-01

    Previous ground penetrating radar (GRP) studies around 50,000 year old Meteor Crater revealed the potential for rapid, inexpensive, and non-destructive sub-surface investigations for deep reflectors (generally greater than 10 m). New GRP results are summarized focusing the shallow sub-surfaces (1-2 m) around Meteor Crater and the main crater at Odessa. The following subject areas are covered: (1) the thickness, distribution, and nature of the contact between surrounding alluvial deposits and distal ejecta; and (2) stratigraphic relationships between both the ejecta and alluvium derived from both pre and post crater drainages. These results support previous conclusions indicating limited vertical lowering (less than 1 m) of the distal ejecta at Meteor Crater and allow initial assessment of the gradational state if the Odessa craters.

  13. Flat panel display - Impurity doping technology for flat panel displays

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Toshiharu [Advanced Technology Planning, Sumitomo Eaton Nova Corporation, SBS Tower 9F, 10-1, Yoga 4-chome, Setagaya-ku, 158-0097 Tokyo (Japan)]. E-mail: suzuki_tsh@senova.co.jp

    2005-08-01

    Features of the flat panel displays (FPDs) such as liquid crystal display (LCD) and organic light emitting diode (OLED) display, etc. using low temperature poly-Si (LTPS) thin film transistors (TFTs) are briefly reviewed comparing with other FPDs. The requirements for fabricating TFTs used for high performance FPDs and system on glass (SoG) are addressed. This paper focuses on the impurity doping technology, which is one of the key technologies together with crystallization by laser annealing, formation of high quality gate insulator and gate-insulator/poly-Si interface. The issues to be solved in impurity doping technology for state of the art and future TFTs are clarified.

  14. An extension to flat band ferromagnetism

    Science.gov (United States)

    Gulacsi, M.; Kovacs, G.; Gulacsi, Z.

    2014-11-01

    From flat band ferromagnetism, we learned that the lowest energy half-filled flat band gives always ferromagnetism if the localized Wannier states on the flat band satisfy the connectivity condition. If the connectivity conditions are not satisfied, ferromagnetism does not appear. We show that this is not always the case namely, we show that ferromagnetism due to flat bands can appear even if the connectivity condition does not hold due to a peculiar behavior of the band situated just above the flat band.

  15. Length spectra and degeneration of flat metrics

    CERN Document Server

    Duchin, Moon; Rafi, Kasra

    2009-01-01

    In this paper we consider flat metrics (semi-translation structures) on surfaces of finite type. There are two main results. The first is a complete description of when a set of simple closed curves is spectrally rigid, that is, when the length vector determines a metric among the class of flat metrics. Secondly, we give an embedding into the space of geodesic currents and use this to get a boundary for the space of flat metrics. The geometric interpretation is that flat metrics degenerate to "mixed structures" on the surface: part flat metric and part measured foliation.

  16. Morphology, origin and evolution of Pleistocene submarine canyons, New Jersey continental slope

    Science.gov (United States)

    Bhatnagar, T.; Mountain, G. S.

    2015-12-01

    Submarine canyons serve as important conduits for transport of detrital sediments from nearshore and shelf environments to adjacent deep marine basins. However, the processes controlling the formation, maintenance, and fill of these sediment pathways are complex. This study presents an investigation of these systems at the New Jersey continental margin using a grid of high-resolution, 48-channel seismic reflection data collected in 1995 on the R/V Oceanus cruise Oc270 as a part of the STRATAFORM initiative. The aim is to shed new light on the origin and role of submarine canyons in Pleistocene sedimentation beneath the outer shelf and upper continental slope. Preliminary investigation of the Pleistocene interval reveals prominent unconformities tied to and dated with published studies at 7 sites drilled by ODP Legs 150 and 174A. The profiles of the continental slope unveil a series of abandoned and now buried submarine canyons that have influenced the development of modern canyons. Mapping these systems has revealed a range of canyon geometries, including U, V-shaped and flat-bottomed cross sections, each suggesting different histories. At least three types of seismic facies constitute the canyon fills: parallel onlap, interpreted as infilling by alternating coarser turbidites and finer hemipelagic sediments, chaotic infill, signifying structureless, massive debris flow deposition, and lateral accretion infill by both turbidity and bottom currents. Canyon formation and development appear to be strongly influenced by variations in sediment supply, grain size, and currents on the continental slope. One goal of our research is to establish if the canyons were initiated by failures at the base of the slope followed by upslope erosion, or by erosion at the shelf slope transition, and then downslope extension by erosive events. No single model accounts for all canyons. The history of these canyons may elucidate the extent to which the shelf was exposed during sea

  17. Concrete Cutting Refinement for Crater Repair

    Science.gov (United States)

    2015-08-01

    ER D C/ G SL T R- 15 -2 9 Concrete Cutting Refinement for Crater Repair G eo te ch ni ca l a nd S tr uc tu re s La bo ra to ry...by ERDC, visit the ERDC online library at http://acwc.sdp.sirsi.net/client/default. ERDC/GSL TR-15-29 August 2015 Concrete Cutting Refinement...equipment in both soft and hard aggregate-mixed concrete . The investigated equipment included the Vermeer RW1236W and CC1531, Caterpillar SW45 and

  18. A Spanish Tagset for the CRATER Project

    CERN Document Server

    Sánchez-León, F

    1994-01-01

    This working paper describes the Spanish tagset to be used in the context of CRATER, a CEC funded project aiming at the creation of a multilingual (English, French, Spanish) aligned corpus using the International Telecommunications Union corpus. In this respect, each version of the corpus will be (or is currently) tagged. Xerox PARC tagger will be adapted to Spanish in order to perform the tagging of the Spanish version. This tagset has been devised as the ideal one for Spanish, and has been posted to several lists in order to get feedback to it.

  19. Catalog of crater lakes from Costa Rica

    Science.gov (United States)

    Ramirez, C. J.; Mora-Amador, R.; González, G.

    2010-12-01

    Costa Rica has a diversity of volcanic crater lakes that can be classified into two groups: hot and cold lakes. The country contains at least 5% of the world's hot lakes. Costa Rica has 2 hot hyperacidic lakes, both of them on active volcanoes, the Rincón de la Vieja (38.0°C, pH = 0 - 1) and the Poás Laguna Caliente (36.1°C - 56°C, pH = 0.55 - 0.74), nowadays the Poás hot lake is the most active crater lake in the world, with more than 200 eruptions only on 2010. One of the most studied cold crater lakes is Irazú (13°C, pH = 3.5), that used to contain bubbling and clear areas of upwelling involving CO2 liberation and subaqueous fumaroles with temperatures up to 50°C, but since 2005 the lake presents an important descend until April 2010 when it disappeared. On February 9, 2003, Irazú's lake underwent a drastic change of color, from clear green to mustard with reddish loops, similar to the color of the waters of Lake Nyos after the gas burst of August 1986. Other studied cold lakes include Botos, Chato, and Tenorio, all at the summit of Quaternary volcanoes as well as Barva and Danta, located in recent pyroclastic cones. Some cold lakes are located in Holocene maar-type explosion craters, among them are Congo, Bosque Alegre, Hule, and Río Cuarto. These last two have undergone repeated rapid reddish color changes over the last 10 years, in association with fish kills and the liberation of apparently sulfurous scents. On March 2010, University of Costa Rica was the host of the 7th Workshop on Volcanic Lakes, part of the Commission of Volcanic Lakes of the IAVCEI, 51 participants from 14 countries attended the workshop; they presented 27 talks and 17 posters, also they visited and sample 4 of the lakes mentioned above (Botos, Irazú, Río Cuarto and Hule). Level of Study: 1: few or no data, 2: regular, 3: acceptable

  20. Non-Perturbative Flat Direction Decay

    CERN Document Server

    Basboll, A; Riva, F; West, S M; Basboll, Anders; Maybury, David; Riva, Francesco; West, Stephen M.

    2007-01-01

    We argue that supersymmetric flat direction vevs can decay non-perturbatively via preheating. Considering the case of a single flat direction, we explicitly calculate the scalar potential in the unitary gauge for a U(1) theory and show that the mass matrix for excitations around the flat direction has non-diagonal entries which vary with the phase of the flat direction vev. Furthermore, this mass matrix has 2 zero eigenvalues (associated with the excitations along the flat direction) whose eigenstates change with time. We show that these 2 light degrees of freedom are produced copiously in the non-perturbative decay of the flat direction vev. We also comment on the application of these results to the MSSM flat direction H_uL.

  1. Salivary gland cell differentiation and organization on micropatterned PLGA nanofiber craters.

    Science.gov (United States)

    Soscia, David A; Sequeira, Sharon J; Schramm, Robert A; Jayarathanam, Kavitha; Cantara, Shraddha I; Larsen, Melinda; Castracane, James

    2013-09-01

    There is a need for an artificial salivary gland as a long-term remedy for patients suffering from salivary hypofunction, a leading cause of chronic xerostomia (dry mouth). Current salivary gland tissue engineering approaches are limited in that they either lack sufficient physical cues and surface area needed to facilitate epithelial cell differentiation, or they fail to provide a mechanism for assembling an interconnected branched network of cells. We have developed highly-ordered arrays of curved hemispherical "craters" in polydimethylsiloxane (PDMS) using wafer-level integrated circuit (IC) fabrication processes, and lined them with electrospun poly-lactic-co-glycolic acid (PLGA) nanofibers, designed to mimic the three-dimensional (3-D) in vivo architecture of the basement membrane surrounding spherical acini of salivary gland epithelial cells. These micropatterned scaffolds provide a method for engineering increased surface area and were additionally investigated for their ability to promote cell polarization. Two immortalized salivary gland cell lines (SIMS, ductal and Par-C10, acinar) were cultured on fibrous crater arrays of various radii and compared with those grown on flat PLGA nanofiber substrates, and in 3-D Matrigel. It was found that by increasing crater curvature, the average height of the cell monolayer of SIMS cells and to a lesser extent, Par-C10 cells, increased to a maximum similar to that seen in cells grown in 3-D Matrigel. Increasing curvature resulted in higher expression levels of tight junction protein occludin in both cell lines, but did not induce a change in expression of adherens junction protein E-cadherin. Additionally, increasing curvature promoted polarity of both cell lines, as a greater apical localization of occludin was seen in cells on substrates of higher curvature. Lastly, substrate curvature increased expression of the water channel protein aquaporin-5 (Aqp-5) in Par-C10 cells, suggesting that curved nanofiber substrates

  2. Flat lens for seismic waves

    CERN Document Server

    Brule, Stephane; Guenneau, Sebastien

    2016-01-01

    A prerequisite for achieving seismic invisibility is to demonstrate the ability of civil engineers to control seismic waves with artificially structured soils. We carry out large-scale field tests with a structured soil made of a grid consisting of cylindrical and vertical holes in the ground and a low frequency artificial source (< 10 Hz). This allows the identification of a distribution of energy inside the grid, which can be interpreted as the consequence of an effective negative refraction index. Such a flat lens reminiscent of what Veselago and Pendry envisioned for light opens avenues in seismic metamaterials to counteract the most devastating components of seismic signals.

  3. 36 CFR 7.2 - Crater Lake National Park.

    Science.gov (United States)

    2010-07-01

    ... 36 Parks, Forests, and Public Property 1 2010-07-01 2010-07-01 false Crater Lake National Park. 7.2 Section 7.2 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.2 Crater Lake National Park. (a)...

  4. Fluvial erosion as a mechanism for crater modification on Titan

    Science.gov (United States)

    Neish, C. D.; Molaro, J. L.; Lora, J. M.; Howard, A. D.; Kirk, R. L.; Schenk, P.; Bray, V. J.; Lorenz, R. D.

    2016-05-01

    There are few identifiable impact craters on Titan, especially in the polar regions. One explanation for this observation is that the craters are being destroyed through fluvial processes, such as weathering, mass wasting, fluvial incision and deposition. In this work, we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on Titan. We find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as Cassini, given enough time and a large enough erosion rate. A difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in Titan's crater population. Fluvial erosion also removes central peaks and fills in central pits, possibly explaining their infrequent occurrence in Titan craters. Although many craters on Titan appear to be modified by aeolian infilling, fluvial modification is necessary to explain the observed impact crater morphologies. Thus, it is an important secondary modification process even in Titan's drier equatorial regions.

  5. Proceedings of the Geophysical Laboratory - Lawrence Radiation Laboratory Cratering Symposium

    Energy Technology Data Exchange (ETDEWEB)

    Nordyke, M. D.

    1961-10-01

    The geological papers in this morning's session will deal descriptively with surficial features and end products of impact craters caused by meteorite falls. Such items as breccia, structural deformation, normal and inverse stratigraphy, glass (fused rock), and coesite will frequently be mentioned. Meteor and explosion crater data are presented.

  6. Numerical Modeling of Shatter Cones Development in Impact Craters

    Science.gov (United States)

    Baratoux, D.; Melosh, H. J.

    2003-03-01

    We present a new model for the formation of shatter cones in impact craters. Our model has been tested by means of numerical simulations. Our results are consistent with the observations of shatter cones in natural impact craters and explosions experiments.

  7. Impact craters on venus: initial analysis from magellan.

    Science.gov (United States)

    Phillips, R J; Arvidson, R E; Boyce, J M; Campbell, D B; Guest, J E; Schaber, G G; Soderblom, L A

    1991-04-12

    Magellan radar images of 15 percent of the planet show 135 craters of probable impact origin. Craters more than 15 km across tend to contain central peaks, multiple central peaks, and peak rings. Many craters smaller than 15 km exhibit multiple floors or appear in clusters; these phenomena are attributed to atmospheric breakup of incoming meteoroids. Additionally, the atmosphere appears to have prevented the formation of primary impact craters smaller than about 3 km and produced a deficiency in the number of craters smaller than about 25 km across. Ejecta is found at greater distances than that predicted by simple ballistic emplacement, and the distal ends of some ejecta deposits are lobate. These characteristics may represent surface flows of material initially entrained in the atmosphere. Many craters are surrounded by zones of low radar albedo whose origin may have been deformation of the surface by the shock or pressure wave associated with the incoming meteoroid. Craters are absent from several large areas such as a 5 million square kilometer region around Sappho Patera, where the most likely explanation for the dearth of craters is volcanic resurfacing. There is apparently a spectrum of surface ages on Venus ranging approximately from 0 to 800 million years, and therefore Venus must be a geologically active planet.

  8. Impact craters on Venus: Initial analysis from Magellan

    Science.gov (United States)

    Phillips, R.J.; Arvidson, R. E.; Boyce, J.M.; Campbell, D.B.; Guest, J.E.; Schaber, G.G.; Soderblom, L.A.

    1991-01-01

    Magellan radar images of 15 percent of the planet show 135 craters of probable impact origin. Craters more than 15 km across tend to contain central peaks, multiple central peaks, and peak rings. Many craters smaller than 15 km exhibit multiple floors or appear in clusters; these phenomena are attributed to atmospheric breakup of incoming meteoroids. Additionally, the atmosphere appears to have prevented the formation of primary impact craters smaller than about 3 km and produced a deficiency in the number of craters smaller than about 25 km across. Ejecta is found at greater distances than that predicted by simple ballistic emplacement, and the distal ends of some ejecta deposits are lobate. These characteristics may represent surface flows of material initially entrained in the atmosphere. Many craters are surrounded by zones of low radar albedo whose origin may have been deformation of the surface by the shock or pressure wave associated with the incoming meteoroid. Craters are absent from several large areas such as a 5 million square kilometer region around Sappho Patera, where the most likely explanation for the dearth of craters is volcanic resurfacing, There is apparently a spectrum of surface ages on Venus ranging approximately from 0 to 800 million years, and therefore Venus must be a geologically active planet.

  9. Recent Sand Avalanching on Rabe Crater Dunes

    Science.gov (United States)

    2000-01-01

    Dark streaks on the steep, down-wind slopes of sand dunes in Rabe Crater are seen at several locations in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image. These streaks indicate relatively recent (i.e., in the past few years or less) movement of sand down these slopes.Sand dunes move forward by the combined action of wind that drives sand up the shallow slope on the windward side of the dune (in this case, the slopes that face toward the lower right) and the avalanching of this sand down the steeper, lee-side slope. The steep slope is also known as the slip face. The dark streaks indicated by arrows are evidence for sand avalanches that occurred within a few months or years of the time when the picture was taken in March 1999. Other streaks which are seen criss-crossing the dunes may be the result of passing dust devils. This image is illuminated from the upper left and located in Rabe Crater of the Hellespontus-Noachis region near 44.2oS, 325.6oW.

  10. Water balance for Crater Lake, Oregon

    Science.gov (United States)

    Nathenson, Manuel

    1992-01-01

    A water balance for Crater Lake, Oregon, is calculated using measured lake levels and precipitation data measured at Park Headquarters and at a gage on the North Rim. Total water supply to the lake from precipitation and inflow from the crater walls is found to be 224 cm/y over the area of the lake. The ratio between water supply to the lake and precipitation at Park Headquarters is calculated as 1.325. Using leakage determined by Phillips (1968) and Redmond (1990), evaporation from the lake is approximately 85 cm/y. Calculations show that water balances with precipitation data only from Park Headquarters are unable to accurately define the water-level variation, whereas the addition of yearly precipitation data from the North Rim reduces the average absolute deviation between calculated and modeled water levels by one half. Daily precipitation and water-level data are modeled assuming that precipitation is stored on the rim as snow during fall and winter and released uniformly during the spring and early summer. Daily data do not accurately define the water balance, but they suggest that direct precipitation on the lake is about 10 % higher than that measured at Park Headquarters and that about 17 % of the water supply is from inflow from the rim.

  11. A Giant Crater on 90 Antiope?

    CERN Document Server

    Descamps, P; Michalowski, T; Berthier, J; Pollock, J; Wiggins, P; Birlan, M; Colas, F; Vachier, F; Fauvaud, S; Fauvaud, M; Sareyan, J -P; Pilcher, F; Klinglesmith, D A

    2009-01-01

    Mutual event observations between the two components of 90 Antiope were carried out in 2007-2008. The pole position was refined to lambda0 = 199.5+/-0.5 eg and beta0 = 39.8+/-5 deg in J2000 ecliptic coordinates, leaving intact the physical solution for the components, assimilated to two perfect Roche ellipsoids, and derived after the 2005 mutual event season (Descamps et al., 2007). Furthermore, a large-scale geological depression, located on one of the components, was introduced to better match the observed lightcurves. This vast geological feature of about 68 km in diameter, which could be postulated as a bowl-shaped impact crater, is indeed responsible of the photometric asymmetries seen on the "shoulders" of the lightcurves. The bulk density was then recomputed to 1.28+/-0.04 gcm-3 to take into account this large-scale non-convexity. This giant crater could be the aftermath of a tremendous collision of a 100-km sized proto-Antiope with another Themis family member. This statement is supported by the fact ...

  12. Chemical hazards from acid crater lakes

    Science.gov (United States)

    van Bergen, M. J.; Sumarti, S.; Heikens, A.; Bogaard, T. A.; Hartiyatun, S.

    2003-04-01

    Acid crater lakes, which are hosted by a considerable number of active volcanoes, form a potential threat for local ecosystems and human health, as they commonly contain large amounts of dissolved chemicals. Subsurface seepage or overflow can lead to severe deterioration of the water quality of rivers and wells, as observations around several of these volcanoes have shown. The Ijen crater lake in East Java (Indonesia) is a striking example, as this reservoir of hyperacid (pHdental fluorosis is widespread among the ca. 100,000 residents of the area. A conspicuous spatial correlation between fluoride concentrations and the irrigation system suggest that long-term (century) infiltration of irrigation water may have affected the quality of groundwater. Fluorosis is also a problem in some villages within the caldera, where well water sources may have a more direct subsurface connection with the lake system. From our observations we conclude that water-quality monitoring is especially needed for health reasons in volcanic areas where volatile elements, derived from passively degassing magma, are intercepted by (sub) surface water bodies.

  13. Evolution of Occator Crater on (1) Ceres

    Science.gov (United States)

    Nathues, A.; Platz, T.; Thangjam, G.; Hoffmann, M.; Mengel, K.; Cloutis, E. A.; Le Corre, L.; Reddy, V.; Kallisch, J.; Crown, D. A.

    2017-03-01

    The dwarf planet Ceres (diameter 939 km) is the largest object in the main asteroid belt. Recent investigations suggest that Ceres is a thermally evolved, volatile-rich body with potential geological activity, a body which was never completely molten but possibly differentiated into a rocky core, an ice-rich mantle, and which may contain remnant internal liquid water. Thermal alteration and exogenic material infall contribute to producing a (dark) carbonaceous chondritic-like surface containing ammoniated phyllosilicates. Here we report imaging and spectroscopic analyses of Occator crater derived from the Framing Camera and the Visible and Infrared Spectrometer onboard Dawn. We found that the central bright spot (Cerealia Facula) of Occator is ∼30 Myr younger than the crater itself. The central spot is located in a central pit which contains a dome that is spectrally homogenous, exhibiting absorption features that are consistent with carbonates. Multiple radial fractures across the dome indicate an extrusive formation process. Our results lead us to conclude that the floor region was subject to past endogenic activity. Dome and bright material in its vicinity formed likely due to a long-lasting, periodic, or episodic ascent of bright material from a subsurface reservoir rich in carbonates. Originally triggered by an impact event, gases, possibly dissolved from a subsurface water/brine layer, enabled material rich in carbonates to ascend through fractures and be deposited onto the surface.

  14. Viscous relaxation of Ganymede's impact craters: Constraints on heat flux

    Science.gov (United States)

    Bland, Michael; Singer, Kelsi N.; McKinnon, William B.; Schenk, Paul M.

    2017-01-01

    Measurement of crater depths in Ganymede’s dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation [see companion paper: Singer, K.N., Schenk, P. M., Bland, M.T., McKinnon, W.B., (2017). Relaxed impact craters on Ganymede: Regional variations and high heat flow. Icarus, submitted]. These viscously relaxed craters provide insight into the thermal history of the dark terrain: the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere. Here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred. We show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone, even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite’s history. For craters with diameter ≥ 10 km, heat fluxes of 40–50 mW m-2−2"> can reproduce the observed crater depths, but only if the fluxes are sustained for ∼1 Gyr. These craters can also be explained by shorter-lived “heat pulses” with magnitudes of ∼100 mW m-2−2"> and timescales of 10–100 Myr. At small crater diameters (4 km) the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mW m-2−2"> are sustained for 1 Gyr. The extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation, such as topographic degradation, are also in play at small crater diameters. The timing of the relaxation event(s) is poorly constrained due to the sparsity of adequate topographic information, though it likely occurred in Ganymede’s middle history (neither recently, nor shortly after satellite formation). The consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event

  15. Acoustic fluidization and the scale dependence of impact crater morphology

    Science.gov (United States)

    Melosh, H. J.; Gaffney, E. S.

    1983-01-01

    A phenomenological Bingham plastic model has previously been shown to provide an adequate description of the collapse of impact craters. This paper demonstrates that the Bingham parameters may be derived from a model in which acoustic energy generated during excavation fluidizes the rock debris surrounding the crater. Experimental support for the theoretical flow law is presented. Although the Bingham yield stress cannot be computed without detailed knowledge of the initial acoustic field, the Bingham viscosity is derived from a simple argument which shows that it increases as the 3/2 power of crater diameter, consistent with observation. Crater collapse may occur in material with internal dissipation Q as low as 100, comparable to laboratory observations of dissipation in granular materials. Crater collapse thus does not require that the acoustic field be regenerated during flow.

  16. Acoustic fluidization and the scale dependence of impact crater morphology

    Science.gov (United States)

    Melosh, H. J.; Gaffney, E. S.

    1983-11-01

    A phenomenological Bingham plastic model has previously been shown to provide an adequate description of the collapse of impact craters. This paper demonstrates that the Bingham parameters may be derived from a model in which acoustic energy generated during excavation fluidizes the rock debris surrounding the crater. Experimental support for the theoretical flow law is presented. Although the Bingham yield stress cannot be computed without detailed knowledge of the initial acoustic field, the Bingham viscosity is derived from a simple argument which shows that it increases as the 3/2 power of crater diameter, consistent with observation. Crater collapse may occur in material with internal dissipation Q as low as 100, comparable to laboratory observations of dissipation in granular materials. Crater collapse thus does not require that the acoustic field be regenerated during flow.

  17. Devolatilization or melting of carbonates at Meteor Crater, AZ?

    Science.gov (United States)

    Hörz, F.; Archer, P. D.; Niles, P. B.; Zolensky, M. E.; Evans, M.

    2015-06-01

    We have investigated the carbonates in the impact melts and in a monolithic clast of highly shocked Coconino sandstone of Meteor Crater, AZ to evaluate whether melting or devolatilization is the dominant response of carbonates during high-speed meteorite impact. Both melt- and clast-carbonates are calcites that have identical crystal habits and that contain anomalously high SiO2 and Al2O3. Also, both calcite occurrences lack any meteoritic contamination, such as Fe or Ni, which is otherwise abundantly observed in all other impact melts and their crystallization products at Meteor Crater. The carbon and oxygen isotope systematics for both calcite deposits suggest a low temperature environment (Meteor Crater. Although confined to Meteor Crater, these findings are in stark contrast to Osinski et al. (2008) who proposed that melting of carbonates, rather than devolatilization, is the dominant process during hypervelocity impact into carbonate-bearing targets, including Meteor Crater.

  18. Mass Movement on Vesta at Steep Scarps and Crater Rims

    Science.gov (United States)

    Krohn, K.; Jaumann, R.; Otto, K.; Hoogenboom, T.; Wagner, R.; Buczkowski, D. L.; Garry, B.; Williams, D. A.; Yingst, R. A.; Scully, J.; De Sanctis, M. C.; Kneissl, T.; Schmedemann, N.; Kersten, E.; Stephan, K.; Matz, K.-D.; Pieters, C. M.; Preusker, F.; Roatsch, T.; Schenk, P.; Russell, C. T.; Raymond, C. A.

    2014-01-01

    The Quadrangles Av-11 and Av-12 on Vesta are located at the northern rim of the giant Rheasilvia south polar impact basin. The primary geologic units in Av-11 and Av-12 include material from the Rheasilvia impact basin formation, smooth material and different types of impact crater structures (such as bimodal craters, dark and bright crater ray material and dark ejecta material). Av-11 and Av-12 exhibit almost the full range of mass wasting features observed on Vesta, such as slump blocks, spur-and-gully morphologies and landslides within craters. Processes of collapse, slope instability and seismically triggered events force material to slump down crater walls or scarps and produce landslides or rotational slump blocks. The spur-and-gully morphology that is known to form on Mars is also observed on Vesta; however, on Vesta this morphology formed under dry conditions.

  19. Flat coalgebraic fixed point logics

    CERN Document Server

    Schröder, Lutz

    2010-01-01

    Fixed point logics have a wide range of applications in computer science, in particular in artificial intelligence and concurrency. The most expressive logics of this type are the mu-calculus and its relatives. However, popular fixed point logics tend to trade expressivity for simplicity and readability, and in fact often live within the single variable fragment of the mu-calculus. The family of such flat fixed point logics includes, e.g., CTL, the *-nesting-free fragment of PDL, and the logic of common knowledge. Here, we extend this notion to the generic semantic framework of coalgebraic logic, thus covering a wide range of logics beyond the standard mu-calculus including, e.g., flat fragments of the graded mu-calculus and the alternating-time mu-calculus (such as ATL), as well as probabilistic and monotone fixed point logics. Our main results are completeness of the Kozen-Park axiomatization and a timed-out tableaux method that matches EXPTIME upper bounds inherited from the coalgebraic mu-calculus but avo...

  20. Polyurethane adhesives in flat roofs

    Directory of Open Access Journals (Sweden)

    Bogárová Markéta

    2017-01-01

    Full Text Available It is necessary to stabilize individual layers of flat roofs, mainly because of wind suction. Apart from anchoring and surcharge, these layers can be secured by bonding. At present gluing is an indispensable and widely used stabilization method. On our market we can found many types of adhesives, most widely used are based on polyurethane. This paper focuses on problematic about stabilization thermal insulation from expanded polystyrene to vapor barrier from bitumen. One of the main issues is to calculate the exact amount of adhesive, which is required to guarantee the resistance against wind suction. In this problematic we can not find help neither in technical data sheets provided by the manufactures. Some of these data sheets contain at least information about amount of adhesive depending on location in roof plane and building height, but they do not specify the strength of such connection. It was therefore resorted to select several representatives polyurethane adhesives and their subsequent testing on specimens simulating the flat roof segment. The paper described the test methodology and results for two types of polyurethane adhesives.

  1. Geology and Volcanology of Kima'Kho Mountain, Northern British Columbia: A Pleistocene Glaciovolcanic Edifice

    Science.gov (United States)

    Turnbull, M.; Porritt, L. A.; Edwards, B. R.; Russell, K.

    2014-12-01

    Kima'Kho Mountain is a 1.8 Ma (40Ar/39Ar of 1.82 +/- 40 ka) Pleistocene an alkali-olivine basaltic tuya situated in northern British Columbia. The volcanic edifice rises 460 m from its base and comprises a central vent, dominated by lapilli-tuff and minor pillow lava and dykes; and a surrounding plateau underlain by a sequence of dipping beds of basaltic tuff-breccia and capped by a series of flat-lying, subaerial lava flows. We present a 1:10,000 geological map for Kima'Kho Mountain building on the preliminary work of Ryane et al. (2010). We use the volcanic stratigraphy to explore the implications of three unique features. (1) The central cone comprises massive to crudely-bedded lapilli tuffs containing abundant armoured lapilli - cores of highly-vesicular pyroclasts coated with blocky to cuspate vitric ash. These units suggest an explosive origin from within an ice-enclosed lake, and deposited by wet, dilute pyroclastic surge events. (2) The entire stratigraphic sequence hosts at least two "passage zones" (cf. Jones, 1969); the presence and geometry of these passage zones constrain ice thicknersses at the time of eruption and inform on the englacial lake dynamics. (3) Lastly, our field-based stratigraphic relationships are at odds with the classic tuya model (i.e. an effusive onset to the eruption, forming pillow basalts, followed by explosive activity). Our field mapping suggests an alternative model of tuya architecture, involving a highly-energetic, sustained explosive onset creating a tephra cone that become emergent followed by effusive eruption to create lavas and a subaqueous lava-fed delta. Jones, J. G. Intraglacial volcanoes of the Laugarvatn region, south-west Iceland-I. Geological Society of London Quarterly Journal 124, 197-211 (1969). Ryane, C., Edwards, B. R. & Russell, J. K. The volcanic stratigraphy of Kima'Kho Mountain: A Pleistocene tuya, northwestern British Columbia. Geological Survey of Canada, Current Research 2011-104, 12p, doi:10

  2. Small craters on the meteoroid and space debris impact experiment

    Science.gov (United States)

    Humes, Donald H.

    1995-01-01

    Examination of 9.34 m(exp 2) of thick aluminum plates from the Long Duration Exposure Facility (LDEF) using a 25X microscope revealed 4341 craters that were 0.1 mm in diameter or larger. The largest was 3 mm in diameter. Most were roughly hemispherical with lips that were raised above the original plate surface. The crater diameter measured was the diameter at the top of the raised lips. There was a large variation in the number density of craters around the three-axis gravity-gradient stabilized spacecraft. A model of the near-Earth meteoroid environment is presented which uses a meteoroid size distribution based on the crater size distribution on the space end of the LDEF. An argument is made that nearly all the craters on the space end must have been caused by meteoroids and that very few could have been caused by man-made orbital debris. However, no chemical analysis of impactor residue that will distinguish between meteoroids and man-made debris is yet available. A small area (0.0447 m(exp 2)) of one of the plates on the space end was scanned with a 200X microscope revealing 155 craters between 10 micron and 100 micron in diameter and 3 craters smaller than 10 micron. This data was used to extend the size distribution of meteoroids down to approximately 1 micron. New penetration equations developed by Alan Watts were used to relate crater dimensions to meteoroid size. The equations suggest that meteoroids must have a density near 2.5 g/cm(exp 3) to produce craters of the shape found on the LDEF. The near-Earth meteoroid model suggests that about 80 to 85 percent of the 100 micron to 1 mm diameter craters on the twelve peripheral rows of the LDEF were caused by meteoroids, leaving 15 to 20 percent to be caused by man-made orbital debris.

  3. Interpretation of Lunar Topography: Impact Cratering and Surface Roughness

    Science.gov (United States)

    Rosenburg, Margaret A.

    This work seeks to understand past and present surface conditions on the Moon using two different but complementary approaches: topographic analysis using high-resolution elevation data from recent spacecraft missions and forward modeling of the dominant agent of lunar surface modification, impact cratering. The first investigation focuses on global surface roughness of the Moon, using a variety of statistical parameters to explore slopes at different scales and their relation to competing geological processes. We find that highlands topography behaves as a nearly self-similar fractal system on scales of order 100 meters, and there is a distinct change in this behavior above and below approximately 1 km. Chapter 2 focuses this analysis on two localized regions: the lunar south pole, including Shackleton crater, and the large mare-filled basins on the nearside of the Moon. In particular, we find that differential slope, a statistical measure of roughness related to the curvature of a topographic profile, is extremely useful in distinguishing between geologic units. Chapter 3 introduces a numerical model that simulates a cratered terrain by emplacing features of characteristic shape geometrically, allowing for tracking of both the topography and surviving rim fragments over time. The power spectral density of cratered terrains is estimated numerically from model results and benchmarked against a 1-dimensional analytic model. The power spectral slope is observed to vary predictably with the size-frequency distribution of craters, as well as the crater shape. The final chapter employs the rim-tracking feature of the cratered terrain model to analyze the evolving size-frequency distribution of craters under different criteria for identifying "visible" craters from surviving rim fragments. A geometric bias exists that systematically over counts large or small craters, depending on the rim fraction required to count a given feature as either visible or erased.

  4. LU60645GT and MA132843GT Catalogues of Lunar and Martian Impact Craters Developed Using a Crater Shape-based Interpolation Crater Detection Algorithm for Topography Data

    Science.gov (United States)

    Salamuniccar, Goran; Loncaric, Sven; Mazarico, Erwan Matias

    2012-01-01

    For Mars, 57,633 craters from the manually assembled catalogues and 72,668 additional craters identified using several crater detection algorithms (CDAs) have been merged into the MA130301GT catalogue. By contrast, for the Moon the most complete previous catalogue contains only 14,923 craters. Two recent missions provided higher-quality digital elevation maps (DEMs): SELENE (in 1/16° resolution) and Lunar Reconnaissance Orbiter (we used up to 1/512°). This was the main motivation for work on the new Crater Shape-based interpolation module, which improves previous CDA as follows: (1) it decreases the number of false-detections for the required number of true detections; (2) it improves detection capabilities for very small craters; and (3) it provides more accurate automated measurements of craters' properties. The results are: (1) LU60645GT, which is currently the most complete (up to D>=8 km) catalogue of Lunar craters; and (2) MA132843GT catalogue of Martian craters complete up to D>=2 km, which is the extension of the previous MA130301GT catalogue. As previously achieved for Mars, LU60645GT provides all properties that were provided by the previous Lunar catalogues, plus: (1) correlation between morphological descriptors from used catalogues; (2) correlation between manually assigned attributes and automated measurements; (3) average errors and their standard deviations for manually and automatically assigned attributes such as position coordinates, diameter, depth/diameter ratio, etc; and (4) a review of positional accuracy of used datasets. Additionally, surface dating could potentially be improved with the exhaustiveness of this new catalogue. The accompanying results are: (1) the possibility of comparing a large number of Lunar and Martian craters, of e.g. depth/diameter ratio and 2D profiles; (2) utilisation of a method for re-projection of datasets and catalogues, which is very useful for craters that are very close to poles; and (3) the extension of the

  5. Creation of High Resolution Terrain Models of Barringer Meteorite Crater (Meteor Crater) Using Photogrammetry and Terrestrial Laser Scanning Methods

    Science.gov (United States)

    Brown, Richard B.; Navard, Andrew R.; Holland, Donald E.; McKellip, Rodney D.; Brannon, David P.

    2010-01-01

    Barringer Meteorite Crater or Meteor Crater, AZ, has been a site of high interest for lunar and Mars analog crater and terrain studies since the early days of the Apollo-Saturn program. It continues to be a site of exceptional interest to lunar, Mars, and other planetary crater and impact analog studies because of its relatively young age (est. 50 thousand years) and well-preserved structure. High resolution (2 meter to 1 decimeter) digital terrain models of Meteor Crater in whole or in part were created at NASA Stennis Space Center to support several lunar surface analog modeling activities using photogrammetric and ground based laser scanning techniques. The dataset created by this activity provides new and highly accurate 3D models of the inside slope of the crater as well as the downslope rock distribution of the western ejecta field. The data are presented to the science community for possible use in furthering studies of Meteor Crater and impact craters in general as well as its current near term lunar exploration use in providing a beneficial test model for lunar surface analog modeling and surface operation studies.

