Shatter cones formed in large-scale experimental explosion craters

NASA Technical Reports Server (NTRS)

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.

Covariant C and O Isotope Trends in Some Terrestrial Carbonates and ALH 84001: Possible Linkage Through Similar Formation Processes

NASA Technical Reports Server (NTRS)

Volk, Kathryn E.; Niles, Paul B.; Socki, Richard A.

2011-01-01

Carbonate minerals found on the surface of Mars and in martian meteorites indicate that liquid water has played a significant role in the planet's history. These findings have raised questions regarding the history of the martian hydrosphere and atmosphere as well as the possibility of life. Sunset Crater, Arizona is a dry environment with relatively high evaporation and brief periods of precipitation. This environment resembles Mars and may make Sunset Crater a good analog to martian carbonates. In this study we sought to identify discrete micro-scale isotopic variation within the carbonate crusts in Sunset Crater to see if they resembled the micro-scale isotope variation found in ALH 84001 carbonates. Sunset Crater carbonate formation may be used as a martian analog and ultimately provide insight into carbonate formation in ALH 84001.

Significant achievements in the Planetary Geology Program. [geologic processes, comparative planetology, and solar system evolution

NASA Technical Reports Server (NTRS)

Head, J. W. (Editor)

1978-01-01

Developments reported at a meeting of principal investigators for NASA's planetology geology program are summarized. Topics covered include: constraints on solar system formation; asteriods, comets, and satellites; constraints on planetary interiors; volatiles and regoliths; instrument development techniques; planetary cartography; geological and geochemical constraints on planetary evolution; fluvial processes and channel formation; volcanic processes; Eolian processes; radar studies of planetary surfaces; cratering as a process, landform, and dating method; and the Tharsis region of Mars. Activities at a planetary geology field conference on Eolian processes are reported and techniques recommended for the presentation and analysis of crater size-frequency data are included.

Modelling of crater formation on anode surface by high-current vacuum arcs

NASA Astrophysics Data System (ADS)

Tian, Yunbo; Wang, Zhenxing; Jiang, Yanjun; Ma, Hui; Liu, Zhiyuan; Geng, Yingsan; Wang, Jianhua; Nordlund, Kai; Djurabekova, Flyura

2016-11-01

Anode melting and crater formation significantly affect interruption of high-current vacuum arcs. The primary objective of this paper is to theoretically investigate the mechanism of anode surface crater formation, caused by the combined effect of surface heating during the vacuum arc and pressure exerted on the molten surface by ions and electrons from the arc plasma. A model of fluid flow and heat transfer in the arc anode is developed and combined with a magnetohydrodynamics model of the vacuum arc plasma. Crater formation is observed in simulation for a peak arcing current higher than 15 kA on 40 mm diam. Cu electrodes spaced 10 mm apart. The flow of liquid metal starts after 4 or 5 ms of arcing, and the maximum velocities are 0.95 m/s and 1.39 m/s for 20 kA and 25 kA arcs, respectively. This flow redistributes thermal energy, and the maximum temperature of the anode surface does not remain in the center. Moreover, the condition for the liquid droplet formation on the anode surfaces is developed. The solidification process after current zero is also analyzed. The solidification time has been found to be more than 3 ms after 25 kA arcing. The long solidification time and sharp features on crater rims induce Taylor cone formation.

Processes of lunar crater degradation - Changes in style with geologic time

NASA Technical Reports Server (NTRS)

Head, J. W.

1975-01-01

Relative age schemes of crater degradation are calibrated to radiometric dates obtained from lunar samples, changes in morphologic features are analyzed, and the style and rate of lunar surface degradation processes are modeled in relation to lunar geologic time. A comparison of radiometric age scales and the relative degradation of morphologic features for craters larger than about 5 km in diameter shows that crater degradation can be divided into two periods: Period I, prior to about 3.9 billion years ago and characterized by a high meteoritic influx rate and the formation of large multiringed basins, and Period II, from about 3.9 billion years ago to the present and characterized by a much lower influx rate and a lack of large multiringed basins. Diagnostic features for determining the relative ages of craters are described, and crater modification processes are considered, including primary impacts, lateral sedimentation, proximity weathering, landslides, and tectonism. It is suggested that the fundamental degradation of early Martian craters may be associated with erosional and depositional processes related to the intense bombardment characteristics of Period I.

Geomorphology of crater and basin deposits - Emplacement of the Fra Mauro formation

NASA Technical Reports Server (NTRS)

Morrison, R. H.; Oberbeck, V. R.

1975-01-01

Characteristics of continuous deposits near lunar craters larger than about 1 km wide are considered, and it is concluded that (1) concentric dunes, radial ridges, and braided lineations result from deposition of the collision products of ejecta from adjacent pairs of similarly oriented secondary-crater chains and are, therefore, concentrations of secondary-crater ejecta; (2) intracrater ridges are produced within preexisting craters surrounding a fresh primary crater by ricocheting and focusing of secondary-crater ejecta from the preexisting craters' walls; and (3) secondary cratering has produced many of the structures of the continuous deposits of relatively small lunar craters and is the dominant process for emplacement of most of the radial facies of the continuous deposits of large lunar craters and basins. The percentages of Imbrium ejecta in deposits and the nature of Imbrium sculpturing are investigated.

Volatile-rich Crater Interior Deposits on Mars: An Energy Balance Model of Modification

NASA Technical Reports Server (NTRS)

Russell, Patrick S.; Head, James W.; Hecht, Michael H.

2003-01-01

Several craters on Mars are partially filled by material emplaced by post-impact processes. Populations of such craters include those in the circumsouth polar cap region, in Arabia Terra, associated with the Medusae Fossae Formation, and in the northern lowlands proximal to the north polar cap. In this study, crater fill material refers to an interior mound, generally separated from the interior walls of the crater by a trough that may be continuous along the crater s circumference (i.e. a ring-shaped trough), or may only partially contact the crater walls (i.e. a crescent-shaped trough). The fill deposit is frequently off-center from the crater center and may be asymmetric, (i.e. not circular) in plan view shape. Here we test the hypothesis that asymmetries in volatile fill shape, profile, and center-location within a crater result from asymmetries in local energy balance within the crater due mainly to variation of solar insolation and radiative effects of the crater walls over the crater interior. We first focus on Korolev crater in the northern lowlands. We can then apply this model to other craters in different regions. If asymmetry in morphology and location of crater fill are consistent with radiative-dominated asymmetries in energy budget within the crater, then 1) the volatile-rich composition of the fill is supported (this process should not be effective at shaping volcanic or sedimentary deposits), and 2) the dominant factor determining the observed shape of volatile-rich crater fill is the local radiative energy budget within the crater (and erosive processes such as eolian deflation are not necessary).

Gully formation in terrestrial simple craters: Meteor Crater, USA and Lonar Crater, India

NASA Astrophysics Data System (ADS)

Kumar, P.; Head, J. W.; Kring, D. A.

2007-12-01

Geomorphic features such as gullies, valley networks, and channels on Mars have been used as a proxy to understand the climate and landscape evolution of Mars. Terrestrial analogues provide significant insight as to how the various exogenic and endogenic processes might contribute to the evolution of these martian landscapes. We describe here a terrestrial example from Meteor Crater, which shows a spectacular development of gullies throughout the inner wall in response to rainwater precipitation, snow melting and groundwater discharge. As liquid water has been envisaged as one of the important agents of landscape sculpturing, Meteor Crater remains a useful landmark, where planetary geologists can learn some lessons. We also show here how the lithology and structural framework of this crater controls the gully distribution. Like many martian impact craters, it was emplaced in layered sedimentary rocks with an exceptionally well-developed centripetal drainage pattern consisting of individual alcoves, channels and fans. Some of the gullies originate from the rim crest and others from the middle crater wall, where a lithologic transition occurs. Deeply incised alcoves are well-developed on the soft sandstones of the Coconino Formation exposed on the middle crater wall, beneath overlying dolomite. In general, the gully locations are along crater wall radial fractures and faults, which are favorable locales of groundwater flow and discharge; these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow, causing degradation. Like martian craters, channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor. In addition, lake sediments on the crater floor provide significant evidence of a past pluvial climate, when groundwater seeped from springs on the crater wall. Caves exposed on the lower crater level may point to percolation of surface runoff and selective discharge through fractures on the crater wall. Similar relationships are seen at Lonar Crater, India. Although these hydrological processes continue at Meteor Crater today, conditions at the crater are much more arid than they were soon after impact, reflecting a climatic shift similar in direction to that inferred for Mars.