  6. Paleoecological and archaeological implications of a late Pleistocene/Early holocene record of vegetation and climate from the pacific coastal plain of panama

    Science.gov (United States)

    Piperno, Dolores R.; Jones, John G.

    2003-01-01

    A phytolith record from Monte Oscuro, a crater lake located 10 m above sea level on the Pacific coastal plain of Panama, shows that during the Late Pleistocene the lake bed was dry and savanna-like vegetation expanded at the expense of tropical deciduous forest, the modern potential vegetation. A significant reduction of precipitation below current levels was almost certainly required to effect the changes observed. Core sediment characteristics indicate that permanent inundation of the Monte Oscuro basin with water occurred at about 10,500 14C yr B.P. Pollen and phytolith records show that deciduous tropical forest expanded into the lake's watershed during the early Holocene. Significant burning of the vegetation and increases of weedy plants at ca. 7500 to 7000 14C yr B.P. indicate disturbance, which most likely resulted from early human occupation of the seasonal tropical forest near Monte Oscuro and the development of slash-and-burn methods of cultivation.

  7. Riddles in the Dark: Imaging Inside Mercury's Permanently Shadowed Craters

    Science.gov (United States)

    Ernst, C. M.; Chabot, N. L.; Denevi, B. W.; Nair, H.; Deutsch, A. N.; Murchie, S. L.; Robinson, M. S.; Blewett, D. T.; Head, J. W.; Harmon, J. K.; Neumann, G. A.; Solomon, S. C.

    2013-12-01

    Numerous lines of evidence independently point to the presence of water ice in Mercury's polar regions: Earth-based radar shows radar-bright regions; Mariner 10 and MESSENGER Mercury Dual Imaging System (MDIS) images reveal that these regions are permanently (south polar region) or persistently (north polar region) shadowed; neutron spectrometry indicates hydrogen-rich material; thermal models support the presence of water ice; and Mercury Laser Altimeter (MLA) reflectance measurements at 1064 nm show high and low reflectance deposits consistent in location to where models predict surface and buried water ice, respectively. Throughout 2013, MESSENGER executed a campaign dedicated to imaging the permanently shadowed crater floors of Mercury's north polar region using sunlight scattered from nearby terrain. The campaign makes use of the broadband clear filter (central wavelength 700 nm, bandwidth 600 nm) of the MDIS wide-angle camera (WAC) to target and image radar-bright areas within all host craters > 10 km in diameter under multiple lighting conditions. To date, MESSENGER has imaged the interiors of nearly 20 craters that host radar-bright deposits, including the largest such deposits near the north pole that are likely to host surface water ice. The images reveal a variety of surface morphologies, ranging from the smooth crater floor of the fresh Kandinsky crater, to the moderately cratered floor of Tolkien crater, and to the battered floor of Prokofiev crater, in which the permanently shadowed region does not differ morphologically from the rest of the crater floor. Thus, no distinct morphology is identified in association with polar deposits, and craters hosting such material span the typical range of degradation states relative to their illuminated counterparts. MDIS images also reveal albedo differences in craters with floors not fully in permanent shadow. Prokofiev provides a special environment for viewing a radar- and MLA-bright region suspected to host

  8. Theory and experiments on centrifuge cratering

    Science.gov (United States)

    Schmidt, R. M.; Holsapple, K. A.

    1980-01-01

    Centrifuge experimental techniques provide possibilities for laboratory simulation of ground motion and cratering effects due to explosive loadings. The results of a similarity analysis for the thermomechanical response of a continuum show that increased gravity is a necessary condition for subscale testing when identical materials for both model and prototype are being used. The general similarity requirements for this type of subscale testing are examined both theoretically and experimentally. The similarity analysis is used to derive the necessary and sufficient requirements due to the general balance and jump equations and gives relations among all the scale factors for size, density, stress, body forces, internal energy, heat supply, heat conduction, heat of detonation, and time. Additional constraints due to specific choices of material constitutive equations are evaluated separately. The class of constitutive equations that add no further requirements is identified. For this class of materials, direct simulation of large-scale cratering events at small scale on the centrifuge is possible and independent of the actual constitutive equations. For a rate-independent soil it is shown that a small experiment at gravity g and energy E is similar to a large event at 1 G but with energy equal to g3E. Consequently, experiments at 500 G with 8 grams of explosives can be used to simulate a kiloton in the field. A series of centrifuge experiments was performed to validate the derived similarity requirements and to determine the practicality of applying the technique to dry granular soils having little or no cohesion. Ten shots using Ottawa sand at various gravities confirmed reproducibility of results in the centrifuge environment, provided information on particle size effects, and demonstrated the applicability of the derived similitude requirements. These experiments used 0.5-4 grams of pentaerythritol-tetranitrate (PETN) and 1.7 grams of lead-azide explosives. They

  9. "Flat-Fish" Vacuum Chamber

    CERN Multimedia

    CERN PhotoLab

    1978-01-01

    The picture shows a "Flat-Fish" vacuum chamber being prepared in the ISR workshop for testing prior to installation in the Split Field Magnet (SFM) at intersection I4. The two shells of each part were hydroformed from 0.15 mm thick inconel 718 sheet (with end parts in inconel 600 for easier manual welding to the arms) and welded toghether with two strips which were attached by means of thin stainless steel sheets to the Split Field Magnet poles in order to take the vertical component of the atmospheric pressure force. This was the thinnest vacuum chamber ever made for the ISR. Inconel material was chosen for its high elastic modulus and strenght at chamber bake-out temperature. In this picture the thin sheets transferring the vertical component of the atmosferic pressure force are attached to a support frame for testing. See also 7712182, 7712179.

  10. Exploration of water jet generated by Q-switched laser induced water breakdown with different depths beneath a flat free surface.

    Science.gov (United States)

    Chen, Ross C C; Yu, Y T; Su, K W; Chen, J F; Chen, Y F

    2013-01-14

    The dynamics of a water jet on a flat free surface are investigated using a nanosecond pulsed laser for creating an oscillating bubble with different depths beneath the free surface. A thin jet is shown to deform a crater surface resulted from surface depression and cause a circular ring-shaped crater on the connection surface between the crater of surface depression and the thin jet. The collapse of this circular ring-shaped crater is proposed to the crown-like formation around a thick jet. The evolution of the bubble depth suggests a classification of four distinctive ranges of the bubble depths: non-crown formation when the parameter of bubble depth over the maximum bubble radius γ ≤ 0.5, unstable crown formation when 0.5 ≤ γ ≤ 0.6, crown-like structure with a complete crown wall when 0.6 ≤ γ ≤ 1.1, and non-crown formation when 1.1 ≤ γ. Furthermore, the orientation of the crown wall gradually turns counterclockwise to vertical direction with increasing γ from 0.5 to 1.1, implying a high correlation between the orientation of the crown wall and the depth of the bubble. This correlation is explained and discussed by the directional change of the jet eruption from the collapse of circular ring-shaped crater.

  11. Flat laminated microbial mat communities

    Science.gov (United States)

    Franks, Jonathan; Stolz, John F.

    2009-10-01

    Flat laminated microbial mats are complex microbial ecosystems that inhabit a wide range of environments (e.g., caves, iron springs, thermal springs and pools, salt marshes, hypersaline ponds and lagoons, methane and petroleum seeps, sea mounts, deep sea vents, arctic dry valleys). Their community structure is defined by physical (e.g., light quantity and quality, temperature, density and pressure) and chemical (e.g., oxygen, oxidation/reduction potential, salinity, pH, available electron acceptors and donors, chemical species) parameters as well as species interactions. The main primary producers may be photoautotrophs (e.g., cyanobacteria, purple phototrophs, green phototrophs) or chemolithoautophs (e.g., colorless sulfur oxidizing bacteria). Anaerobic phototrophy may predominate in organic rich environments that support high rates of respiration. These communities are dynamic systems exhibiting both spatial and temporal heterogeneity. They are characterized by steep gradients with microenvironments on the submillimeter scale. Diel oscillations in the physical-chemical profile (e.g., oxygen, hydrogen sulfide, pH) and species distribution are typical for phototroph-dominated communities. Flat laminated microbial mats are often sites of robust biogeochemical cycling. In addition to well-established modes of metabolism for phototrophy (oxygenic and non-oxygenic), respiration (both aerobic and anaerobic), and fermentation, novel energetic pathways have been discovered (e.g., nitrate reduction couple to the oxidation of ammonia, sulfur, or arsenite). The application of culture-independent techniques (e.g., 16S rRNA clonal libraries, metagenomics), continue to expand our understanding of species composition and metabolic functions of these complex ecosystems.

  12. Representability of Hom Implies Flatness

    Indian Academy of Sciences (India)

    Nitin Nitsure

    2004-02-01

    Let be a projective scheme over a noetherian base scheme , and let $\\mathcal{F}$ be a coherent sheaf on . For any coherent sheaf $\\mathcal{E}$ on , consider the set-valued contravariant functor $\\hom_{(\\mathcal{E},\\mathcal{F})}$ on -schemes, defined by $\\hom_{(\\mathcal{E},\\mathcal{F})}(T)=\\mathrm{Hom}(\\mathcal{E}_T,\\mathcal{F}_T)$ where $\\mathcal{E}_T$ and $\\mathcal{F}_T$ are the pull-backs of $\\mathcal{E}$ and $\\mathcal{F}$ to $X_T=X×_s T$. A basic result of Grothendieck ([EGA], III 7.7.9) says that if $\\mathcal{F}$ is flat over then $\\hom_{(\\mathcal{E},\\mathcal{F})}$ is representable for all $\\mathcal{E}$. We prove the converse of the above, in fact, we show that if is a relatively ample line bundle on over such that the functor $\\hom_{(L^{-n},\\mathcal{F})}$ is representable for infinitely many positive integers , then $\\mathcal{F}$ is flat over . As a corollary, taking $X=S$, it follows that if $\\mathcal{F}$ is a coherent sheaf on then the functor $T\\mapsto H^0(T,\\mathcal{F}_T)$ on the category of -schemes is representable if and only if $\\mathcal{F}$ is locally free on . This answers a question posed by Angelo Vistoli. The techniques we use involve the proof of flattening stratification, together with the methods used in proving the author's earlier result (see [N1]) that the automorphism group functor of a coherent sheaf on is representable if and only if the sheaf is locally free.

  13. Obliquity and precession as pacemakers of Pleistocene deglaciations

    CERN Document Server

    Feng, Fabo

    2015-01-01

    The Milankovitch theory states that the orbital eccentricity, precession, and obliquity of the Earth influence our climate by modulating the summer insolation at high latitudes in the northern hemisphere. Despite considerable success of this theory in explaining climate change over the Pleistocene epoch (2.6 to 0.01 Myr ago), it is inconclusive with regard to which combination of orbital elements paced the 100 kyr glacial-interglacial cycles over the late Pleistocene. Here we explore the role of the orbital elements in pacing the Pleistocene deglaciations by modeling ice-volume variations in a Bayesian approach. When comparing models, this approach takes into account the uncertainties in the data as well as the different degrees of model complexity. We find that the Earth's obliquity (axial tilt) plays a dominant role in pacing the glacial cycles over the whole Pleistocene, while precession only becomes important in pacing major deglaciations after the transition of the dominant period from 41 kyr to 100 kyr ...

  14. Global deep-sea extinctions during the Pleistocene ice ages

    Science.gov (United States)

    Hayward, Bruce W.

    2001-07-01

    The dark, near-freezing environment of the deep oceans is regarded as one of the most stable habitats on Earth, and this stability is generally reflected in the slow turnover rates (extinctions and appearances) of the organisms that live there. By far the best fossil record of deep-sea organisms is provided by the shells of benthic foraminifera (Protista). A little-known global extinction of deep-sea benthic foraminifera occurred during the Pleistocene ice ages. In the southwest Pacific, it caused the disappearance of at least two families, 15 genera, and 48 species (˜15% 25% of the fauna) of dominantly uniserial, elongate foraminifera with distinctive apertural modifications. These forms progressively died back and became extinct during glacial periods in the late Pliocene to middle Pleistocene (ca. 2.5 0.6 Ma); most extinctions occurred between 1.0 and 0.6 Ma, at the time of the middle Pleistocene climatic revolution. This first high-resolution study of this extinction event indicates that it was far more significant for deep-sea diversity loss than previously reported (10 species). The middle Pleistocene extinction was the most dramatic last phase of a worldwide decline in the abundance of these elongate forms, a phase that began during cooling near the Eocene-Oligocene boundary and continued during the middle Miocene. Clearly these taxa declined when the world cooled, but the reason is yet to be resolved.

  15. Late Pleistocene adult mortality patterns and modern human establishment.

    Science.gov (United States)

    Trinkaus, Erik

    2011-01-25

    The establishment of modern humans in the Late Pleistocene, subsequent to their emergence in eastern Africa, is likely to have involved substantial population increases, during their initial dispersal across southern Asia and their subsequent expansions throughout Africa and into more northern Eurasia. An assessment of younger (20-40 y) versus older (>40 y) adult mortality distributions for late archaic humans (principally Neandertals) and two samples of early modern humans (Middle Paleolithic and earlier Upper Paleolithic) provides little difference across the samples. All three Late Pleistocene samples have a dearth of older individuals compared with Holocene ethnographic/historical samples. They also lack older adults compared with Holocene paleodemographic profiles that have been critiqued for having too few older individuals for subsistence, social, and demographic viability. Although biased, probably through a combination of preservation, age assessment, and especially Pleistocene mobility requirements, these adult mortality distributions suggest low life expectancy and demographic instability across these Late Pleistocene human groups. They indicate only subtle and paleontologically invisible changes in human paleodemographics with the establishment of modern humans; they provide no support for a life history advantage among early modern humans.

  16. The role of ice sheets in the pleistocene climate

    NARCIS (Netherlands)

    Oerlemans, J.

    1991-01-01

    Northern hemisphere ice sheets have played an important role in the climatic evolution of the Pleistocene. The characteristic time-scale of icesheet growth has the same order-of-magnitude as that for the orbital insolation variations. The interaction with the solid earth, the importance of the therm

  17. Relaxation Time and the Problem of the Pleistocene

    Directory of Open Access Journals (Sweden)

    Steven M. Holland

    2013-04-01

    Full Text Available Although changes in habitat area, driven by changes in sea level, have long been considered as a possible cause of marine diversity change in the Phanerozoic, the lack of Pleistocene extinction in the Californian Province has raised doubts, given the large and rapid sea-level changes during the Pleistocene. Neutral models of metacommunities presented here suggest that diversity responds rapidly to changes in habitat area, with relaxation times of a few hundred to a few thousand years. Relaxation time is controlled partly by metacommunity size, implying that different provinces or trophic levels might have measurably different responses to changes in habitable area. Geologically short relaxation times imply that metacommunities should be able to stay nearly in equilibrium with all but the most rapid changes in area. A simulation of the Californian Province during the Pleistocene confirms this, with the longest lags in diversity approaching 20 kyr. The apparent lack of Pleistocene extinction in the Californian Province likely results from the difficulty of sampling rare species, coupled with repopulation from adjacent deep-water or warm-water regions.

  18. Significance of Two New Pleistocene Plant Records from Western Europe

    Science.gov (United States)

    Field, Michael H.; Velichkevich, Felix Y.; Andrieu-Ponel, Valerie; Woltz, Phillipe

    2000-09-01

    The first records of extinct Caulinia goretskyi (Dorofeev) Dorofeev (synonym Najas goretskyi Dorofeev) in western Europe and of Potamogeton occidentalis M.H. Field sp. nov. were obtained from plant macrofossil analyses of Middle Pleistocene temperate stage deposits exposed at Trez Rouz, Brittany, France. Palynological assemblages recovered suggest correlation with the Holsteinian Stage. This discovery greatly expands the western limit of the paleogeographical distribution of Caulinia goretskyi. The record of Potamogeton occidentalis indicates an affinity with the eastern Asiatic flora, as the fruits resemble those of the extant Potamogeton maackianus A. Bennett. Other extinct Pleistocene species related to P. maackianus have been described, and it is possible to follow the development of this group through the Pleistocene in the European fossil record. These new finds illustrate the importance of a complete paleobotanical approach (both plant macrofossil and palynological analyses). The plant macrofossil assemblages not only provide detailed insight into local vegetation and environment, because they are often not transported long distances (in temperate areas) and can frequently be identified to species level; they can also offer the opportunity to investigate Pleistocene evolutionary trends.

  19. The Morphology of Craters on Mercury: Results from MESSENGER Flybys

    Science.gov (United States)

    Barnouin, Oliver S.; Zuber, Maria T.; Smith, David E.; Neumann, Gregory A.; Herrick, Robert R.; Chappelow, John E.; Murchie, Scott L.; Prockter, Louise M.

    2012-01-01

    Topographic data measured from the Mercury Laser Altimeter (MLA) and the Mercury Dual Imaging System (MDIS) aboard the MESSENGER spacecraft were used for investigations of the relationship between depth and diameter for impact craters on Mercury. Results using data from the MESSENGER flybys of the innermost planet indicate that most of the craters measured with MLA are shallower than those previously measured by using Mariner 10 images. MDIS images of these same MLA-measured craters show that they have been modified. The use of shadow measurement techniques, which were found to be accurate relative to the MLA results, indicate that both small bowl-shaped and large complex craters that are fresh possess depth-to-diameter ratios that are in good agreement with those measured from Mariner 10 images. The preliminary data also show that the depths of modified craters are shallower relative to fresh ones, and might provide quantitative estimates of crater in-filling by subsequent volcanic or impact processes. The diameter that defines the transition from simple to complex craters on Mercury based on MESSENGER data is consistent with that reported from Mariner 10 data.

  20. Noachian and more recent phyllosilicates in impact craters on Mars.

    Science.gov (United States)

    Fairén, Alberto G; Chevrier, Vincent; Abramov, Oleg; Marzo, Giuseppe A; Gavin, Patricia; Davila, Alfonso F; Tornabene, Livio L; Bishop, Janice L; Roush, Ted L; Gross, Christoph; Kneissl, Thomas; Uceda, Esther R; Dohm, James M; Schulze-Makuch, Dirk; Rodríguez, J Alexis P; Amils, Ricardo; McKay, Christopher P

    2010-07-06

    Hundreds of impact craters on Mars contain diverse phyllosilicates, interpreted as excavation products of preexisting subsurface deposits following impact and crater formation. This has been used to argue that the conditions conducive to phyllosilicate synthesis, which require the presence of abundant and long-lasting liquid water, were only met early in the history of the planet, during the Noachian period (> 3.6 Gy ago), and that aqueous environments were widespread then. Here we test this hypothesis by examining the excavation process of hydrated minerals by impact events on Mars and analyzing the stability of phyllosilicates against the impact-induced thermal shock. To do so, we first compare the infrared spectra of thermally altered phyllosilicates with those of hydrated minerals known to occur in craters on Mars and then analyze the postshock temperatures reached during impact crater excavation. Our results show that phyllosilicates can resist the postshock temperatures almost everywhere in the crater, except under particular conditions in a central area in and near the point of impact. We conclude that most phyllosilicates detected inside impact craters on Mars are consistent with excavated preexisting sediments, supporting the hypothesis of a primeval and long-lasting global aqueous environment. When our analyses are applied to specific impact craters on Mars, we are able to identify both pre- and postimpact phyllosilicates, therefore extending the time of local phyllosilicate synthesis to post-Noachian times.

  1. Fluvial erosion of impact craters: Earth and Mars

    Science.gov (United States)

    Baker, V. R.

    1984-01-01

    Geomorphic studies of impact structures in central Australia are being used to understand the complexities of fluvial dissection in the heavily cratered terrains of Mars. At Henbury, Northern Territory, approximately 12 small meteorite craters have interacted with a semiarid drainage system. The detailed mapping of the geologic and structural features at Henbury allowed this study to concentrate on degradational landforms. The breaching of crater rims by gullies was facilitated by the northward movement of sheetwash along an extensive pediment surface extending from the Bacon Range. South-facing crater rims have been preferentially breached because gullies on those sides were able to tap the largest amounts of runoff. At crater 6 a probable rim-gully system has captured the headward reaches of a pre-impact stream channel. The interactive history of impacts and drainage development is critical to understanding the relationships in the heavily cratered uplands of Mars. Whereas Henbury craters are younger than 4700 yrs. B.P., the Gosses Bluff structure formed about 130 million years ago. The bluff is essentially an etched central peak composed of resistant sandstone units. Fluvial erosion of this structure is also discussed.

  2. The effect of craters on the lunar neutron flux

    CERN Document Server

    Eke, V R; Diserens, S; Ryder, M; Yeomans, P E L; Teodoro, L F A; Elphic, R C; Feldman, W C; Hermalyn, B; Lavelle, C M; Lawrence, D J

    2015-01-01

    The variation of remotely sensed neutron count rates is measured as a function of cratercentric distance using data from the Lunar Prospector Neutron Spectrometer. The count rate, stacked over many craters, peaks over the crater centre, has a minimum near the crater rim and at larger distances it increases to a mean value that is up to 1% lower than the mean count rate observed over the crater. A simple model is presented, based upon an analytical topographical profile for the stacked craters fitted to data from the Lunar Orbiter Laser Altimeter (LOLA). The effect of topography coupled with neutron beaming from the surface largely reproduces the observed count rate profiles. However, a model that better fits the observations can be found by including the additional freedom to increase the neutron emissivity of the crater area by ~0.35% relative to the unperturbed surface. It is unclear what might give rise to this effect, but it may relate to additional surface roughness in the vicinities of craters. The ampl...

  3. The Microstructure of Lunar Micrometeorite Impact Craters

    Science.gov (United States)

    Noble, S. K.; Keller, L. P.; Christoffersen, R.; Rahman, Z.

    2016-01-01

    The peak of the mass flux of impactors striking the lunar surface is made up of objects approximately 200 micrometers in diameter that erode rocks, comminute regolith grains, and produce agglutinates. The effects of these micro-scale impacts are still not fully understood. Much effort has focused on evaluating the physical and optical effects of micrometeorite impacts on lunar and meteoritic material using pulsed lasers to simulate the energy deposited into a substrate in a typical hypervelocity impact. Here we characterize the physical and chemical changes that accompany natural micrometeorite impacts into lunar rocks with long surface exposure to the space environment (12075 and 76015). Transmission electron microscope (TEM) observations were obtained from cross-sections of approximately 10-20 micrometers diameter craters that revealed important micro-structural details of micrometeorite impact processes, including the creation of npFe (sup 0) in the melt, and extensive deformation around the impact site.

  4. Slope activity in Gale crater, Mars

    Science.gov (United States)

    Dundas, Colin M.; McEwen, Alfred S.

    2015-01-01

    High-resolution repeat imaging of Aeolis Mons, the central mound in Gale crater, reveals active slope processes within tens of kilometers of the Curiosity rover. At one location near the base of northeastern Aeolis Mons, dozens of transient narrow lineae were observed, resembling features (Recurring Slope Lineae) that are potentially due to liquid water. However, the lineae faded and have not recurred in subsequent Mars years. Other small-scale slope activity is common, but has different spatial and temporal characteristics. We have not identified confirmed RSL, which Rummel et al. (Rummel, J.D. et al. [2014]. Astrobiology 14, 887–968) recommended be treated as potential special regions for planetary protection. Repeat images acquired as Curiosity approaches the base of Aeolis Mons could detect changes due to active slope processes, which could enable the rover to examine recently exposed material.

  5. Martian fluvial conglomerates at Gale crater.

    Science.gov (United States)

    Williams, R M E; Grotzinger, J P; Dietrich, W E; Gupta, S; Sumner, D Y; Wiens, R C; Mangold, N; Malin, M C; Edgett, K S; Maurice, S; Forni, O; Gasnault, O; Ollila, A; Newsom, H E; Dromart, G; Palucis, M C; Yingst, R A; Anderson, R B; Herkenhoff, K E; Le Mouélic, S; Goetz, W; Madsen, M B; Koefoed, A; Jensen, J K; Bridges, J C; Schwenzer, S P; Lewis, K W; Stack, K M; Rubin, D; Kah, L C; Bell, J F; Farmer, J D; Sullivan, R; Van Beek, T; Blaney, D L; Pariser, O; Deen, R G

    2013-05-31

    Observations by the Mars Science Laboratory Mast Camera (Mastcam) in Gale crater reveal isolated outcrops of cemented pebbles (2 to 40 millimeters in diameter) and sand grains with textures typical of fluvial sedimentary conglomerates. Rounded pebbles in the conglomerates indicate substantial fluvial abrasion. ChemCam emission spectra at one outcrop show a predominantly feldspathic composition, consistent with minimal aqueous alteration of sediments. Sediment was mobilized in ancient water flows that likely exceeded the threshold conditions (depth 0.03 to 0.9 meter, average velocity 0.20 to 0.75 meter per second) required to transport the pebbles. Climate conditions at the time sediment was transported must have differed substantially from the cold, hyper-arid modern environment to permit aqueous flows across several kilometers.

  6. Flyover Animation of Becquerel Crater on Mars

    Science.gov (United States)

    2008-01-01

    [figure removed for brevity, see original site] View the Movie Click on image to view the movie This simulated flyover shows rhythmic layers of sedimentary rock inside Becquerel crater on Mars. The animation uses three-dimensional modeling based on a stereo pair of images from the High Resolution Imaging Science Experiment (HiRISE) on NASA's Mars Reconnaissance Orbiter. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace & Technologies Corp., Boulder, Colo.

  7. Ancient aqueous environments at Endeavour crater, Mars

    Science.gov (United States)

    Arvidson, R. E.; Squyres, S. W.; Bell, J.F.; Catalano, J.G.; Clark, B. C.; Crumpler, L.S.; de Souza, P.A.; Fairén, A.G.; Farrand, W. H.; Fox, V.K.; Gellert, Ralf; Ghosh, A.; Golombeck, M.P.; Grotzinger, J.P.; Guinness, E.A.; Herkenhoff, Kenneth E.; Jolliff, B.L.; Knoll, A.H.; Li, R.; McLennan, S.M.; Ming, D. W.; Mittlefehldt, D. W.; Moore, Johnnie N.; Morris, R.V.; Murchie, S.L.; Parker, T.J.; Paulsen, G.; Rice, J.W.; Ruff, S.W.; Smith, M.D.; Wolff, M.J.

    2014-01-01

    Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe+3-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.

  8. Martian Fluvial Conglomerates at Gale Crater

    Science.gov (United States)

    Williams, R. M. E.; Grotzinger, J. P.; Dietrich, W. E.; Gupta, S.; Sumner, D. Y.; Wiens, R. C.; Mangold, N.; Malin, M. C.; Edgett, K. S.; Maurice, S.; Forni, O.; Gasnault, O.; Ollila, A.; Newsom, H. E.; Dromart, G.; Palucis, M. C.; Yingst, R. A.; Anderson, R. B.; Herkenhoff, K. E.; Le Mouélic, S.; Goetz, W.; Madsen, M. B.; Koefoed, A.; Jensen, J. K.; Bridges, J. C.; Schwenzer, S. P.; Lewis, K. W.; Stack, K. M.; Rubin, D.; Kah, L. C.; Bell, J. F.; Farmer, J. D.; Sullivan, R.; Van Beek, T.; Blaney, D. L.; Pariser, O.; Deen, R. G.; Kemppinen, Osku; Bridges, Nathan; Johnson, Jeffrey R.; Minitti, Michelle; Cremers, David; Edgar, Lauren; Godber, Austin; Wadhwa, Meenakshi; Wellington, Danika; McEwan, Ian; Newman, Claire; Richardson, Mark; Charpentier, Antoine; Peret, Laurent; King, Penelope; Blank, Jennifer; Weigle, Gerald; Schmidt, Mariek; Li, Shuai; Milliken, Ralph; Robertson, Kevin; Sun, Vivian; Baker, Michael; Edwards, Christopher; Ehlmann, Bethany; Farley, Kenneth; Griffes, Jennifer; Miller, Hayden; Newcombe, Megan; Pilorget, Cedric; Rice, Melissa; Siebach, Kirsten; Stolper, Edward; Brunet, Claude; Hipkin, Victoria; Léveillé, Richard; Marchand, Geneviève; Sobrón Sánchez, Pablo; Favot, Laurent; Cody, George; Steele, Andrew; Flückiger, Lorenzo; Lees, David; Nefian, Ara; Martin, Mildred; Gailhanou, Marc; Westall, Frances; Israël, Guy; Agard, Christophe; Baroukh, Julien; Donny, Christophe; Gaboriaud, Alain; Guillemot, Philippe; Lafaille, Vivian; Lorigny, Eric; Paillet, Alexis; Pérez, René; Saccoccio, Muriel; Yana, Charles; Aparicio, Carlos Armiens; Caride Rodríguez, Javier; Carrasco Blázquez, Isaías; Gómez Gómez, Felipe; Elvira, Javier Gómez; Hettrich, Sebastian; Lepinette Malvitte, Alain; Marín Jiménez, Mercedes; Frías, Jesús Martínez; Soler, Javier Martín; Torres, F. Javier Martín; Molina Jurado, Antonio; Sotomayor, Luis Mora; Muñoz Caro, Guillermo; Navarro López, Sara; González, Verónica Peinado; García, Jorge Pla; Rodriguez Manfredi, José Antonio; Planelló, Julio José Romeral; Alejandra Sans Fuentes, Sara; Sebastian Martinez, Eduardo; Torres Redondo, Josefina; O'Callaghan, Roser Urqui; Zorzano Mier, María-Paz; Chipera, Steve; Lacour, Jean-Luc; Mauchien, Patrick; Sirven, Jean-Baptiste; Manning, Heidi; Fairén, Alberto; Hayes, Alexander; Joseph, Jonathan; Squyres, Steven; Thomas, Peter; Dupont, Audrey; Lundberg, Angela; Melikechi, Noureddine; Mezzacappa, Alissa; DeMarines, Julia; Grinspoon, David; Reitz, Günther; Prats, Benito; Atlaskin, Evgeny; Genzer, Maria; Harri, Ari-Matti; Haukka, Harri; Kahanpää, Henrik; Kauhanen, Janne; Paton, Mark; Polkko, Jouni; Schmidt, Walter; Siili, Tero; Fabre, Cécile; Wray, James; Wilhelm, Mary Beth; Poitrasson, Franck; Patel, Kiran; Gorevan, Stephen; Indyk, Stephen; Paulsen, Gale; Bish, David; Schieber, Juergen; Gondet, Brigitte; Langevin, Yves; Geffroy, Claude; Baratoux, David; Berger, Gilles; Cros, Alain; Uston, Claude d.; Lasue, Jérémie; Lee, Qiu-Mei; Meslin, Pierre-Yves; Pallier, Etienne; Parot, Yann; Pinet, Patrick; Schröder, Susanne; Toplis, Mike; Lewin, Éric; Brunner, Will; Heydari, Ezat; Achilles, Cherie; Oehler, Dorothy; Sutter, Brad; Cabane, Michel; Coscia, David; Szopa, Cyril; Robert, François; Sautter, Violaine; Nachon, Marion; Buch, Arnaud; Stalport, Fabien; Coll, Patrice; François, Pascaline; Raulin, François; Teinturier, Samuel; Cameron, James; Clegg, Sam; Cousin, Agnès; DeLapp, Dorothea; Dingler, Robert; Jackson, Ryan Steele; Johnstone, Stephen; Lanza, Nina; Little, Cynthia; Nelson, Tony; Williams, Richard B.; Jones, Andrea; Kirkland, Laurel; Treiman, Allan; Baker, Burt; Cantor, Bruce; Caplinger, Michael; Davis, Scott; Duston, Brian; Fay, Donald; Hardgrove, Craig; Harker, David; Herrera, Paul; Jensen, Elsa; Kennedy, Megan R.; Krezoski, Gillian; Krysak, Daniel; Lipkaman, Leslie; McCartney, Elaina; McNair, Sean; Nixon, Brian; Posiolova, Liliya; Ravine, Michael; Salamon, Andrew; Saper, Lee; Stoiber, Kevin; Supulver, Kimberley; Van Beek, Jason; Zimdar, Robert; French, Katherine Louise; Iagnemma, Karl; Miller, Kristen; Summons, Roger; Goesmann, Fred; Hviid, Stubbe; Johnson, Micah; Lefavor, Matthew; Lyness, Eric; Breves, Elly; Dyar, M. Darby; Fassett, Caleb; Blake, David F.; Bristow, Thomas; DesMarais, David; Edwards, Laurence; Haberle, Robert; Hoehler, Tori; Hollingsworth, Jeff; Kahre, Melinda; Keely, Leslie; McKay, Christopher; Bleacher, Lora; Brinckerhoff, William; Choi, David; Conrad, Pamela; Dworkin, Jason P.; Eigenbrode, Jennifer; Floyd, Melissa; Freissinet, Caroline; Garvin, James; Glavin, Daniel; Harpold, Daniel; Mahaffy, Paul; Martin, David K.

    2013-05-01

    Observations by the Mars Science Laboratory Mast Camera (Mastcam) in Gale crater reveal isolated outcrops of cemented pebbles (2 to 40 millimeters in diameter) and sand grains with textures typical of fluvial sedimentary conglomerates. Rounded pebbles in the conglomerates indicate substantial fluvial abrasion. ChemCam emission spectra at one outcrop show a predominantly feldspathic composition, consistent with minimal aqueous alteration of sediments. Sediment was mobilized in ancient water flows that likely exceeded the threshold conditions (depth 0.03 to 0.9 meter, average velocity 0.20 to 0.75 meter per second) required to transport the pebbles. Climate conditions at the time sediment was transported must have differed substantially from the cold, hyper-arid modern environment to permit aqueous flows across several kilometers.

  9. Ancient aqueous environments at Endeavour crater, Mars.

    Science.gov (United States)

    Arvidson, R E; Squyres, S W; Bell, J F; Catalano, J G; Clark, B C; Crumpler, L S; de Souza, P A; Fairén, A G; Farrand, W H; Fox, V K; Gellert, R; Ghosh, A; Golombek, M P; Grotzinger, J P; Guinness, E A; Herkenhoff, K E; Jolliff, B L; Knoll, A H; Li, R; McLennan, S M; Ming, D W; Mittlefehldt, D W; Moore, J M; Morris, R V; Murchie, S L; Parker, T J; Paulsen, G; Rice, J W; Ruff, S W; Smith, M D; Wolff, M J

    2014-01-24

    Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe(+3)-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.

  10. Late Pleistocene stratigraphy of a carbonate platform margin, Exumas, Bahamas

    Science.gov (United States)

    Aalto, K. R.; Dill, Robert F.

    1996-05-01

    Detailed field studies of the southern Exuma Cays on the eastern margin of the Great Bahama Bank show a complex history of late Pleistocene island construction. Pleistocene rocks include island core eolianites, overlain at island margins by fossil patch reefs and reef sands, which in turn are overlain by, and/or grade laterally into, talus breccia cones derived from the erosion of island core eolianite at paleo-seacliffs situated at approximately 5-6 m above present mean high tide. Laminated pedogenic calcrete widely caps Pleistocene rocks. Minor zones of penetrative subsurface calcretization, developed in association with root growth, occur along permeable horizons, including: contacts between talus units or crossbed sets, along tension joints, and (possibly) at the Pleistocene reef-eolianite contact. Among Pleistocene eolianite samples studied in thin-section, the relative proportions of ooids-intraclasts+grapestones-skeletal grains-peloids are approximately 48:39:6:7. Marginal to the Exuma Sound and on the Brigantine Cays, a greater proportion of ooids have peloidal nuclei and cortices with numerous laminae, which may reflect ooid derivation from shelf margin and broad platform interior regions that were characterized by high wave energy during ooid formation. Between these two areas, ooids are more commonly superficial and have cortices with few laminae and nuclei composed of subrounded micrite or pelmicrite intraclasts. Such ooid nuclei are most likely derived from storm erosion of partially cemented seafloor muds. Some skeletal-rich eolianite in this region may reflect local sediment input from platform margin reefs, or may be part of an older(?) stratigraphic unit.

  11. Crater Morphologies on Pluto and Charon: Anticipating New Horizons

    Science.gov (United States)

    Schenk, P.; Bray, V. J.; McKinnon, W. B.; White, O. L.; Moore, J. M.