A Frost Enhanced Landscape

NASA Image and Video Library

2015-12-23

The arc of hills in this image from NASA Mars Reconnaissance Orbiter spacecraft is the rim of an old and infilled impact crater. The sediments that were deposited within the crater have since formed polygonal cracks due to repeated cycles of freezing and thawing. The process of polygon formation is common at these polar latitudes, but polygons are not always as striking as they are here. In this image, the polygons have been highlighted by persistent frost in the cracks. The crater rim constrains the polygon formation within the crater close to the rim, creating a spoke and ring pattern of cracks. This leads to more rectangular polygons than those near the center of the crater. The polygons close to the center of the crater display a more typical pattern. A closer look shows some of these central polygons, which have smaller polygons within them, and smaller polygons within those smaller polygons, which makes for a natural fractal. http://photojournal.jpl.nasa.gov/catalog/PIA20289

Impact into the earth's ocean floor - Preliminary experiments, a planetary model, and possibilities for detection

NASA Technical Reports Server (NTRS)

Mckinnon, W. B.

1982-01-01

Impact processes and plate tectonics are invoked in an experimental study of craters larger than 100 km in diameter on the ocean floor. Although the results obtained from 22-caliber (383 m/sec) ammunition experiments using dense, saturated sand as a target medium cannot be directly scaled to large events, the phenomenology exhibited is that expected of actual craters on the ocean floor: steep, mixed ejecta plume, gravitational adjustment of the crater to form a shallow basin, and extensive reworking of the ejecta, rim, and floor materials by violent collapse of the transient water cavity. Excavation into the mantle is predicted, although asthenospheric influence on outer ring formation is not. The clearest geophysical signature of such a crater is not topography; detection should instead be based on gravity and geoid anomalies due to uplift of the Moho, magnetic anomalies, and seismic resolution of the Moho uplift and crater formation fault planes.

The Mechanics of Peak-Ring Impact Crater Formation from the IODP-ICDP Expedition 364

NASA Astrophysics Data System (ADS)

Melosh, H.; Collins, G. S.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

The Chicxulub impact crater is one of very few peak-ring impact craters on Earth. While small (less than 3 km on Earth) impact craters are typically bowl-shaped, larger craters exhibit central peaks, which in still larger (more than about 100 km on Earth) craters expand into mountainous rings with diameters close to half that of the crater rim. The origin of these peak rings has been contentious: Such craters are far too large to create in laboratory experiments and remote sensing of extraterrestrial examples has not clarified the mechanics of their formation. Two principal models of peak ring formation are currently in vogue, the "nested crater" model, in which the peak ring originates at shallow depths in the target, and the "dynamic collapse" model in which the peak ring is uplifted at the base of a collapsing, over-steepened central peak and its rocks originate at mid-crustal depths. IODP-ICDP Expedition 364 sought to elucidate, among other important goals, the mechanics of peak ring formation in the young (66 Myr), fresh, but completely buried Chicxulub impact crater. The cores from this borehole now show unambiguously that the rocks in the Chicxulub peak ring originated at mid-crustal depths, apparently ruling out the nested crater model. These rocks were shocked to pressures on the order of 10-35 GPa and were so shattered that their densities and seismic velocities now resemble those of sedimentary rocks. The morphology of the final crater, its structure as revealed in previous seismic imaging, and the results from the cores are completely consistent with modern numerical models of impact crater excavation and collapse that incorporate a model for post-impact weakening. Subsequent to the opening of a ca. 100 km diameter and 30 km deep transient crater, this enormous hole in the crust collapsed over a period of about 10 minutes. Collapse was enabled by movement of the underlying rocks, which briefly behaved in the manner of a high-viscosity fluid, a brittle deformation state described by the process of "acoustic" fluidization initiated by strong elastic vibrations accompanying the opening and collapse of the crater. The shattered core, cut by both melt rock and clastic dikes, is consistent with the block model of acoustic fluidization supporting its application to crater collapse both on the Earth and on other planets.

Subsurface volatile content of martian double-layer ejecta (DLE) craters

USGS Publications Warehouse

Viola, Donna; McEwen, Alfred S.; Dundas, Colin M.; Byrne, Shane

2017-01-01

Excess ice is widespread throughout the martian mid-latitudes, particularly in Arcadia Planitia, where double-layer ejecta (DLE) craters also tend to be abundant. In this region, we observe the presence of thermokarstically-expanded secondary craters that likely form from impacts that destabilize a subsurface layer of excess ice, which subsequently sublimates. The presence of these expanded craters shows that excess ice is still preserved within the adjacent terrain. Here, we focus on a 15-km DLE crater that contains abundant superposed expanded craters in order to study the distribution of subsurface volatiles both at the time when the secondary craters formed and, by extension, remaining today. To do this, we measure the size distribution of the superposed expanded craters and use topographic data to calculate crater volumes as a proxy for the volumes of ice lost to sublimation during the expansion process. The inner ejecta layer contains craters that appear to have undergone more expansion, suggesting that excess ice was most abundant in that region. However, both of the ejecta layers had more expanded craters than the surrounding terrain. We extrapolate that the total volume of ice remaining within the entire ejecta deposit is as much as 74 km3 or more. The variation in ice content between the ejecta layers could be the result of (1) volatile preservation from the formation of the DLE crater, (2) post-impact deposition in the form of ice lenses; or (3) preferential accumulation or preservation of subsequent snowfall. We have ruled out (2) as the primary mode for ice deposition in this location based on inconsistencies with our observations, though it may operate in concert with other processes. Although none of the existing DLE formation hypotheses are completely consistent with our observations, which may merit a new or modified mechanism, we can conclude that DLE craters contain a significant quantity of excess ice today.

Ejecta from Targets Strong and Weak: Experimental Measurements of Strength Controlled and Strengthless Craters

NASA Astrophysics Data System (ADS)

Hermalyn, B.

2014-09-01

This study presents novel time-resolved 3D measurements of the impact ejecta through crater formation and the arresting process that ceases growth into a variety of targets exhibiting a spectrum of different strengths of interest on planetary bodies.

Snow-avalanche impact craters in southern Norway: Their morphology and dynamics compared with small terrestrial meteorite craters

NASA Astrophysics Data System (ADS)

Matthews, John A.; Owen, Geraint; McEwen, Lindsey J.; Shakesby, Richard A.; Hill, Jennifer L.; Vater, Amber E.; Ratcliffe, Anna C.