    2014-12-01

    Impact craters are among the few geologic features we have some confidence will be present in the Pluto/Charon system. Crater morphologies are important as tracers of thermal history (through the mechanism of viscous relaxation), and can be used to probe through icy crusts (in terms of excavating deeper layers as on Ganymede or penetrating through floating ice shells as on Europa). New Horizons will have the opportunity to examine crater morphologies on Pluto to resolutions Charon to ~250 meters over significant areas. Stereo-derived topography maps are anticipated over 20-35% of each body. The first task will be to place the observed craters (assuming they are not deeply eroded) into Solar System context. Crater morphology on icy satellites is controlled primarily by surface gravity. Charon has similar surface gravity to the icy Saturnian satellites and we expect craters on Charon to resemble those seen by Cassini, where the dominant landform will be prominent central peaks. Pluto surface gravity is midway between Ganymede and Rhea. Triton, with similar surface gravity and internal composition to Pluto, is of no help due to the paucity of resolved craters there. This opens the possibility of observing landforms seen on Ganymede, such as central dome craters, palimpsests and perhaps even a multiring basin or two, albeit at larger diameters than we would see on Ganymede. Several issues complicate our rosy picture. A key unresolved concern is that impact velocities in the Pluto system are only a few km/s, in the low end of the hypervelocity range. Numerical models imply possible differences during excavation, producing deeper simple craters than on the icy satellites. Impacts occurring at velocities well below the mean (topographic data sets is unclear. Any viscous relaxation (driven by internal or modest tidal heating) or mass wasting erosion (by volatile redistribution) will also work to reduce crater depths on Pluto in different ways, but cratering onto the likely

  12. On Mercury's past rotation, in light of its large craters

    Science.gov (United States)

    Knibbe, Jurriën Sebastiaan; van Westrenen, Wim

    2017-01-01

    We have simulated in-orbit variations of the impact flux and spatial distributions of >100 km diameter (D) crater production for Mercury in its current 3:2 and hypothetical 2:1 and 1:1 spin-orbit resonances. Results show that impact fluxes and D > 100 km cratering are non-uniform for these rotational states when Mercury's orbit is significantly eccentric. Variations in the impact flux and D > 100 km cratering depend on the orbital elements of Mercury and its impactors. The observed spatial distribution of large Mercurian craters is difficult to generate by cratering in Mercury's current 3:2 spin-orbit resonance, but can be produced by cratering in a former 1:1 (as previously proposed by Wieczorek et al., 2012) or 2:1 spin-orbit resonance. We have calculated capture probabilities at spin-orbit resonances for a rigid Mercury. If Mercury's initial rotation was prograde, we find that a higher order spin-orbit resonance is the most likely first capture for feasible (low) values of Mercury's past triaxiality. In light of Mercury's crater record, we examined the possibility that impacts have initiated transitions in past spin-orbit resonances. Although the number of craters whose generating impact would have destabilized a spin-orbit resonance is sensitive to the crater scaling procedure, any initial rotational state of Mercury has likely been destabilized by impacts. An initial and permanent 3:2 spin-orbit resonance capture seems untenable. Mercury's tidal torque decelerates Mercury's rotation for the most likely range of Mercury's orbital eccentricity. Only one or two craters are candidate relics of an impact-event that facilitates an instantaneous transition from a former synchronous rotation to the 3:2 spin-orbit resonance, and only for a small crater scaling factor. We propose a rotational evolution trajectory for Mercury with visits to spin-orbit resonances of decreasing order including a substantial period in the 2:1 spin-orbit resonance, which can account for the

  13. Late Pliocene/Early Pleistocene environments inferred from the Lake El'gygytgyn pollen record

    Science.gov (United States)

    Andreev, Andrei; Wennrich, Volker; Tarasov, Pavel; Raschke (Morozova), Elena; Brigham-Grette, Julie; Nowaczyk, Norbert; Melles, Martin

    2014-05-01

    The Arctic is known to play a crucial role within the global climate system. The mid-Pliocene (3-3.5 Ma) is considered to be the most probable scenario of the future climate changes. However, reliable climate projections are hampered by the complexity of the underlying natural variability and feedback mechanisms. An important prerequisite for the validation and improvement of the future projections is a better understanding of the long-term environmental history of the Arctic. Unfortunately, formation of continuous paleoenvironmental records in the Arctic was widely restricted due to repeated glaciations. Continuous sequences that penetrate the entire Quaternary and further into the Pliocene are highly desired and would enable to validate the temperature rise during the mid-Pliocene that was proposed by former studies. Such a record has now become available from Lake El'gygytgyn (67º30'N, 172º05E') located in a meteorite impact crater in north-eastern Siberia. The impact nearly 3.6 Ma ago formed an 18 km wide hole in the ground that then filled with water. The retrieved lake sediments have trapped pollen from a several thousand square-kilometer source area providing reliable insights into regional and over-regional millennial-scale vegetation and climate changes of the Arctic since the Pliocene. The ''El'gygytgyn Drilling Project" of ICDP has completed three holes in the center of the lake, penetrating about 318 m thick lake sediments and about 200 m of the impact rocks below. Because of its unusual origin and high-latitude setting in western Beringia, scientific drilling at Lake El'gygytgyn offered unique opportunities for paleoclimate research, allowing time-continuous climatic and environmental reconstructions back into the Pliocene. Late Pliocene and Early Pleistocene pollen assemblages can be subdivided into 55 pollen zones, which reflect the main environmental fluctuations in the region 3.55-2.15 Ma BP. Pollen-based climate reconstructions show that

  14. Morphometry and Morphology of Fresh Craters on Titan

    Science.gov (United States)

    Kirk, R. L.; Wood, C. A.; Neish, C.; Lucas, A.; Hayes, A. G.; Cassini Radar Team

    2011-12-01

    Cassini RADAR imagery obtained on Titan flyby T77 revealed a 40-km diameter fresh impact crater at 11.6° N 44.6° W. This is only the 8th crater identified with high confidence (Wood et al., 2010, Icarus 206, 334), and the 3rd (after Sinlap D=79 km and Ksa D=30 km) for which the depth can be estimated by comparing the foreshortening of the near and far walls. This "autostereo" technique yields an estimated depth of 680 m. The T77 image forms a stereo pair with the T17 discovery image of Ksa from which we estimate the depth of Ksa at 750-800 m, in close agreement with SARTopo data. The depth of Sinlap is 760 m based on SARTopo. Depth-diameter ratios for these craters thus range from 0.01 to 0.025 and the depths are comparable to but 200-400 m shallower than fresh craters of the same size on Ganymede (Bray et al., 2008, Met. Planet Sci. 43, 1979). The depth differences could be explained by initial crater morphometry, by relaxation in a different thermal environment, or (perhaps most plausibly given the bland floors of even the freshest Titan craters) to sedimentary infill. In contrast, the 18x36 km elliptical depression at Sotra Facula is much deeper than Ganymede craters of similar size (d=1500 m from stereo), supporting the conclusion that it is not an impact crater. All three craters exhibit a relatively radar-bright annulus around the outer edge of the floor, possibly as the result of mass wasting of blocky materials from the crater walls. The central part of each crater is darker. The central darker floor of the new crater is symmetrical and featureless, whereas Ksa has a bright central ring 7 km in diameter. Stereo spot heights indicate the ring is 350±100 m above the outer floor. This height is in close agreement with the scaling for Ganymede crater central peaks from Bray et al. (2008). The darker floor area of Sinlap is substantially asymmetrical with a small bright central spot whose elevation is unknown. The new crater has continuous, radar

  15. Dental microwear and diet of the Plio-Pleistocene hominin Paranthropus boisei.

    Directory of Open Access Journals (Sweden)

    Peter S Ungar

    Full Text Available The Plio-Pleistocene hominin Paranthropus boisei had enormous, flat, thickly enameled cheek teeth, a robust cranium and mandible, and inferred massive, powerful chewing muscles. This specialized morphology, which earned P. boisei the nickname "Nutcracker Man", suggests that this hominin could have consumed very mechanically challenging foods. It has been recently argued, however, that specialized hominin morphology may indicate adaptations for the consumption of occasional fallback foods rather than preferred resources. Dental microwear offers a potential means by which to test this hypothesis in that it reflects actual use rather than genetic adaptation. High microwear surface texture complexity and anisotropy in extant primates can be associated with the consumption of exceptionally hard and tough foods respectively. Here we present the first quantitative analysis of dental microwear for P. boisei. Seven specimens examined preserved unobscured antemortem molar microwear. These all show relatively low complexity and anisotropy values. This suggests that none of the individuals consumed especially hard or tough foods in the days before they died. The apparent discrepancy between microwear and functional anatomy is consistent with the idea that P. boisei presents a hominin example of Liem's Paradox, wherein a highly derived morphology need not reflect a specialized diet.

  16. Late Pleistocene and Holocene tephrostratigraphy of interior Alaska and Yukon: Key beds and chronologies over the past 30,000 years

    Science.gov (United States)

    Davies, Lauren J.; Jensen, Britta J. L.; Froese, Duane G.; Wallace, Kristi L.

    2016-08-01

    The Aleutian Arc-Alaska Peninsula and Wrangell volcanic field are the main source areas for tephra deposits found across Alaska and northern Canada, and increasingly, tephra from these eruptions have been found further afield in North America, Greenland, and Europe. However, there have been no broad scale reviews of the Late Pleistocene and Holocene tephrostratigraphy for this region since the 1980s, and this lack of data is hindering progress in identifying these tephra both locally and regionally. To address this gap and the variable quality of associated geochemical and chronological data, we undertake a detailed review of the latest Pleistocene to Holocene tephra found in interior Alaska and Yukon. This paper discusses nineteen tephra that have distributions beyond southwest Alaska and that have the potential to become, or already are, important regional markers. This includes three 'modern' events from the 20th century, ten with limited data availability but potentially broad distributions, and six that are widely reported in interior Alaska and Yukon. Each tephra is assessed in terms of chronology, geochemistry and distribution, with new Bayesian age estimates and geochemical data when possible. This includes new major-element geochemical data for Crater Peak 1992, Redoubt 1989-90, and two andesitic tephra from St Michael Island (Tephra D), as well as revised age estimates for Dawson tephra, Oshetna, Hayes set H, Aniakchak CFE II, and the White River Ashes, northern and eastern lobes.

  17. The fractured Moon: Production and saturation of porosity in the lunar highlands from impact cratering

    Science.gov (United States)

    Soderblom, Jason M.; Evans, Alexander J.; Johnson, Brandon C.; Melosh, H. Jay; Miljković, Katarina; Phillips, Roger J.; Andrews-Hanna, Jeffrey C.; Bierson, Carver J.; Head, James W.; Milbury, Colleen; Neumann, Gregory A.; Nimmo, Francis; Smith, David E.; Solomon, Sean C.; Sori, Michael M.; Wieczorek, Mark A.; Zuber, Maria T.

    2015-09-01

    We have analyzed the Bouguer anomaly (BA) of ~1200 complex craters in the lunar highlands from Gravity Recovery and Interior Laboratory observations. The BA of these craters is generally negative, though positive BA values are observed, particularly for smaller craters. Crater BA values scale inversely with crater diameter, quantifying how larger impacts produce more extensive fracturing and dilatant bulking. The Bouguer anomaly of craters larger than 93-19+47 km in diameter is independent of crater size, indicating that there is a limiting depth to impact-generated porosity, presumably from pore collapse associated with either overburden pressure or viscous flow. Impact-generated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than ~30 km in diameter, consistent with an ~8 km thick lunar megaregolith, whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces.

  18. Craters and basins on Ganymede and Callisto - Morphological indicators of crustal evolution

    Science.gov (United States)

    Passey, Q. R.; Shoemaker, E. M.

    The morphologic characteristics of craters and palimpsests on Ganymede and Callisto are surveyed, and the crustal properties of these satellites and the evolution of the properties are studied. The morphology of bowl-shaped craters, smooth-floored craters, craters without central peaks, craters with central pits, chain craters on Callisto, the Gilgamesh and Western Equatorial Basins on Ganymede, crater palimpsests and penepalimpsests, multiring structures on Callisto, and the Galileo Regio rimmed furrow system on Ganymede are described individually. The crustal evolution is addressed by examining the development of the Galileo Regio system, the distribution of crater retention ages, the record of ray clusters, the thermal history of the lithosphere of Ganymede, and the origin of the central pits. It is suggested that as the lithosphere of each satellite cooled and thickened, crater retentivity spread as a wave from the polar regions and the antapex toward the apex; at any given location, progressively larger craters were retained with the passage of time.

  19. Scoria Cone and Tuff Ring Stratigraphy Interpreted from Ground Penetrating Radar, Rattlesnake Crater, Arizona

    Science.gov (United States)

    Kruse, S. E.; McNiff, C. M.; Marshall, A. M.; Courtland, L. M.; Connor, C.; Charbonnier, S. J.; Abdollahzadeh, M.; Connor, L.; Farrell, A. K.; Harburger, A.; Kiflu, H. G.; Malservisi, R.; Njoroge, M.; Nushart, N.; Richardson, J. A.; Rookey, K.

    2013-12-01

    Numerous recent studies have demonstrated that detailed investigation of scoria cone and maar morphology can reveal rich details the eruptive and erosion histories of these volcanoes. A suite of geophysical surveys were conducted to images Rattlesnake Crater in the San Francisco Volcanic Field, AZ, US. We report here the results of ~3.4 km of ground penetrating radar (GPR) surveys that target the processes of deposition and erosion on the pair of cinder cones that overprint the southeast edge of Rattlesnake crater and on the tuff ring that forms the crater rim. Data were collected with 500, 250, 100, and 50 MHz antennas. The profiles were run in a radial direction down the northeast flanks of the cones (~1 km diameter, ~120 meters height) , and on the inner and outer margins of the oblong maar rim (~20-80 meters height). A maximum depth of penetration of GPR signal of ~15m was achieved high on the flanks of scoria cones. A minimum depth of essentially zero penetration occurred in the central crater. We speculate that maximum penetration occurs near the peaks of the cones and crater rim because ongoing erosion limits new soil formation. Soil formation would tend to increase surface conductivity and hence decrease GPR penetration. Soil is probably better developed within the crater, precluding significant radar penetration there. On the northeast side of the gently flattened rim of the easternmost scoria cone, the GPR profile shows internal layering that dips ~20 degrees northeast relative to the current ground surface. This clearly indicates that the current gently dipping surface is not a stratigraphic horizon, but reflects instead an erosive surface into cone strata that formed close to the angle of repose. Along much of the cone flanks GPR profiles show strata dipping ~4-5 degrees more steeply than the current surface, suggesting erosion has occurred over most of the height of the cone. An abrupt change in strata attitude is observed at the gradual slope

  20. Focal rigidity of flat tori

    Directory of Open Access Journals (Sweden)

    Ferry Kwakkel

    2011-12-01

    Full Text Available Given a closed Riemannian manifold (M, g, i.e. compact and boundaryless, there is a partition of its tangent bundle TM = ∪iΣi called the focal decomposition of TM. The sets Σi are closely associated to focusing of geodesics of (M, g, i.e. to the situation where there are exactly i geodesic arcs of the same length joining points p and q in M. In this note, we study the topological structure of the focal decomposition of a closed Riemannian manifold and its relation with the metric structure of the manifold. Our main result is that flat n-tori, n > 2, are focally rigid in the sense that if two flat tori are focally equivalent then the tori are isometric up to rescaling. The case n = 2 was considered before by F. Kwakkel.Dada uma variedade Riemanniana (M, g fechada, isto é, compacta e sem bordo, existe uma partição de seu fibrado tangente TM = ∪iΣi chamada decomposição focal de TM. Os conjuntos Σi estão intimamente associados ao modo como focalizam as geodésicas de (M,g, isto é, à situação em que existem exatamente i arcos de geodésica de mesmo comprimento unindo pontos p e q em M. Nesta nota, estudamos a estrutura topológica da decomposição focal de uma variedade Riemanniana fechada e sua relação com a estrutura métrica de M. Nosso principal resultado é que n-toros planos, n > 2, são focalmente rigidos, isto é, se dois toros planos são focalmente equivalentes, então os dois toros são isométricos módulo mudança de escala. O caso n = 2 foi considerado anteriormente por F. Kwakkel.

  1. On the Origin of the Crestone Crater: Low-Latitude Periglacial Features in San Luis Valley, Colorado

    Science.gov (United States)

    Schwans, E.; Meng, T. M.; Prudhomme, K.; Morgan, M. L.

    2015-12-01

    this claim. Results indicate that the Crestone Crater and nearby similar structures are relic collapsed hydraulic pingos, formed during Pleistocene periglacial activity. This conclusion provides further insight into periglacial landforms at low latitudes while demonstrating the value of LiDAR analysis of small geologic features on a regional scale.

  2. Depth of Cracking beneath Impact Craters: New Constraint for Impact Velocity

    OpenAIRE

    Ahrens, Thomas J.; Xia, Kaiwen; Coker, Demirkan

    2002-01-01

    Both small-scale impact craters in the laboratory and less than 5 km in diameter bowl-shaped craters on the Earth are strength (of rock) controlled. In the strength regime, crater volumes are nearly proportional to impactor kinetic energy. The depth of the cracked rock zone beneath such craters depends on both impactor energy and velocity. Thus determination of the maximum zone of cracking constrains impact velocity. We show this dependency for small-scale laboratory craters where the cracked...

  3. Scaling craters in carbonates: Electron paramagnetic resonance analysis of shock damage

    OpenAIRE

    Polanskey, Carol A.; Ahrens, Thomas J.

    1994-01-01

    Carbonate samples from the 8.9-Mt nuclear (near-surface explosion) crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance (EPR). Samples from below the OAK apparent crater floor were obtained from six boreholes, as well as ejecta recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen and Kaibab limestone, which had been...

  4. Flat hat glass diffractive optical beam shaper

    Science.gov (United States)

    Reichel, Steffen; Petzold, Uwe; Biertuempfel, Ralf; Vogt, Helge

    2009-02-01

    Many laser applications need a homogeneous - so called flat hat - light distribution in the application area. However, many laser emit Gaussian shaped light. The technology of diffractive optical elements (DOE) can be used to shape the Gaussian beam into a flat hat beam at a compact length. SCHOTT presents a DOE design of a flat hat DOE beam shaper made out of optical glass. Here the material glass has the significant advantage of high laser durability, low scattering losses, high resistance to temperature, moisture, and chemicals compared to polymer DOEs. Simulations and measurements on different DOEs for different wavelength, laser beam width, and laser divergence are presented. Surprisingly the flat hat DOE beam shaper depends only weakly on wavelength and beam width but strongly on laser divergence. Based on the good agreement between simulation and measurement an improved flat hat DOE beam shaper is also presented.

  5. Alberca De Guadalupe Maar Crater, Zacapu Basin : A Rare Type of Volcano within the Michoacán-Guanajuato Volcanic Field, México

    Science.gov (United States)

    Kshirsagar, P. V.; Siebe, C.; Guilbaud, M. N.; Salinas, S.

    2014-12-01

    Phreato-magmatic vents (esp. maar craters) are rare in the ~40,000 Km2 Plio-Quaternary monogenetic Michoacán-Guanajuato Volcanic Field (MGVF) located in the central part of the Mexican Volcanic Belt. In contrast to >1000 scoria cones, only 2 dozen phreato-magmatic monogenetic vents (e.g. tuff cones, tuff rings, and maars) have been identified. About half of these form a cluster near Valle de Santiago in the Lerma river valley at the northern margin of the MGVF, while the others occur in a rather scattered fashion. Here we discuss the origin of Alberca de Guadalupe maar crater, one of the three phreato-magmatic vents (in addition to El Caracol and Alberca de Los Espinos) that occur within the boundaries of the inter-montane lacustrine Zacapu basin, a tectonic graben bound by an ENE-WSW normal fault system. The maar crater came into existence between 20,000 and 23,000 y BP, forming a 140 m deep hole in the otherwise planar surrounding ground of theearly Pleistocene lava flows of Cerro Pelón.The maar crater has a diameter of ~1 Km and bears a 9 m deep lake. Eruptive products include typical surge deposits that are best exposed around the rim and inner crater walls. They are poorly sorted (Mdø= -1.56 to -3.75, ø= 1.43 to 3.23), rich in accidental lithics (angular andesitic lava and ignimbrite clasts) constituting 51-88% of the deposit with few juveniles (basaltic andesite with phenocrysts of plagioclase, olivine, and pyroxene in a quenched glassy matrix; SiO2=54-58 wt. %). Dry surge units are friable and clast-supported, in contrast the wet surge units are fairly indurated and bear accretionary lapilli. Bedding is frequently distorted by ballistic impact-sag structures. The entire construct is disrupted by an E-W trending regional fault, downthrowing the northern part by ~30 m.The unusual formation of this maar crater in the semi-arid highlands of Zacapu was favored by the local hydrological and topographical conditions. Such conditions still prevail in several

  6. A Colder Early Mars: Insight from Crater Wall Slope Statistics

    Science.gov (United States)

    Kreslavsky, M. A.; Head, J. W.

    2017-10-01

    Statistics of crater wall slopes in the martian tropics indicates that fluvial erosion in the Late Noachian was minor and episodic. At lower elevations erosion lasted longer, into the Hesperian, which implies a thicker incondensable atmosphere.

  7. Impact Metamorphism of Sandstones at Amguid Crater, Algeria

    Science.gov (United States)

    Sahoui, R.; Belhai, D.

    2016-08-01

    Amguid is a 450 m diameter sample crater; it is emplaced in Lower Devonian sandstones.We have carried out a petrographic study in order to investigate shock effects recorded in these sandstones and define shock stages in Amguid.

  8. Bullialdus Crater: Correlations Between KREEP and Local Mineralogy

    Science.gov (United States)

    Klima, R. L.; Lawrence, D.; Cahill, J. T. S.; Hagerty, J.

    2012-03-01

    We explore the pyroxenes in and around Bullialdus Crater, examining relationships between lithology, thorium content, and hydroxylated material to help constrain about the source region and character of KREEP on the lunar nearside.

  9. Radar glory from buried craters on icy moons

    Science.gov (United States)

    Eshleman, Von R.

    1986-10-01

    Three ice-covered moons of Jupiter, in comparison with rocky planets and earth's moon, produce radar echoes of astounding strengths and bizarre polarizations. Scattering from buried craters can explain these and other anomalous properties of the echoes. The role of such craters is analogous to that of the water droplets that create the apparition known as 'the glory', the optically bright region surrounding an observer's shadow on a cloud. Both situations involve the electromagnetic phenomenon of total internal reflection at a dielectric interface, operating in a geometry that strongly favors exact backscattering. Dim surface craters are transformed into bright glory holes by being buried under somewhat denser material, thereby increasing the intensity of their echoes by factors of hundreds. The dielectric interface thus formed at the crater walls nicely accounts for the unusual polarizations of the echoes.

  10. Planetary science: Meteor Crater formed by low-velocity impact

    Science.gov (United States)

    Melosh, H. J.; Collins, G. S.

    2005-03-01

    Meteor Crater in Arizona was the first terrestrial structure to be widely recognized as a meteorite impact scar and has probably been more intensively studied than any other impact crater on Earth. We have discovered something surprising about its mode of formation - namely that the surface-impact velocity of the iron meteorite that created Meteor Crater was only about 12 km s-1. This is close to the 9.4 km s-1 minimum originally proposed but far short of the 15-20 km s-1 that has been widely assumed - a realization that clears up a long-standing puzzle about why the crater does not contain large volumes of rock melted by the impact.

  11. Degradation sequence of young lunar craters from orbital infrared survey

    Science.gov (United States)

    Wieczorek, M. A.; Mendell, W. W.

    1993-01-01

    Using new software, nighttime thermal maps of the lunar surface have been generated from data obtained by the Apollo 17 Infrared Scanning Radiometer (ISR) in lunar orbit. Most of the thermal anomalies observed in the maps correspond to fresh lunar craters because blocks on the lunar surface maintain a thermal contrast relative to surrounding soil during the lunar night. Craters of Erastosthenian age and older - relatively young by lunar standards - have developed soil covers that make them almost indistinguishable from their surroundings in the thermal data. Thermal images of Copernican age craters show various stages of a degradation process, allowing the craters to be ranked by age. The ISR data should yield insights into lunar surface evolution as well as a more detailed understanding of the bombardment history after formation of the great mare basins.

  12. Meteor Crater: Energy of formation - Implications of centrifuge scaling

    Science.gov (United States)

    Schmidt, R. M.

    1980-01-01

    Recent work on explosive cratering has demonstrated the utility of performing subscale experiments on a geotechnic centrifuge to develop scaling rules for very large energy events. The present investigation is concerned with an extension of this technique to impact cratering. Experiments have been performed using a projectile gun mounted directly on the centrifuge rotor to launch projectiles into a suitable soil container undergoing centripetal accelerations in excess of 500 G. The pump tube of a two-stage light-gas gun was used to attain impact velocities of approximately 2 km/sec. The results of the experiments indicate that the energy of formation of any large impact crater depends upon the impact velocity. This dependence, shown for the case of Meteor Crater, is consistent with analogous results for the specific energy dependence of explosives and is expected to persist to impact velocities in excess of 25 km/sec.

  13. Planetary science: Meteor Crater formed by low-velocity impact.

    Science.gov (United States)

    Melosh, H J; Collins, G S

    2005-03-10

    Meteor Crater in Arizona was the first terrestrial structure to be widely recognized as a meteorite impact scar and has probably been more intensively studied than any other impact crater on Earth. We have discovered something surprising about its mode of formation--namely that the surface-impact velocity of the iron meteorite that created Meteor Crater was only about 12 km s(-1). This is close to the 9.4 km s(-1) minimum originally proposed but far short of the 15-20 km s(-1) that has been widely assumed--a realization that clears up a long-standing puzzle about why the crater does not contain large volumes of rock melted by the impact.

  14. Vegetation damage and recovery after Chiginagak Volcano Crater drainage event

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — From August 20 — 23, 2006, I revisited Chiginigak volcano to document vegetation recovery after the crater drainage event that severely damaged vegetation in May of...

  15. Cosmology in Conformally Flat Spacetime

    Science.gov (United States)

    Endean, Geoffrey

    1997-04-01

    A possible solution to cosmological age and redshift-distance difficulties has recently been proposed by applying the appropriate conformally flat spacetime (CFS) coordinates to the standard solution of the field equations in a standard dust model closed universe. Here it is shown that CFS time correctly measures the true age of the universe, thus answering a major theoretical objection to the proposal. It is also shown that the CFS interpretation leads to a strong Copernican principle and is in all other respects wholly self-consistent. The deceleration parameter q0 is related to t0, the present age of the universe divided by L, the scale length of its curvature (an absolute constant). The values of q0 and L are approximately 5/6 and 9.2 × 109 yr, respectively. It is shown that the universe started everywhere simultaneously, with no recession velocity until the effects of its closed topology became significant. Conclusions to the contrary in standard theory (the big bang) stem from a different definition of recession velocity. The theoretical present cosmological mass density is quantified as 4.4 × 10-27 kg m-3 approximately, thus greatly reducing, in a closed universe, the observational requirement to find hidden mass. It is also shown that the prediction of standard theory, for a closed universe, of collapse toward a big crunch termination, will not in fact take place.

  16. Morphology of Lonar Crater, India: Comparisons and implications

    Science.gov (United States)

    Fudali, R.F.; Milton, D.J.; Fredriksson, K.; Dube, A.

    1980-01-01

    Lonar Crater is a young meteorite impact crater emplaced in Deccan basalt. Data from 5 drillholes, a gravity network, and field mapping are used to reconstruct its original dimensions, delineate the nature of the pre-impact target rocks, and interpret the emplacement mode of the ejecta. Our estimates of the pre-erosion dimensions are: average diameter of 1710 m; average rim height of 40 m (30-35 m of rim rock uplift, 5-10 m of ejected debris); depth of 230-245 m (from rim crest to crater floor). The crater's circularity index is 0.9 and is unlikely to have been lower in the past. There are minor irregularities in the original crater floor (present sediment-breccia boundary) possibly due to incipient rebound effects. A continuous ejecta blanket extends an average of 1410 m beyond the pre-erosion rim crest. In general, 'fresh' terrestrial craters, less than 10 km in diameter, have smaller depth/diameter and larger rim height/diameter ratios than their lunar counterparts. Both ratios are intermediate for Mercurian craters, suggesting that crater shape is gravity dependent, all else being equal. Lonar demonstrates that all else is not always equal. Its depth/diameter ratio is normal but, because of less rim rock uplift, its rim height/diameter ratio is much smaller than both 'fresh' terrestrial and lunar impact craters. The target rock column at Lonar consists of one or more layers of weathered, soft basalt capped by fresh, dense flows. Plastic deformation and/or compaction of this lower, incompetent material probably absorbed much of the energy normally available in the cratering process for rim rock uplift. A variety of features within the ejecta blanket and the immediately underlying substrate, plus the broad extent of the blanket boundaries, suggest that a fluidized debris surge was the dominant mechanism of ejecta transportation and deposition at Lonar. In these aspects, Lonar should be a good analog for the 'fluidized craters' of Mars. ?? 1980 D. Reidel

  17. Impact crater formation: a simple application of solid state physics

    OpenAIRE

    Celebonovic, V.; Souchay, J.

    2010-01-01

    This contribution is a first step aiming to address a general question: what can be concluded on impact craters which exist on various planetary system objects, by combining astronomical data and known theoretical results from solid state physics. Assuming that the material of the target body is of crystaline structure,it is shown that a simple calculation gives the possibility of estimating the speed of the impactor responsible for the creation of a crater.A test value,calculated using obser...

  18. Ceres' internal structure as inferred from its large craters

    Science.gov (United States)

    Marchi, Simone; Raymond, Carol; Fu, Roger; Ermakov, Anton I.; O'Brien, David P.; De Sanctis, Cristina; Ammannito, Eleonora; Russell, Christopher T.

    2016-10-01

    The Dawn spacecraft has gathered important data about the surface composition, internal structure, and geomorphology of Ceres, revealing a cratered landscape. Digital terrain models and global mosaics have been used to derive a global catalog of impact craters larger than 10 km in diameter. A surface dichotomy appears evident: a large fraction of the northern hemisphere is heavily cratered as the result of several billion of years of collisions, while portions of the equatorial region and southern hemisphere are much less cratered. The latter are associated with the presence of the two largest (~270-280 km) impact craters, Kerwan and Yalode. The global crater count shows a severe depletion for diameters larger than 100-150 km with respect to collisional models and other large asteroids, like Vesta. This is a strong indication that a significant population of large cerean craters has been obliterated over geological time-scales. This observation is supported by the overall topographic power spectrum of Ceres, which shows that long wavelengths in topography are suppressed (that is, flatter surface) compared to short wavelengths.Viscous relaxation of topography may be a natural culprit for the observed paucity of large craters. Relaxation accommodated by the creep of water ice is expected to result in much more rapid and complete decay of topography than inferred. In contrast, we favor a strong crust composed of a mixture of silicates and salt species (depression, known as Vendimia Planitia. The overall topography of Vendimia Planitia is compatible with a partially relaxed mega impact structure. The presence of such a large scale depression bears implications for the rheology of the deeper interior, potentially implying a transition to higher viscosity/higher density materials at a depth of ~200 km. This is compatible with the presence of a central mass concentration, as inferred from gravity measurements.

  19. Mechanical and Geological Effects of Impact Cratering on Ida

    Science.gov (United States)

    Asphaug, Erik; Moore, Jeffrey M.; Morrison, David; Benz, Willy; Nolan, Michael C.; Sullivan, Robert J.

    1996-03-01

    Asteroids respond to impact stresses differently from either laboratory specimens or large planets. Gravity is typically so small that seismic disturbances of a few cm s-1can devastate unconsolidated topography. Yet the presence of regolith and the likelihood that many asteroids are gravitational assemblages tell us that gravity cannot generally be ignored. We use numerical models for impact fracture in solids to examine the initial stage of crater formation on asteroid 243 Ida, up to the cessation of fracture and the establishment of the cratering flow; at this stage we can infer final crater diameters but not profiles. We find that a modified strength scaling applies for craters up to a few 100 m in diameter forming in rock subject to Ida's gravity, and that gravity controls all craters larger than ∼1 km. “Bright annuli” around a number of intermediate craters may be the result of low-velocity surface disturbances, rather than bright proximal ejecta deposits. We also consider large impactors, to which Ida presents a curved, finite target surface with irregular gravity. These can excavate asymmetrical concavities. Stresses from large events can refocus and cause fracture far from the crater; using the shape of Ida as a basis for 3D hydrocode simulations, we show that impact genesis of the Vienna Regio concavity can cause fracture in Pola Regio, where grooves are observed in spacecraft images. Other simulations indicate that the formation of the ∼10 km crater Azzurra might have reopened these fractures, which may account for their fresh appearance. This mechanism of groove formation requires an interior which coherently transmits elastic stress. While this precludes a classic “rubble pile” asteroid, it does allow well-joined fault planes, and welded blocks or pores smaller than the stress pulse.

  20. Melt water-driven gully formation in Moni Crater, Mars

    Science.gov (United States)

    Glines, N. H.; Gulick, V. C.; Freeman, P. M.

    2015-12-01

    The southern mid-latitude 5-km diameter Moni Crater (47S, 18.5E) in Noachis Terra is typical of many small craters of this latitude, containing both gullies on its walls and arcuate ridges on its floor. Interpreted by Howard (2003) and others as remnant terminal moraines, these ridges are located at the distal margins of the gullies' debris aprons, suggesting a possible association in their formation. Our results suggest that these arcuate ridges might result from the downslope movement of ice-rich deposits that pushed pre-existing ice-rich crater floor deposits into a moraine-like ridge. The pre-existing floor deposits can be interpreted to be a form of sublimated Concentric Crater Fill (CCF), which would have been among the first ice deposits to erode the Moni Crater walls. If we assume the arcuate ridges to be glacial moraines, then we can also assume the same processes that elevated the ridges also provided melt water to form the gullies. There is evidence that water and ice deposit-related processes incised the gully headwalls, exposing bedrock, plucking boulders, and initiating fractures, through ice-wedging or surface abrasion. HiRISE images (~25cm/pixel) show shallow gullies extending several tens of meters beyond the crater rim, exploiting possible fractures or lineation in the rock. Melt water from these ice deposits, or snow melt, is a potential gully formation mechanism that would be consistent with the shallow runoff-like drainage morphology extending above the gully alcoves and beyond the crater rim. An initial phase of rapid melt water flows would also explain the wider degraded remnant channels we see on the crater slopes. The more gradual melting of ice frozen around headwall rocks could explain a secondary phase of melt water flows that form the more-recent channels.

  1. Surficial geology of the Chicxulub impact crater, Yucatan, Mexico

    Science.gov (United States)

    Pope, Kevin O.; Ocampo, Adriana C.; Duller, Charles E.

    1993-01-01

    The Chicxulub impact crater in northwestern Yucatan, Mexico is the primary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kilometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 +/- 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limestones outside. The boundary forms a barrier to lateral ground water migration, resulting in increased flows, dissolution, and collapse thus forming the cenotes. The subsurface geology indicates that the fracturing that created the Cenote Ring is related to slumping in the rim of the buried crater, differential thicknesses in the rocks overlying the crater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's center, and the associated faults, fractures, and stratigraphy indicate that the crater may be approximately 240 km in diameter.

  2. Projectile remnants in central peaks of lunar impact craters

    Science.gov (United States)

    Yue, Z.; Johnson, B. C.; Minton, D. A.; Melosh, H. J.; di, K.; Hu, W.; Liu, Y.

    2013-06-01

    The projectiles responsible for the formation of large impact craters are often assumed to melt or vaporize during the impact, so that only geochemical traces or small fragments remain in the final crater. In high-speed oblique impacts, some projectile material may survive, but this material is scattered far down-range from the impact site. Unusual minerals, such as magnesium-rich spinel and olivine, observed in the central peaks of many lunar craters are therefore attributed to the excavation of layers below the lunar surface. Yet these minerals are abundant in many asteroids, meteorites and chondrules. Here we use a numerical model to simulate the formation of impact craters and to trace the fate of the projectile material. We find that for vertical impact velocities below about 12kms-1, the projectile may both survive the impact and be swept back into the central peak of the final crater as it collapses, although it would be fragmented and strongly deformed. We conclude that some unusual minerals observed in the central peaks of many lunar impact craters could be exogenic in origin and may not be indigenous to the Moon.

  3. Map showing the Elko crater field, Elko County, Nevada

    Science.gov (United States)

    Ketner, Keith B.; Roddy, David J.

    1980-01-01

    The Elko crater field consists of two arrays of rimmed craters in the valleys of Dorsey, Susie, and McClellan Creeks, 30 to 50 km north of Elko, Nevada. In the principal array, more the 165 craters are scattered irregularly in an area 3 km wide and 20 km long. Most of the the craters are circular but some, formed by overlap, are oval or irregular. They range from 5 m to 250 m in diameter and the relief of the largest ones, from the sedimentary floor of the cater to the top of the rim, is at least 6 m. The surficial material of the rims is principally gravel similar to that in the surrounding terrane. The surficial material inside the craters is primarily silt, probably blown in by the wind, and pebbles, apparently washed in from the rims. There is also a later of volcanic ash at a depth of about 2 m. This ash was identified by its physical and mineralogical composition as the Mazama ash (R. E. Wilcox, oral commun., 1976), a ±6600 year old ash bed also present in the alluvium of Dorsey and Susie Creeks. The craters are presently interpreted as having been formed by a meteor shower although no meteor material has been discovered. Investigation is continuing.

  4. Impact cratering as a major process in planet formation: Projectile identification of meteorite craters

    Science.gov (United States)

    Schmidt, G.; Kratz, K.

    2009-12-01

    Ancient surfaces of solid planets show that impact cratering is a major process in planet formation. Understanding origin and influence of impactors on the chemical composition of planets (core, mantle and crust) it is important to know the relative abundances of highly siderophile elements (Os, Ir, Ru, Pt, Rh, Pd) in the silicate mantle and crust of planets and meteorites. Refractory highly siderophile elements, such as Os and Ir, are abundant in most meteorites but depleted in crustal rocks (low target/meteorite ratios) and thus the most reliable elements for projectile identification. However, target/meteorite ratios are high if target rocks consist of mantle rocks. In such cases elements are enriched in impactites due to relatively high abundances (ng/g level) in target rocks to make the identification of projectile types difficult (e.g., Gardnos impact structure in Norway). The Ru/Ir ratio is the most reliable key ratio that rules out Earth primitive upper mantle (PUM) derived refractory highly siderophile element components in impactites. The well established Ru/Ir ratio of the Earth mantle of 2.0 ± 0.1 (e.g. Schmidt and Kratz 2004) is significantly above the chondritic ratios varying from 1.4 to 1.6. On Earth Rh/Ir, Ru/Ir, Pd/Ir, and Pt/Os derived from PUM match the ratios of group IV irons with fractionated trace element patterns. The question raise if HSE in mantle rocks are added to the accreting Earth by a late bombardment of pre-differentiated objects or the cores of these objects (magmatic iron meteorites as remnants of the first planetesimals, e.g. Kleine et al. 2009) or some unsampled inner solar system materials from the Mercury-Venus formation region, not sampled through meteorite collections (Schmidt 2009). The PGE and Ni systematics of the upper continental crust (UCC) closely resembles group IIIAB iron meteorites with highly fractionated refractory trace element patterns, pallasites, and the evolved suite of Martian meteorites (representing

  5. 100 New Impact Crater Sites Found on Mars

    Science.gov (United States)

    Kennedy, M. R.; Malin, M. C.

    2009-12-01

    Recent observations constrain the formation of 100 new impact sites on Mars over the past decade; 19 of these were found using the Mars Global Surveyor Mars Orbiter Camera (MOC), and the other 81 have been identified since 2006 using the Mars Reconnaissance Orbiter Context Camera (CTX). Every 6 meter/pixel CTX image is examined upon receipt and, where they overlap images of 0.3-240 m/pixel scale acquired by the same or other Mars-orbiting spacecraft, we look for features that may have changed. New impact sites are initially identified by the presence of a new dark spot or cluster of dark spots in a CTX image. Such spots may be new impact craters, or result from the effect of impact blasts on the dusty surface. In some (generally rare) cases, the crater is sufficiently large to be resolved in the CTX image. In most cases, however, the crater(s) cannot be seen. These are tentatively designated as “candidate” new impact sites, and the CTX team then creates an opportunity for the MRO spacecraft to point its cameras off-nadir and requests that the High Resolution Imaging Science Experiment (HiRISE) team obtain an image of ~0.3 m/pixel to confirm whether a crater or crater cluster is present. It is clear even from cursory examination that the CTX observations are areographically biased to dusty, higher albedo areas on Mars. All but 3 of the 100 new impact sites occur on surfaces with Lambert albedo values in excess of 23.5%. Our initial study of MOC images greatly benefited from the initial global observations made in one month in 1999, creating a baseline date from which we could start counting new craters. The global coverage by MRO Mars Color Imager is more than a factor of 4 poorer in resolution than the MOC Wide Angle camera and does not offer the opportunity for global analysis. Instead, we must rely on partial global coverage and global coverage that has taken years to accumulate; thus we can only treat impact rates statistically. We subdivide the total data

  6. Complete mitochondrial genome and phylogeny of Pleistocene mammoth Mammuthus primigenius.

    Directory of Open Access Journals (Sweden)

    Evgeny I Rogaev

    2006-03-01

    Full Text Available Phylogenetic relationships between the extinct woolly mammoth (Mammuthus primigenius, and the Asian (Elephas maximus and African savanna (Loxodonta africana elephants remain unresolved. Here, we report the sequence of the complete mitochondrial genome (16,842 base pairs of a woolly mammoth extracted from permafrost-preserved remains from the Pleistocene epoch--the oldest mitochondrial genome sequence determined to date. We demonstrate that well-preserved mitochondrial genome fragments, as long as approximately 1,600-1700 base pairs, can be retrieved from pre-Holocene remains of an extinct species. Phylogenetic reconstruction of the Elephantinae clade suggests that M. primigenius and E. maximus are sister species that diverged soon after their common ancestor split from the L. africana lineage. Low nucleotide diversity found between independently determined mitochondrial genomic sequences of woolly mammoths separated geographically and in time suggests that north-eastern Siberia was occupied by a relatively homogeneous population of M. primigenius throughout the late Pleistocene.

  7. Macroecological analyses support an overkill scenario for late Pleistocene extinctions

    Directory of Open Access Journals (Sweden)

    J. A. F. Diniz-Filho

    Full Text Available The extinction of megafauna at the end of Pleistocene has been traditionally explained by environmental changes or overexploitation by human hunting (overkill. Despite difficulties in choosing between these alternative (and not mutually exclusive scenarios, the plausibility of the overkill hypothesis can be established by ecological models of predator-prey interactions. In this paper, I have developed a macroecological model for the overkill hypothesis, in which prey population dynamic parameters, including abundance, geographic extent, and food supply for hunters, were derived from empirical allometric relationships with body mass. The last output correctly predicts the final destiny (survival or extinction for 73% of the species considered, a value only slightly smaller than those obtained by more complex models based on detailed archaeological and ecological data for each species. This illustrates the high selectivity of Pleistocene extinction in relation to body mass and confers more plausibility on the overkill scenario.

  8. Mid Pleistocene foraminiferal mass extinction coupled with phytoplankton evolution

    Science.gov (United States)

    Kender, Sev; McClymont, Erin L.; Elmore, Aurora C.; Emanuele, Dario; Leng, Melanie J.; Elderfield, Henry

    2016-06-01

    Understanding the interaction between climate and biotic evolution is crucial for deciphering the sensitivity of life. An enigmatic mass extinction occurred in the deep oceans during the Mid Pleistocene, with a loss of over 100 species (20%) of sea floor calcareous foraminifera. An evolutionarily conservative group, benthic foraminifera often comprise >50% of eukaryote biomass on the deep-ocean floor. Here we test extinction hypotheses (temperature, corrosiveness and productivity) in the Tasman Sea, using geochemistry and micropalaeontology, and find evidence from several globally distributed sites that the extinction was caused by a change in phytoplankton food source. Coccolithophore evolution may have enhanced the seasonal `bloom' nature of primary productivity and fundamentally shifted it towards a more intra-annually variable state at ~0.8 Ma. Our results highlight intra-annual variability as a potential new consideration for Mid Pleistocene global biogeochemical climate models, and imply that deep-sea biota may be sensitive to future changes in productivity.

  9. Martian Cratering 10. Progress in use of crater counts to interpret geological processes: Examples from two debris aprons

    Science.gov (United States)

    Hartmann, William K.; Werner, Stephanie C.

    2010-06-01

    Recent controversies about systems of crater-count dating have been largely resolved, and with continuing refinements, crater counts will offer a fundamental geological tool to interpret not only ages, but also the nature of geological processes altering the surface of Mars. As an example of the latter technique, we present data on two debris aprons east of Hellas. The aprons show much shorter survival times of small craters than do the nearby contiguous plains. The order-of-magnitude depths of layers involved in the loss process can be judged from the depths of the affected craters. We infer that ice-rich layers in the top tens of meters of both aprons have lost crater topography within the last few 10 8 yr, probably due to flow or sublimation of ice-rich materials. Mantling by ice-rich deposits, associated with climate change cycles of obliquity change, has probably also affected both the aprons and the plains. The crater-count tool thus adds chronological and vertical dimensional information to purely morphological studies.

  10. Book review: From the Pleistocene to the Holocene

    Directory of Open Access Journals (Sweden)

    John Edward Dockall

    2015-09-01

    Full Text Available From the Pleistocene to the Holocene, edited by Bousman and Vierra, resets our thinking on the pace and overall patterns of transitions in North America at this time.  This book brings together detailed archaeological syntheses from multiple geographic regions.  The result is a volume that stands alone as a new interpretative framework for cultural change during the transition from the last Ice Age to the beginning of the Holocene. 

  11. Early Pleistocene aquatic resource use in the Turkana Basin.

    Science.gov (United States)

    Archer, Will; Braun, David R; Harris, Jack W K; McCoy, Jack T; Richmond, Brian G

    2014-12-01

    Evidence for the acquisition of nutritionally dense food resources by early Pleistocene hominins has implications for both hominin biology and behavior. Aquatic fauna may have comprised a source of highly nutritious resources to hominins in the Turkana Basin at ∼1.95 Ma. Here we employ multiple datasets to examine the issue of aquatic resource use in the early Pleistocene. This study focuses on four components of aquatic faunal assemblages (1) taxonomic diversity, (2) skeletal element proportion, (3) bone fragmentation and (4) bone surface modification. These components are used to identify associations between early Pleistocene aquatic remains and hominin behavior at the site of FwJj20 in the Koobi Fora Fm. (Kenya). We focus on two dominant aquatic species: catfish and turtles. Further we suggest that data on aquatic resource availability as well as ethnographic examples of aquatic resource use complement our observations on the archaeological remains from FwJj20. Aquatic food items provided hominins with a valuable nutritional alternative to an exclusively terrestrial resource base. We argue that specific advantages afforded by an aquatic alternative to terrestrial resources include (1) a probable reduction in required investment of energy relative to economic return in the form of nutritionally dense food items, (2) a decrease in the technological costs of resource acquisition, and (3) a reduced level of inter-specific competition associated with carcass access and an associated reduction of predation risk relative to terrestrial sources of food. The combined evidence from FwJj20 suggests that aquatic resources may have played a substantial role in early Pleistocene diets and these resources may have been overlooked in previous interpretations of hominin behavior.

  12. SBC Internal Lamp P-flat Monitoring

    Science.gov (United States)

    Avila, R. J.; Chiaberge, M.; Bohlin, R.

    2016-03-01

    We report on a Cycle 23 calibration program to monitor the status of the SBC P-flat. We find random pixel to pixel changes to be small, with only 2% of pixels having changed by more than 3. There are coherent changes that we measure to be above the poisson errors, in some regions as high as 4% peak to peak. We recommend that the ACS team obtain new observations in order to create a new P-flat. We also measured the degradation of the deuterium lamp used to create internal flats. The brightness of the lamp is currently 65% of its initial level, the degradation being dependent on lifetime usage.

  13. Lunar cold spots and crater production on the Moon

    Science.gov (United States)

    Williams, Jean-Pierre; Bandfield, Joshua

    2016-10-01

    A new class of small, fresh impact craters has been recently identified on the Moon through the systematic mapping of lunar surface temperatures by the Diviner Lunar Radiometer instrument aboard the Lunar Reconnaissance Orbiter [1]. These craters are distinguished by anomalously low nighttime temperatures at distances ~10–100 crater radii. This thermal behavior indicates that impacts modify the surrounding regolith surfaces making them highly insulating with little evidence for either significant deposition or erosion of surface material [2]. These thermophysically distinct surfaces, or "cold spots", appear to be common to all recent impacts and provide a means of uniquely identifying the most recent impact craters on the Moon. We have conducted a survey of the crater population associated with cold spots. Comparison with existing crater chronology models [e.g., 3] constrains the retention-age of the cold spots to ~200,000 yr with a size-frequency distribution (SFD) slope that is consistent with the modeled production function. This implies the rate at which cold spots fade to background levels is independent of initial cold spot size and that the SFD of crater production in the last 200 ka is similar to the long-term average used to establish modeled production functions, though the rate of cratering may have varied [4]. In addition, we observe a longitudinal heterogeneity in cold spot crater density that is consistent with that predicted to occur as a result of the Moon's synchronous rotation [5] and has been observed in the rayed crater population [6], with the cold spot density at the apex of motion (90°W) nearly twice that observed at the antapex (90°E).[1] Bandfield, J., et al. (2011) JGR 116, E00H02. [2] Bandfield, J., et al. (2014) Icarus, 231, 221-231. [3] Neukum, G., et al. (2001) SSR 96, 55–86. [4] Mazrouei, S. et al. (2015) LPSC 46, 2331. [5] Le Fleuvre, M., and Wieczorek, M. A. (2011) Icarus 214, 1-20. [6] Morota, T. and Furumoto, M. (2002) EPSL

  14. The general indications of an impact crater using integrated geophysical methods

    Science.gov (United States)

    Kiu, Y. C.; Rosli, S.; Azwin, I. N.; Mokhtar, S.

    2017-07-01

    The study area located at the tropical region which may induced a deeply eroded structure over a complex subsurface. Therefore, the geophysical methods were applied to estimate crater dimension and study the signature of an impact crater. Commonly, an impact crater is characterized with the aid of potential field method which can cover larger area and cost effective. The application of seismic measurements is to complement the potential fields' method for better data interpretation. This study emphasized on utilizing integrated study of geophysical methods which include potential field method (ground magnetic) and seismic for bedrock delineation on impact crater structure characterization. The results induced a positive signs of impact crater which associate with a few indications on crater type and its structures. The integration of ground magnetic and seismic refraction reveal the Bukit Bunuh impact crater is a complex crater. Both of the geophysical methods agreed with the notable size impact crater of 5 km with central uplift at the Bukit Bunuh area.

  15. Craters on Earth, Moon, and Mars - Multivariate classification and mode of origin

    Science.gov (United States)

    Pike, R. J.

    1974-01-01

    Testing extraterrestrial craters and candidate terrestrial analogs for morphologic similitude is treated as a problem in numerical taxonomy. According to a principal-components solution and a cluster analysis, 402 representative craters on the Earth, the Moon, and Mars divide into two major classes of contrasting shapes and modes of origin. Craters of net accumulation of material (cratered lunar domes, Martian calderas, and all terrestrial volcanoes except maars and tuff rings) group apart from craters of excavation (terrestrial meteorite impact and experimental explosion craters, typical Martian craters, and all other lunar craters). Maars and tuff rings belong to neither group but are transitional. The classification criteria are four independent attributes of topographic geometry derived from seven descriptive variables by the principal-components transformation. Morphometric differences between crater bowl and raised rim constitute the strongest of the four components.

  16. Combined obliquity and precession pacing of late Pleistocene deglaciations.

    Science.gov (United States)

    Huybers, Peter

    2011-12-08

    Milankovitch proposed that Earth resides in an interglacial state when its spin axis both tilts to a high obliquity and precesses to align the Northern Hemisphere summer with Earth's nearest approach to the Sun. This general concept has been elaborated into hypotheses that precession, obliquity or combinations of both could pace deglaciations during the late Pleistocene. Earlier tests have shown that obliquity paces the late Pleistocene glacial cycles but have been inconclusive with regard to precession, whose shorter period of about 20,000 years makes phasing more sensitive to timing errors. No quantitative test has provided firm evidence for a dual effect. Here I show that both obliquity and precession pace late Pleistocene glacial cycles. Deficiencies in time control that have long stymied efforts to establish orbital effects on deglaciation are overcome using a new statistical test that focuses on maxima in orbital forcing. The results are fully consistent with Milankovitch's proposal but also admit the possibility that long Southern Hemisphere summers contribute to deglaciation.

  17. Obliquity pacing of the late Pleistocene glacial terminations.

    Science.gov (United States)

    Huybers, Peter; Wunsch, Carl

    2005-03-24

    The 100,000-year timescale in the glacial/interglacial cycles of the late Pleistocene epoch (the past approximately 700,000 years) is commonly attributed to control by variations in the Earth's orbit. This hypothesis has inspired models that depend on the Earth's obliquity (approximately 40,000 yr; approximately 40 kyr), orbital eccentricity (approximately 100 kyr) and precessional (approximately 20 kyr) fluctuations, with the emphasis usually on eccentricity and precessional forcing. According to a contrasting hypothesis, the glacial cycles arise primarily because of random internal climate variability. Taking these two perspectives together, there are currently more than thirty different models of the seven late-Pleistocene glacial cycles. Here we present a statistical test of the orbital forcing hypothesis, focusing on the rapid deglaciation events known as terminations. According to our analysis, the null hypothesis that glacial terminations are independent of obliquity can be rejected at the 5% significance level, whereas the corresponding null hypotheses for eccentricity and precession cannot be rejected. The simplest inference consistent with the test results is that the ice sheets terminated every second or third obliquity cycle at times of high obliquity, similar to the original proposal by Milankovitch. We also present simple stochastic and deterministic models that describe the timing of the late-Pleistocene glacial terminations purely in terms of obliquity forcing.

  18. Mediterranean Outflow Water variability during the Early Pleistocene

    Science.gov (United States)

    Kaboth, Stefanie; Grunert, Patrick; Lourens, Lucas

    2017-08-01

    Gaining insights into the evolution of Mediterranean Outflow Water (MOW) during the Early Pleistocene has been so far hampered by the lack of available palaeoclimatic archives. Here we present the first benthic foraminifera stable oxygen and carbon isotope records and grain-size data from IODP Expedition 339 Site U1389 presently located within the upper core of the MOW in the Gulf of Cadiz for the time interval between 2.6 and 1.8 Ma. A comparison with an intermediate water mass record from the Mediterranean Sea strongly suggest an active MOW supplying Site U1389 on glacial-interglacial timescales during the Early Pleistocene. We also find indication that the increasing presence of MOW in the Gulf of Cadiz during the investigated time interval aligns with the progressive northward protrusion of Mediterranean sourced intermediate water masses into the North Atlantic, possibly modulating the intensification of the North Atlantic Meridional Overturning Circulation at the same time. Additionally, our results suggest that MOW flow strength was already governed by precession and semi-precession cyclicity during the Early Pleistocene against the background of glacial-interglacial variability.

  19. Early Pleistocene occurrence of Acheulian technology in North China

    Science.gov (United States)

    Li, Xingwen; Ao, Hong; Dekkers, Mark J.; Roberts, Andrew P.; Zhang, Peng; Lin, Shan; Huang, Weiwen; Hou, Yamei; Zhang, Weihua; An, Zhisheng

    2017-01-01

    Acheulian tools with their associated level of cognizance heralded a major threshold in the evolution of hominin technology, culture and behavior. Thus, unraveling occurrence ages of Acheulian technology across different regions worldwide constitutes a key aspect of understanding the archeology of early human evolution. Here we present a magneto-cyclochronology for the Acheulian assemblage from Sanmenxia Basin, Loess Plateau, North China. Our results place a sequence of stable normal and reversed paleomagnetic polarities within a regional lithostratigraphic context. The Acheulian assemblage is dated to be older than the Matuyama-Brunhes boundary at 0.78 Ma, and is found in strata that are probably equivalent to a weak paleosol subunit within loess layer L9 in the Chinese loess-paleosol sequence, which corresponds to marine isotope stage (MIS) 23, a relatively subdued interglacial period with age range of ∼0.89-0.92 Ma. This age of ∼0.9 Ma implies that Acheulian stone tools were unambiguously present in North China during the Early Pleistocene. It distinctly enlarges the geographic distribution of Acheulian technology and brings its occurrence in North China back into the Early Pleistocene, which is contemporaneous with its first emergence in Europe. Combined with other archeological records, the larger area over which Acheulian technology existed in East Asia during the terminal Early Pleistocene has important implications for understanding early human occupation of North China.

  20. Flatness Control Using Roll Coolant Based on Predicted Flatness Variation in Cold Rolling Mills

    Science.gov (United States)

    Dohmae, Yukihiro; Okamura, Yoshihide

    Flatness control for cold rolling mills is one of the important technologies for improving of product quality and productivity. In particular, poor flatness leads to strip tearing in the extreme case and, moreover, it significantly reduces productivity. Therefore, various flatness control system has been developed. The main actuators for flatness control are classified into two types; one is mechanical equipment such as roll bender, the other is roll coolant, which controls thermal expansion of roll. Flatness variation such as center buckle or edge wave is mainly controlled by mechanical actuator which has high response characteristics. On another front, flatness variation of local zone can be controlled by roll coolant although one's response is lower than the response of mechanical actuator. For accomplishing good flatness accuracy in cold rolling mills, it is important to improve the performance of coolant control moreover. In this paper, a new coolant control method based on flatness variation model is described. In proposed method, the state of coolant spray on or off is selected to minimize the flatness deviation by using predicted flatness variation. The effectiveness of developed system has been demonstrated by application in actual plant.

  1. Chicxulub Impact Crater and Yucatan Carbonate Platform - PEMEX Oil Exploratory Wells Revisited

    Science.gov (United States)

    Pérez-Drago, G.; Gutierrez-Cirlos, A. G.; Pérez-Cruz, L.; Urrutia-Fucugauchi, J.

    2008-12-01

    Geophysical oil exploration surveys carried out by PEMEX in the 1940's revealed occurrence of an anomalous pattern of semi-circular concentric gravity anomalies. The Bouguer gravity anomalies covered an extensive area over the flat carbonate platform in the northwestern Yucatan Peninsula; strong density contrasts were suggestive of a buried igneous complex or basement uplift beneath the carbonates, which was referred as the Chicxulub structure. The exploration program carried out afterwards included a drilling program, starting with Chicxulub-1 well in 1952 and comprising eight deep boreholes through the 1970s. An aeromagnetic survey in late 1970's showed high amplitude anomalies in the gravity anomaly central sector. Thus, research showing Chicxulub as a large complex impact crater formed at the K/T boundary was built on the PEMEX decades-long exploration program. Despite frequent reference to PEMEX information and samples, original data and cores have not been openly available for detailed evaluation and integration with results from recent investigations. Core samples largely remain to be analyzed and interpreted in the context of recent marine, aerial and terrestrial geophysical surveys and the drilling/coring projects of UNAM and ICDP. In this presentation we report on the stratigraphy and paleontological data for PEMEX wells: Chicxulub- 1 (1582m), Sacapuc-1 (1530m), Yucatan-6 (1631m), Ticul-1 (3575m) Yucatan-4 (2398m), Yucatan-2 (3474m), Yucatan-5A (3003m) and Yucatan-1 (3221m). These wells remain the deepest drilled in Chicxulub, providing samples of impact lithologies, carbonate sequences and basement, which give information on post- and pre-impact stratigraphy and crystalline basement. We concentrate on stratigraphic columns, lateral correlations and integration with UNAM and ICDP borehole data. Current plans for deep drilling in Chicxulub crater target the peak ring and central sector, with offshore and onshore boreholes proposed to the IODP and ICDP

  2. B^F Theory and Flat Spacetimes

    CERN Document Server

    Waelbroeck, Henri

    2009-01-01

    We propose a reduced constrained Hamiltonian formalism for the exactly soluble $B \\wedge F$ theory of flat connections and closed two-forms over manifolds with topology $\\Sigma^3 \\times (0,1)$. The reduced phase space variables are the holonomies of a flat connection for loops which form a basis of the first homotopy group $\\pi_1(\\Sigma^3)$, and elements of the second cohomology group of $\\Sigma^3$ with value in the Lie algebra $L(G)$. When $G=SO(3,1)$, and if the two-form can be expressed as $B= e\\wedge e$, for some vierbein field $e$, then the variables represent a flat spacetime. This is not always possible: We show that the solutions of the theory generally represent spacetimes with ``global torsion''. We describe the dynamical evolution of spacetimes with and without global torsion, and classify the flat spacetimes which admit a locally homogeneous foliation, following Thurston's classification of geometric structures.

  3. On certain geodesic conjugacies of flat cylinders

    Indian Academy of Sciences (India)

    C S ARAVINDA; H A GURURAJA

    2017-06-01

    We prove $C^0$-conjugacy rigidity of any flat cylinder among two different classes of metrics on the cylinder, namely among the class of rotationally symmetric metrics and among the class of metrics without conjugate points.

  4. Fuzzy Neural Model for Flatness Pattern Recognition

    Institute of Scientific and Technical Information of China (English)

    JIA Chun-yu; SHAN Xiu-ying; LIU Hong-min; NIU Zhao-ping

    2008-01-01

    For the problems occurring in a least square method model,a fuzzy model,and a neural network model for flatness pattern recognition,a fuzzy neural network model for flatness pattern recognition with only three-input and three-output signals was proposed with Legendre orthodoxy polynomial as basic pattern,based on fuzzy logic expert experiential knowledge and genetic-BP hybrid optimization algorithm.The model not only had definite physical meanings in its inner nodes,but also had strong self-adaptability,anti-interference ability,high recognition precision,and high velocity,thereby meeting the demand of high-precision flatness control for cold strip mill and providing a convenient,practical,and novel method for flatness pattern recognition.

  5. Improved ferrous shielding for flat cables

    Science.gov (United States)

    Drechsler, R. J.

    1969-01-01

    To improve shielding of flat multicore cables, a thin, seamless ferrous shield around all cores optimizes low frequency magnetic shielding. Such shielding is covered with an ultrathin seamless coat of highly conductive nonferrous material.

  6. Pleistocene and Holocene geomorphological development in the Algarve, southern Portugal

    Science.gov (United States)

    Chester, David K.

    2012-06-01

    A detailed chronological framework for Pleistocene and Holocene geomorphology and landscape evolution in the Algarve is proposed. With regards to the Pleistocene, attention has focused on the origin, dating and stratigraphy of the Ludo Formation. Subsuming the classifications of earlier writers, it is now proposed that during the Pliocene a marine transgression occurred across a tectonically controlled basin that was constrained by the mountains of the Algarve interior to the north. Fluvial sands were then deposited in a regressive phase during the late Pliocene/early Pleistocene, while braided streams operating under semi-arid conditions subsequently laid down sands and gravels in the middle and upper Pleistocene. Lying unconformably over the Ludo Formation is an alluvial deposit (Odiáxere gravels and Loulé sands) of late Pleistocene/early Holocene date that is found within the river valleys of the Algarve. In the early-Holocene (ca.10, 000-ca.7000 BP) and early late-Holocene (ca.5000-ca.3000 BP), the situation in the Algarve was one of climatic amelioration (i.e., warmer and wetter conditions), rising sea levels, vegetation colonization, soil development and towards the end of this period trenching of the Odiáxere gravels and Loulé sands. From ca.3000 BP evidence is abundant that humans became important geomorphological agents either acting on their own or in combination with climatic factors. From around 5000 BP, conditions became dryer and, between ca.3000 BP and ca.700 BP, clearance of land by pre-Roman, Roman, and especially Islamic agricultural settlers caused widespread erosion and the deposition of extensive spreads of topsoil dominated sediment within river valleys (i.e., the Holocene terrace) and in coastal estuaries. A period followed up to 1900 CE when agricultural practices were less damaging to the soil, erosion was reduced and the Holocene terrace - together with coastal and estuarine deposits - was incised. In the past century and under

  7. Plio-Pleistocene aardvarks (Mammalia, Tubulidentata from East Africa

    Directory of Open Access Journals (Sweden)

    T. Lehmann

    2008-08-01

    Full Text Available The Tubulidentata are unique among mammals for being the only order represented nowadays by a single living species, Orycteropus afer: the aardvark. Nevertheless, it is one of the least studied mammalian orders. Aardvarks are currently distributed all over sub-Saharan Africa, but the fossil record extends their spatial range to Europe and Asia. The earliest known Tubulidentata are ca. 20 million years old. About 14 species and three to four genera have been recognised so far, but since the late Pliocene, aardvarks have only been represented by a single genus and are restricted to Africa. The extant aardvark is the only species of Tubulidentata with a large distribution area, i.e. the African continent. There are three known Plio-Pleistocene African species of aardvark: Orycteropus afer (Pallas, 1766, O. crassidens MacInnes, 1956, and O. djourabensis Lehmann et al., 2004. Fossils of these species have been discovered in North-Africa, Kenya, and Chad respectively. The present study is focused on the aardvark material found in the Plio-Pleistocene of East Africa (Ethiopia, Kenya. New specimens from Asa Issie (Ethiopia and East Turkana (Kenya are described, and published ones are re-examined in the light of the latest discoveries. This study demonstrates that Kenyan specimens identified as O. crassidens are in fact representatives of the Chadian O. djourabensis. Moreover, additional material from Ethiopia and Kenya shows a close relationship with the latter species too. The presence of specimens of O. djourabensis in Chad and in Kenya during the Plio-Pleistocene implies that this taxon is the oldest-known species of aardvark to have experienced a continental dispersal. It also shows that Tubulidentates were able to cross Africa from east-west during Plio-Pleistocene times, despite the presence of the Rift Valley. It is however not possible to infer the centre of origin of O. djourabensis. Finally, this study suggests that two species of aardvark

  8. High performance flat plate solar collector

    Science.gov (United States)

    Lansing, F. L.; Reynolds, R.

    1976-01-01

    The potential use of porous construction is presented to achieve efficient heat removal from a power producing solid and is applied to solar air heaters. Analytical solutions are given for the temperature distribution within a gas-cooled porous flat plate having its surface exposed to the sun's energy. The extracted thermal energy is calculated for two different types of plate transparency. Results show the great improvement in performance obtained with porous flat plate collectors as compared with analogous nonporous types.

  9. Evolution of Circular Polarization Ratio (CPR) Profiles of Kilometer-scale Craters on the Lunar Maria

    Science.gov (United States)

    King, I. R.; Fassett, C. I.; Thomson, B. J.; Minton, D. A.; Watters, W. A.

    2017-01-01

    When sufficiently large impact craters form on the Moon, rocks and unweathered materials are excavated from beneath the regolith and deposited into their blocky ejecta. This enhances the rockiness and roughness of the proximal ejecta surrounding fresh impact craters. The interior of fresh craters are typically also rough, due to blocks, breccia, and impact melt. Thus, both the interior and proximal ejecta of fresh craters are usually radar bright and have high circular polarization ratios (CPR). Beyond the proximal ejecta, radar-dark halos are observed around some fresh craters, suggesting that distal ejecta is finer-grained than background regolith. The radar signatures of craters fade with time as the regolith grows.

  10. Acid Sulfate Alteration in Gusev Crater, Mars

    Science.gov (United States)

    Morris, R. V.; Ming, D. W.; Catalano, J. G.

    2016-01-01

    The Mars Exploration Rover (MER) Spirit landed on the Gusev Crater plains west of the Columbia Hills in January, 2004, during the Martian summer (sol 0; sol = 1 Martian day = 24 hr 40 min). Spirit explored the Columbia Hills of Gusev Crater in the vicinity of Home Plate at the onset on its second winter (sol approximately 900) until the onset of its fourth winter (sol approximately 2170). At that time, Spirit became mired in a deposit of fined-grained and sulfate-rich soil with dust-covered solar panels and unfavorable pointing of the solar arrays toward the sun. Spirit has not communicated with the Earth since sol 2210 (January, 2011). Like its twin rover Opportunity, which landed on the opposite side of Mars at Meridiani Planum, Spirit has an Alpha Particle X-Ray Spectrometer (APXS) instrument for chemical analyses and a Moessbauer spectrometer (MB) for measurement of iron redox state, mineralogical speciation, and quantitative distribution among oxidation (Fe(3+)/sigma Fe) and coordination (octahedral versus tetrahedral) states and mineralogical speciation (e.g., olivine, pyroxene, ilmenite, carbonate, and sulfate). The concentration of SO3 in Gusev rocks and soils varies from approximately 1 to approximately 34 wt%. Because the APXS instrument does not detect low atomic number elements (e.g., H and C), major-element oxide concentrations are normalized to sum to 100 wt%, i.e., contributions of H2O, CO2, NO2, etc. to the bulk composition care not considered. The majority of Gusev samples have approximately 6 plus or minus 5 wt% SO3, but there is a group of samples with high SO3 concentrations (approximately 30 wt%) and high total iron concentrations (approximately 20 wt%). There is also a group with low total Fe and SO3 concentrations that is also characterized by high SiO2 concentrations (greater than 70 wt%). The trend labeled "Basaltic Soil" is interpreted as mixtures in variable proportions between unaltered igneous material and oxidized and SO3-rich basaltic

  11. Persistent Aeolian Activity at Endeavour Crater, Mars

    Science.gov (United States)

    Chojnacki, M.; Michaels, T. I.; Fenton, L. K.

    2013-12-01

    Long-term monitoring of sites that are known to have active dunes and ripples is generally limited to 3 Mars-Years (MY). Here, we discuss new results of dune activity and albedo change in Endeavour crater (EC), Meridiani Planum (MP) that record eight MY of aeolian activity. MP dune fields often show large yearly variations in albedo; EC darkened by ~12% in TES albedo between MY 24 and 26 (from 0.14 to 0.12). THEMIS VIS albedo of dunes did not change significantly from MY 26 to 29, but did decrease notably (~15 %) in MY 30. These darkening events are most likely related to aeolian-driven dust cleaning (e.g., removal by saltating sand, dust devils). For example, the Opportunity rover (poised on the western rim of EC) observed evidence for a MY 31 dune field dust-clearing event. HiRISE monitoring of MP has shown it be one of the most active regions outside of north polar latitudes. Paired images of western EC taken 3 MY apart show clear evidence for dune modification that include: ripple migration, change in dune perimeters, exposure of previously buried light-toned rock, and/or burial of rock by sand (Fig. 1a-1b). Dune slip face movement is evident for most dunes, where crests and aprons advanced (2-7 m) in the downwind direction (to the SSE) at rates of 0.7-2.3 m per MY. Small dome dunes in the eastern EC were found to have a large degree of aeolian activity (e.g., deflation and/or translation) by an earlier study that used MGS-MRO images (MY 24-30). New MY 31 images validate earlier observations, showing clear evidence for bedform deflation where dunes often occupy less area (~50%) than in earlier MY 29 images (Fig. 1c-1d). Areal removal rates are on par with earlier estimates. Bedform modification and sand streamer orientation appear to be caused by a NNW wind regime, consistent with earlier observations, mesoscale modeling, and the transport direction of barchans to the west. Dunes in EC are now known to be periodically (consistently?) active from over a decade

  12. Pleistocene and Holocene Iberian flora: a complete picture and review

    Science.gov (United States)

    González Sampériz, Penélope

    2010-05-01

    A detailed analysis of the location and composition of Iberian vegetation types during the whole Pleistocene and Holocene periods shows a complex patched landscape with persistence of different types of ecosystems, even during glacial times. In addition, recent, high-resolution palaeoecological records are changing the traditional picture of post-glacial vegetation succession in the Iberian Peninsula. The main available charcoal and pollen sequences include, coniferous and deciduous forest, steppes, shrublands, savannahs and glacial refugia during the Pleistocene for Meso-thermophytes (phytodiversity reservoirs), in different proportions. This panorama suggests an environmental complexity that relates biotic responses to climate changes forced by Milankovitch cycles, suborbital forcings and by the latitudinal and physiographic particularities of the Iberian Peninsula. Thus, many factors are critical in the course of vegetational developments and strong regional differences are observed since the Early Pleistocene. Currently, the flora of Iberia is located in two biogeographical/climatic regions: the Eurosiberian and the Mediterranean. The first one includes northern and northwestern areas of the peninsula, where post-glacial responses of vegetation are very similar to Central Europe, although with some particularities due to its proximity to both the Atlantic Ocean and the Mediterranean region. The second one comprises the main territory of Iberia and shows more complex patterns and singularities, now and in the past. Steppe landscapes dominated extensive areas over all the territory during the cold spells of the Quaternary, especially during the Late Pleistocene up to the Last Glacial Maximum, but differences in composition of the dominant taxa (Compositae versus Artemisia) are observed since the Early Pleistocene, probably related to moisture regional gradients. Coastal shelves and intramountainous valleys, even in continental areas, are spots of floristic

  13. Venus - Maxwell Montes and Cleopatra Crater

    Science.gov (United States)

    1991-01-01

    This Magellan full-resolution image shows Maxwell Montes, and is centered at 65 degrees north latitude and 6 degrees east longitude. Maxwell is the highest mountain on Venus, rising almost 11 kilometers (6.8 miles) above mean planetary radius. The western slopes (on the left) are very steep, whereas the eastern slopes descend gradually into Fortuna Tessera. The broad ridges and valleys making up Maxwell and Fortuna suggest that the topography resulted from compression. Most of Maxwell Montes has a very bright radar return; such bright returns are common on Venus at high altitudes. This phenomenon is thought to result from the presence of a radar reflective mineral such as pyrite. Interestingly, the highest area on Maxwell is less bright than the surrounding slopes, suggesting that the phenomenon is limited to a particular elevation range. The pressure, temperature, and chemistry of the atmosphere vary with altitude; the material responsible for the bright return probably is only stable in a particular range of atmospheric conditions and therefore a particular elevation range. The prominent circular feature in eastern Maxwell is Cleopatra. Cleopatra is a double-ring impact basin about 100 kilometers (62 miles) in diameter and 2.5 kilometers (1.5 miles) deep. A steep-walled, winding channel a few kilometers wide breaks through the rough terrain surrounding the crater rim. A large amount of lava originating in Cleopatra flowed through this channel and filled valleys in Fortuna Tessera. Cleopatra is superimposed on the structures of Maxwell Montes and appears to be undeformed, indicating that Cleopatra is relatively young.