2017-11-01

This regional inventory and study of a globally uncommon landform type reveals similarities in form and process between craters produced by snow-avalanche and meteorite impacts. Fifty-two snow-avalanche impact craters (mean diameter 85 m, range 10-185 m) were investigated through field research, aerial photographic interpretation and analysis of topographic maps. The craters are sited on valley bottoms or lake margins at the foot of steep avalanche paths (α = 28-59°), generally with an easterly aspect, where the slope of the final 200 m of the avalanche path (β) typically exceeds 15°. Crater diameter correlates with the area of the avalanche start zone, which points to snow-avalanche volume as the main control on crater size. Proximal erosional scars ('blast zones') up to 40 m high indicate up-range ejection of material from the crater, assisted by air-launch of the avalanches and impulse waves generated by their impact into water-filled craters. Formation of distal mounds up to 12 m high of variable shape is favoured by more dispersed down-range deposition of ejecta. Key to the development of snow-avalanche impact craters is the repeated occurrence of topographically-focused snow avalanches that impact with a steep angle on unconsolidated sediment. Secondary craters or pits, a few metres in diameter, are attributed to the impact of individual boulders or smaller bodies of snow ejected from the main avalanche. The process of crater formation by low-density, low-velocity, large-volume snow flows occurring as multiple events is broadly comparable with cratering by single-event, high-density, high-velocity, small-volume projectiles such as small meteorites. Simple comparative modelling of snow-avalanche events associated with a crater of average size (diameter 85 m) indicates that the kinetic energy of a single snow-avalanche impact event is two orders of magnitude less than that of a single meteorite-impact event capable of producing a crater of similar size, which is consistent with the incremental development of snow-avalanche impact craters through the Holocene.

Crater size estimates for large-body terrestrial impact

NASA Technical Reports Server (NTRS)

Schmidt, Robert M.; Housen, Kevin R.

1988-01-01

Calculating the effects of impacts leading to global catastrophes requires knowledge of the impact process at very large size scales. This information cannot be obtained directly but must be inferred from subscale physical simulations, numerical simulations, and scaling laws. Schmidt and Holsapple presented scaling laws based upon laboratory-scale impact experiments performed on a centrifuge (Schmidt, 1980 and Schmidt and Holsapple, 1980). These experiments were used to develop scaling laws which were among the first to include gravity dependence associated with increasing event size. At that time using the results of experiments in dry sand and in water to provide bounds on crater size, they recognized that more precise bounds on large-body impact crater formation could be obtained with additional centrifuge experiments conducted in other geological media. In that previous work, simple power-law formulae were developed to relate final crater diameter to impactor size and velocity. In addition, Schmidt (1980) and Holsapple and Schmidt (1982) recognized that the energy scaling exponent is not a universal constant but depends upon the target media. Recently, Holsapple and Schmidt (1987) includes results for non-porous materials and provides a basis for estimating crater formation kinematics and final crater size. A revised set of scaling relationships for all crater parameters of interest are presented. These include results for various target media and include the kinematics of formation. Particular attention is given to possible limits brought about by very large impactors.

Geologic Mapping of Vesta

NASA Technical Reports Server (NTRS)

Yingst, R. A.; Mest, S. C.; Berman, D. C.; Garry, W. B.; Williams, D. A.; Buczkowski, D.; Jaumann, R.; Pieters, C. M.; De Sanctis, M. C.; Frigeri, A.;

Ancient impact and aqueous processes at Endeavour Crater, Mars

USGS Publications Warehouse

Squyres, S. W.; Arvidson, R. E.; Bell, J.F.; Calef, F.J.; Clark, B. C.; Cohen, B. A.; Crumpler, L.A.; de Souza, P. A.; Farrand, W. H.; Gellert, Ralf; 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.

2012-01-01

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.

Modeling concentric crater fill in Utopia Planitia, Mars, with an ice flow line model

NASA Astrophysics Data System (ADS)

Weitz, N.; Zanetti, M.; Osinski, G. R.; Fastook, J. L.

2018-07-01

Impact craters in the mid-latitudes of Mars are commonly filled to variable degrees with some combination of ice, dust, and rocky debris. Concentric surface features visible in these craters have been linked to debris transportation and glacial and periglacial processes. Concentric crater fill (CCF) observed today are interpreted to be the remains of repeated periods of accumulation and sublimation during the last tens to hundreds of million years. Previous work suggests that during phases of high obliquity, ice accumulates in crater interiors and begins to flow down steep crater slopes, slowly filling the crater. During times of low obliquity ice is protected from sublimation through a surface debris layer consisting of dust and rocky material. Here, we use an ice flow line model to understand the development of concentric crater fill. In a regional study of Utopia Planitia craters, we address questions about the influence of crater size on the CCF formation process, the time scales needed to fill an impact crater with ice, and explore commonly described flow features of CCF. We show that observed surface debris deposits as well as asymmetric flow features can be reproduced with the model. Using surface mass balance data from global climate models and a credible obliquity scenario, we find that craters less than 80 km in diameter can be entirely filled in less than 8 My, beginning as recently as 40 Ma ago. Uncertainties in input variables related to ice viscosity do not change the overall behavior of ice flow and the filling process. We model CCF for the Utopia Planitia region and find subtle trends for crater size versus fill level, crater size versus sublimation reduction by the surface debris layer, and crater floor elevation versus fill level.

Topography and Geomorphology of the Interior of Occator Crater on Ceres

NASA Astrophysics Data System (ADS)

Jaumann, Ralf

2017-04-01

With a diameter of 92km, Occator is one of the most prominent craters on Ceres. Its depth ranges from 4.8km along the crater rim to -1.1km at the crater floor with respect to a reference ellipsoid. Occator shows a set of specific features such as post impact formation crater filling including multiple flow features, a central pit with a dome in its center, extensional tectonics expressed as linear radial and concentric graben, and spectral variations indicating a complex formation process. We processed 550 LAMO stereo images from Cycle01-Cycle11 with a resolution of 35m/pixel to generate a high-resolution digital terrain model (DTM) of the Occator impact structure. Occator crater has mass wasting deposits originating from the crater rims and walls, which extend into the crater for 10 to 20km. However, in the southeast and northeast these mass wasting deposits are completely covered by crater floor plains material that extends from the crater center to the rim, ponding against the crater walls. The flows also superimpose the mass wasting deposits from the rims [1]. Furthermore, crater densities on Occator's interior deposits are slightly lower than on its ejecta blanket, indicating post-impact formation or target parameter variation between consolidated melt and unconsolidated ejecta deposits [2,3,4]. The terrain northwest of the central area is very rough, shows mass wasting deposits and is about 2km thick w.r.t the rim of the central pit. The plains to the southeast are smooth, pond against the crater wall, and are less than 500m thick w.r.t. the rim of the central pit The central pit is about 3.5km wide and 600m deep while the dome rises 250m within the pit [5]. In the northeast, multiple flows approaching the crater rim very closely. These flow plains are also less than 500m thick w.r.t. the rim of the central pit. Some of the flows seem to have been superposed on the lower parts of the crater wall and then flowed back into depressions of the plains. The flows to the northeast appear to originate from the central region and move slightly uphill. This indicates either a feeding zone that pushes the flows forward by supplying low-viscosity material or an extended subsidence of the crater center, possibly after discharging a subsurface reservoir [1,2], or lateral oscillations of an impact melt sheet during emplacement. The plains material covers an area of about 4750km2 with an average depth of about 250m resulting in a body of plains material of about 1200km3. The plains material is slightly younger than the impact event and the bright deposits are even younger than the plains material. Post impact processes might be due to impact melt, hydrothermal alteration, or cryovolcanic crater filling [1] K. Krohn et al, GRL43, 11994, (2016). [2] R. Jaumann et al., LPSC47, 1455 (2016). [3] N. Schmedemann et al, GRL43, 11987. (2016) [4] A. Neesemann, et al., Icarus, in prep. [5] P. Schenk, et al., LPSC47 (2016).

Transient features and growth behavior of artificial cracks during the initial damage period.