  14. Topological properties of flat electroencephalography's state space

    Science.gov (United States)

    Ken, Tan Lit; Ahmad, Tahir bin; Mohd, Mohd Sham bin; Ngien, Su Kong; Suwa, Tohru; Meng, Ong Sie

    2016-02-01

    Neuroinverse problem are often associated with complex neuronal activity. It involves locating problematic cell which is highly challenging. While epileptic foci localization is possible with the aid of EEG signals, it relies greatly on the ability to extract hidden information or pattern within EEG signals. Flat EEG being an enhancement of EEG is a way of viewing electroencephalograph on the real plane. In the perspective of dynamical systems, Flat EEG is equivalent to epileptic seizure hence, making it a great platform to study epileptic seizure. Throughout the years, various mathematical tools have been applied on Flat EEG to extract hidden information that is hardly noticeable by traditional visual inspection. While these tools have given worthy results, the journey towards understanding seizure process completely is yet to be succeeded. Since the underlying structure of Flat EEG is dynamic and is deemed to contain wealthy information regarding brainstorm, it would certainly be appealing to explore in depth its structures. To better understand the complex seizure process, this paper studies the event of epileptic seizure via Flat EEG in a more general framework by means of topology, particularly, on the state space where the event of Flat EEG lies.

  15. Rock and Soil Physical Properties at the MER Gusev Crater and Meridiani Planum Landing Sites

    Science.gov (United States)

    Richter, L.; Arvidson, R.; Bell, J.; Cabrol, N.; Gorevan, S.; Greeley, R.; Herkenhoff, K.; Ming, D.; Sullivan, R.; Mer Athena Science Team

    Following the successful landings of both Mars Exploration Rover (MER) vehicles at Gusev Crater and Meridiani Planum, respectively, their Athena suite of instruments is being used to study the geologic history of these two very different landing sites on Mars that had been selected on the basis of showing different types of evidence for aqueous processes in the planet's past. Utilizing the on-board instruments as well as the rovers' mobility system, a wide range of physical properties investigations is carried out as well -- the subject of this abstract - that provide additional information on the geology and processes at the sites. Results of the mission in general as well as of the physical properties studies thus far greatly exceed expectations in that observations and measurements by both vehicles show a rich variety in materials and processes: the Gusev site in the vicinity of the lander is remarkably flat and generally devoid of large rocks along traverses up to the time of this writing (˜ Sol 50) and suggestive of a deflated surface with generally only thin veneers of bright dust while exhibiting evidence of a widespread occurrence of a crust from cemented fines that has been observed to fail in the form of blocky clods when disturbed by vehicle rolling action; numerous small and shallow depressions -- presumably created by impacts - are observed at the site which are infilled with bright, fine-grained material that likewise appears indurated and which was studied by a trenching experiment; small ripple bedforms are scattered across the site and were characterized in terms of particle size distributions. At the Meridiani site, studies so far -- up to ˜ Sol 33 -- have focussed on soils and the rock outcrop encountered within the ˜ 20 m diameter crater that the spacecraft came to rest in: from a physical properties point of view, a mantle of dark, well-sorted, apparently basaltic sand with small to moderate cohesion has been of interest -- and has been

  16. Eruptive history of the Ubehebe Crater cluster, Death Valley, California

    Science.gov (United States)

    Fierstein, Judy; Hildreth, Wes

    2017-04-01

    A sequence of late Holocene eruptions from the Ubehebe Crater cluster in Death Valley was short-lived, emplacing several phreatomagmatic and magmatic deposits. Seven craters form the main group, which erupted along a north-south alignment 1.5 km long. At least five more make a 500-m east-west alignment west of the main crater group. One more is an isolated shallow crater 400 m south of that alignment. All erupted through Miocene fanglomerate and sandstone, which are now distributed as comminuted matrix and lithic clasts in all Ubehebe deposits. Stratigraphic evidence showing that all Ubehebe strata were emplaced within a short time interval includes: (1) deposits from the many Ubehebe vents make a multi-package sequence that conformably drapes paleo-basement topography with no erosive gullying between emplacement units; (2) several crater rims that formed early in the eruptive sequence are draped smoothly by subsequent deposits; and (3) tack-welded to agglutinated spatter and bombs that erupted at various times through the sequence remained hot enough to oxidize the overlying youngest emplacement package. In addition, all deposits sufficiently consolidated to be drilled yield reliable paleomagnetic directions, with site mean directions showing no evidence of geomagnetic secular variation. Chemical analyses of juvenile components representing every eruptive package yield a narrow range in major elements [SiO2 (48.65-50.11); MgO (4.98-6.23); K2O (2.24-2.39)] and trace elements [Rb (28-33); Sr (1513-1588); Zr (373-404)]. Despite lithologic similarities, individual fall units can be traced outward from vent by recording layer thicknesses, maximum scoria and lithic sizes, and juvenile clast textural variations. This permits reconstruction of the eruptive sequence, which produced a variety of eruptive styles. The largest and northernmost of the craters, Ubehebe Crater, is the youngest of the group. Its largely phreatomagmatic deposits drape all of the others, thicken in

  17. Recognition of Terrestrial Impact Craters with COSMO-SkyMed

    Science.gov (United States)

    Virelli, M.; Staffieri, S.; Battagliere, M. L.; Komatsu, G.; Di Martino, M.; Flamini, E.; Coletta, A.

    2016-08-01

    All bodies having a solid surface, without distinction, show, with greater or lesser evidence, the marks left by the geological processes they undergone during their evolution. There is a geomorphological feature that is evident in all the images obtained by the probes sent to explore our planetary system: impact craters.Craters formed by the impact of small cosmic bodies have dimensions ranging from some meters to hundreds of kilometers. However, for example on the Lunar regolith particles, have been observed also sub- millimeter craters caused by dust impacts. The kinetic energy of the impactor, which velocity is in general of the order of tens km/s, is released in fractions of a second, generally in a explosive way, generating complex phenomena that transform not only the morphology of the surface involved by the impact, but also the mineralogy and crystallography of the impacted material. Even our planet is not immune to these impacts. At present, more than 180 geological structures recognized as of impact origin are known on Earth.In this article, we aim to show how these impact structures on Earth's surface are observed from space. To do this, we used the images obtained by the COSMO-SkyMed satellite constellation.Starting from 2013, ASI proposed, in collaboration with the Astrophysical Observatory of Turin and University D'Annunzio of Chieti, the realization of an Encyclopedic Atlas of Terrestrial Impact Craters using COSMO-SkyMed data that will become the first atlas of all recognized terrestrial impact craters based on images acquired by a X band radar. To observe these impact craters all radar sensor modes have been used, according to the size of the analyzed crater.The project includes research of any new features that could be classified as impact craters and, for the sites whereby it is considered necessary, the implementation of a geological survey on site to validate the observations.In this paper an overview of the Atlas of Terrestrial Impact

  18. Karakul: a young complex impact crater in the Pamir, Tajikistan

    Science.gov (United States)

    Bouley, S.; Baratoux, D.; Baratoux, L.; Colas, F.; Dauvergne, J.; Losiak, A.; Vaubaillon, J.; Bourdeille, C.; Jullien, A.; Ibadinov, K.

    2011-12-01

    A fascinating controversy has been recently renewed about the origin of the Karakul depression in the Pamir (Tajikistan, 39°1'N, 73°27'E), about 4000 m above sea level. Based on the work of E. Gurov reporting breccia and shock features in minerals, the circular depression was mentioned in the Earth Impact Database as one of the largest complex craters, about 50 km in diameter. However, recent studies have suggested that the basin is actually a NW-SE extensional rift. We report the preliminary results of a new expedition in the Karakul area that successfully took place in June 2011. Different types of rocks have been observed, including metamorphosed sediments, granite, limestone, and rare occurrence. The granite appears to be the youngest rock predating the crater, with an age of 230-190 My2. The most exciting preliminary result is the finding of shatter cones in metamorphosed sediments in the northern part of the peninsula. Breccias (not necessary impact-breccia) occur as floats on the central island, and were also found in the northern part of the rim. Thin sections are in preparation at the time of writing, and the report on the search for shock features in granite and breccias will be presented at the conference. The age of the crater is unknown, but is necessarily younger than the India-Asia collision, 55 - 60 My ago. On the basis of the oldest sediments filling the depression, the crater has been tentatively attributed to Neogene, or Pliocene, and would be then younger than 23 My. Consequences of the formation of a large complex crater in the recent geological history of the Pamir have yet to be explored. In a context of elevated convergence rate and rapid exhumation, the site offers the possibility to investigate the possible interactions between impact cratering and tectonic activity. The formation of a 50 km crater has considerable effects on the environment, at least at the regional scale, suggesting the search for such effects in the sediment record

  19. Raman spectroscopy of shocked gypsum from a meteorite impact crater

    Science.gov (United States)

    Brolly, Connor; Parnell, John; Bowden, Stephen

    2017-07-01

    Impact craters and associated hydrothermal systems are regarded as sites within which life could originate on Earth, and on Mars. The Haughton impact crater, one of the most well preserved craters on Earth, is abundant in Ca-sulphates. Selenite, a transparent form of gypsum, has been colonized by viable cyanobacteria. Basement rocks, which have been shocked, are more abundant in endolithic organisms, when compared with un-shocked basement. We infer that selenitic and shocked gypsum are more suitable for microbial colonization and have enhanced habitability. This is analogous to many Martian craters, such as Gale Crater, which has sulphate deposits in a central layered mound, thought to be formed by post-impact hydrothermal springs. In preparation for the 2020 ExoMars mission, experiments were conducted to determine whether Raman spectroscopy can distinguish between gypsum with different degrees of habitability. Ca-sulphates were analysed using Raman spectroscopy and results show no significant statistical difference between gypsum that has experienced shock by meteorite impact and gypsum, which has been dissolved and re-precipitated as an evaporitic crust. Raman spectroscopy is able to distinguish between selenite and unaltered gypsum. This shows that Raman spectroscopy can identify more habitable forms of gypsum, and demonstrates the current capabilities of Raman spectroscopy for the interpretation of gypsum habitability.

  20. Chemical abundances of giant stars in the Crater stellar system

    CERN Document Server

    Bonifacio, P; Zaggia, S; François, P; Sbordone, L; Andrievsky, S M; Korotin, S A

    2015-01-01

    We obtained spectra for two giants of Crater (Crater J113613-105227 and Crater J113615-105244) using X-Shooter at the VLT. The spectra have been analysed with the MyGIsFoS code using a grid of synthetic spectra computed from one dimensional, Local Thermodynamic Equilibrium (LTE) model atmospheres. Effective temperature and surface gravity have been derived from photometry measured from images obtained by the Dark Energy Survey. The radial velocities are 144.3+-4.0 km/s for Crater J113613-105227 and and 134.1+-4.0 km/s for Crater J113615-105244. The metallicities are [Fe/H]=-1.73 and [Fe/H]=-1.67, respectively. Beside the iron abundance we could determine abundances for nine elements: Na, Mg, Ca, Ti, V, Cr, Mn, Ni and Ba. For Na and Ba we took into account deviations from LTE, since the corrections are significant. The abundance ratios are similar in the two stars and resemble those of Galactic stars of the same metallicity. On the deep photometric images we could detect several stars that lie to the blue of t...

  1. Inferring conduit process from population studies of cinder cone craters

    Science.gov (United States)

    Bemis, Karen G.

    2014-05-01

    One of the most observable aspects of magma conduits is of course their exit to the Earth's surface: the volcanic crater. The craters resulting from small mostly-monogenetic volcanic eruptions vary in considerable in size and shape, even after accounting for variation in size. Presumably, these variations tell us something about the state of the conduit at least in the ending stages of eruption. But what? This work explores the statistical properties of crater populations in Guatemala and elsewhere and speculates on the conduit processes that may explain the complex behavior. Crater depths are strongly correlated with cone slopes even when normalized by cone diameter, which suggests the importance of the impact of the volatile content (which may influence slope through fragmentation and the resulting grain size) and the duration of eruption (which may influence whether the cone is built to its maximum slope) despite erosion acting to reduce observed crater depths (cone slopes are known to decrease with erosion but cone diameters increase).

  2. Vapor plumes: A neglected aspect of impact cratering

    Science.gov (United States)

    Melosh, H. J.

    1991-06-01

    When a meteorite or comet strikes the surface of the planet or satellite at typical interplanetary velocities of 10-40 km/sec, the projectile and a quantity of the target body vaporize and expand out of the growing crater at high speed. The crater continues to grow after the vapor plume has formed and the series of ejecta deposits is laid down ballistically while the crater collapses into its final morphology. Although the vapor plume leaves little evidence of its existence in the crater structure of surface deposits, it may play a major role in a number of impact-related processes. The vapor plume expanding away from the site of an impact carries 25-50 percent of the total impact energy. Although the plume's total mass is only a few times the mass of the projectile, its high specific energy content means that it is the fastest and most highly shocked material in the cratering event. The mean velocity of expansion can easily exceed the escape velocity of the target plane, so that the net effect of a sufficiently high-speed impact is to erode material from the planet.

  3. Flat H Frangible Joint Evolution

    Science.gov (United States)

    Diegelman, Thomas E.; Hinkel, Todd J.; Benjamin, Andrew; Rochon, Brian V.; Brown, Christopher W.

    2016-01-01

    Space vehicle staging and separation events require pyrotechnic devices. They are single-use mechanisms that cannot be tested, nor can failure-tolerant performance be demonstrated in actual flight articles prior to flight use. This necessitates the implementation of a robust design and test approach coupled with a fully redundant, failure-tolerant explosive mechanism to ensure that the system functions even in the event of a single failure. Historically, NASA has followed the single failure-tolerant (SFT) design philosophy for all human-rated spacecraft, including the Space Shuttle Program. Following the end of this program, aerospace companies proposed building the next generation human-rated vehicles with off-the-shelf, non-redundant, zero-failure-tolerant (ZFT) separation systems. Currently, spacecraft and launch vehicle providers for both the Orion and Commercial Crew Programs (CCPs) plan to deviate from the heritage safety approach and NASA's SFT human rating requirements. Both programs' partners have base-lined ZFT frangible joints for vehicle staging and fairing separation. These joints are commercially available from pyrotechnic vendors. Non-human-rated missions have flown them numerous times. The joints are relatively easy to integrate structurally within the spacecraft. In addition, the separation event is debris free, and the resultant pyro shock is lower than that of other design solutions. It is, however, a serious deficiency to lack failure tolerance. When used for critical applications on human-rated vehicles, a single failure could potentially lead to loss of crew (LOC) or loss of mission (LOM)). The Engineering and Safety & Mission Assurance directorates within the NASA Johnson Space Center took action to address this safety issue by initiating a project to develop a fully redundant, SFT frangible joint design, known as the Flat H. Critical to the ability to retrofit on launch vehicles being developed, the SFT mechanisms must fit within the same

  4. Katabatically Driven Downslope Windstorm-Type Flows on the Inner Sidewall of Arizona's Barringer Meteorite Crater

    Science.gov (United States)

    Whiteman, C. D.; Lehner, M.; Hoch, S.; Hills, M.; Haiden, T.; Feigenwinter, I.; Grudzielanek, M.; Maric, M.; Kalthoff, N.; Vogt, R.; Cermak, J.; Rotunno, R.; Calhoun, R.; Cherukuru, N.; Adler, B.

    2015-12-01

    The second Meteor Crater Experiment (METCRAX II) conducted in October 2013 at Arizona's Barringer Meteorite Crater investigated hydraulic-analogue atmospheric flows that cascade into the crater basin over its southwest rim. These intruding downslope windstorm-type flows are produced when the depth of the temperature inversion and accompanying southwesterly downslope flow on the surrounding gently sloping plain exceeds the height of the crater rim. As the southwesterly katabatic flow approaches the crater it decelerates, splits around the crater at elevations below the crater rim, and cascades over the crater rim at upper elevations. The intruding cold katabatic air accelerates down the inner sidewall of the crater, perturbing the prexisting shallow inversion on the crater floor, sometimes creating the atmospheric equivalent of ocean or lake basin seiches. When the cold air intrusions are strong, warm air is brought down into the crater from the upwind atmosphere above the mesoscale inversion, and hydraulic jumps may form on the southwest side of the crater while leaving the rest of the crater atmosphere relatively undisturbed. In this talk, evidence for these flow features will be presented, featuring dual Doppler and time-lapse IR animations of the intruding flows.

  5. Late Pleistocene to Holocene soil development and environments in the Long Gang Volcanic Field area, Jilin Province, NE China

    Science.gov (United States)

    Sauer, Daniela; Zhang, Xinrong; Knöbel, Jette; Maerker, Lutz

    2014-05-01

    Late Pleistocene to Holocene shifts of climate and vegetation in the Long Gang Volcanic Field in NE China have been reconstructed, e. g. by Steblich et al. (2009), based on Maar lake sediment cores. In this study, we investigated soil development during the Late Pleistocene and Holocene and linked it to the climate and vegetation reported in the literature. Three pedons were described and analyzed on a crater wall surrounding a maar. The lower part of the slope is covered by basic pyroclastics that are obviously younger than the maar itself. Pedon 1 is located on the upper slope, where the younger pyroclastics are not present; thus it developed over the entire Holocene and part of the Late Pleistocene. Pedon 2 is on the toe slope and developed from the young basic pyroclastics. Vegetation remains, charred by fire that was caused by the volcanic ash fall, were found in the lowermost part of the pyroclastics layer, on top of a paleosol. Charcoal fragments were dated to 18950-18830 cal BP (using INTCAL 09). Thus, pedon 2 developed since around 18.9 ka BP, whereas the development of the paleosol that was buried under the pyroclastics (pedon 3), was stopped at this time. Pedons 1 and 2 are Vitric Andosols, developed mainly from basic pyroclastics, as evidenced by the composition of rock fragments in the soils, comprising 78 / 81 mass % lapilli and 22 / 19 mass % gneiss fragments, respectively. Pedon 3 is a Cutanic Luvisol (Chromic) that developed entirely from gneiss fragments produced by the maar explosion. Lab data suggest increasing intensity of pedogenesis in the direction: Pedon 3 (paleosol) < Pedon 2 < Pedon 1, reflected e. g. in increasing Fed/Fet ratios, decreasing molar ratios of (Ca+K+Na)/Al, and decreasing pH. However, it needs to be considered that lapilli are more readily weatherable than gneiss fragments. The profile morphology of the paleosol, characterized by reddish-brown color (7.5YR), strong angular blocky structure and well-expressed illuvial clay

  6. Thickness of a Europan ice shell from impact crater simulations.

    Science.gov (United States)

    Turtle, E P; Pierazzo, E

    2001-11-09

    Several impact craters on Jupiter's satellite Europa exhibit central peaks. On the terrestrial planets, central peaks consist of fractured but competent rock uplifted during cratering. Therefore, the observation of central peaks on Europa indicates that an ice layer must be sufficiently thick that the impact events did not completely penetrate it. We conducted numerical simulations of vapor and melt production during cratering of water ice layers overlying liquid water to estimate the thickness of Europa's icy crust. Because impacts disrupt material well beyond the zone of partial melting, our simulations put a lower limit on ice thickness at the locations and times of impact. We conclude that the ice must be more than 3 to 4 kilometers thick.

  7. Gullies and Layers in Crater Wall in Newton

    Science.gov (United States)

    2002-01-01

    This dramatic view of gullies emergent from layered outcrops occurs on the wall of a crater within the much larger impact basin, Newton. Newton Crater and its surrounding terrain exhibit many examples of gullies on the walls of craters and troughs. The gullies exhibit meandering channels with fan-shaped aprons of debris located downslope. The gullies are considered to have been formed by erosion--both from a fluid (such as water) running downslope, and by slumping and landsliding processes driven by the force of gravity. This picture was obtained by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in March 2001; it is illuminated from the upper left and covers an area 3 km (1.9 mi) across.

  8. Crater-related flow features on Ceres - Implications for cryovolcanism

    Science.gov (United States)

    Jaumann, R.; Krohn, K.; Stephan, K.; Otto, K. A.; Schmedemann, N.; Wagner, R. J.; Matz, K. D.; Tosi, F.; Zambon, F.; von der Gathen, I.; Schulzeck, F.; Buczkowski, D.; Hiesinger, H.; McSween, H. Y., Jr.; Pieters, C. M.; Preusker, F.; Roatsch, T.; Raymond, C. A.; Russell, C. T.; Williams, D. A.

    2016-12-01

    Some craters on Ceres show post-impact modifications, like the deposition of extended plains laced with pits, lobate flows, and ponded material [1]. We found those features on craters with a bluish spectral signature, such as Haulani, Ikapati, Occator and Kupalo. Lobate flows of Haulani and Kupalo originating from the crest of the central ridge [1,2] partly overwhelming the mass wasting deposits from the rim, indicating possible post-impact resurfacing processes [3,4]. The drop height-to-runout length ratio of several flow features of the four craters reveals a coefficient of friction of Castillo-Rogez J.C. and McCord T.B., 2010, Icarus 203, 443-459. [6] Fu et al., 2015, AGU #P23D-02. [7] De Sanctis M.C., et al., 2015, Nature 528, 241-244. [8] Neumann W., et al., 2016, LPSC #2307. [9] Schmedemann N., et al., 2016, LPSC # 2236.

  9. Artificial Crater Formation on Satellite Surfaces Using an Orbiting Railgun

    Science.gov (United States)

    Dissly, R. W.; Miller, K. L.; Carlson, R. J.

    2003-01-01

    The specification of greater than 45kW of disposable power available on the JIMO spacecraft raises the possibility of a new class of instrumentation that has utility at such power levels. In this presentation we discuss the concept of an electromagnetic mass driver that can launch projectiles from orbit around one of the Galilean satellites directed on a trajectory that will impact the satellite surface. The resulting impact will create a crater that will provide information on the mechanical properties of surface and near-surface materials, expose subsurface materials for remote spectral identification, and form a vapor cloud that can be sensed for composition either remotely or in-situ. An analog for such a controlled cratering experiment is Deep Impact, a mission to observe the crater and ensuing ejecta cloud formed by a ballistic projectile into a comet surface in July, 2005.

  10. New impact craters and meteoroid densities on Mars

    Science.gov (United States)

    Ivanov, B.; Melosh, H. J.; McEwen, A.

    2011-10-01

    Repetitive high-resolution imaging of Mars revealed new small impact craters with known dates of formation (see [1, 2] and references in [2]). After ~2006 the discovery rate became a linear function of time, so we can use the discovery rate as a proxy for the modern bombardment rate. The low-mass Martian atmosphere is dense enough to shatter roughly half of the meteoroids, resulting in the crater clusters. Separation distances in these clusters put some constraints on the density and strength of meteoroids. The atmospheric deceleration and breakup of meteoroids complicate the Mars/Moon comparison and attempts to verify the crater related timescale (e.g. [3]). At the same time observations of impact sites with known formation dates allow us to analyze the rate of modern surface changes due to wind/dust interaction.

  11. Complex Volcanism at Oppenheimer U Floor-Fractured Crater

    Science.gov (United States)

    Gaddis, L. R.; Bennett, K.; Horgan, B.; McBride, Marie; Stopar, J.; Lawrence, S.; Gustafson, J. O.; Giguere, T.

    2017-01-01

    Recent remote sensing studies have identified complex volcanism in the floor-fractured crater (FFC) Oppenheimer U, located in the northwest floor of Oppenheimer crater (35.2degS, 166.3degW, 208 km dia., Figure 1) within the "South Pole - Aitken basin" (SPA) region of the lunar far side. Up to 15 sites of pyroclastic volcanism have been identified in the floor of Oppenheimer crater. Studies of Moon Mineralogy Mapper data (M3, 0.4-3 microns, 86 bands, [5]) indicated that the pyroclastic deposits are comprised of mixtures of clinopyroxene and iron-rich glass, with the Oppenheimer U deposit showing variable composition within the FFC and having the most iron-rich volcanic glass thus far identified on the Moon. Here we examine the floor of Oppenheimer U in more detail and show evidence for possible multiple eruptive vents.

  12. Shock-induced effects in calcite from Cactus Crater

    Science.gov (United States)

    Vizgirda, J.; Ahrens, T. J.; Tsay, F.-D.

    1980-01-01

    The paper discusses shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.

  13. Artificial Crater Formation on Satellite Surfaces Using an Orbiting Railgun

    Science.gov (United States)

    Dissly, R. W.; Miller, K. L.; Carlson, R. J.

    2003-01-01

    The specification of greater than 45kW of disposable power available on the JIMO spacecraft raises the possibility of a new class of instrumentation that has utility at such power levels. In this presentation we discuss the concept of an electromagnetic mass driver that can launch projectiles from orbit around one of the Galilean satellites directed on a trajectory that will impact the satellite surface. The resulting impact will create a crater that will provide information on the mechanical properties of surface and near-surface materials, expose subsurface materials for remote spectral identification, and form a vapor cloud that can be sensed for composition either remotely or in-situ. An analog for such a controlled cratering experiment is Deep Impact, a mission to observe the crater and ensuing ejecta cloud formed by a ballistic projectile into a comet surface in July, 2005.

  14. Hydrological Modeling of the Jezero Crater Outlet-Forming Flood

    Science.gov (United States)

    Fassett, Caleb I.; Goudge, Timothy A.

    2017-01-01

    Jezero crater is a site of prime scientific interest because it was a lake early in Mars history. Preserved clay- and carbonate-bearing sedimentary fans on Jezero's western and northwestern margin (Fig. 2) are accessible to future exploration. Geologic context [1] and stratigraphic analysis of the western fan strongly support the interpretation that these fans were deposited as deltas into the lake. This has helped establish Jezero as one of the final candidate landing sites for Mars 2020. The high level of certainty that Jezero was a lake results from the existence of its outlet valley, which required filling of the crater to form [e.g., 1,4]. Here, we specifically focus on how this outlet valley was carved by the dam breach flood that eroded the eastern crater rim. We have completed preliminary modeling in both 1D and 2D of the outlet's formation.

  15. Shatter cones formed in large-scale experimental explosion craters

    Science.gov (United States)

    Roddy, D. J.; Davis, L. K.

    1977-01-01

    In 1968, a series of 0.5-ton and 100-ton TNT explosion experiments were conducted in granitic rock near Cedar City, Utah, as part of a basic research program on cratering and shock wave propagation. Of special interest was the formation of an important type of shock metamorphic feature, shatter cones. A description is presented of the first reported occurrence of shatter cones in high explosion trials. A background to shatter cone studies is presented and attention is given to the test program, geology and physical properties of the test medium, the observed cratering, and the formational pressures for shatter cones. The high explosion trials conducted demonstrate beyond any doubt, that shatter cones can be formed by shock wave processes during cratering and that average formational pressures in these crystalline rocks are in the 20-60 kb range.

  16. Diagenetic Mineralogy at Gale Crater, Mars

    Science.gov (United States)

    Vaniman, David; Blake, David; Bristow, Thomas F.; Chipera, Steve; Gellert, Ralf; Ming, Douglas; Morris, Richard; Rampe, E. B.; Rapin, William

    2015-01-01

    Three years into exploration of sediments in Gale crater on Mars, the Mars Science Laboratory rover Curiosity has provided data on several modes and episodes of diagenetic mineral formation. Curiosity determines mineralogy principally by X-ray diffraction (XRD), but with supporting data from thermal-release profiles of volatiles, bulk chemistry, passive spectroscopy, and laser-induced breakdown spectra of targeted spots. Mudstones at Yellowknife Bay, within the landing ellipse, contain approximately 20% phyllosilicate that we interpret as authigenic smectite formed by basalt weathering in relatively dilute water, with associated formation of authigenic magnetite as in experiments by Tosca and Hurowitz [Goldschmidt 2014]. Varied interlayer spacing of the smectite, collapsed at approximately 10 A or expanded at approximately 13.2 A, is evidence of localized diagenesis that may include partial intercalation of metal-hydroxyl groups in the approximately 13.2 A material. Subsequent sampling of stratigraphically higher Windjana sandstone revealed sediment with multiple sources, possible concentration of detrital magnetite, and minimal abundance of diagenetic minerals. Most recent sampling has been of lower strata at Mount Sharp, where diagenesis is widespread and varied. Here XRD shows that hematite first becomes abundant and products of diagenesis include jarosite and cristobalite. In addition, bulk chemistry identifies Mg-sulfate concretions that may be amorphous or crystalline. Throughout Curiosity's traverse, later diagenetic fractures (and rarer nodules) of mm to dm scale are common and surprisingly constant and simple in Ca-sulfate composition. Other sulfates (Mg,Fe) appear to be absent in this later diagenetic cycle, and circumneutral solutions are indicated. Equally surprising is the rarity of gypsum and common occurrence of bassanite and anhydrite. Bassanite, rare on Earth, plays a major role at this location on Mars. Dehydration of gypsum to bassanite in the

  17. Chemostratigraphy of Lower Mount Sharp, Gale Crater

    Science.gov (United States)

    Wiens, R. C.; Frydenvang, J.; Watkins, J. A.; Mangold, N.; Le Deit, L.; Blaney, D. L.; Bridges, J.; Forni, O.; Gasda, P. J.; Gasnault, O.; Lanza, N.; Maurice, S.; Milliken, R.; Newsom, H. E.; Ollila, A. M.; Vasavada, A. R.

    2016-12-01

    The Curiosity rover is ascending Mt. Sharp, a large sedimentary mound at the center of Gale crater, Mars. Over the last two years Curiosity has progressed across the Murray formation, which is the lowermost exposed member of the Mt. Sharp Group, and consists mostly of thinly laminated lacustrine deposits. During this traverse, Curiosity has encountered two additional units: The Stimson unit consists of eolian cross-bedded sandstones that unconformably drape the Murray and are interpreted as remnants of ancient dunes post-dating the lacustrine period. An enigmatic blocky unit has also been encountered in the vicinity of Brandberg (sol 1160) and Bimbe (1398). The geologic nature of this unit is unclear, but Bimbe in particular provides the only conglomerates observed on Mt. Sharp. In contrast to Bradbury rise, Bimbe conglomerates contain angular clasts. These fluvial sediments could source from further up Mt. Sharp. Over 4000 elemental composition observations have been made by ChemCam on > 400 targets on Mt. Sharp. In contrast to the Bradbury group which contains more felsic coarse-grained material than average Mars, initial Murray at Pahrump (sols 750-900) shows a reversal, with coarse-grained interbedded sandstones closer to average Mars and fine-grained material shows more felsic compositions (higher Al, Si). At Marias Pass (sol 1000), finely laminated layers of nearly pure silica (e.g., > 85 wt. % SiO2) were encountered in Murray, and opal and tridymite were observed by CheMin at Buckskin. Bridger Basin (sol 1120) revealed clear fracture-related silica enrichments cross-cutting both Murray and Stimson units, suggesting strong groundwater interaction post-dating both units. Bimbe conglomerates have diverse compositions, while dark-toned blocky floats have high Na2O (> 4.5 wt. %) but low Al2O3 (< 9 wt. %), much lower than Jake_M (sol 45). A significant observation starting in the Murray Unit is the presence of boron and Na enrichments (likely NaCl) in and around

  18. Impact craters at falling of large asteroids in Ukraine

    Science.gov (United States)

    Vidmachenko, A. P.

    2016-05-01

    Catastrophes of different scale that are associated with the fall of celestial bodies to the Earth - occurred repeatedly in its history. But direct evidence of such catastrophes has been discovered recently. Thus, in the late 1970s studies of terrestrial rocks showed that in layers of the earth's crust that corresponded to the period of 65 million years before the present, marked by the mass extinction of some species of living creatures, and the beginning of the rapid development of others. It was then - a large body crashed to Earth in the Gulf of Mexico in Central America. The consequence of this is the Chicxulub crater with a diameter of ~170 km on Yucatan Peninsula. Modern Earth's surface retains many traces of collisions with large cosmic bodies. To indicate the craters with a diameter of more than 2 km using the name "astrobleme". Today, it found more than 230. The largest astroblems sizes exceeding 200 km. Ukraine also has some own astroblems. In Ukraine, been found nine large impact craters. Ukrainian crystalline shield, because of its stability for a long time (more than 1.5 billion years), has the highest density of large astroblems on the Earth's surface. The largest of the Ukrainian astroblems is Manevytska. It has a diameter of 45 km. There are also Ilyinetskyi (7 km), Boltysh (25 km), Obolon' (20 km), Ternivka (12-15 km), Bilylivskyi (6 km), Rotmystrivka (3 km) craters. Zelenohayska astrobleme founded near the village Zelenyi Gay in Kirovograd region and consists of two craters: larger with diameter 2.5-3.5 km and smaller - with diameter of 800 m. The presence of graphite, which was the basis for the research of the impact diamond in astroblems of this region. As a result, the diamonds have been found in rocks of Ilyinetskyi crater; later it have been found in rocks in the Bilylivska, Obolon' and other impact structures. The most detailed was studied the geological structure and the presence of diamonds in Bilylivska astrobleme

  19. Starting Conditions for Hydrothermal Systems Underneath Martian Craters: Hydrocode Modeling

    Science.gov (United States)

    Pierazzo, E.; Artemieva, N. A.; Ivanov, B. A.

    2004-01-01

    Mars is the most Earth-like of the Solar System s planets, and the first place to look for any sign of present or past extraterrestrial life. Its surface shows many features indicative of the presence of surface and sub-surface water, while impact cratering and volcanism have provided temporary and local surface heat sources throughout Mars geologic history. Impact craters are widely used ubiquitous indicators for the presence of sub-surface water or ice on Mars. In particular, the presence of significant amounts of ground ice or water would cause impact-induced hydrothermal alteration at Martian impact sites. The realization that hydrothermal systems are possible sites for the origin and early evolution of life on Earth has given rise to the hypothesis that hydrothermal systems may have had the same role on Mars. Rough estimates of the heat generated in impact events have been based on scaling relations, or thermal data based on terrestrial impacts on crystalline basements. Preliminary studies also suggest that melt sheets and target uplift are equally important heat sources for the development of a hydrothermal system, while its lifetime depends on the volume and cooling rate of the heat source, as well as the permeability of the host rocks. We present initial results of two-dimensional (2D) and three-dimensional (3D) simulations of impacts on Mars aimed at constraining the initial conditions for modeling the onset and evolution of a hydrothermal system on the red planet. Simulations of the early stages of impact cratering provide an estimate of the amount of shock melting and the pressure-temperature distribution in the target caused by various impacts on the Martian surface. Modeling of the late stage of crater collapse is necessary to characterize the final thermal state of the target, including crater uplift, and distribution of the heated target material (including the melt pool) and hot ejecta around the crater.