PubMed

Ma, Bin; Wang, Ke; Lu, Menglei; Zhang, Li; Zhang, Lei; Zhang, Jinlong; Cheng, Xinbin; Wang, Zhanshan

2017-02-01

The laser damage of transmission elements contains a series of complex processes and physical phenomena. The final morphology is a crater structure with different sizes and shapes. The formation and development of the crater are also accompanied by the generation, extension, and submersion of cracks. The growth characteristics of craters and cracks are important in the thermal-mechanism damage research. By using pump-probe detection and an imaging technique with a nanosecond pulsewidth probe laser, we obtained the formation time of the crack structure in the radial and circumferential directions. We carried out statistical analysis in angle, number, and crack length. We further analyzed the relationship between cracks and stress intensity or laser irradiation energy as well as the crack evolution process and the inner link between cracks and pit growth. We used an artificial indentation defect to investigate the time-domain evolution of crack growth, growth speed, transient morphology, and the characteristics of crater expansion. The results can be used to elucidate thermal stress effects on cracks, time-domain evolution of the damage structure, and the damage growth mechanism.

Comparison Between Terrestrial Explosion Crater Morphology in Floating Ice and Europan Chaos

NASA Technical Reports Server (NTRS)

Billings, S. E.; Kattenhorn, S. A.

2003-01-01

Craters created by explosives have been found to serve as valuable analogs to impact craters, within limits. Explosion craters have been created in floating terrestrial ice in experiments related to clearing ice from waterways. Features called chaos occur on the surface of Europa s floating ice shell. Chaos is defined as a region in which the background plains have been disrupted. Common features of chaos include rafted blocks of pre-existing terrain suspended in a matrix of smooth or hummocky material; low surface albedo; and structural control on chaos outline shape by pre-existing lineaments. All published models of chaos formation call on endogenic processes whereby chaos forms through thermal processes. Nonetheless, we note morphological similarities between terrestrial explosion craters and Europan chaos at a range of scales and consider whether some chaos may have formed by impact. We explore these similarities through geologic and morphologic mapping.

The geology and mechanics of formation of the Fort Rock Dome, Yavapai County, Arizona

USGS Publications Warehouse

Fuis, Gary S.

1996-01-01

The Fort Rock Dome, a craterlike structure in northern Arizona, is the erosional product of a circular domal uplift associated with a Precambrian shear zone exposed within the crater and with Tertiary volcanism. A section of Precambrian to Quaternary rocks is described, and two Tertiary units, the Crater Pasture Formation and the Fort Rock Creek Rhyodacite, are named. A mathematical model of the doming process is developed that is consistent with the history of the Fort Rock Dome.

The Age of Lunar South Circumpolar Craters Haworth, Shoemaker, Faustini, and Shackleton: Implications for Regional Geology, Surface Processes, and Volatile Sequestration

NASA Technical Reports Server (NTRS)

Tye, A. R.; Fassett, C. I.; Head, J. W.; Mazarico, E.; Basilevsky, A. T.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2015-01-01

The interiors of the lunar south circumpolar craters Haworth, Shoemaker, Faustini, and Shackleton contain permanently shadowed regions (PSRs) and have been interpreted to contain sequestered volatiles including water ice. Altimetry data from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter provide a new means of examining the permanently shadowed interiors of these craters in unprecedented detail. In this study, we used extremely high-resolution gridded LOLA data of Haworth, Shoemaker, Faustini, and Shackleton to determine the size-frequency distributions and the spatial density of craters superposing their rims, inner slopes, and floors. Based on their population of superposed D greater than or equal to 2 km craters, Haworth, Shoemaker, and Faustini have pre-Nectarian formation ages. Shackleton is interpreted as having a Late Imbrian age on the basis of craters with diameter D greater than or equal to 0.5 km superposed on its rim. The local density of craters with sub-km diameters across our study area is strongly dependent on slope; because of its steep interior slopes, the lifetime of craters on the interior of Shackleton is limited. The slope-dependence of the small crater population implies that the population in this size range is controlled primarily by the rate at which craters are destroyed. This is consistent with the hypothesis that crater removal and resurfacing is a result of slopedependent processes such as diffusive mass wasting and seismic shaking, linked to micrometeorite and meteorite bombardment. Epithermal neutron flux data and UV albedo data show that these circumpolar PSRs, particularly Shoemaker, may have approximately 1-2% water ice by mass in their highly porous surface regolith, and that Shoemaker may have approximately 5% or more water ice by mass in the near subsurface. The ancient formation ages of Shoemaker, Faustini and Haworth, and the Late Imbrian (approximately 3.5 Ga) crater retention ages of their floors suggests that any water ice that might have been deposited in their permanently shadowed areas was insufficient to modify the superposed crater population since that time.

Investigation of Secondary Craters in the Saturnian System

NASA Astrophysics Data System (ADS)

Hoogenboom, T.; Schenk, P.; White, O. L.

2012-03-01

To derive accurate ages using impact craters, the impact source must be determined. We investigate secondary crater size, frequency, distribution, formation, and crater chain formation on icy satellites throughout the Jupiter and Saturn systems.

Regional variations in degradation and density of Martian craters.

NASA Technical Reports Server (NTRS)

Mcgill, G. E.; Wise, D. U.

1972-01-01

Martian craters visible on Mariner 6 and 7 imagery show a spectrum of topographic types from very fresh to highly degraded. A method of numerical scoring of rim, wall, and floor is proposed to yield a degradation number to classify each crater. Plots of degradation class vs density of large craters are similar for all four regions studied, whereas similar plots for small craters show marked differences between regions. The data suggest general continuity of crater formation and degradation, along with locally sporadic formation and/or degradation of the smallest craters classified. Deucalionis Regio, with an excess of fresh, small craters, experienced an episode of small crater formation (or nondegradation) most recently; Margaritifer Sinus was similarly disturbed at some more remote time. Meridiani Sinus and Hellespontus-Noachis show little or no sign of excess fresh, small craters.

An assessment of crater erosional histories on the Earth and Mars using digital terrain models.

NASA Astrophysics Data System (ADS)

Paul, R. L.; Muller, J.-P.; Murray, J. B.

The research will examine quantitatively the geomorphology of both Terrestrial and Martian craters. The erosional and sub-surface processes will be investigated to understand how these affect a crater's morphology. For example, the Barringer crater in Arizona has an unusual shape. The Earth has a very high percentage of water both in the atmosphere as clouds or rain and under the surface. The presence of water will therefore affect a crater's formation and its subsequent erosional modification. On Mars there is little or no water present currently, though recent observations suggest there may be near-surface ice in some areas. How do craters formed in the Martian environment therefore differ from Terrestrial ones? How has the structure of Martian craters changed in areas of possible fluvial activity? How does the surface material affect crater formation? How does the Earth's fluvial activity affect a crater's evolution? At present, four measurements of circularity have been used to describe a crater (Murray & Guest, 1972). These parameters will be re-examined to see how effectively they describe Terrestrial and Martian craters using high resolution DTMs which were not available at the time of the original study. The model described by Forsberg-Taylor et al. 2004, and others will also be applied to results obtained from the chosen craters to assess how effectively these craters are described. Both hypsometric curves and hydrological analysis will be used to assess crater evolution. A suitable criterion for the selection of Terrestrial and Martian craters is essential for this type of research. Terrestrial craters have been selected in arid or semi-arid terrain with crater diameters larger than one kilometre. Craters less than five million years old would be ideal. However, this was too restrictive and so a variety of crater ages have had to be used. Eight terrestrial craters have been selected in arid or semi-arid areas for study, using the Earth Impact Database and ICEDS. These are: Barringer, Arizona, U.S.A; Goat Paddock, West Australia; Ouarkziz, Algeria; Roter Kamm, Namibia; Talemzane, Algeria; Tenoumer, Mauritania; Tswaing, South Africa 1 and Upheaval Dome, Utah, U.S.A. Comparable Martian craters are in the process of being chosen using the USGS PIGWAD database and the Morphological Catalogue of the Craters of Mars. Digital Terrain Models of each crater using SRTM DEMs and data from the recent Mars Express HRSC will be used at various resolutions (30m upwards) to provide three dimensional models to assess the capabilities of measuring erosional effects. There is also available ASTER DEMs and ASTER Level 1A for terrestrial craters and MOLA tracks for Martian craters. Both laboratory and theoretical models of crater shape and erosion features will provide a better understanding of the processes observed. This will enable us to develop a better explanation of why craters are the shape they are. References. Barlow N., 1987, Crater Size-Frequency Distribution and a Revised Martian Relative Chronology, Icarus, 75, 285-305. Barlow, N., 1995, The degradation of impact craters in Maja Valles and Arabia Mars, Journal GeoPhys. Res., 100, 23307-23316. Earth Impact Database http://www.unb.ca/passc/ImpactDatabase/ Earth PIGWAD database http://webgis.wr.usgs.gov/website/mars%5Fcrater%5Fhtml/viewer.htm ICEDS http://iceds.ge.ucl.ac.uk/ Morphology Catalogue of the Craters of Mars http://selena.sai.msu.ru/Home/Mars_Cat/Mars_Cat.htm Murray J.B, Guest J.E, 1970, Circularities of craters and related structures on Earth and Moon, Modern Geology, 1, 149-159. Forsberg-Taylor N., Howard A.D., 2004, Crater degradation in the Martian Highlands: Morphometric Analysis of the Sinus Sabaeus region and simulation modelling suggest fluvial processes, Journal GeoPhys Res., 109, E05002. 2

[INVITED] On the mechanisms of single-pulse laser-induced backside wet etching

NASA Astrophysics Data System (ADS)

Tsvetkov, M. Yu.; Yusupov, V. I.; Minaev, N. V.; Akovantseva, A. A.; Timashev, P. S.; Golant, K. M.; Chichkov, B. N.; Bagratashvili, V. N.

2017-02-01

Laser-induced backside wet etching (LIBWE) of a silicate glass surface at interface with a strongly absorbing aqueous dye solution is studied. The process of crater formation and the generated optoacoustic signals under the action of single 5 ns laser pulses at the wavelength of 527 nm are investigated. The single-pulse mode is used to avoid effects of incubation and saturation of the etched depth. Significant differences in the mechanisms of crater formation in the ;soft; mode of laser action (at laser fluencies smaller than 150-170 J/cm2) and in the ;hard; mode (at higher laser fluencies) are observed. In the ;soft; single-pulse mode, LIBWE produces accurate craters with the depth of several hundred nanometers, good shape reproducibility and smooth walls. Estimates of temperature and pressure of the dye solution heated by a single laser pulse indicate that these parameters can significantly exceed the corresponding critical values for water. We consider that chemical etching of glass surface (or molten glass) by supercritical water, produced by laser heating of the aqueous dye solution, is the dominant mechanism responsible for the formation of crater in the ;soft; mode. In the ;hard; mode, the produced craters have ragged shape and poor pulse-to-pulse reproducibility. Outside the laser exposed area, cracks and splits are formed, which provide evidence for the shock induced glass fracture. By measuring the amplitude and spectrum of the generated optoacoustic signals it is possible to conclude that in the ;hard; mode of laser action, intense hydrodynamic processes induced by the formation and cavitation collapse of vapor-gas bubbles at solid-liquid interface are leading to the mechanical fracture of glass. The LIBWE material processing in the ;soft; mode, based on chemical etching in supercritical fluids (in particular, supercritical water) is very promising for structuring of optical materials.

Impact Cratering Processes as Understood Through Martian and Terrestrial Analog Studies

NASA Astrophysics Data System (ADS)

Caudill, C. M.; Osinski, G. R.; Tornabene, L. L.

2016-12-01

Impact ejecta deposits allow an understanding of subsurface lithologies, volatile content, and other compositional and physical properties of a planetary crust, yet development and emplacement of these deposits on terrestrial bodies throughout the solar system is still widely debated. Relating relatively well-preserved Martian ejecta to terrestrial impact deposits is an area of active research. In this study, we report on the mapping and geologic interpretation of 150-km diameter Bakhuysen Crater, Mars, which is likely large enough to have produced a significant volume of melt, and has uniquely preserved ejecta deposits. Our mapping supports the current formation hypothesis for Martian crater-related pitted material, where pits are likened to collapsed degassing features identified at the Ries and Haughton terrestrial impact structures. As hot impact melt-bearing ejecta deposits are emplaced over volatile-saturated material during crater formation, a rapid degassing of the underlying layer results in lapilli-like fluid and gas flow pipes which may eventually lead to collapse features on the surface. At the Haughton impact structure, degassing pipes are related to crater fracture and fault systems; this is analogous to structure and collapse pits mapped in Bakhuysen Crater. Based on stratigraphic superposition, surface and flow texture, and morphological and thermophysical mapping of Bakhuysen, we interpret the top-most ejecta unit to be likely melt-bearing and analogous to terrestrial impact deposits (e.g., Ries suevites). Furthermore, we suggest that Chicxulub is an apt terrestrial comparison based on its final diameter and the evidence of a ballistically-emplaced and volatile-entrained initial ejecta. This is significant as Bakhuysen ejecta deposits may provide insight into larger impact structures where limited exposures make studies difficult. This supports previous work which suggests that given similarities in volatile content and subsurface stratigraphy, mechanisms of multi-unit ejecta emplacement extend to impact cratering processes on comparable rocky bodies. The widespread pitted material, ejecta rampart and lobe formations, and distal debris flows associated with Bakhuysen impactite emplacement further indicates a volatile-rich Martian crust during its formation.

Geological mapping of lunar highland crater Lalande: Topographic configuration, morphology and cratering process

NASA Astrophysics Data System (ADS)

Li, Bo; Ling, Zongcheng; Zhang, Jiang; Chen, Jian; Liu, ChangQing; Bi, Xiangyu

2018-02-01

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 the Mare Insularum. It is a complex crater in Copernican era and has three distinguishing features: high silicic anomaly, the highest Th abundance and special landforms on its floor. There are some low-relief bulges on the left of Lalande's floor with regular circle or ellipse shapes. They are ∼250-680 m wide and ∼30-91 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. We estimated the absolute model ages of the ejecta deposits, several melt ponds and the hummocky floor and determined the ratio of diameter and depth of the crater Lalande. In addition, we found some similar bugle features within other Copernican-aged craters and there were no volcanic source vents on Lalande's floor. Thus, 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 floor. Based on Kaguya Terrain Camera (TC) ortho-mosaic and Digital Terrain Model (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 provided us a chance to understand some details of the cratering process and elevation differences on the floor. We proposed that subsidence due to melt cooling, late-stage wall collapse and rocks uplifted from beneath the surface could be the possible causes of the observed elevation differences on Lalande's floor.

The Geology of the Marcia Quadrangle of Asteroid Vesta: Assessing the Effects of Large, Young Craters

NASA Technical Reports Server (NTRS)

Williams, David A.; Denevi, Brett W.; Mittlefehldt, David W.; Mest, Scott C.; Schenk, Paul M.; Yingst, R. Aileen; Buczowski, Debra L.; Scully, Jennifer E. C.; Garry, W. Brent; McCord, Thomas B.;

Volatile-rich Crater Interior Deposits in the Polar Regions of Mars: Evidence for Ice Cap Advance and Retreat

NASA Technical Reports Server (NTRS)

Russell, Patrick S.; Head, James W.; Hecht, Michael H.