  20. Survey of TES high albedo events in Mars' northern polar craters

    Science.gov (United States)

    Armstrong, J.C.; Nielson, S.K.; Titus, T.N.

    2007-01-01

    Following the work exploring Korolev Crater (Armstrong et al., 2005) for evidence of crater interior ice deposits, we have conducted a survey of Thermal Emission Spectroscopy (TES) temperature and albedo measurements for Mars' northern polar craters larger than 10 km. Specifically, we identify a class of craters that exhibits brightening in their interiors during a solar longitude, Ls, of 60 to 120 degrees, roughly depending on latitude. These craters vary in size, latitude, and morphology, but appear to have a specific regional association on the surface that correlates with the distribution of subsurface hydrogen (interpreted as water ice) previously observed on Mars. We suggest that these craters, like Korolev, exhibit seasonal high albedo frost events that indicate subsurface water ice within the craters. A detailed study of these craters may provide insight in the geographical distribution of the ice and context for future polar missions. Copyright 2007 by the American Geophysical Union.

  1. Sub-Surface Excavation of Transient Craters in Porous Targets: Explaining the Impact Delay

    Science.gov (United States)

    Bowling, T. J.; Melosh, H. J.

    2012-03-01

    We numerically investigate the subsurface excavation of the transient crater in the earliest moments after the Deep Impact event. At high target porosities the crater remains hidden from observation long enough to explain the "impact delay."

  2. Properties of Ejecta Blanket Deposits Surrounding Morasko Meteorite Impact Craters (Poland)

    Science.gov (United States)

    Szokaluk, M.; Muszyński, A.; Jagodziński, R.; Szczuciński, W.

    2016-08-01

    Morasko impact craters are a record of the fall of a meteorite into the soft sediments. The presented results illustrate the geological structure of the area around the crater as well as providing evidence of the occurrence of ejecta blanket.

  3. Search for Impact Craters in Iran: Citizen Science as a Useful Method

    CERN Document Server

    Pourkhorsandi, Hamed

    2013-01-01

    To recognition probable impact craters in Iran, we use Google Earth data in the first step. Some probable structures identified and studies suggest non-impact origin for them. Studies on other craters in Iran are in progress.

  4. The Links Between Target Properties and Layered Ejecta Craters in Acidalia and Utopia Planitiae Mars

    Science.gov (United States)

    Jones, E.; Osinski, G. R.

    2013-08-01

    Layered ejecta craters on Mars may form from excavation into subsurface volatiles. We examine a new catalogue of martian craters to decipher differences between the single- and double-layered ejecta populations in Acidalia and Utopia.

  5. Pleistocene dynamics of the Pacific South Equatorial Countercurrent

    Science.gov (United States)

    Nuernberg, D.; Raddatz, J.; Rippert, N.; Tiedemann, R.

    2014-12-01

    The Western Pacific Warm Pool (WPWP) with extremely high sea-surface-temperatures (SST) is a key area for global climate. It also acts as a crossroad for mode and intermediate water masses such as the South Equatorial Countercurrent (SECC) transporting water masses originating from higher latitudes. The SECC flows above the main thermocline and strongly interacts with the Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ). To constrain changes in sea-surface and subsurface water mass dynamics affecting thermocline depth, we reconstruct SST, subSST and salinity conditions using combined δ18O and Mg/Ca signals of surface (Globigerinoides ruber, Globigerinoides sacculifer) and subsurface dwelling (Globorotalia tumida) planktonic foraminifera. Our study is based on RV SONNE SO-225 piston cores retrieved from Manihiki plateau, which is located at the southeastern margin of the WPWP (between ~ 5°S-15°S and 170-160°W). The proxy records cover the last ~ 3 Myr SSTMg/Ca remained nearly constant throughout the entire Pleistocene varying between ~30 to 32 (°C), while the subSSTMg/Ca reconstructions reveal pronounced variations from ~10 to 16 (°C). Our results imply that the WPWP thermocline depth has undergone significant vertical movements throughout the Pleistocene. Notably, thermocline depth is continuously decreasing from the early to the late Pleistocene, and coincides with the change from the 41 kyr to a dominant 100 kyr climate periodicity between 1 and 1.7 Ma. We hypothesize that the repeated change in thermocline depth is due to either 1) changes in mode or intermediate water masses advection from Southern Ocean sources via "ocean tunneling", 2) changes in the tropical Pacific wind regime, and/or 3) changes in the Western Pacific Monsoon sytem.

  6. Middle Pleistocene hominin teeth from Longtan Cave, Hexian, China.

    Science.gov (United States)

    Xing, Song; Martinón-Torres, María; Bermúdez de Castro, José María; Zhang, Yingqi; Fan, Xiaoxiao; Zheng, Longting; Huang, Wanbo; Liu, Wu

    2014-01-01

    Excavations at the Longtan Cave, Hexian, Anhui Province of Eastern China, have yielded several hominin fossils including crania, mandibular fragments, and teeth currently dated to 412 ± 25 ka. While previous studies have focused on the cranial remains, there are no detailed analyses of the dental evidence. In this study, we provide metric and morphological descriptions and comparisons of ten teeth recovered from Hexian, including microcomputed tomography analyses. Our results indicate that the Hexian teeth are metrically and morphologically primitive and overlap with H. ergaster and East Asian Early and mid-Middle Pleistocene hominins in their large dimensions and occlusal complexities. However, the Hexian teeth differ from H. ergaster in features such as conspicuous vertical grooves on the labial/buccal surfaces of the central incisor and the upper premolar, the crown outline shapes of upper and lower molars and the numbers, shapes, and divergences of the roots. Despite their close geological ages, the Hexian teeth are also more primitive than Zhoukoudian specimens, and resemble Sangiran Early Pleistocene teeth. In addition, no typical Neanderthal features have been identified in the Hexian sample. Our study highlights the metrical and morphological primitive status of the Hexian sample in comparison to contemporaneous or even earlier populations of Asia. Based on this finding, we suggest that the primitive-derived gradients of the Asian hominins cannot be satisfactorily fitted along a chronological sequence, suggesting complex evolutionary scenarios with the coexistence and/or survival of different lineages in Eurasia. Hexian could represent the persistence in time of a H. erectus group that would have retained primitive features that were lost in other Asian populations such as Zhoukoudian or Panxian Dadong. Our study expands the metrical and morphological variations known for the East Asian hominins before the mid-Middle Pleistocene and warns about the

  7. Pleistocene microvertebrates from fissure-fillings in Thailand

    Science.gov (United States)

    Chaimanee, Yaowalak; Jaeger, Jean-Jacques; Suteethorn, Varavudh

    Microvertebrates (and among them specially, rodents) have contributed to the elaboration of precise biochronological time scales and to the reconstitution of Pleistocene paleoenvironments in several parts of the world (North America, Africa, Europe and Japan). They have been demonstrated to be highly sensitive to climatic changes since they are very sensitive to vegetation changes. Up to now, no data is available for Southeast Asia and very few information is available concerning the nature of climatic changes which affected that part of the tropical world during the Pleistocene. In the past few years, we have discovered several fissure fillings in Thailand yielding numerous remains of microvertebrates which have been extracted by dissolution in acetic acid solution. These deposits are the result of the feeding activity of predators, like owls or diurnal raptors, whose pellets are accumulated in caves or fissures. Eleven localities, located in Central (2), Eastern (1), Western (2) and Peninsular Thailand (6) have been investigated so far. Several rodent species, belonging to 9 genera of Murinae (rats and mice) and 9 genera of Sciuridae (squirrels) have been identified in these localities. The most important differences with the extant representatives often concern the size of the teeth of these fossil species. The meaning of these size differences is not yet clearly understood since they can be attributed either to significant time differences between localities (microevolution) or as the result of size variations related to climatic changes (clinical variations). More data will have to be collected to calibrate the temporal frame. Already, important modification of the geographic distribution of some species have been discovered which testify that during the Pleistocene, significative climatic changes have affected Southeast Asia. For example, Exilisciurus, a squirrel which is presently restricted to Borneo has been recognized in Peninsular Thailand. Also, Iomys

  8. Middle Pleistocene hominin teeth from Longtan Cave, Hexian, China.

    Directory of Open Access Journals (Sweden)

    Song Xing

    Full Text Available Excavations at the Longtan Cave, Hexian, Anhui Province of Eastern China, have yielded several hominin fossils including crania, mandibular fragments, and teeth currently dated to 412 ± 25 ka. While previous studies have focused on the cranial remains, there are no detailed analyses of the dental evidence. In this study, we provide metric and morphological descriptions and comparisons of ten teeth recovered from Hexian, including microcomputed tomography analyses. Our results indicate that the Hexian teeth are metrically and morphologically primitive and overlap with H. ergaster and East Asian Early and mid-Middle Pleistocene hominins in their large dimensions and occlusal complexities. However, the Hexian teeth differ from H. ergaster in features such as conspicuous vertical grooves on the labial/buccal surfaces of the central incisor and the upper premolar, the crown outline shapes of upper and lower molars and the numbers, shapes, and divergences of the roots. Despite their close geological ages, the Hexian teeth are also more primitive than Zhoukoudian specimens, and resemble Sangiran Early Pleistocene teeth. In addition, no typical Neanderthal features have been identified in the Hexian sample. Our study highlights the metrical and morphological primitive status of the Hexian sample in comparison to contemporaneous or even earlier populations of Asia. Based on this finding, we suggest that the primitive-derived gradients of the Asian hominins cannot be satisfactorily fitted along a chronological sequence, suggesting complex evolutionary scenarios with the coexistence and/or survival of different lineages in Eurasia. Hexian could represent the persistence in time of a H. erectus group that would have retained primitive features that were lost in other Asian populations such as Zhoukoudian or Panxian Dadong. Our study expands the metrical and morphological variations known for the East Asian hominins before the mid-Middle Pleistocene and

  9. Impact crater formation: a simple application of solid state physics

    CERN Document Server

    Celebonovic, V

    2010-01-01

    This contribution is a first step aiming to address a general question: what can be concluded on impact craters which exist on various planetary system objects, by combining astronomical data and known theoretical results from solid state physics. Assuming that the material of the target body is of crystaline structure,it is shown that a simple calculation gives the possibility of estimating the speed of the impactor responsible for the creation of a crater.A test value,calculated using observed data on the composition of some asteroids,gives a value of the speed in good agreement with results of celestial mechanics.

  10. The "human" statistics of terrestrial impact cratering rate

    CERN Document Server

    Jetsu, L

    1997-01-01

    The most significant periodicities in the terrestrial impact crater record are due to the human-signal: the bias of assigning integer values for the crater ages. This bias seems to have eluded the proponents and opponents of real periodicity in the occurrence of these events, as well as the theorists searching for an extraterrestrial explanation for such periodicity. The human-signal should be seriously considered by scientists in astronomy, geology and paleontology when searching for a connection between terrestrial major comet or asteroid impacts and mass extinctions of species.

  11. Parameters critical to the morphology of fluidization craters

    Science.gov (United States)

    Siegal, B. S.; Gold, D. P.

    1973-01-01

    In order to study further the role of fluidization on the moon, a laboratory investigation was undertaken on two particulate material size fractions to determine the effect of variables, such as, duration of gas streaming, gas pressure, and 'regolith' thickness on the morphology of fluidization craters. A 3.175-mm cylindrical vent was used to simulate a gas streaming conduit. Details of the fluidization chamber are discussed together with questions of experimental control, aspects of nomenclature, crater measurements, and the effect of variables.

  12. Improved Measurement of Ejection Velocities From Craters Formed in Sand

    Science.gov (United States)

    Cintala, Mark J.; Byers, Terry; Cardenas, Francisco; Montes, Roland; Potter, Elliot E.

    2014-01-01

    A typical impact crater is formed by two major processes: compression of the target (essentially equivalent to a footprint in soil) and ejection of material. The Ejection-Velocity Measurement System (EVMS) in the Experimental Impact Laboratory has been used to study ejection velocities from impact craters formed in sand since the late 1990s. The original system used an early-generation Charge-Coupled Device (CCD) camera; custom-written software; and a complex, multicomponent optical system to direct laser light for illumination. Unfortunately, the electronic equipment was overtaken by age, and the software became obsolete in light of improved computer hardware.

  13. Mapping nuclear craters on Enewetak Atoll, Marshall Islands

    Science.gov (United States)

    Hampson, John C., Jr.

    1986-01-01

    In 1984, the U.S. Geological Survey conducted a detailed geologic analysis of two nuclear test craters at Enewetak Atoll, Marshall Islands, on behalf of the Defense Nuclear Agency. A multidisciplinary task force mapped the morphology, surface character, and subsurface structure of two craters, OAK and KOA. The field mapping techniques include echo sounding, sidescan sonar imaging, single-channel and multichannel seismic reflection profiling, a seismic refraction survey, and scuba and submersible operations. All operations had to be navigated precisely and correlatable with subsequent drilling and sampling operations.

  14. Exploring oceanic impact crater mechanics through numerical models

    Science.gov (United States)

    Wünnemann, K.; Lange, M. A.

    2002-12-01

    The mechanics of oceanic impact events differ in several ways from the processes that accompany the strike of an asteroid on land. In order to explore the cratering process on a water-covered target, a series of 2D hydrocode simulations have been carried out. Whereas crater structures on continental targets are the result of a gravity-driven collapse of the transient cavity that is formed immediately after the impact, we show that oceanic impact structures are additionally modified by strong water movements along the ocean-sea floor interface. Water currents directed both inwardly and outwardly from the impact point result in significant structural disturbances of the pelagic sediments. These currents are treated in the numerical models through an analysis of massless tracer particles movement initially placed in the target. In the models it is shown, that the modification of the ocean floor by water currents takes place, regardless of whether or not the residual kinetic energy of the impactor is large enough to penetrate the water column and to form a crater at the ocean floor. This hypothesis verified by an investigation of the so far only known deep sea impact structure, the Eltanin impact structure. Here a zone of chaotically deposited sediments was found but no depression in the ocean floor has been detected. Strong water surges play also an import role in the modification of crater structures at relatively shallow water depth on the continental shelf. This has been observed in the formation of gullies at the Lockne structure in Sweden. Even more surprisingly is the existence of a ringed impact structure in the North Sea, the Silverpit crater, which has a diameter of only 20 km. We explain the formation of a ring structure, which has not previously been thought possible at such a small scale, via numerical modelling by extremely weak strength properties of the target rocks. This kind of strength softening may be due to the fact, that water is involved in the

  15. Pleistocene cohesive debris flows at Nevado de Toluca Volcano, central Mexico

    Science.gov (United States)

    Capra, L.; Macías, J. L.

    2000-10-01

    During the Pleistocene, intense hydrothermal alteration promoted a flank failure of the southern portion of Nevado de Toluca volcano. This event produced a debris avalanche that transformed into a cohesive debris flow (Pilcaya deposit) owing to water saturation and weakness of the altered pre-avalanche rocks. The Pilcaya debris flow traveled along a narrow tectonic depression up to a distance of 40 km and then spread over a flat plain reaching up to 55 km from the volcano summit. This transition zone corresponds with a sudden break in slope from 5 to 0.5° that caused a rapid reduction in velocity and thickening of the flow that consequently reduced its competence to transport large particles. The resulting deposit thickens from 15 to 40 m, and contains boulders up to 15 m in diameter that form hummocky morphology close to the transitional zone. Sometime after the emplacement of the Pilcaya debris flow, heavy rains and superficial drainage contributed to remobilize the upper portions of the deposit causing two secondary lahars. These debris flows called El Mogote, traveled up to 75 km from the volcano. The edifice collapse generated lahars with a total volume of 2.8 km 3 that devastated an approximate area of 250 km 2. The area versus volume plot for both deposits shows that the magnitude of the event is comparable to other cohesive debris flows such as the Teteltzingo lahar (Pico de Orizaba, Mexico) and the Osceola mudflow (Mount Rainier, Wa). The Pilcaya debris flow represents additional evidence of debris flow transformed from a flank failure, a potentially devastating phenomenon that could threaten distant areas from the volcano previously considered without risk.

  16. WFC3 UVIS Detector: Improved Flat Fields

    Science.gov (United States)

    Dahlen, Tomas; Mack, J.; Sabbi, E.; WFC3 Team

    2012-01-01

    We describe the improved flat field calibration for a set of UVIS broad-band filters that were delivered to MAST in August 2011. The total change peak-to-peak with respect to the previous pipeline flats ranges from 3.6% to 5.6%, increasing with wavelength. The flat-fields previously used in the pipeline were obtained during ground testing and contained a large reflection ghost (or flare) that affected 40% of the field. A simplified geometric model of the internal light reflections has been used to remove the flare from the ground flats. Residual low-frequency structures caused by differences in the ground-based and in-flight optical paths were then computed using photometry of Omega Centauri, observed at various roll angles and with large dithered steps. Furthermore, photometry in a range of apertures has been used to study the UVIS PSF in detail. For radii smaller than 0.4" (10 pixels) the PSF is strongly dependent on both the detector position and on the telescope focus at the time of observation. Therefore, the new pipeline flat fields have been normalized to "infinite" aperture by applying local aperture corrections to 10 pixels, making them more generally applicable.

  17. CPR evolution of kilometer-scale craters on the lunar mare

    Science.gov (United States)

    King, Isabel; Fassett, Caleb; Thomson, Bradley J.; Minton, David A.; Watters, Wesley A.

    2016-10-01

    This study analyzes the 12.6-cm radar signature of kilometer-scale craters using data from the Mini-RF instrument on the Lunar Reconnaissance Orbiter. We examine the circular polarization ratio (CPR), which is sensitive to rockiness and surface roughness at the decimeter scale, to determine if there is a relationship between CPR signature and age for craters on the lunar mare. The craters come from an existing dataset of >13,000 craters ranging 800 m to 5 km in diameter that have previously determined degradation states based on their topography. The locations of craters in the original data set were manually co-registered to Mini-RF level 2 observations from the PDS, and for each crater, radial CPR profiles were extracted. In total, there were 5,142 unique craters with Mini-RF observations; 914 craters had repeat measurements that were used to assess uncertainties in CPR profiles. To characterize the time evolution of CPR, the craters were analyzed by finding the median profiles for groups of craters sorted by age and diameter. The highest CPR values are found in the interiors of the craters, and for craters ≤2 km, the freshest craters have the highest CPR values. In the ejecta, fresh craters exhibit the highest CPR, and this decreases with time until an equilibrium is reached. As expected from theory, larger craters' profiles evolve less quickly, with only minor changes in CPR inside their rim and a slower decrease of CPR in their ejecta. In conjunction with other datasets like topography, optical maturity, and rockiness, these data are important for constraining models of regolith evolution and crater degradation on the Moon.

  18. Cleopatra crater on Venus - Venera 15/16 data and impact/volcanic origin controversy

    Science.gov (United States)

    Basilevsky, A. T.; Ivanov, B. A.

    1990-02-01

    The morphology and morphometry of the 100-km diameter, 2.4-km deep Cleopatra crater on Venus are examined using Venera 15/16 images. The Cleopatra crater is compared to circular structures on Venus, Mercury, Mars, the earth and the moon. Consideration is given to the possible causes for the genesis of the Cleopatra crater. It is concluded that Cleopatra has a clear impact basin morphology with an anomalous crater depth.

  19. Towards an Integrated Geomagnetic Polarity Reversal Timescale for the Pleistocene

    DEFF Research Database (Denmark)

    Rivera, Tiffany; Storey, Michael; Kuiper, Klaudia

    The development of the geomagnetic polarity timescale (GPTS) in the mid 20th century led to the greater understanding of seafloor spreading and plate tectonics (Heirtzler et al., 1968). Over 40 years later, the GPTS continues to be refined, particularly in terms of integrating multiple dating...... of various geologic events. Here, we review the ages of three Pleistocene geomagnetic polarity reversals: the Matuyama-Brunhes (ca. 0.78 Ma), the Cobb Mountain (ca. 1.2 Ma), and the Reunion (ca. 2.1 Ma) events. High-precision astronomically calibrated 40Ar/39Ar ages have been obtained via a Noblesse multi...

  20. Early Pleistocene glacial cycles and the integrated summer insolation forcing.

    Science.gov (United States)

    Huybers, Peter

    2006-07-28

    Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun.

  1. Isotope studies of fossil bones of Pleistocene Yakut horses

    Directory of Open Access Journals (Sweden)

    A. Di Matteo

    2013-01-01

    Full Text Available Well-conserved carcasses of ancient large mammals can be found in permafrost of North-eastern Siberia. Mummified remains of ancient horses are rather rare ones. Complex stable isotope studies of 5 mummies and several horses’ bones from Northern Yakutia were carried out. Results obtained testify to possibility to use carbon isotope composition of hydroxylapatite carbonate from horses’ bones as palaeoclimatic indicator. It was determined relative (warmer or cooler, more dry or humid environmental conditions during our horses’ lives. Preliminary data allow us to suppose that in Late Pleistocene lived in similar landscapes as well in Yakutia as Western Europe.

  2. An in-depth study of Marcia Crater, Vesta

    Science.gov (United States)

    Hiesinger, Harald; Ruesch, Ottaviano; Williams, David A.; Nathues, Andreas; Prettyman, Thomas H.; Tosi, Frederico; De Sanctis, M. Christina; Scully, Jennifer E. C.; Schenk, Paul M.; Aileen Yingst, R.; Denevi, Bret W.; Jaumann, Ralf; Raymond, Carol A.; Russell, Chris T.

    2014-05-01

    After visiting the second most massive asteroid Vesta from July 2011 to September 2012, the Dawn spacecraft is now on its way to asteroid Ceres. Dawn observed Vesta with three instruments: the German Framing Camera (FC), the Italian Visible and InfraRed mapping spectrometer (VIR), and the American Gamma Ray and Neutron Detector (GRaND) [1]. Marcia crater (190°E, 10°N; 68 x 58 km) is the largest of three adjacent impact structures: Marcia (youngest), Calpurnia, and Minucia (oldest). It is the largest well-preserved post-Rheasilvia impact crater, shows a complex geology [2], is young [2], exhibits evidence for gully-like mass wasting [3], contains the largest location of pitted terrain [4], has smooth impact melt ponds [5], shows enhanced spectral pyroxene signatures on its inner walls [2], and has low abundances of OH and H in comparison to the surrounding low-albedo terrain [6, 7]. Geophysically, the broad region of Marcia and Calpurnia craters is characterized by a higher Bouguer gravity, indicating denser material [9]. Williams et al. [2] have produced a detailed geologic map of Marcia crater and the surrounding terrain. They identified several units within Marcia crater, including bright crater material, pitted terrain, and smooth material. Units outside Marcia, include undivided crater ejecta material, bright lobate material, dark lobate material, and dark crater ray material [2]. Because of its extensive ejecta and fresh appearance, the Marcia impact defines a major stratigraphic event, postdating the Rheasilvia impact [2]. However, the exact age of Marcia crater is still under debate. Compositionally, Marcia crater is characterized by higher iron abundances, which were interpreted as more basaltic-eucrite-rich materials suggesting that this region has not been blanketed by diogenitic materials from large impact events [10, 11]. Using FC data, [13] identified "gray material" associated with the ejecta blanket of Marcia crater. This material is characterized

  3. Geological observation of impact craters on Mars and the earth using remote-sensing methods

    Science.gov (United States)

    Garvin, J. B.

    1988-01-01

    It has been suggested that future multispectral and radar remote sensing of Martian craters can be developed on the basis of studies of multispectral and radar signatures of earth craters which are reasonable analogues of the Martian varieties. The present paper is a contribution toward establishing a methodology for detecting the record of very fresh craters on Mars.

  4. Automatic detection of sub-km craters in high resolution planetary images

    Science.gov (United States)

    Urbach, Erik R.; Stepinski, Tomasz F.

    2009-06-01

    Impact craters are among the most studied geomorphic planetary features because they yield information about the past geological processes and provide a tool for measuring relative ages of observed geologic formations. Surveying impact craters is an important task which traditionally has been achieved by means of visual inspection of images. The shear number of smaller craters present in high resolution images makes visual counting of such craters impractical. In this paper we present a method that brings together a novel, efficient crater identification algorithm with a data processing pipeline; together they enable a fully automatic detection of sub-km craters in large panchromatic images. The technical details of the method are described and its performance is evaluated using a large, 12.5 m/pixel image centered on the Nanedi Valles on Mars. The detection percentage of the method is ˜70%. The system detects over 35,000 craters in this image; average crater density is 0.5craters/km2, but localized spots of much higher crater density are present. The method is designed to produce "million craters" global catalogs of sub-km craters on Mars and other planets wherever high resolution images are available. Such catalogs could be utilized for deriving high spatial resolution and high temporal precision stratigraphy on regional or even planetary scale.

  5. Magnetized and Flat Beam Experiment at FAST

    Energy Technology Data Exchange (ETDEWEB)

    Halavanau, A. [Fermilab; Hyun, J. [Sokendai, Tsukuba; Mihalcea, D. [NIU, DeKalb; Piot, P. [NICADD, DeKalb; Sen, T. [Fermilab; Thangaraj, C. [Fermilab

    2017-05-22

    A photocathode, immersed in solenoidal magnetic field, can produce canonical-angular-momentum (CAM) dominated or “magnetized” electron beams. Such beams have an application in electron cooling of hadron beams and can also be uncoupled to yield asymmetric-emittance (“flat”) beams. In the present paper we explore the possibilities of the flat beam generation at Fermilab’s Accelerator Science and Technology (FAST) facility. We present optimization of the beam flatness and four-dimensional transverse emittance and investigate the mapping and its limitations of the produced eigen-emittances to conventional emittances using a skew-quadrupole channel. Possible application of flat beams at the FAST facility are also discussed.

  6. Witten spinors on maximal, conformally flat hypersurfaces

    CERN Document Server

    Frauendiener, Jörg; Szabados, László B

    2011-01-01

    The boundary conditions that exclude zeros of the solutions of the Witten equation (and hence guarantee the existence of a 3-frame satisfying the so-called special orthonormal frame gauge conditions) are investigated. We determine the general form of the conformally invariant boundary conditions for the Witten equation, and find the boundary conditions that characterize the constant and the conformally constant spinor fields among the solutions of the Witten equations on compact domains in extrinsically and intrinsically flat, and on maximal, intrinsically globally conformally flat spacelike hypersurfaces, respectively. We also provide a number of exact solutions of the Witten equation with various boundary conditions (both at infinity and on inner or outer boundaries) that single out nowhere vanishing spinor fields on the flat, non-extreme Reissner--Nordstr\\"om and Brill--Lindquist data sets. Our examples show that there is an interplay between the boundary conditions, the global topology of the hypersurface...

  7. Genetic variation in the southern pines: evolution, migration, and adaptation following the pleistocene

    Science.gov (United States)

    Ronald Schmidtling

    2007-01-01

    Climate has certainly changed over time, requiring genetic change or migration of forest tree species. Little is known about the location of the southern pines during the Pleistocene glaciation, which ended around 14,000 years ago. Macrofossils of spruce (Picea spp.) dating from the late Pleistocene, which are typical of climates much cooler than...

  8. Taming Past LTL and Flat Counter Systems

    CERN Document Server

    Demri, Stéphane; sangnier, Arnaud

    2012-01-01

    Reachability and LTL model-checking problems for flat counter systems are known to be decidable but whereas the reachability problem can be shown in NP, the best known complexity upper bound for the latter problem is made of a tower of several exponentials. Herein, we show that the problem is only NP-complete even if LTL admits past-time operators and arithmetical constraints on counters. Actually, the NP upper bound is shown by adequately combining a new stuttering theorem for Past LTL and the property of small integer solutions for quantifier-free Presburger formulae. Other complexity results are proved, for instance for restricted classes of flat counter systems.

  9. Scalar Curvature and Intrinsic Flat Convergence

    CERN Document Server

    Sormani, Christina

    2016-01-01

    Herein we present open problems and survey examples and theorems concerning sequences of Riemannian manifolds with uniform lower bounds on scalar curvature and their limit spaces. Examples of Gromov and of Ilmanen which naturally ought to have certain limit spaces do not converge with respect to smooth or Gromov-Hausdorff convergence. Thus we focus here on the notion of Intrinsic Flat convergence, developed jointly with Wenger. This notion has been applied successfully to study sequences that arise in General Relativity. Gromov has suggested it should be applied in other settings as well. We first review intrinsic flat convergence, its properties, and its compactness theorems, before presenting the applications and the open problems.

  10. Static cylindrical symmetry and conformal flatness

    CERN Document Server

    Herrera, L; Marcilhacy, G; Santos, N O

    2004-01-01

    We present the whole set of equations with regularity and matching conditions required for the description of physically meaningful static cylindrically symmmetric distributions of matter, smoothly matched to Levi-Civita vacuum spacetime. It is shown that the conformally flat solution with equal principal stresses represents an incompressible fluid. It is also proved that any conformally flat cylindrically symmetric static source cannot be matched through Darmois conditions to the Levi-Civita spacetime. Further evidence is given that when the Newtonian mass per unit length reaches 1/2 the spacetime has plane symmetry.

  11. The flat phase of quantum polymerized membranes

    CERN Document Server

    Coquand, O

    2016-01-01

    We investigate the flat phase of quantum polymerized phantom membranes by means of a nonperturbative renormalization group approach. We first implement this formalism for general quantum polymerized membranes and derive the flow equations that encompass both quantum and thermal fluctuations. We then deduce and analyze the flow equations relevant to study the flat phase and discuss their salient features : quantum to classical crossover and, in each of these regimes, strong to weak coupling crossover. We finally illustrate these features in the context of free standing graphene physics.

  12. Ultimate resolution of indefinite metamaterial flat lenses

    CERN Document Server

    Bénédicto, Jessica; Pollès, Rémi; Moreau, Antoine

    2013-01-01

    We show that any metallo-dielectric multilayer with a hyperbolic dispersion relation can actually be characterized by a complex effective index. This refractive index, extracted from the complex Bloch band diagram, can be directly linked to the super-resolution of a flat lens made of this so- called indefinite metamaterials. This allows for a systematic optimization of the lens design, leading to structures that are outperforming state-of-art flat lenses. We show that, even when fully taking absorption into account, our design provides super-resolved images for visible light up to a distance of one wavelength from the lens edge.

  13. Late Pleistocene fishes of the Tennessee River Basin: an analysis of a late Pleistocene freshwater fish fauna from Bell Cave (site ACb-2) in Colbert County, Alabama, USA

    OpenAIRE

    Jacquemin, Stephen J.; Jun A. Ebersole; Dickinson, William C.; Charles N Ciampaglio

    2016-01-01

    The Tennessee River Basin is considered one of the most important regions for freshwater biodiversity anywhere on the globe. The Tennessee River Basin currently includes populations of at least half of the described contemporary diversity of extant North American freshwater fishes, crayfish, mussel, and gastropod species. However, comparatively little is known about the biodiversity of this basin from the Pleistocene Epoch, particularly the late Pleistocene (∼10,000 to 30,000 years B.P.) lead...

  14. Channels on Dunes in Russell Crater

    Science.gov (United States)

    2006-01-01

    Hundreds of enigmatic small channels are seen to carve into the slopes of these dark sand dunes lying within Russell Crater on Mars. These features were previously identified as gullies in images from the Mars Orbiter Camera (MOC) on Mars Global Surveyor, but the higher resolution HiRISE image brings out many new details and mysteries. The channels extend from near the top of the dunes to their bases, indicating that some fluid material carved into the sand. The channels commonly begin as smaller tributaries joined together, suggesting several sources of fluid. Distinct dark spots are located near where the channels seem to originate. Several channels appear to originate at alcoves. Several of these channels have sinuous middle reaches while others are straighter. Further down slope, some channel edges appear elevated above the surrounding terrain, particularly in the lower reaches. The channels seem to terminate abruptly, with no deposition of material, unlike at the bases of some other gullies on Mars that are not on dunes. One hypothesis for the origin of the channels, which has previously been proposed by the MOC team, is that CO2 (or maybe H2O) frost is deposited on the dunes in shadows or at night. Some frost may also be incorporated into the internal parts of the dunes due to natural avalanching. When the frost is eventually heated by sunlight, rapid sublimation triggers an avalanche of fluidized sand, forming a gully. HiRISE will continue to target small channel features such as these and may return to search for any changes over time. Image PSP_001440_1255 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on November 16, 2006. The complete image is centered at -54.2 degrees latitude, 12.9 degrees East longitude. The range to the target site was 251.4 km (157.1 miles). At this distance the image scale is 50.3 cm/pixel (with 2 x 2 binning) so objects 151 cm across are resolved. The

  15. Arctic East Siberia had a lower latitude in the Pleistocene

    CERN Document Server

    Wölfli, W

    2006-01-01

    In Arctic East Siberia many remains of mammoths have been found. In this region there is not sufficient sunlight over the year to allow for the growth of the plants on which these animals feed. Consequently the latitude of these regions must have been lower before the end of the Pleistocene than at present. It is a challenge to reconstruct this geographic shift of the poles in a manner compa- tible with known facts. A possible sequence of events is described here. It as- sumes an additional planet, which must since have disappeared. This is possible, if it moved in an extremely eccentric orbit and was hot as a result of tidal work and solar radiation. During a few million years evaporation of this planet led to a disk-shaped cloud of ions moving around the Sun. This cloud partially shielded the Earth from the solar radiation, producing the alteration of cold and warm periods characterizing the Pleistocene. The degree of shielding is sensitive to the inclination of Earth's orbit, which has a period of 100000 y...

  16. Brain ontogeny and life history in Pleistocene hominins

    Science.gov (United States)

    Hublin, Jean-Jacques; Neubauer, Simon; Gunz, Philipp

    2015-01-01

    A high level of encephalization is critical to the human adaptive niche and emerged among hominins over the course of the past 2 Myr. Evolving larger brains required important adaptive adjustments, in particular regarding energy allocation and life history. These adaptations included a relatively small brain at birth and a protracted growth of highly dependent offspring within a complex social environment. In turn, the extended period of growth and delayed maturation of the brain structures of humans contribute to their cognitive complexity. The current palaeoanthropological evidence shows that, regarding life history and brain ontogeny, the Pleistocene hominin taxa display different patterns and that one cannot simply contrast an ‘ape-model’ to a ‘human-model’. Large-brained hominins such as Upper Pleistocene Neandertals have evolved along their own evolutionary pathway and can be distinguished from modern humans in terms of growth pattern and brain development. The life-history pattern and brain ontogeny of extant humans emerged only recently in the course of human evolution. PMID:25602066

  17. Late Pleistocene and Holocene mammal extinctions on continental Africa

    Science.gov (United States)

    Faith, J. Tyler

    2014-01-01

    Understanding the cause of late Quaternary mammal extinctions is the subject of intense debate spanning the fields of archeology and paleontology. In the global context, the losses on continental Africa have received little attention and are poorly understood. This study aims to inspire new discussion of African extinctions through a review of the extinct species and the chronology and possible causes of those extinctions. There are at least 24 large mammal (> 5 kg) species known to have disappeared from continental Africa during the late Pleistocene or Holocene, indicating a much greater taxonomic breadth than previously recognized. Among the better sampled taxa, these losses are restricted to the terminal Pleistocene and early Holocene, between 13,000 and 6000 yrs ago. The African extinctions preferentially affected species that are grazers or prefer grasslands. Where good terrestrial paleoenvironmental records are present, extinctions are associated with changes in the availability, productivity, or structure of grassland habitats, suggesting that environmental changes played a decisive role in the losses. In the broader evolutionary context, these extinctions represent recent examples of selective taxonomic winnowing characterized by the loss of grassland specialists and the establishment of large mammal communities composed of more ecologically flexible taxa over the last million years. There is little reason to believe that humans played an important role in African extinctions.

  18. Plio-Pleistocene Biogenic Opal Deposition in the Southern Ocean

    Science.gov (United States)

    Kuhn, G.; Gersonde, R.

    2002-12-01

    About 2/3 of the annual supply of silicic acid to the World Ocean is buried in the Southern Ocean as biogenic silica (BSi), formed by diatoms and radiolaria in surface waters and exported to the seafloor. Main BSi accumulation occurs in an area between the sea ice edge and the Polar Front Zone and seems to be steered by a complex interaction of biological and physical parameters governing the modern Southern Ocean ecosystem. Sediment cores recovered during Ocean Drilling Program Leg 177 and expeditions with RV POLARSTERN reveal the history of the opal deposition in the Atlantic and Pacific sector of the Southern Ocean during the Pliocene and the Pleistocene. This period is characterized by distinct changes and variability in global climate and ocean circulation that can be related to the spatial-temporal distribution of BSi deposition on long and short time scales. Changes in ocean circulation, water mass structure, sea ice and climatic variability that impact the distribution of silicic acid and the development of coarsly silicified diatoms (e.g. Actinocyclus ingens, Thalassiosira antarctica, Fragilariopsis kerguelensis), presenting the major carriers of biogenic opal, control past BSi deposition in the Southern Ocean. Major deposition in the area of the modern Southern Ocean opal belt starts at the Plio/Pleistocene transition. Such strong export of BSi and related organic carbon might have reinforced the trend of global cooling observed since the Mid-Pliocene climate optimum.