2003-01-01

Many craters on Mars are partially filled by distinctive material emplaced by post-impact processes. This crater fill material is an interior mound which is generally separated from the walls of the crater by a trough that may be continuous along the crater circumference (i.e. a ring-shaped trough), or which may only partially contact the crater walls (i.e. a crescent-shaped trough). The fill deposit is frequently offset from the crater center and may be asymmetric in plan view. Populations of such craters include those in the circum-south polar cap region, in Arabia Terra, associated with the Medusae Fossae Formation, and in the northern lowlands proximal to the north polar cap. We focus on those craters in circumpolar regions and assess their relationship to polar cap advance and retreat, especially the possibility that fill material represents remnants of a formerly larger contiguous cap. Volatile-rich deposits have the property of being modifiable by the local stability of the solid volatile, which is governed by local energy balance. Here we test the hypothesis that asymmetries in volatile fill shape, profile, and center-location within a crater result from asymmetries in local energy balance within the crater, due mainly to variation of solar insolation and radiative effects of the crater walls over the crater interior. Model profiles of crater fill are compared with MOLA topographic profiles to assess this hypothesis. If asymmetry in morphology and location of crater fill are consistent with radiative-dominated asymmetries in energy budget within the crater, then 1) the volatile-rich composition of the fill is supported (this process should not be effective at shaping volcanic or sedimentary deposits), and 2) the dominant factor determining the observed shape of volatile-rich crater fill is the local radiative energy budget (and erosive processes such as eolian deflation are secondary or unnecessary). We also use a geographic and energy model approach to specifically test the idea that material in partially filled craters around the south pole may once have been contiguous to the cap and may have been sustained and modified by radiative processes specific to the crater environment (as opposed to the surrounding plains) as the cap retreated.

The Degradational History of Endeavour Crater, Mars

NASA Technical Reports Server (NTRS)

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 processes. Such degradation is consistent with 1) the interpretation of a pediment on the rim flanks of Endeavour, 2) the formation of features such as Marathon Valley, 3) the nearly complete removal of ejecta at Cape York, 4) preservation of a thicker section of ejecta at Cape Tribulation and perhaps, 5) the origin of some gaps in the rim around the crater. A paucity of debris shed from the rim indicates most degradation occurred prior to embayment by the plains rocks.

Experimental Investigation of the Formation of Complex Craters

NASA Astrophysics Data System (ADS)

Martellato, E.; Dörfler, M. A.; Schuster, B.; Wünnemman, K.; Kenkmann, T.

2017-09-01

The formation of complex impact craters is still poorly understood, because standard material models fail to explain the gravity-driven collapse at the observed size-range of a bowl-shaped transient crater into a flat-floored crater structure with a central peak or ring and terraced rim. To explain such a collapse the so-called Acoustic Fluidization (AF) model has been proposed. The AF assumes that heavily fractured target rocks surrounding the transient crater are temporarily softened by an acoustic field in the wake of an expanding shock wave generated upon impact. The AF has been successfully employed in numerous modeling studies of complex crater formation; however, there is no clear relationship between model parameters and observables. In this study, we present preliminary results of laboratory experiments aiming at relating the AF parameters to observables such as the grain size, average wave length of the acoustic field and its decay time τ relative to the crater formation time.

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

USGS Publications Warehouse

Horton, J. Wright; 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.

Application of high explosion cratering data to planetary problems

NASA Technical Reports Server (NTRS)

Oberbeck, V. R.

1977-01-01

The present paper deals with the conditions of explosion or nuclear cratering required to simulate impact crater formation. Some planetary problems associated with three different aspects of crater formation are discussed, and solutions based on high-explosion data are proposed. Structures of impact craters and some selected explosion craters formed in layered media are examined and are related to the structure of lunar basins. The mode of ejection of material from impact craters is identified using explosion analogs. The ejection mode is shown to have important implications for the origin of material in crater and basin deposits. Equally important are the populations of secondary craters on lunar and planetary surfaces.

Craters and Granular Jets Generated by Underground Cavity Collapse

NASA Astrophysics Data System (ADS)

Loranca-Ramos, F. E.; Carrillo-Estrada, J. L.; Pacheco-Vázquez, F.

2015-07-01

We study experimentally the cratering process due to the explosion and collapse of a pressurized air cavity inside a sand bed. The process starts when the cavity breaks and the liberated air then rises through the overlying granular layer and produces a violent eruption; it depressurizes the cavity and, as the gas is released, the sand sinks under gravity, generating a crater. We find that the crater dimensions are totally determined by the cavity volume; the pressure does not affect the morphology because the air is expelled vertically during the eruption. In contrast with impact craters, the rim is flat and, regardless of the cavity shape, it evolves into a circle as the cavity depth increases or if the chamber is located deep enough inside the bed, which could explain why most of the subsidence craters observed in nature are circular. Moreover, for shallow spherical cavities, a collimated jet emerges from the collision of sand avalanches that converge concentrically at the bottom of the depression, revealing that collapse under gravity is the main mechanism driving the jet formation.

Martian Central Pit Craters

NASA Technical Reports Server (NTRS)

Hillman, E.; Barlow, N. G.

2005-01-01

Impact craters containing central pits are rare on the terrestrial planets but common on icy bodies. Mars is the exception among the terrestrial planets, where central pits are seen on crater floors ( floor pits ) as well as on top of central peaks ( summit pits ). Wood et al. [1] proposed that degassing of subsurface volatiles during crater formation produced central pits. Croft [2] argued instead that central pits might form during the impact of volatile-rich comets. Although central pits are seen in impact craters on icy moons such as Ganymede, they do show some significant differences from their martian counterparts: (a) only floor pits are seen on Ganymede, and (b) central pits begin to occur at crater diameters where the peak ring interior morphology begins to appear in terrestrial planet craters [3]. A study of craters containing central pits was conducted by Barlow and Bradley [4] using Viking imagery. They found that 28% of craters displaying an interior morphology on Mars contain central pits. Diameters of craters containing central pits ranged from 16 to 64 km. Barlow and Bradley noted that summit pit craters tended to be smaller than craters containing floor pits. They also noted a correlation of central pit craters with the proposed rings of large impact basins. They argued that basin ring formation fractured the martian crust and allowed subsurface volatiles to concentrate in these locations. They favored the model that degassing of the substrate during crater formation was responsible for central pit formation due to the preferential location of central pit craters along these basin rings.

Geologic investigation of layered mound of Henry Crater, Mars: Implications for history of ancient hydrological activities in the region

NASA Astrophysics Data System (ADS)

Sarkar, Samarpita; Sinha, Rishitosh Kumar; Banerjee, Debabrata; Vijayan, S.

2016-07-01

Craters around the Schiaparelli Basin (sim460 km diameter; 2.71^circS 16.77^circE) on Mars are distributed in a unique combination that includes infilled craters with mound on their floors. The mounds have preserved intriguing layers in stratigraphy that has exposed pristine sets of geomorphic and geochemical signatures bearing strong implications towards understanding geological history of Mars. With a view to avail the maximum scientific benefit from this unique geological assemblage on Mars, we have carried out remote analysis of stratigraphy of layers exposed over Henry crater's (sim150 km diameter; 10.79^circN 23.45^circE) mound (rising sim2km from floor) to infer the origin and episodes of geological events occurred in the region. Henry crater is situated approximately 500 km northeast of Schiaparelli Basin. Using crater counting technique the age of the topmost surface of the crater mound is found to be sim3.64 Ga since the exposure of this strata post complete infilling. The stratigraphy of consistent and conformable layers in the crater interior acts as a proxy of the long-lived event of sediment deposition in a rather quiescent condition. Distinct layering can be traced across the crater from the mound to the crater wall across the floor. Evidence for differential erosion of deposited materials, wherein local geological setup developed in the different parts of the crater interior is preserved. Using MRO HiRISE & CTX images, distinct spatial distribution of morphological features distributed in stratigraphy is observed that reveals the dominant geological agents behind their formation, viz. temporal hydrological and eolian processes. The morphological features were aided with an understanding of the composition of the exposed sedimentary succession. MRO CRISM based mineralogical investigation reveals diagnostic signature of the hydrated sulfate mineral Kieserite. Based on the thermodynamic properties of Kieserite and apparent lack of desiccation cracks in the scale of observation, it is inferred that the water level inside the crater did not experience fluctuation. Rather on systematic compilation of the mineralogical and morphological data, it is inferred that the mound formation process was gradual and can be correlated with the water level inside the crater at various stages during the recession stage.