  19. New Middle Pleistocene hominin cranium from Gruta da Aroeira (Portugal).

    Science.gov (United States)

    Daura, Joan; Sanz, Montserrat; Arsuaga, Juan Luis; Hoffmann, Dirk L; Quam, Rolf M; Ortega, María Cruz; Santos, Elena; Gómez, Sandra; Rubio, Angel; Villaescusa, Lucía; Souto, Pedro; Mauricio, João; Rodrigues, Filipa; Ferreira, Artur; Godinho, Paulo; Trinkaus, Erik; Zilhão, João

    2017-03-28

    The Middle Pleistocene is a crucial time period for studying human evolution in Europe, because it marks the appearance of both fossil hominins ancestral to the later Neandertals and the Acheulean technology. Nevertheless, European sites containing well-dated human remains associated with an Acheulean toolkit remain scarce. The earliest European hominin crania associated with Acheulean handaxes are at the sites of Arago, Atapuerca Sima de los Huesos (SH), and Swanscombe, dating to 400-500 ka (Marine Isotope Stage 11-12). The Atapuerca (SH) fossils and the Swanscombe cranium belong to the Neandertal clade, whereas the Arago hominins have been attributed to an incipient stage of Neandertal evolution, to Homo heidelbergensis, or to a subspecies of Homo erectus A recently discovered cranium (Aroeira 3) from the Gruta da Aroeira (Almonda karst system, Portugal) dating to 390-436 ka provides important evidence on the earliest European Acheulean-bearing hominins. This cranium is represented by most of the right half of a calvarium (with the exception of the missing occipital bone) and a fragmentary right maxilla preserving part of the nasal floor and two fragmentary molars. The combination of traits in the Aroeira 3 cranium augments the previously documented diversity in the European Middle Pleistocene fossil record.

  20. Homo naledi and Pleistocene hominin evolution in subequatorial Africa

    Science.gov (United States)

    Berger, Lee R; Hawks, John; Dirks, Paul HGM; Elliott, Marina; Roberts, Eric M

    2017-01-01

    New discoveries and dating of fossil remains from the Rising Star cave system, Cradle of Humankind, South Africa, have strong implications for our understanding of Pleistocene human evolution in Africa. Direct dating of Homo naledi fossils from the Dinaledi Chamber (Berger et al., 2015) shows that they were deposited between about 236 ka and 335 ka (Dirks et al., 2017), placing H. naledi in the later Middle Pleistocene. Hawks and colleagues (Hawks et al., 2017) report the discovery of a second chamber within the Rising Star system (Dirks et al., 2015) that contains H. naledi remains. Previously, only large-brained modern humans or their close relatives had been demonstrated to exist at this late time in Africa, but the fossil evidence for any hominins in subequatorial Africa was very sparse. It is now evident that a diversity of hominin lineages existed in this region, with some divergent lineages contributing DNA to living humans and at least H. naledi representing a survivor from the earliest stages of diversification within Homo. The existence of a diverse array of hominins in subequatorial comports with our present knowledge of diversity across other savanna-adapted species, as well as with palaeoclimate and paleoenvironmental data. H. naledi casts the fossil and archaeological records into a new light, as we cannot exclude that this lineage was responsible for the production of Acheulean or Middle Stone Age tool industries. DOI: http://dx.doi.org/10.7554/eLife.24234.001 PMID:28483041

  1. Microbial Habitability and Pleistocene Aridification of the Asian Interior.

    Science.gov (United States)

    Wang, Jiuyi; Lowenstein, Tim K; Fang, Xiaomin

    2016-06-01

    Fluid inclusions trapped in ancient halite can contain a community of halophilic prokaryotes and eukaryotes that inhabited the surface brines from which the halite formed. Long-term survival of bacteria and archaea and preservation of DNA have been reported from halite, but little is known about the distribution of microbes in buried evaporites. Here we report the discovery of prokaryotes and single-celled algae in fluid inclusions in Pleistocene halite, up to 2.26 Ma in age, from the Qaidam Basin, China. We show that water activity (aw), a measure of water availability and an environmental control on biological habitability in surface brines, is also related to microbe entrapment in fluid inclusions. The aw of Qaidam Basin brines progressively decreased over the last ∼1 million years, driven by aridification of the Asian interior, which led to decreased precipitation and water inflow and heightened evaporation rates. These changes in water balance produced highly concentrated brines, which reduced the habitability of surface lakes and decreased the number of microbes trapped in halite. By 0.13 Ma, the aw of surface brines approached the limits tolerated by halophilic prokaryotes and algae. These results show the response of microbial ecosystems to climate change in an extreme environment, which will guide future studies exploring deep life on Earth and elsewhere in the Solar System. Halite fluid inclusions-Ancient microbes-Water activity-Qaidam Basin-Pleistocene aridification. Astrobiology 16, 379-388.

  2. Middle Pleistocene hominids from Olduvai Gorge, northern Tanzania.

    Science.gov (United States)

    Rightmire, G P

    1980-08-01

    Cranial, dental, and mandibular remains of eight Olduvai hominids are described in detail. Four individuals were recovered in situ in Beds II to IV, while three more are most probably derived from Bed IV, the Masek Beds and the Lower Ndutu Beds. One specimen is of uncertain provenance. Deposits from which the fossils were collected range from late Lower Pleistocene to Middle Pleistocene in age. Of particular interest are three fragmentary lower jaws, which can be compared to mandibles of Homo erectus known from localities in Northwest Africa and China. Olduvai hominid 22, a nearly complete half mandible with crowns of P3-M2 in place, shares many anatomical features with fossils from Ternifine and Choukoutien. This individual is also similar to a jaw from the Kapthurin Formation west of Lake Baringo, Kenya. How best to interpret these comparisons is not clear, but in view of marked similarities between specimens representing geographically diverse populations from different time periods, it may be unwise to rely on mandibular evidence alone to document the presence of regional lineages. Gradual change and continuity within a sequence of Northwest African Homo fossils has been endorsed by many workers, but such hypotheses cannot be tested adequately with the fragmentary jaws available.

  3. Mineralogy of a mudstone at Yellowknife Bay, Gale crater, Mars

    NARCIS (Netherlands)

    Vaniman, D.T.; Bish, D.L.; Ming, D.W.; Bristow, T.F.; Morris, R.V.; Blake, D.F.; Chipera, S.J.; Morrison, S.M.; Treiman, A.H.; Rampe, E.B.; Rice, M.; Achilles, C.N.; Grotzinger, J.P.; McLennan, S.M.; Williams, J.; Bell III, J.F.; Newsom, H.E.; Downs, R.T.; Maurice, S.; Sarrazin, P.; Yen, A.S.; Morookian, J.M.; Farmer, J.D.; Stack, K.; Milliken, R.E.; Ehlmann, B.L.; Sumner, D.Y.; Berger, G.; Crisp, J.A.; Hurowitz, J.A.; Anderson, R.; Des Marais, D.J.; Stolper, E.M.; Edgett, K.S.; Gupta, S.; Spanovich, N.; MSL Science Team, the

    2014-01-01

    Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John

  4. Foraminiferal repopulation of the late Eocene Chesapeake Bay impact crater

    Science.gov (United States)

    Poag, C. Wylie

    2012-01-01

    The Chickahominy Formation is the initial postimpact deposit in the 85km-diameter Chesapeake Bay impact crater, which is centered under the town of Cape Charles, Virginia, USA. The formation comprises dominantly microfossil-rich, silty, marine clay, which accumulated during the final ~1.6myr of late Eocene time. At cored sites, the Chickahominy Formation is 16.8-93.7m thick, and fills a series of small troughs and subbasins, which subdivide the larger Chickahominy basin. Nine coreholes drilled through the Chickahominy Formation (five inside the crater, two near the crater margin, and two ~3km outside the crater) record the stratigraphic and paleoecologic succession of 301 indigenous species of benthic foraminifera, as well as associated planktonic foraminifera and bolboformids. Two hundred twenty of these benthic species are described herein, and illustrated with scanning electron photomicrographs. Absence of key planktonic foraminiferal and Bolboforma species in early Chickahominy sediments indicates that detrimental effects of the impact also disturbed the upper oceanic water column for at least 80-100kyr postimpact. After an average of ~73kyr of stressed, rapidly fluctuating paleoenvironments, which were destabilized by after-effects of the impact, most of the cored Chickahominy subbasins maintained stable, nutrient-rich, low-oxygen bottom waters and interstitial microhabitats for the remaining ~1.3myr of late Eocene time.

  5. Impact craters as biospheric microenvironments, Lawn Hill Structure, Northern Australia.

    Science.gov (United States)

    Lindsay, John; Brasier, Martin

    2006-04-01

    Impact craters on Mars act as traps for eolian sediment and in the past may have provided suitable microenvironments that could have supported and preserved a stressed biosphere. If this is so, terrestrial impact structures such as the 18-km-diameter Lawn Hill Structure, in northern Australia, may prove useful as martian analogs. We sampled outcrop and drill core from the carbonate fill of the Lawn Hill Structure and recorded its gamma-log signature. Facies data along with whole rock geochemistry and stable isotope signatures show that the crater fill is an outlier of the Georgina Basin and was formed by impact at, or shortly before, approximately 509-506 million years ago. Subsequently, it was rapidly engulfed by the Middle Cambrian marine transgression, which filled it with shallow marine carbonates and evaporites. The crater formed a protected but restricted microenvironment in which sediments four times the thickness of the nearby basinal succession accumulated. Similar structures, common on the martian surface, may well have acted as biospheric refuges as the planet's water resources declined. Low-pH aqueous environments on Earth similar to those on Mars, while extreme, support diverse ecologies. The architecture of the eolian crater fill would have been defined by long-term ground water cycles resulting from intermittent precipitation in an extremely arid climate. Nutrient recycling, critical to a closed lacustrine sub-ice biosphere, could be provided by eolian transport onto the frozen water surface.

  6. Impact Crater Experiments for Introductory Physics and Astronomy Laboratories

    Science.gov (United States)

    Claycomb, J. R.

    2009-01-01

    Activity-based collisional analysis is developed for introductory physics and astronomy laboratory experiments. Crushable floral foam is used to investigate the physics of projectiles undergoing completely inelastic collisions with a low-density solid forming impact craters. Simple drop experiments enable determination of the average acceleration,…

  7. Tsiolkovskiy Crater Thermophysical Anomaly: Massive Impact Melt or Surface Modification?

    Science.gov (United States)

    Greenhagen, Benjamin; Neish, C.; Williams, J.; Petro, N.; Hayne, P.; Bandfield, J.

    2013-10-01

    Analyses of data from the Diviner Lunar Radiometer have been used to identify an area of elevated rock abundance and nighttime soil temperature in and around Tsiolkovskiy Crater. Previous studies (e.g. Bandfield et al., 2011) have established a clear relationship between Diviner-derived rock abundances and crater age (most rocks are weathered into regolith within ~1 Ga) that would indicate a relatively young age for Tsiolkovskiy. However, the previously published ages for Tsiolkovskiy’s mare-fill (a lower limit on the crater age) are generally within the range 3.5 ± 0.3 Ga. To study the discrepancy between crater age and apparent “fresh” appearance we have used new datasets from Diviner, Mini-RF, and LROC to probe the near-surface regolith at variable depth and scales. We evaluated several hypotheses for the origin of this anomaly including: (1) inaccuracies in the published age estimates, (2) unusually high abundances of locally-derived, highly competent impact melt, (3) inclusion of significant blocky material from Aristarchus antipodal ejecta, and (4) recent surface modification or disruption. The results of our study favor (2) locally-derived, highly competent impact melt, and (5) recent surface modification or disruption over other mechanisms. This presentation will focus on describing the implications of the favored mechanisms.

  8. Crater formation by single ions, cluster ions and ion "showers"

    CERN Document Server

    Djurabekova, Flyura; Timko, Helga; Nordlund, Kai; Calatroni, Sergio; Taborelli, Mauro; Wuensch, Walter

    2011-01-01

    The various craters formed by giant objects, macroscopic collisions and nanoscale impacts exhibit an intriguing resemblance in shapes. At the same time, the arc plasma built up in the presence of sufficiently high electric fields at close look causes very similar damage on the surfaces. Although the plasma–wall interaction is far from a single heavy ion impact over dense metal surfaces or the one of a cluster ion, the craters seen on metal surfaces after a plasma discharge make it possible to link this event to the known mechanisms of the crater formations. During the plasma discharge in a high electric field the surface is subject to high fluxes (~1025 cm-2s-1) of ions with roughly equal energies typically of the order of a few keV. To simulate such a process it is possible to use a cloud of ions of the same energy. In the present work we follow the effect of such a flux of ions impinging the surface in the ‘‘shower’’ manner, to find the transition between the different mechanisms of crater formati...

  9. Unusual bacterioplankton community structure in ultra-oligotrophic Crater Lake

    Science.gov (United States)

    Urbach, Ena; Vergin, Kevin L.; Morse, Ariel

    2001-01-01

    The bacterioplankton assemblage in Crater Lake, Oregon (U.S.A.), is different from communities found in other oxygenated lakes, as demonstrated by four small subunit ribosomal ribonucleic acid (SSU rRNA) gene clone libraries and oligonucleotide probe hybridization to RNA from lake water. Populations in the euphotic zone of this deep (589 m), oligotrophic caldera lake are dominated by two phylogenetic clusters of currently uncultivated bacteria: CL120-10, a newly identified cluster in the verrucomicrobiales, and ACK4 actinomycetes, known as a minor constituent of bacterioplankton in other lakes. Deep-water populations at 300 and 500 m are dominated by a different pair of uncultivated taxa: CL500-11, a novel cluster in the green nonsulfur bacteria, and group I marine crenarchaeota. b-Proteobacteria, dominant in most other freshwater environments, are relatively rare in Crater Lake (marine crenarchaeota and green nonsulfur bacteria. Comparison of Crater Lake to other lakes studied by rRNA methods suggests that selective factors structuring Crater Lake bacterioplankton populations may include low concentrations of available trace metals and dissolved organic matter, chemistry of infiltrating hydrothermal waters, and irradiation by high levels of ultraviolet light.

  10. Fluid mechanical scaling of impact craters in unconsolidated granular materials

    Science.gov (United States)

    Miranda, Colin S.; Dowling, David R.

    2015-11-01

    A single scaling law is proposed for the diameter of simple low- and high-speed impact craters in unconsolidated granular materials where spall is not apparent. The scaling law is based on the assumption that gravity- and shock-wave effects set crater size, and is formulated in terms of a dimensionless crater diameter, and an empirical combination of Froude and Mach numbers. The scaling law involves the kinetic energy and speed of the impactor, the acceleration of gravity, and the density and speed of sound in the target material. The size of the impactor enters the formulation but divides out of the final empirical result. The scaling law achieves a 98% correlation with available measurements from drop tests, ballistic tests, missile impacts, and centrifugally-enhanced gravity impacts for a variety of target materials (sand, alluvium, granulated sugar, and expanded perlite). The available measurements cover more than 10 orders of magnitude in impact energy. For subsonic and supersonic impacts, the crater diameter is found to scale with the 1/4- and 1/6-power, respectively, of the impactor kinetic energy with the exponent crossover occurring near a Mach number of unity. The final empirical formula provides insight into how impact energy partitioning depends on Mach number.

  11. Clues to the Relative Timing of Lakes in Gale Crater

    Science.gov (United States)

    Dietrich, W. E.; Palucis, M. C.; Parker, T.; Rubin, D.; Lewis, K.; Sumner, D.; Williams, R. M. E.

    2014-07-01

    In Gale Crater two higher deltas appear to record the deposition into lakes associated with the cutting of Farah Vallis. At the entrance canyon to Mt. Sharp a possible back stepping fan/delta sequence may record a later rising lake level.

  12. Centrifuge Modeling of Explosion-Induced Craters in Unsaturated Sand

    Science.gov (United States)

    1992-11-01

    crater volume (V), the heat of detonation per unit mass (Q), initial density of the explosive (6), initial density of the soil (p), material strength...cyclotrimethylene trinitramine (RDX) and 6 percent Exon 461 (Baker et al., 1980) . Based on the heat of detonation , the TNT equivalent weightL for PBX 9407 and RDX

  13. A new study of crater concentric ridges on the Moon

    Science.gov (United States)

    Atwood-Stone, Corwin; Bray, Veronica J.; McEwen, Alfred S.

    2016-07-01

    Crater concentric ridges (CCRs) are topographic ridges found in the ejecta blankets of fresh few-kilometer-scale lunar craters. These ridges, which were last studied in detail in the late 1970 s (referred to as 'lunar concentric dunes'), were hypothesized to form due to ballistic impact sedimentation and erosion. We have surveyed the Moon to find 59 craters with CCRs and have constructed mosaics of these craters where possible using high-resolution LROC NAC (Lunar Reconnaissance Orbiter Camera-Narrow Angle Camera) images. We then map from some of these mosaics in order to measure the CCRs and examine their morphologies. Ejecta scaling models and some of our observations of the CCRs contradict the current hypothesis for the formation of these features. We therefore propose new hypotheses to consider for the formation of CCRs, specifically interaction of ejecta with initial topography or formation via interactions of shocks in the ejecta. Additionally, for the first time we have found CCRs on Mercury, but they are rare or absent on Mars.

  14. Venus - Stereo Image Pair of Crater Geopert-Meyer

    Science.gov (United States)

    1993-01-01

    During the third global cycle of Magellan's radar mapping mission, images were obtained at viewing angles that were slightly different than those used in the first two cycles. This strategy was designed to produce stereo image pairs, which take advantage of distortions induced by the different views to provide details of the surface topography. This is a stereo image pair of crater Geopert-Meyer, named for the 20th Century Polish physicist and Nobel laureate (60 degrees north latitude, 26.5 degrees east longitude). The crater, 35 kilometers (22 miles) in diameter, lies above an escarpment at the edge of a ridge belt in southern Ishtar Terra. West of the crater the scarp has more than one kilometer (0.6 mile) of relief. Perception of relief may be obtained with stereo glasses or a stereoscope. Some individuals may be able to fuse the images without the aid of those devices. The radar illumination for both images is from the west, or left side of the scene. Incidence angles are: (Cycle 1 (left) 28 degrees, Cycle 3 (right) 15 degrees from vertical. Analysis of stereo image pairs allows planetary scientists to resolve details of topographic relationships on Venusian craters, volcanoes, mountain belts and fault zones. The spatial resolution of this topographic information is approximately ten times better than that obtained by Magellan's altimetry experiment.

  15. Target and Projectile: Material Effects on Crater Excavation and Growth

    Science.gov (United States)

    Anderson, J. L. B.; Burleson, T.; Cintala, Mark J.

    2010-01-01

    Scaling relationships allow the initial conditions of an impact to be related to the excavation flow and final crater size and have proven useful in understanding the various processes that lead to the formation of a planetary-scale crater. In addition, they can be examined and tested through laboratory experiments in which the initial conditions of the impact are known and ejecta kinematics and final crater morphometry are measured directly. Current scaling relationships are based on a point-source assumption and treat the target material as a continuous medium; however, in planetary-scale impacts, this may not always be the case. Fragments buried in a megaregolith, for instance, could easily approach or exceed the dimensions of the impactor; rubble-pile asteroids could present similar, if not greater, structural complexity. Experiments allow exploration into the effects of target material properties and projectile deformation style on crater excavation and dimensions. This contribution examines two of these properties: (1) the deformation style of the projectile, ductile (aluminum) or brittle (soda-lime glass) and (2) the grain size of the target material, 0.5-1 mm vs. 1-3 mm sand.

  16. Cratering on Titan: A Pre-Cassini Perspective

    Science.gov (United States)

    Lorenz, R. D.

    1997-01-01

    The NASA-ESA Cassini mission, comprising a formidably instrumented orbiter and parachute-borne probe to be launched this October, promises to reveal a crater population on Titan that has been heretofore hidden by atmospheric haze. This population on the largest remaining unexplored surface in the solar system will be invaluable in comparative planetological studies, since it introduces evidence of the atmospheric effects of cratering on an icy satellite. Here, I highlight some impact features we may hope to find and could devote some modeling effort toward. Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s Atmosphere -94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface.Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s; Atmosphere about 94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface. Titan is comparable to Callisto and Ganymede for strength/gravity, Mars/Earth/Venus for atmospheric interaction, and Hyperion, Rhea, and Iapetus for impactor distribution. The leading/trailing asymmetry of crater density from heliocentric impactors is expected to be about 5-6, in the absence of resurfacing. Any Saturnocentric impactor population is likely to alter this. In particular the impact disruption of Hyperion is noted; because of the 3:4 orbital resonance with Titan, fragments from the proto-Hyperion breakup would have rapidly accreted onto Titan. Titan's resurfacing history is of course unknown. The disruption of impactors into fragments that individually create small craters is expected to occur. A crude estimate suggests a maximum separation of about 2 km

  17. Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars

    NARCIS (Netherlands)

    Freissinet, C.; Glavin, D. P.; Mahaffy, P. R.; Miller, K. E.; Eigenbrode, J. L.; Summons, R. E.; Brunner, A. E.; Buch, A.; Szopa, C.; Archer, P. D.; Franz, H. B.; Atreya, S. K.; Brinckerhoff, W. B.; Cabane, M.; Coll, P.; Conrad, P. G.; Des Marais, D. J.; Dworkin, J. P.; Fairén, A. G.; François, P.; Grotzinger, J. P.; Kashyap, S.; ten Kate, I. L.; Leshin, L. A.; Malespin, C. A.; Martin, M. G.; Martin-Torres, F. J.; Mcadam, A. C.; Ming, D. W.; Navarro-González, R.; Pavlov, A. A.; Prats, B. D.; Squyres, S. W.; Steele, A.; Stern, J. C.; Sumner, D. Y.; Sutter, B.; Zorzano, M. P.

    2015-01-01

    The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. C

  18. Cratering on Titan: A Pre-Cassini Perspective

    Science.gov (United States)

    Lorenz, R. D.

    1997-01-01

    The NASA-ESA Cassini mission, comprising a formidably instrumented orbiter and parachute-borne probe to be launched this October, promises to reveal a crater population on Titan that has been heretofore hidden by atmospheric haze. This population on the largest remaining unexplored surface in the solar system will be invaluable in comparative planetological studies, since it introduces evidence of the atmospheric effects of cratering on an icy satellite. Here, I highlight some impact features we may hope to find and could devote some modeling effort toward. Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s Atmosphere -94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface.Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s; Atmosphere about 94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface. Titan is comparable to Callisto and Ganymede for strength/gravity, Mars/Earth/Venus for atmospheric interaction, and Hyperion, Rhea, and Iapetus for impactor distribution. The leading/trailing asymmetry of crater density from heliocentric impactors is expected to be about 5-6, in the absence of resurfacing. Any Saturnocentric impactor population is likely to alter this. In particular the impact disruption of Hyperion is noted; because of the 3:4 orbital resonance with Titan, fragments from the proto-Hyperion breakup would have rapidly accreted onto Titan. Titan's resurfacing history is of course unknown. The disruption of impactors into fragments that individually create small craters is expected to occur. A crude estimate suggests a maximum separation of about 2 km

  19. A year of convective vortex activity at Gale crater

    Science.gov (United States)

    Steakley, Kathryn; Murphy, James

    2016-11-01

    Atmospheric convective vortices, which become dust devils when they entrain dust from the surface, are prominent features within Mars' atmosphere which are thought to be a primary contributor to the planet's background dust opacity. Buoyantly produced in convectively unstable layers at a planet's surface, these vertically aligned vortices possess rapidly rotating and ascending near-surface warm air and are readily identified by temporal signatures of reduced atmospheric surface pressure measured within the vortex as it passes by. We investigate such signatures in surface pressure measurements acquired by the Rover Environmental Monitoring Station aboard the Mars Science Laboratory rover located within Gale crater. During the first 707 sols of the mission, 245 convective vortices are identified with pressure drops in the range of 0.30-2.86 Pa with a median value of 0.67 Pa. The cumulative distribution of their pressure drops follows a power law of slope -2.77 and we observe seasonal and diurnal trends in their activity. The vast majority of these pressure signatures lack corresponding reductions in REMS-measured UV flux, suggesting that these vortices rarely cast shadows upon the rover and therefore are most often dust-free. The relatively weak-magnitude, dustless vortices at Gale crater are consistent with predictions from mesoscale modeling indicating that the planetary boundary layer is suppressed within the crater and are also consistent with the almost complete absence of both dust devils within Mars Science Laboratory camera images and Gale crater surface dust devil streaks within orbiter images.

  20. The large crater origin of SNC meteorites. [Shergottite, Nakhlite, Chassigny

    Science.gov (United States)

    Vickery, A. M.; Melosh, H. J.

    1987-01-01

    A large body of evidence strongly suggests that the shergottite, nakhlite, and Chassigny (SNC) meteorites are from Mars. Various mechanisms for the ejection of large rocks at Martian escape velocity (5 km/sec) have been investigated, but none has proved wholly satisfactory. This article examines a number of possible ejection and cosmic-ray exposure histories to determine which is most plausible. For each possible history, the Melosh (1984, 1985, 1987) spallation model is used to estimate the size of the crater required to produce ejecta fragments of the required size with velocities not less than 5 km/sec and to produce a total mass of solid ejecta consistent with the observed mass flux of SNC meteorites. Estimates of crater production rates on Mars are then used to evaluate the probability that sufficiently large craters have formed during the available time. The results indicate that the SNC meteorites were probably ejected from a very large crater (greater than 100 kilometers in diameter) about 200 million years ago, and that cosmic-ray exposure of the recovered meteorites was initiated after collisional fragmentation of the original ejecta in space at much later times (0.5 to 10 million years ago).

  1. Wildfires Caused by Formation of Small Impact Craters: A Kaali Crater Case

    Science.gov (United States)

    Losiak, Anna; Belcher, Claire; Hudspith, Victoria; Zhu, Menghua; Bronikowska, Malgorzata; Jõeleht, Argo; Plado, Juri

    2016-04-01

    Formation of ~200-km Chicxulub 65 Ma ago was associated with release of significant amount of thermal energy [1,2,3] which was sufficient to start wildfires that had either regional [4] or global [5] range. The evidence for wildfires caused by impacts smaller than Chicxulub is inconclusive. On one hand, no signs of fires are associated with the formation of 24-km Ries crater [6]. On the other hand, the Tunguska site was burned after the impact and the numerical models of the bolide-produced thermal radiation suggest that the Tunguska-like event would produce a thermal flux to the surface that is sufficient to ignite pine needles [7]. However, in case of Tunguska the only proof for the bolide starting the fire comes from an eyewitness description collected many years after the event. Some authors [8] suggest that this fire might have been caused "normaly" later during the same year, induced on dead trees killed by the Tunguska fall. More recently it was observed that the Chelyabinsk meteor [9] - smaller than Tunguska event - did not produced a fire. In order to explore this apparent relationship in more detail, we have studied the proximal ejecta from a 100-m in diameter, ~3500 years old [10] Kaali crater (Estonia) within which we find pieces of charred organic material. Those pieces appear to have been produced during the impact, according to their stratigraphic location and following 14C analysis [19] as opposed to pre- or post-impact forest fires. In order to determine the most probable formation mechanism of the charred organic material found within Kaali proximal ejecta blanket, we: 1) Analyzed charcoal under SEM to identify the charred plants and determine properties of the charcoal related to the temperature of its formation [11]. Detected homogenization of cell walls suggests that at least some pieces of charcoal were formed at >300 °C [11]. 2) Analyzed the reflectance properties of the charred particles in order to determine the intensity with which

  2. Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean

    Science.gov (United States)

    Rai, Ajai K.; Srinivasan, M. S.

    1994-12-01

    An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence. The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water (AABW). Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in the relative abundance of U. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by low abundance of U. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence of Bulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas. B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative abundance of Stilostomella lepidula occurs close to the Early/Late Pleistocene boundary.

  3. Numerical modeling of Stickney crater and its aftermath

    Science.gov (United States)

    Schwartz, Stephen R.; Michel, Patrick; Bruck Syal, Megan; Owen, J. Michael; Miller, Paul L.; Richardson, Derek C.; Zhang, Yun

    2016-10-01

    Phobos is characterized by a large crater called Stickney. Its collisional formation and its aftermath have important implications on the final structure, morphology, and surface properties of Phobos that still need further clarification. This is particularly important in the current environment, with space mission concepts to Phobos under active study by several space agencies. SPH hydrocode simulations of the impact that formed Stickney crater [1] have been performed. Using the Soft-Sphere Discrete Element Method (SSDEM) collisional routine of the N-body code pkdgrav [2], we take the outcome of SPH simulations as inputs and model the ensuing phase of the crater formation process and its ejecta evolution under the gravitational influence of Phobos and Mars. In our simulations, about 9 million particles comprise Phobos' shape [3], and the evolution of particles that are expected to form or leave the crater is followed using multiple plausible orbits for Phobos around Mars. We track the immediate fate of low-speed ejecta (~3-8 m/s), allowing us to test an hypothesis [4] that they may scour certain groove marks that have been observed on Phobos' surface and to quantify the amounts and locations of re-impacting ejecta. We also compute the orbital fate of ejecta whose speed is below the system escape speed (about 3 km/s). This allows us to estimate the thickness and distribution of the final ejecta blanket and to check whether crater chains may form. Finally, particles forming the crater walls are followed until achieving stability, allowing us to estimate the final crater depth and diameter. We will show examples of these simulations from a set of SPH initial conditions and over a range of parameters (e.g., material friction coefficients). Work ongoing to cover a larger range of plausible impact conditions, allowing us to explore different scenarios to explain Phobos' observed properties and to infer more, giving useful constraints to space mission studies. [1] Bruck

  4. Distribution, morphology, and origins of Martian pit crater chains

    Science.gov (United States)

    Wyrick, Danielle; Ferrill, David A.; Morris, Alan P.; Colton, Shannon L.; Sims, Darrell W.

    2004-06-01

    Pit craters are circular to elliptical depressions found in alignments (chains), which in many cases coalesce into linear troughs. They are common on the surface of Mars and similar to features observed on Earth and other terrestrial bodies. Pit craters lack an elevated rim, ejecta deposits, or lava flows that are associated with impact craters or calderas. It is generally agreed that the pits are formed by collapse into a subsurface cavity or explosive eruption. Hypotheses regarding the formation of pit crater chains require development of a substantial subsurface void to accommodate collapse of the overlying material. Suggested mechanisms of formation include: collapsed lava tubes, dike swarms, collapsed magma chamber, substrate dissolution (analogous to terrestrial karst), fissuring beneath loose material, and dilational faulting. The research described here is intended to constrain current interpretations of pit crater chain formation by analyzing their distribution and morphology. The western hemisphere of Mars was systematically mapped using Mars Orbiter Camera (MOC) images to generate ArcView™ Geographic Information System (GIS) coverages. All visible pit crater chains were mapped, including their orientations and associations with other structures. We found that pit chains commonly occur in areas that show regional extension or local fissuring. There is a strong correlation between pit chains and fault-bounded grabens. Frequently, there are transitions along strike from (1) visible faulting to (2) faults and pits to (3) pits alone. We performed a detailed quantitative analysis of pit crater morphology using MOC narrow angle images, Thermal Emission Imaging System (THEMIS) visual images, and Mars Orbiter Laser Altimeter (MOLA) data. This allowed us to determine a pattern of pit chain evolution and calculate pit depth, slope, and volume. Volumes of approximately 150 pits from five areas were calculated to determine volume size distribution and regional

  5. Earth's Largest Meteorite Impact Craters discovered in South America?

    Science.gov (United States)

    Kellndorfer, J. M.; Schmidt-Falkenberg, H.

    2014-12-01

    Novel analysis of high resolution InSAR-based digital elevation data from the year 2001 Shuttle Radar Topography Mission combined with a recently produced dataset of pan-tropical vegetation height from ALOS-1 SAR and IceSAT/GLAS Lidar estimates led to the quasi-bald-Earth discovery of four sizable near-perfect circle arcs in South America under dense tropical forests ranging in length from 216 km to 441 km. Terrain elevation profiles of cross-sections across the arcs show a distinct vertical rising and falling in elevations of hundreds of meters over a horizontal distance of tens of kilometers. It is hypothesized that these sizable arcs and associated rim-like topographic terrain features are remnants of huge meteorite impact craters with diameters ranging from 770 km to 1,310 km, thus forming potentially the largest known impact carter structures discovered on Earth today. The potential impact crater rim structures are located north of the eastern Amazon River, in the coastal region of Recife and Natal, and in the Brazilian, Bolivian and Paraguayan border region encompassing the Pantanal. Elevation profiles, hillshades and gray-shaded elevation maps were produced to support the geomorphologic analysis. It is also speculated whether in three of the four potential impact craters, central uplift domes or peaks, which are typical for complex impact crater structures can be identified. The worlds largest iron ore mining area of Carajás in Para, Brazil, falls exactly in the center of the largest hypothesized circular impact crater showing topographic elevations similar to the rim structure discovered 655 km to the north-north-west. Based on the topographic/geomorphologic driven hypothesis, geologic exploration of these topographic features is needed to test whether indeed meteorite impact craters could be verified, what the more exact ellipsoidal shapes of the potential impact craters might be, and to determine when during geologic times the impacts would have taken

  6. Anticipated Electrical Environment Within Permanently Shadowed Lunar Craters

    Science.gov (United States)

    Farrell, W. M.; Stubbs, T. J.; Halekas, J. S.; Killen, R. M.; Delory, G. T.; Collier, M. R.; Vondrak, R. R.

    2010-01-01

    Shadowed locations ncar the lunar poles arc almost certainly electrically complex regions. At these locations near the terminator, the local solar wind flows nearly tangential to the surface and interacts with large-scale topographic features such as mountains and deep large craters, In this work, we study the solar wind orographic effects from topographic obstructions along a rough lunar surface, On the leeward side of large obstructions, plasma voids are formed in the solar wind because of the absorption of plasma on the upstream surface of these obstacles, Solar wind plasma expands into such voids) producing an ambipolar potential that diverts ion flow into the void region. A surface potential is established on these leeward surfaces in order to balance the currents from the expansion-limited electron and ion populations, Wc find that there arc regions ncar the leeward wall of the craters and leeward mountain faces where solar wind ions cannot access the surface, leaving an electron-rich plasma previously identified as an "electron cloud." In this case, some new current is required to complete the closure for current balance at the surface, and we propose herein that lofted negatively charged dust is one possible (nonunique) compensating current source. Given models for both ambipolar and surface plasma processes, we consider the electrical environment around the large topographic features of the south pole (including Shoemaker crater and the highly varied terrain near Nobile crater), as derived from Goldstone radar data, We also apply our model to moving and stationary objects of differing compositions located on the surface and consider the impact of the deflected ion flow on possible hydrogen resources within the craters

  7. Chemical variations observed on Aeolis Mons in Gale Crater, Mars

    Science.gov (United States)

    Frydenvang, Jens; Gasda, Patrick J.; Thompson, Lucy; Hurowitz, Joel; Grotzinger, John P.; Blaney, Diana L.; Gellert, Ralf; Wiens, Roger; Vasavada, Ashwin R.; MSL Science Team

    2016-10-01

    The extraordinarily extensive exposure of hematite-, clay-, sulfate-bearing stratigraphic layers in the lower part of Aeolis Mons was the primary reason Gale Crater was selected as the landing site for the Mars Science Laboratory rover, Curiosity. 753 martian solar days (sols) after the Curiosity rover landed in Gale Crater in August 2012, and after driving more than 9 km, the Curiosity rover arrived at the first exposure of the Murray formation, the basal layer of Aeolis Mons. The Murray formation is a thinly laminated lacustrine mudstone showing stratification down to the millimeter scale. This supports the idea that the stratigraphic layers of Aeolis Mons are sedimentary, and likely deposited in a series of long-lived lakes extending into the early Hesperian time, as recently described by Grotzinger et al. (Science, vol. 350, 2015). The chemical variations observed throughout the Murray formation by the ChemCam and APXS instruments in the 600+ sols since first arriving at Aeolis Mons will be presented. While Murray remains thinly laminated throughout the 30+ vertical meters of stratigraphy explored, large chemical variations are observed. The most extreme variations arise from likely co-located detrital and diagenetic silica enrichments in Murray. Remarkably, an associated diagenetic silica enrichment is also observed in the unconformably overlying eolian sandstone of the Stimson formation in that location. The detrital enrichment provides evidence of how the source region chemistry varied as the sedimentary layers of Aeolis Mons were deposited. Conversely, the diagenetic enrichment observed across both the Murray and Stimson formations provides compelling evidence for the presence of subsurface fluids in Gale Crater, thousands to millions of years after the crater lakes disappeared. This evidence of liquid water greatly extends the timescale in which Gale Crater might have been habitable.