Hollows on Mercury: MESSENGER evidence for geologically recent volatile-related activity.

PubMed

Blewett, David T; Chabot, Nancy L; Denevi, Brett W; Ernst, Carolyn M; Head, James W; Izenberg, Noam R; Murchie, Scott L; Solomon, Sean C; Nittler, Larry R; McCoy, Timothy J; Xiao, Zhiyong; Baker, David M H; Fassett, Caleb I; Braden, Sarah E; Oberst, Jürgen; Scholten, Frank; Preusker, Frank; Hurwitz, Debra M

2011-09-30

High-resolution images of Mercury's surface from orbit reveal that many bright deposits within impact craters exhibit fresh-appearing, irregular, shallow, rimless depressions. The depressions, or hollows, range from tens of meters to a few kilometers across, and many have high-reflectance interiors and halos. The host rocks, which are associated with crater central peaks, peak rings, floors, and walls, are interpreted to have been excavated from depth by the crater-forming process. The most likely formation mechanisms for the hollows involve recent loss of volatiles through some combination of sublimation, space weathering, outgassing, or pyroclastic volcanism. These features support the inference that Mercury's interior contains higher abundances of volatile materials than predicted by most scenarios for the formation of the solar system's innermost planet.

Using THEMIS thermal infrared observations of rays from Corinto crater to study secondary crater formation on Mars

NASA Astrophysics Data System (ADS)

Williams, J. P.

2017-12-01

Corinto crater (16.95°N, 141.72°E), a 13.8 km diameter crater in Elysium Planitia, displays dramatic rays in Mars Odyssey's Thermal Emission Imaging System (THEMIS) nighttime infrared imagery where high concentrations of secondary craters have altered the thermophysical properties of the martian surface. The THEMIS observations provide a record of secondary crater formation in the region and ray segments are identified up to 2000 km ( 145 crater radii) distance [1][2]. Secondary craters are likely to have the largest influence on model surfaces ages between 0.1 to a few Myr as there is the potential for one or two sizeable craters to project secondary craters onto those surfaces and thus alter the crater size-frequency distribution (CSFD) with an instantaneous spike in crater production [3]. Corinto crater is estimated to be less than a few Ma [4] placing the formation of its secondaries within this formative time period. Secondary craters superposed on relatively young impact craters that predate Corinto provide observations of the secondary crater populations. Crater counts at 520 and 660 km distance from Corinto (38 and 48 crater radii respectively), were conducted. Higher crater densities were observed within ray segments, however secondary craters still influenced the CSFD where ray segments were not apparent, resulting in steepening in the CSFD. Randomness analysis confirms an increase in clustering as diameters decrease suggesting an increasing fraction of secondary craters at smaller diameters, both within the ray and outside. The counts demonstrate that even at nearly 50 crater radii, Corinto secondaries still influence the observed CSFD, even outside of any obvious rays. Crater populations used to derive model ages on many geologically young regions on Mars, such as glacial and periglacial landforms related to obliquity excursions that occur on 106 - 107 yr cycles, should be used cautiously and analyzed for any evidence, either morphologic or statistical, for secondary cratering that may potentially influence the derived age. [1] Williams et al. (2017) MAPS, in press. [2] Bloom et al. (2014) Mars 8th, #1289. [3] Hartmann and Daubar (2017), MAPS, 52, 493- 510. [4] Hundal et al. (2017), LPSC, #1726.

The geomorphology of Rhea - Implications for geologic history and surface processes

NASA Technical Reports Server (NTRS)

Moore, J. M.; Horner, V. M.; Greeley, R.

1985-01-01

Morphological analyses of landforms on Rhea are used to define three physiographic provinces: cratered terrain 1 undifferentiated; cratered terrain 1 lineated; and cratered terrain 2. The important statigraphic relationships between the different provinces are examined with respect to major impact basins and tectonic features. It is shown that the formation of multiringed basins may have caused, or at least controlled the locations of major resurfacing and mantling events. The diameters of the central peaks relative to the impact crater diameters are found to be significantly larger than those within the craters of the moon or Mercury. Both cratered and noncrater lineaments have regional orientations which do not fit current global or regional stress models. On the basis of the morphological analysis, a chronological order is established for the origin of the three provinces: the cratered terrain 1 province was formed first; and cratered terrain 1 lineated and cratered terrain 2 were formed second, and last, respectively. It is shown that the chronological order is generally consistent with current theoretical models of the evolution of Rhea.

Gullies and Craters and Dunes, Oh My!

NASA Image and Video Library

2017-06-02

This unnamed, approximately 30-kilometer diameter crater, formed in the Southern highlands of Mars. This image from NASA's Mars Reconnaissance Orbiter shows regions of geologic diversity within, making this an interesting spot for scientists to study how different Martian processes interact with each other. Gullies, or channels formed by fluids such as water or lava, cut into the rim and sides of this crater. The presence of gullies can reveal clues about the ancient history of Mars, such as the amount of flowing fluid needed to form them and roughly how long ago that happened. This crater may also host features actively changing on the surface of Mars known as "recurring slope lineae" (RSL). Manifesting as dark streaks on steep slopes such as the walls of craters, scientists posit briny flows of small volumes of water as a possible RSL formation method. Studying the behavior of RSL further may provide evidence for the presence of water on Mars today. Moving toward the crater floor, one can observe patterns indicative of dunes. Dunes arise from the breakdown of exposed rocks by wind and subsequent manipulation of the eroded sand particles into wave-like structures. The presence of dust devil tracks provides additional evidence for significant wind activity at this location. These dunes are very dusty and so likely haven't been active (moved) in some time. HiRISE also captured a small, relatively fresh crater on the floor near the dunes. One of the most ubiquitous processes in the solar system, impact cratering can drastically change the surface of a planetary body. As such, craters provide sources of comparison between planets, moons, and other bodies across the solar system. Impacts still occur today, helping scientists find relative ages of different areas of a planet and discover materials buried under the surface. All of these processes have altered the surface of Mars in the past and continue to do so today. Since gully formation, wind erosion, and impact cratering could have interacted with each other for many years, planetary scientists find it difficult to work backwards and make definitive statements about ancient Martian history. However, HiRISE imagery has aided in closing these gaps in our scientific knowledge. https://photojournal.jpl.nasa.gov/catalog/PIA21654

Mass movement on Vesta at steep scarps and crater rims

NASA Astrophysics Data System (ADS)

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.

2014-12-01

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.

Mass Movement on Vesta at Steep Scarps and Crater Rims

NASA Technical Reports Server (NTRS)

Krohn, K.; Jaumann, R.; Otto, K.; Hoogenboom, T.; Wagner, R.; Buczkowski, D. L.; Garry, B.; Williams, D. A.; Yingst, R. A.; Scully, J.;

Scientific Drilling of Impact Craters - Well Logging and Core Analyses Using Magnetic Methods (Invited)

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Perez-Cruz, L. L.; Velasco-Villarreal, M.

2013-12-01

Drilling projects of impact structures provide data on the structure and stratigraphy of target, impact and post-impact lithologies, providing insight on the impact dynamics and cratering. Studies have successfully included magnetic well logging and analyses in core and cuttings, directed to characterize the subsurface stratigraphy and structure at depth. There are 170-180 impact craters documented in the terrestrial record, which is a small proportion compared to expectations derived from what is observed on the Moon, Mars and other bodies of the solar system. Knowledge of the internal 3-D deep structure of craters, critical for understanding impacts and crater formation, can best be studied by geophysics and drilling. On Earth, few craters have yet been investigated by drilling. Craters have been drilled as part of industry surveys and/or academic projects, including notably Chicxulub, Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake, Ries and El gygytgyn craters. Inclusion of continuous core recovery expanded the range of paleomagnetic and rock magnetic applications, with direct core laboratory measurements, which are part of the tools available in the ocean and continental drilling programs. Drilling studies are here briefly reviewed, with emphasis on the Chicxulub crater formed by an asteroid impact 66 Ma ago at the Cretaceous/Paleogene boundary. Chicxulub crater has no surface expression, covered by a kilometer of Cenozoic sediments, thus making drilling an essential tool. As part of our studies we have drilled eleven wells with continuous core recovery. Magnetic susceptibility logging, magnetostratigraphic, rock magnetic and fabric studies have been carried out and results used for lateral correlation, dating, formation evaluation, azimuthal core orientation and physical property contrasts. Contributions of magnetic studies on impact age, cratering, target-impactite stratigraphy, ejecta, impact dynamics, hydrothermal alterations and post-impact processes are presented. The challenges and perspectives of drilling studies of impact craters are discussed.