  8. Under trees and water at Crater Lake National Park, Oregon

    Science.gov (United States)

    Robinson, Joel E.; Bacon, Charles R.; Wayne, Chris

    2012-01-01

    Crater Lake partially fills the caldera that formed approximately 7,700 years ago during the eruption of a 12,000-ft-high volcano known as Mount Mazama. The caldera-forming, or climactic, eruption of Mount Mazama devastated the surrounding landscape, left a thick deposit of pumice and ash in adjacent valleys, and spread a blanket of volcanic ash as far away as southern Canada. Prior to the climactic event, Mount Mazama had a 400,000-year history of volcanic activity similar to other large Cascade volcanoes such as Mounts Shasta, Hood, and Rainier. Since the caldera formed, many smaller, less violent eruptions occurred at volcanic vents below Crater Lake's surface, including Wizard Island. A survey of Crater Lake National Park with airborne LiDAR (Light Detection And Ranging) resulted in a digital elevation map of the ground surface beneath the forest canopy. The average resolution is 1.6 laser returns per square meter yielding vertical and horizontal accuracies of ±5 cm. The map of the floor beneath the surface of the 1,947-ft-deep (593-m-deep) Crater Lake was developed from a multibeam sonar bathymetric survey and was added to the map to provide a continuous view of the landscape from the highest peak on Mount Scott to the deepest part of Crater Lake. Four enlarged shaded-relief views provide a sampling of features that illustrate the resolution of the LiDAR survey and illustrate its utility in revealing volcanic landforms and subtle features of the climactic eruption deposits. LiDAR's high precision and ability to "see" through the forest canopy reveal features that may not be easily recognized-even when walked over-because their full extent is hidden by vegetation, such as the 1-m-tall arcuate scarp near Castle Creek.

  9. A cold hydrological system in Gale crater, Mars

    Science.gov (United States)

    Fairén, Alberto G.; Stokes, Chris R.; Davies, Neil S.; Schulze-Makuch, Dirk; Rodríguez, J. Alexis P.; Davila, Alfonso F.; Uceda, Esther R.; Dohm, James M.; Baker, Victor R.; Clifford, Stephen M.; McKay, Christopher P.; Squyres, Steven W.

    2014-04-01

    Gale crater is a ~154-km-diameter impact crater formed during the Late Noachian/Early Hesperian at the dichotomy boundary on Mars. Here we describe potential evidence for ancient glacial, periglacial and fluvial (including glacio-fluvial) activity within Gale crater, and the former presence of ground ice and lakes. Our interpretations are derived from morphological observations using high-resolution datasets, particularly HiRISE and HRSC. We highlight a potential ancient lobate rock-glacier complex in parts of the northern central mound, with further suggestions of glacial activity in the large valley systems towards the southeast central mound. Wide expanses of ancient ground ice may be indicated by evidence for very cohesive ancient river banks and for the polygonal patterned ground common on the crater floor west of the central mound. We extend the interpretation to fluvial and lacustrine activity to the west of the central mound, as recorded by a series of interconnected canyons, channels and a possible lake basin. The emerging picture from our regional landscape analyses is the hypothesis that rock glaciers may have formerly occupied the central mound. The glaciers would have provided the liquid water required for carving the canyons and channels. Associated glaciofluvial activity could have led to liquid water running over ground ice-rich areas on the basin floor, with resultant formation of partially and/or totally ice-covered lakes in parts of the western crater floor. All this hydrologic activity is Hesperian or younger. Following this, we envisage a time of drying, with the generation of polygonal patterned ground and dune development subsequent to the disappearance of the surface liquid and frozen water.

  10. Noncommutative Topological Half-flat Gravity

    CERN Document Server

    García-Compéan, H; Ramírez, C

    2004-01-01

    We formulate a noncommutative description of topological half-flat gravity in four dimensions. BRST symmetry of this topological gravity is deformed through a twisting of the usual BRST quantization of noncommutative gauge theories. Finally it is argued that resulting moduli space of instantons is characterized by the solutions of a noncommutative version of the Plebanski's heavenly equation.

  11. Affleck Dine leptogenesis via multiple flat directions

    CERN Document Server

    Kamada, Kohei

    2008-01-01

    We investigate the Affleck-Dine mechanism when multiple flat directions have large values simultaneously. We consider in detail the case when both $LH_u$ and $H_uH_d$ flat directions are operative with a non-renormalizable superpotential. In case Hubble induced A-terms are present for these two flat directions, their initial values are determined completely by the potential and there are no ambiguities how they are mixed. Moreover, CP is violated even when the Hubble parameter is large due to the Hubble induced A-term and cross coupling in F-term, so that the lepton asymmetry is generated just after the end of inflation. As a result, compared with the case of single flat direction, the resultant lepton-to-entropy ratio is enhanced by a factor of $H_{osc}/m_{3/2}$, where $H_{osc}$ is the Hubble parameter at the onset of oscillation and $m_{3/2}$ is the gravitino mass. However, when Hubble induced A-terms do not exist, there remains indefiniteness of initial phases and CP is violated spontaneously by the phase ...

  12. η-Invariant and Flat Vector Bundles

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    We present an alternate definition of the mod Z component of the AtiyahPatodi-Singer η invariant associated to (not necessary unitary) fiat vector bundles, which identifies explicitly its real and imaginary parts. This is done by combining a deformation of flat connections introduced in a previous paper with the analytic continuation procedure appearing in the original article of Atiyah, Parodi and Singer.

  13. Chemically patterned flat stamps for microcontact printing

    NARCIS (Netherlands)

    Sharpe, Ruben B.A.; Burdinski, Dirk; Huskens, Jurriaan; Zandvliet, Harold J.W.; Reinhoudt, David N.; Poelsema, Bene

    2005-01-01

    Locally oxidized patterns on flat poly(dimethylsiloxane) stamps for microcontact printing were used as a platform for the transfer of a hydrophilic fluorescent ink to a glass substrate. The contrast was found to be limited. These locally oxidized patterns were conversely used as barriers for the tra

  14. Minimal Flat Resolutions of Artinian Modules

    Institute of Scientific and Technical Information of China (English)

    Sh. Payrovi

    2005-01-01

    The purpose of this paper is to establish connection between the minimal flat resolutions of Artinian modules and the concept of cosequences in commutative algebra.The main result of this paper leads to a characterization of local Cohen-Macaulay rings in terms of vanishing property of the dual Bass numbers of certain Artinian modules.

  15. Wideband Flat Radomes Using Inhomogeneous Planar Layers

    Directory of Open Access Journals (Sweden)

    Mohammad Khalaj-Amirhosseini

    2008-01-01

    Full Text Available Inhomogeneous planar layers (IPLs are optimally designed as flat radomes in a desired frequency range. First, the electric permittivity function of the IPL is expanded in a truncated Fourier series. Then, the optimum values of the coefficients of the series are obtained through an optimization approach. The performance of the proposed structure is verified using some examples.

  16. Design scenarios for flat panel photobioreactors

    NARCIS (Netherlands)

    Slegers, P.M.; Wijffels, R.H.; Straten, van G.; Boxtel, van A.J.B.

    2011-01-01

    Evaluation of the potential of algae production for biofuel and other products at various locations throughout the world requires assessment of algae productivity under varying light conditions and different reactor layouts. A model was developed to predict algae biomass production in flat panel

  17. Holography of 3d Flat Cosmological Horizons

    CERN Document Server

    Bagchi, Arjun; Fareghbal, Reza; Simon, Joan

    2013-01-01

    We provide a first derivation of the Bekenstein-Hawking entropy of 3d flat cosmological horizons in terms of the counting of states in a dual field theory. These horizons appear in the shifted-boost orbifold of R^{1,2}, the flat limit of non-extremal rotating BTZ black holes. These 3d geometries carry non-zero charges under the asymptotic symmetry algebra of R^{1,2}, the 3d Bondi-Metzner-Sachs (BMS3) algebra. The dual theory has the symmetries of the 2d Galilean Conformal Algebra, a contraction of two copies of the Virasoro algebra, which is isomorphic to BMS3. We study flat holography as a limit of AdS3/CFT2 to semi-classically compute the density of states in the dual, exactly reproducing the bulk entropy in the limit of large charges. Our flat horizons, remnants of the BTZ inner horizons also satisfy a first law of thermodynamics. We comment on how the dual theory reproduces the bulk first law and how cosmological bulk excitations are matched with boundary quantum numbers.

  18. Crater Morphometry and Crater Degradation on Mercury: Mercury Laser Altimeter (MLA) Measurements and Comparison to Stereo-DTM Derived Results

    Science.gov (United States)

    Leight, C.; Fassett, C. I.; Crowley, M. C.; Dyar, M. D.

    2017-01-01

    Two types of measurements of Mercury's surface topography were obtained by the MESSENGER (MErcury Surface Space ENvironment, GEochemisty and Ranging) spacecraft: laser ranging data from Mercury Laser Altimeter (MLA) [1], and stereo imagery from the Mercury Dual Imaging System (MDIS) camera [e.g., 2, 3]. MLA data provide precise and accurate elevation meaurements, but with sparse spatial sampling except at the highest northern latitudes. Digital terrain models (DTMs) from MDIS have superior resolution but with less vertical accuracy, limited approximately to the pixel resolution of the original images (in the case of [3], 15-75 m). Last year [4], we reported topographic measurements of craters in the D=2.5 to 5 km diameter range from stereo images and suggested that craters on Mercury degrade more quickly than on the Moon (by a factor of up to approximately 10×). However, we listed several alternative explanations for this finding, including the hypothesis that the lower depth/diameter ratios we observe might be a result of the resolution and accuracy of the stereo DTMs. Thus, additional measurements were undertaken using MLA data to examine the morphometry of craters in this diameter range and assess whether the faster crater degradation rates proposed to occur on Mercury is robust.

  19. Characterization of the Morphometry of Impact Craters Hosting Polar Deposits in Mercury's North Polar Region

    Science.gov (United States)

    Talpe Matthieu; Zuber, Maria T.; Yang, Di; Neumann, Gregory A.; Solomon, Sean C.; Mazarico, Erwan; Vilas, Faith

    2012-01-01

    Earth-based radar images of Mercury show radar-bright material inside impact craters near the planet s poles. A previous study indicated that the polar-deposit-hosting craters (PDCs) at Mercury s north pole are shallower than craters that lack such deposits. We use data acquired by the Mercury Laser Altimeter on the MESSENGER spacecraft during 11 months of orbital observations to revisit the depths of craters at high northern latitudes on Mercury. We measured the depth and diameter of 537 craters located poleward of 45 N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 craters, including nine PDCs. We find that the PDCs appear to have a fresher crater morphology than the non-PDCs and that the radar-bright material has no detectable influence on crater depths, wall slopes, or floor roughness. The statistical similarity of crater depth-diameter relations for the PDC and non-PDC populations places an upper limit on the thickness of the radar-bright material (< 170 m for a crater 11 km in diameter) that can be refined by future detailed analysis. Results of the current study are consistent with the view that the radar-bright material constitutes a relatively thin layer emplaced preferentially in comparatively young craters.

  20. Detection of sub-kilometer craters in high resolution planetary images using shape and texture features

    Science.gov (United States)

    Bandeira, Lourenço; Ding, Wei; Stepinski, Tomasz F.

    2012-01-01

    Counting craters is a paramount tool of planetary analysis because it provides relative dating of planetary surfaces. Dating surfaces with high spatial resolution requires counting a very large number of small, sub-kilometer size craters. Exhaustive manual surveys of such craters over extensive regions are impractical, sparking interest in designing crater detection algorithms (CDAs). As a part of our effort to design a CDA, which is robust and practical for planetary research analysis, we propose a crater detection approach that utilizes both shape and texture features to identify efficiently sub-kilometer craters in high resolution panchromatic images. First, a mathematical morphology-based shape analysis is used to identify regions in an image that may contain craters; only those regions - crater candidates - are the subject of further processing. Second, image texture features in combination with the boosting ensemble supervised learning algorithm are used to accurately classify previously identified candidates into craters and non-craters. The design of the proposed CDA is described and its performance is evaluated using a high resolution image of Mars for which sub-kilometer craters have been manually identified. The overall detection rate of the proposed CDA is 81%, the branching factor is 0.14, and the overall quality factor is 72%. This performance is a significant improvement over the previous CDA based exclusively on the shape features. The combination of performance level and computational efficiency offered by this CDA makes it attractive for practical application.

  1. Ganymede crater dimensions - Implications for central peak and central pit formation and development

    Science.gov (United States)

    Bray, Veronica J.; Schenk, Paul M.; Jay Melosh, H.; Morgan, Joanna V.; Collins, Gareth S.

    2012-01-01

    The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. The differences are thought due to the relative weakness of ice and the possible presence of sub-surface water layers. Digital elevation models constructed from Galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of Ganymede. Measurements were made from multiple profiles across each crater, so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed. The additional depth, slope and volume information reported in this work has enabled study of central peak formation and development, and allowed a quantitative assessment of the various theories for central pit formation. We note a possible difference in the size-morphology progression between small craters on icy and silicate bodies, where central peaks occur in small craters before there is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely, our crater dimension analyses suggest that the size-morphology progression of large lunar craters from central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequently modified to a central pit morphology. Pit formation may occur via the collapse of surface material into a void left by the gradual release of impact-induced volatiles or the drainage of impact melt into sub-crater fractures.

  2. Evidence for Impact-induced Hydrothermal Alteration at the Lonar Crater, India, and Mistastin Lake, Canada

    Science.gov (United States)

    Newsom, H. E.; Hagerty, J. J.

    2003-01-01

    The 50,000 year old, 1.8km diameter Lonar crater is located in Maharashtra, India. This relatively small crater is of particular interest because of its unique morphological and mineralogical properties, which make it a valid analogue for similar craters on the surface of Mars. We show that even in this relatively small crater, substantial hydrothermal alteration of shocked breccias in the floor of the crater has occurred, probably due to the thermal effects of the impact event. The 38 my old, 28 km diameter, Mistastin crater contains an 80 m thick impact melt sheet. We have also documented the presence of alteration phases in the material from this larger crater.

  3. A seismic refraction technique used for subsurface investigations at Meteor Crater, Arizona

    Science.gov (United States)

    Ackermann, H. D.; Godson, R. H.; Watkins, J. S.

    1975-01-01

    A seismic refraction technique for interpreting the subsurface shape and velocity distribution of an anomalous surface feature such as an impact crater is described. The method requires the existence of a relatively deep refracting horizon and combines data obtained from both standard shallow refraction spreads and distant offset shots by using the deep refractor as a source of initial arrivals. Results obtained from applying the technique to Meteor crater generally agree with the known structure of the crater deduced by other investigators and provide new data on an extensive fractured zone surrounding the crater. The breccia lens is computed to extend roughly 190 m below the crater floor, about 30 m less than the value deduced from early drilling data. Rocks around the crater are fractured as distant as 900 m from the rim crest and to a depth of at least 800 m beneath the crater floor.

  4. Role of the granular nature of meteoritic projectiles in impact crater morphogenesis

    CERN Document Server

    Bartali, Roberto; Nahmad-Molinari, Yuri; Sarochi, Damiano; Ruiz-Suárez, J C

    2013-01-01

    By means of novel volume-diameter aspect ratio diagrams, we ponder on the current conception of crater morphogenesis analyzing crater data from beam explosions, hypervelocity collisions and drop experiments and comparing them with crater data from three moons (the Moon, Callisto, and Ganymede) and from our own experimental results. The distinctive volume-diameter scaling laws we discovered make us to conclude that simple and complex craters in satellites and planets could have been formed by granular vs. granular collisions and that central peaks and domes in complex craters were formed by a dynamic confinement of part of the impacting projectile, rather than by the uplift of the target terrain. A granulometric analysis of asteroids and central peaks and domes inside complex craters, shows boulder size distributions consistent with our hypothesis that crater internal features are the remnants of granular impactors.

  5. Plio-Pleistocene volcanic history of the Ahuachapan geothermal system, El Salvador: the Concepcion de Ataco caldera

    Energy Technology Data Exchange (ETDEWEB)

    Partida, Eduardo Gonzalez; Rodriguez, Vicente Torres; Birkle, Peter [Instituto de Investigaciones Electricas (IIE), Dept. de Geotermia, Cuernavaca, Morelos (Mexico)

    1997-12-01

    The Concepcion de Ataco caldera in the Ahuachapan-Chipilapa region is part of the southern, Plio-Pleistocene volcanic belt that borders the Central Graben of El Salvador. About 17 km{sup 3} of primitive lavas erupted between 1.7 and 0.77 Ma, covering basaltic-andesitic lavas and older agglomerates forming the Cuyanausul, Apaneca and Empalizada volcanoes. These lavas preceded the evacuation of 63 km{sup 3} of silicic pyroclastics (i.e. breccias, surge deposits, and ignimbrites) associated with the main caldera cycle. The eruption of this pyroclastic material led to the collapse of a 5 km by 3.5 km caldera between the times of the youngest pre-caldera eruptions (0.77 Ma) and the intrusion of the Himalaya dome (0.28 Ma). The caldera collapse was reactivated at its north eastern flank by a new eruption of pyroclastics of limited areal distribution. These distinctive pyroclastics correspond to laminated tuffs (Cebra tuffs). Domes of dacitic-to-andesitic composition erupted along the caldera border as well as within it. Their magmatism is calc-alkaline; their ages vary between 0.28 and 0.1 Ma. Three phreatic explosions, whose craters are in the eastern part of the Concepcion de Ataco caldera structure, only deposited debris locally. A hydrothermal systems was emplaced during the final stage of the post-magmatic activity, evidenced by areas of hydrothermal alteration and surface manifestations. Four main fault systems, oriented NE-SW, NW-SE, NNW-SSE, and semicircular, have been identified. These faults created relatively high-permeability regions within the caldera and nearby grabens, that are favorable for the development of geothermal systems. (Author)

  6. Automated detection of lunar craters based on object-oriented approach

    Institute of Scientific and Technical Information of China (English)

    YUE ZongYu; LIU JianZhong; WU GanGuo

    2008-01-01

    The object-oriented approach is a powerful method in making classification. With the segmentation of images to objects, many features can be calculated based on the objects so that the targets can be distinguished. However, this method has not been applied to lunar study. In this paper we attempt to apply this method to detecting lunar craters with promising results. Craters are the most obvious features on the moon and they are important for lunar geologic study. One of the important questions in lunar research is to estimate lunar surface ages by examination of crater density per unit area. Hence,proper detection of lunar craters is necessary. Manual crater identification is inefficient, and a more efficient and effective method is needed. This paper describes an object-oriented method to detect lunar craters using lunar reflectance images. In the method, many objects were first segmented from the image based on size, shape, color, and the weights to every layer. Then the feature of "contrast to neighbor objects" was selected to identify craters from the lunar image. In the next step, by merging the adjacent objects belonging to the same class, almost every crater can be taken as an independent object except several very big craters in the study area. To remove the crater rays diagnosed as craters,the feature of "length/width" was further used with suitable parameters to finish recognizing craters.Finally, the result was exported to ArcGIS for manual modification to those big craters and the number of craters was acquired.

  7. Summit crater lake observations, and the location, chemistry, and pH of water samples near Mount Chiginagak volcano, Alaska: 2004-2012

    Science.gov (United States)

    Schaefer, Janet R.; Scott, William E.; Evans, William C.; Wang, Bronwen; McGimsey, Robert G.

    2013-01-01

    Mount Chiginagak is a hydrothermally active volcano on the Alaska Peninsula, approximately 170 km south–southwest of King Salmon, Alaska (fig. 1). This small stratovolcano, approximately 8 km in diameter, has erupted through Tertiary to Permian sedimentary and igneous rocks (Detterman and others, 1987). The highest peak is at an elevation of 2,135 m, and the upper ~1,000 m of the volcano are covered with snow and ice. Holocene activity consists of debris avalanches, lahars, and lava flows. Pleistocene pyroclastic flows and block-and-ash flows, interlayered with andesitic lava flows, dominate the edifice rocks on the northern and western flanks. Historical reports of activity are limited and generally describe “steaming” and “smoking” (Coats, 1950; Powers, 1958). Proximal tephra collected during recent fieldwork suggests there may have been limited Holocene explosive activity that resulted in localized ash fall. A cluster of fumaroles on the north flank, at an elevation of ~1,750 m, commonly referred to as the “north flank fumarole” have been emitting gas throughout historical time (location shown in fig. 2). The only other thermal feature at the volcano is the Mother Goose hot springs located at the base of the edifice on the northwestern flank in upper Volcano Creek, at an elevation of ~160 m (fig. 2, near sites H1, H3, and H4). Sometime between November 2004 and May 2005, a ~400-m-wide, 100-m-deep lake developed in the snow- and ice-filled summit crater of the volcano (Schaefer and others, 2008). In early May 2005, an estimated 3 million cubic meters (3×106 m3) of sulfurous, clay-rich debris and acidic water exited the crater through tunnels at the base of a glacier that breaches the south crater rim. More than 27 km downstream, these acidic flood waters reached approximately 1.3 m above normal water levels and inundated a fertile, salmon-spawning drainage, acidifying the entire water column of Mother Goose Lake from its surface waters to its

  8. Late-Pleistocene precipitation δ18O interpolated across the global landmass

    Science.gov (United States)

    Jasechko, Scott

    2016-08-01

    Global water cycles, ecosystem assemblages, and weathering rates were impacted by the ˜4°C of global warming that took place over the course of the last glacial termination. Fossil groundwaters can be useful indicators of late-Pleistocene precipitation isotope compositions, which, in turn, can help to test hypotheses about the drivers and impacts of glacial-interglacial climate changes. Here, a global catalog of 126 fossil groundwater records is used to interpolate late-Pleistocene precipitation δ18O across the global landmass. The interpolated data show that extratropical late-Pleistocene terrestrial precipitation was near uniformly depleted in 18O relative to the late Holocene. By contrast, tropical δ18O responses to deglacial warming diverged; late-Pleistocene δ18O was higher-than-modern across India and South China but lower-than-modern throughout much of northern and southern Africa. Groundwaters that recharged beneath large northern hemisphere ice sheets have different Holocene-Pleistocene δ18O relationships than paleowaters that recharged subaerially, potentially aiding reconstructions of englacial transport in paleo ice sheets. Global terrestrial late-Pleistocene precipitation δ18O maps may help to determine 3-D groundwater age distributions, constrain Pleistocene mammal movements, and better understand glacial climate dynamics.

  9. The Complicated Geologic Histories of Large Venusian Impact Craters

    Science.gov (United States)

    Rumpf, M. E.; Herrick, R.; Gregg, T. K.

    2005-12-01

    One of the more surprising discoveries from the Magellan imaging campaign was that the impact craters have a spatial distribution closely consistent with a random pattern. First impressions of most craters were that they are also well preserved. These observations led to an initial post-Magellan consensus that the planet is nearly geologically inactive and that activity rapidly ceased a few hundred million years ago. Early mapping efforts were mostly interpreted in terms of a rapid, linear, globally uniform stratigraphic evolution in the nature of volcanism and deformation. A number of challenges to this view have been made as detailed study of the Magellan data has progressed, and several researchers now advocate a more uniformitarian view of the planet. A valuable research tool has been topography derived from Magellan stereo imagery; it provides an order of magnitude improvement in horizontal resolution over the altimetry data (1 km vs. 10 km). Previous studies utilizing the stereo-derived topography have shown that impact craters with radar-dark floors (most of the population) are shallow and probably partially filled with post-impact lavas, and detailed mapping of Mead impact basin (the planet's largest impact structure) has revealed post-impact volcanic embayment. We have recently performed detailed photogeologic mapping, aided by stereo-derived topography, of several 50-100 km diameter impact craters. Most of these craters are not at the top of the stratigraphic column, and in some cases there is a complex, multi-event post-emplacement history. The combined histories of these craters are not consistent with a rapid cessation of geologic activity, and we are still synthesizing the individual histories to evaluate the hypothesis of a linear global stratigraphic evolution. Although the stereo-derived topography greatly aided interpretation, in many cases geologic contacts were ambiguous, individual volcanic flows could not be distinguished, source vents could

  10. A Pleistocene ice core record of atmospheric O2 concentrations

    Science.gov (United States)

    Stolper, D. A.; Bender, M. L.; Dreyfus, G. B.; Yan, Y.; Higgins, J. A.

    2016-09-01

    The history of atmospheric O2 partial pressures (PO2) is inextricably linked to the coevolution of life and Earth’s biogeochemical cycles. Reconstructions of past PO2 rely on models and proxies but often markedly disagree. We present a record of PO2 reconstructed using O2/N2 ratios from ancient air trapped in ice. This record indicates that PO2 declined by 7 per mil (0.7%) over the past 800,000 years, requiring that O2 sinks were ~2% larger than sources. This decline is consistent with changes in burial and weathering fluxes of organic carbon and pyrite driven by either Neogene cooling or increasing Pleistocene erosion rates. The 800,000-year record of steady average carbon dioxide partial pressures (PCO2) but declining PO2 provides distinctive evidence that a silicate weathering feedback stabilizes PCO2 on million-year time scales.

  11. Pleistocene radiolarian biostratigraphy in the South China Sea

    Institute of Scientific and Technical Information of China (English)

    王汝建; Andrea; Abelmann

    1999-01-01

    Based on a quantitative radiolarian analysis, 5 radiolarian zones (NR1-NR5) have been defined at Core 17957-2 from the South China Sea, considering radiolarian zonations from low latitudes. The absolute age assignment of the radiolarian zones and the ranges of the six marker species is based on the direct correlation with the paleomagnetic and isotopic record, respectively. A comparison of the radiolarian stratigraphic data obtained from Core 17957-2 from the South China Sea with those from the equatorial Pacific and the tropical Indian Ocean shows a close similarity to the ages defined in the equatorial Pacific. The obtained biostratigraphic data provide an excellent tool for further dating of Pleistocene sediments in the China Sea.

  12. A complete human pelvis from the Middle Pleistocene of Spain.

    Science.gov (United States)

    Arsuaga, J L; Lorenzo, C; Carretero, J M; Gracia, A; Martínez, I; García, N; Bermúdez de Castro, J M; Carbonell, E

    1999-05-20

    The Middle Pleistocene site of Sima de los Huesos in Sierra de Atapuerca, Spain, has yielded around 2,500 fossils from at least 33 different hominid individuals. These have been dated at more than 200,000 years ago and have been classified as ancestors of Neanderthals. An almost complete human male pelvis (labelled Pelvis 1) has been found, which we associate with two fragmentary femora. Pelvis 1 is robust and very broad with a very long superior pubic ramus, marked iliac flare, and a long femoral neck. This pattern is probably the primitive condition from which modern humans departed. A modern human newborn would pass through the birth canal of Pelvis 1 and this would be even larger in a female individual. We estimate the body mass of this individual at 95 kg or more. Using the cranial capacities of three specimens from Sima de los Huesos, the encephalization quotients are substantially smaller than in Neanderthals and modern humans.

  13. The aftermath of megafaunal extinction: ecosystem transformation in Pleistocene Australia.

    Science.gov (United States)

    Rule, Susan; Brook, Barry W; Haberle, Simon G; Turney, Chris S M; Kershaw, A Peter; Johnson, Christopher N

    2012-03-23

    Giant vertebrates dominated many Pleistocene ecosystems. Many were herbivores, and their sudden extinction in prehistory could have had large ecological impacts. We used a high-resolution 130,000-year environmental record to help resolve the cause and reconstruct the ecological consequences of extinction of Australia's megafauna. Our results suggest that human arrival rather than climate caused megafaunal extinction, which then triggered replacement of mixed rainforest by sclerophyll vegetation through a combination of direct effects on vegetation of relaxed herbivore pressure and increased fire in the landscape. This ecosystem shift was as large as any effect of climate change over the last glacial cycle, and indicates the magnitude of changes that may have followed megafaunal extinction elsewhere in the world.

  14. Upper Middle Pleistocene climate and landscape development of Northern Germany

    Science.gov (United States)

    Urban, B.

    2009-04-01

    The Pleistocene sequence of the Schöningen lignite mine contains a number of interglacial and interstadial limnic and peat deposits, travertine tuff, soils, tills and fluvioglacial sediments as well as loess deposits. The complex Quaternary sequence contains six major cycles with evidence of four interglacials younger than the Elsterian glaciation and preceding the Holocene. The sequence begins with Late Elsterian glacial and three interstadial deposits formed in shallow basins. Cycle I is assigned to late parts of the Holsteinian interglacial. A strong cooling is recorded by a significant increase of Artemisia and grasses during the following Buschhaus A Stadial, which is considered to mark the onset of the Saalian Complex sensu lato (penultimate glacial-complex). The lacustrine sediments of Cycle II, Reinsdorf interglacial sequence (Urban, 1995), have been found to occur at archaeological sites Schöningen 12 and 13 (Thieme,1997). Recent investigations give evidence for at least 13 Local Pollen Assemblage Zones showing a five-fold division of the interglacial and a sequence of five climatic oscillations following the interglacial (Urban, 2006). From the relative high values for grasses and herbs in the inferred forested periods of the interglacial, a warm dry forest steppe climate can be deduced. The stratigraphic position of throwing spears (Thieme, 1997), can clearly be allocated to Reinsdorf Interstadial B (level II-4) characterized by an open pine-birch forest. Uppermost parts (level II-5) represent the transition into a periglacial environment indicating the definite end of cycle II. The Schöningen Interglacial (Cycle III) represents the youngest of the pre-Drenthe (Early Saalian Stadial) interglacials (Urban, 1995). In summary, it can be concluded that the Middle Pleistocene terrestrial pollen record of the Schöningen sequence represents tentative correlatives of MIS 7, 9 and 11. North of Leck (North Friesland, Schleswig-Holstein) sediments of the centre

  15. Late Pleistocene echimyid rodents (Rodentia, Hystricognathi) from northern Brazil.

    Science.gov (United States)

    Ferreira, Thais M F; Olivares, Adriana Itati; Kerber, Leonardo; Dutra, Rodrigo P; Avilla, Leonardo S

    2016-06-07

    Echimyidae (spiny rats, tree rats and the coypu) is the most diverse family of extant South American hystricognath rodents (caviomorphs). Today, they live in tropical forests (Amazonian, coastal and Andean forests), occasionally in more open xeric habitats in the Cerrado and Caatinga of northern South America, and open areas across the southern portion of the continent (Myocastor). The Quaternary fossil record of this family remains poorly studied. Here, we describe the fossil echimyids found in karst deposits from southern Tocantins, northern Brazil. The analyzed specimens are assigned to Thrichomys sp., Makalata cf. didelphoides and Proechimys sp. This is the first time that a fossil of Makalata is reported. The Pleistocene record of echimyids from this area is represented by fragmentary remains, which hinders their determination at specific levels. The data reported here contributes to the understanding of the ancient diversity of rodents of this region, evidenced until now in other groups, such as the artiodactyls, cingulates, carnivores, marsupials, and squamate reptiles.

  16. Palaeodemography of the Atapuerca-SH Middle Pleistocene hominid sample.

    Science.gov (United States)

    Bermúdez de Castro, J M; Nicolás, M E

    1997-01-01

    We report here on the palaeodemographic analysis of the hominid sample recovered to date from the Sima de los Huesos (SH) Middle Pleistocene cave site in the Sierra de Atapuerca (Burgos, Spain). The analysis of the mandibular, maxillary, and dental remains has made it possible to estimate that a minimum of 32 individuals, who probably belonged to the same biological population, are represented in the current SH human hypodigm. The remains of nine-individuals are assigned to males, and nine to females, suggesting that a 1:1 sex ratio characterizes this hominid sample. The survivorship curve shows a low representation of infants and children, a high mortality among the adolescents and prime-age adults, and a low older adult mortality. Longevity was probably no greater than 40 years. This mortality pattern (adolescents and adults); which in some aspects resembles that observed in Neandertals, is quite different from those reported for recent foraging human groups. The adult age-at-death distribution of the SH hominid sample appears to be neither the consequence of underaging the older adults, nor of differential preservation or of the recognition of skeletal remains. Thus if we accept that they had a life history pattern similar to that of modern humans there would appear to be a clear contradiction between the demographic distribution and the demographic viability of the population represented by the SH hominid fossils. The possible representational bias of the SH hominid sample, as well as some aspects of the reproductive biology of the Pleistocene populations are also discussed.

  17. Extended megadroughts in the southwestern United States during Pleistocene interglacials.

    Science.gov (United States)

    Fawcett, Peter J; Werne, Josef P; Anderson, R Scott; Heikoop, Jeffrey M; Brown, Erik T; Berke, Melissa A; Smith, Susan J; Goff, Fraser; Donohoo-Hurley, Linda; Cisneros-Dozal, Luz M; Schouten, Stefan; Sinninghe Damsté, Jaap S; Huang, Yongsong; Toney, Jaime; Fessenden, Julianna; WoldeGabriel, Giday; Atudorei, Viorel; Geissman, John W; Allen, Craig D

    2011-02-24

    The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern. Multi-year droughts during the instrumental period and decadal-length droughts of the past two millennia were shorter and climatically different from the future permanent, 'dust-bowl-like' megadrought conditions, lasting decades to a century, that are predicted as a consequence of warming. So far, it has been unclear whether or not such megadroughts occurred in the southwestern US, and, if so, with what regularity and intensity. Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT. A collapse of drought-tolerant C(4) plant communities during these warm, dry intervals indicates a significant reduction in summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three MAT cycles ∼2 °C in amplitude occurred within Marine Isotope Stage (MIS) 11 and seem to correspond to the muted precessional cycles within this interglacial. In comparison with MIS 11, MIS 13 experienced higher precessional-cycle amplitudes, larger variations in MAT (4-6 °C) and a longer period of extended warmth, suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US. Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that, in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase.

  18. Gorenstein flatness and injectivity over Gorenstein rings

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Let R be a Gorenstein ring.We prove that if I is an ideal of R such that R/I is a semi-simple ring,then the Gorenstein flat dimension of R/I as a right R-module and the Gorenstein injective dimension of R/I as a left R-module are identical.In addition,we prove that if R→S is a homomorphism of rings and SE is an injective cogenerator for the category of left S-modules,then the Gorenstein flat dimension of S as a right R-module and the Gorenstein injective dimension of E as a left R-module are identical.We also give some applications of these results.

  19. Perturbations of spiky strings in flat spacetimes

    CERN Document Server

    Bhattacharya, Soumya; Panigrahi, Kamal L

    2016-01-01

    Perturbations of a class of semiclassical strings known today as spiky strings, are studied using the well-known Jacobi equations for small normal deformations of an embedded timelike surface. It is shown that there exists finite normal perturbations of the spiky string worldsheets embedded in a $2+1$ dimensional flat spacetime. Such perturbations lead to a rounding off the spikes, which, in a way, demonstrates the stable nature of the unperturbed worldsheet. The same features appear for the dual spiky string solution and in the spiky as well as their dual solutions in $3+1$ dimensional flat spacetime. Our results are based on exact solutions of the corresponding Jacobi equations which we obtain and use while constructing the profiles of the perturbed configurations.

  20. Improving the durability of flat roof constructions

    DEFF Research Database (Denmark)

    Rudbeck, Claus Christian; Svendsen, Sv Aa Højgaard

    1999-01-01

    Flat roof constructions are mainly used on commercial, institutional and industrial buildings, where insulation is placed on top of the load-bearing deck and then covered with a roof membrane. Through time, there is a risk that the membrane will allow water passage as holes might form due...... as there is no easy method of drying it. To be able to dry the insulation, and thereby regain the functional requirements of the roofing system, two new solutions for insulating flat roofs with existing materials are proposed for high density mineral wool and expanded polystyrene. Monitoring equipment are part...... to weathering effects or physical loads. Water will then enter the insulation, and as a vapor retarder is normally found below the insulation thus trapping the water in the insulation, the leak can remain undetected for a long period. When the leak is finally discovered, the insulation has to be discharged...