Sedimentary Mounds on Mars: Tracing Present-day Formation Processes into the Past

NASA Technical Reports Server (NTRS)

Niles, P. B.; Michalski, J.; Edwards, C. S.

2014-01-01

High resolution photography and spectroscopy of the martian surface (MOC, HiRISE) from orbit has revolutionized our view of Mars with one and revealed spectacular views of finely layered sedimentary materials throughout the globe [1]. Some of these sedimentary deposits are 'mound' shaped and lie inside of craters (Fig 1). Crater mound deposits are found throughout the equatorial region, as well as ice-rich deposits found in craters in the north and south polar region [2-4]. Despite their wide geographical extent and varying volatile content, the 'mound' deposits have a large number of geomorphic and structural similarities that suggest they formed via equivalent processes. Thus, modern depositional processes of ice and dust can serve as an invaluable analog for interpreting the genesis of ancient sedimentary mound deposits.

Ancient Martian aeolian processes and palaeomorphology reconstructed from the Stimson formation on the lower slope of Aeolis Mons, Gale crater, Mars

USGS Publications Warehouse

Banham, Steve G.; Gupta, Sanjeev; Rubin, David M.; Watkins, Jessica A.; Sumner, Dawn Y.; Edgett, Kenneth S.; Grotzinger, John P.; Lewis, Kevin W.; Edgar, Lauren; Stack, Kathryn M.; Barnes, Robert; Bell, Jame F. III; Day, Mackenzie D.; Ewing, Ryan C.; Lapotre, Mathieu G.A.; Stein, Nathan T.; Rivera-Hernandez, Frances; Vasavada, Ashwin R.

2018-01-01

Reconstruction of the palaeoenvironmental context of Martian sedimentary rocks is central to studies of ancient Martian habitability and regional palaeoclimate history. This paper reports the analysis of a distinct aeolian deposit preserved in Gale crater, Mars, and evaluates its palaeomorphology, the processes responsible for its deposition, and its implications for Gale crater geological history and regional palaeoclimate. Whilst exploring the sedimentary succession cropping out on the northern flank of Aeolis Mons, Gale crater, the Mars Science Laboratory rover Curiosity encountered a decametre‐thick sandstone succession, named the Stimson formation, unconformably overlying lacustrine deposits of the Murray formation. The sandstone contains sand grains characterized by high roundness and sphericity, and cross‐bedding on the order of 1 m in thickness, separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops. The cross‐beds are composed of uniform thickness cross‐laminations interpreted as wind‐ripple strata. Cross‐sets are separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops that are interpreted as dune migration surfaces. Grain characteristics and presence of wind‐ripple strata indicate deposition of the Stimson formation by aeolian processes. The absence of features characteristic of damp or wet aeolian sediment accumulation indicate deposition in a dry aeolian system. Reconstruction of the palaeogeomorphology suggests that the Stimson dune field was composed largely of simple sinuous crescentic dunes with a height of ca10 m, and wavelengths of ca 150 m, with local development of complex dunes. Analysis of cross‐strata dip‐azimuths indicates that the general dune migration direction and hence net sediment transport was towards the north‐east. The juxtaposition of a dry aeolian system unconformably above the lacustrine Murray formation represents starkly contrasting palaeoenvironmental and palaeoclimatic conditions. Stratigraphic relationships indicate that this transition records a significant break in time, with the Stimson formation being deposited after the Murray formation and stratigraphically higher Mount Sharp group rocks had been buried, lithified and subsequently eroded.

Martian subsurface properties and crater formation processes inferred from fresh impact crater geometries

NASA Astrophysics Data System (ADS)

Stewart, Sarah T.; Valiant, Gregory J.

2006-10-01

The geometry of simple impact craters reflects the properties of the target materials, and the diverse range of fluidized morphologies observed in Martian ejecta blankets are controlled by the near-surface composition and the climate at the time of impact. Using the Mars Orbiter Laser Altimeter (MOLA) data set, quantitative information about the strength of the upper crust and the dynamics of Martian ejecta blankets may be derived from crater geometry measurements. Here, we present the results from geometrical measurements of fresh craters 3-50 km in rim diameter in selected highland (Lunae and Solis Plana) and lowland (Acidalia, Isidis, and Utopia Planitiae) terrains. We find large, resolved differences between the geometrical properties of the freshest highland and lowland craters. Simple lowland craters are 1.5-2.0 times deeper (≥5σo difference) with >50% larger cavities (≥2σo) compared to highland craters of the same diameter. Rim heights and the volume of material above the preimpact surface are slightly greater in the lowlands over most of the size range studied. The different shapes of simple highland and lowland craters indicate that the upper ˜6.5 km of the lowland study regions are significantly stronger than the upper crust of the highland plateaus. Lowland craters collapse to final volumes of 45-70% of their transient cavity volumes, while highland craters preserve only 25-50%. The effective yield strength of the upper crust in the lowland regions falls in the range of competent rock, approximately 9-12 MPa, and the highland plateaus may be weaker by a factor of 2 or more, consistent with heavily fractured Noachian layered deposits. The measured volumes of continuous ejecta blankets and uplifted surface materials exceed the predictions from standard crater scaling relationships and Maxwell's Z model of crater excavation by a factor of 3. The excess volume of fluidized ejecta blankets on Mars cannot be explained by concentration of ejecta through nonballistic emplacement processes and/or bulking. The observations require a modification of the scaling laws and are well fit using a scaling factor of ˜1.4 between the transient crater surface diameter to the final crater rim diameter and excavation flow originating from one projectile diameter depth with Z = 2.7. The refined excavation model provides the first observationally constrained set of initial parameters for study of the formation of fluidized ejecta blankets on Mars.

Analysis of impact crater populations and the geochronology of planetary surfaces in the inner solar system

NASA Astrophysics Data System (ADS)

Fassett, Caleb I.

2016-10-01

Analyzing the density of impact craters on planetary surfaces is the only known technique for learning their ages remotely. As a result, crater statistics have been widely analyzed on the terrestrial planets, since the timing and rates of activity are critical to understanding geologic process and history. On the Moon, the samples obtained by the Apollo and Luna missions provide critical calibration points for cratering chronology. On Mercury, Venus, and Mars, there are no similarly firm anchors for cratering rates, but chronology models have been established by extrapolating from the lunar record or by estimating their impactor fluxes in other ways. This review provides a current perspective on crater population measurements and their chronological interpretation. Emphasis is placed on how ages derived from crater statistics may be contingent on assumptions that need to be considered critically. In addition, ages estimated from crater populations are somewhat different than ages from more familiar geochronology tools (e.g., radiometric dating). Resurfacing processes that remove craters from the observed population are particularly challenging to account for, since they can introduce geologic uncertainty into results or destroy information about the formation age of a surface. Regardless of these challenges, crater statistics measurements have resulted in successful predictions later verified by other techniques, including the age of the lunar maria, the existence of a period of heavy bombardment in the Moon's first billion years, and young volcanism on Mars.

Increased depth-diameter ratios in the Medusae Fossae Formation deposits of Mars

NASA Technical Reports Server (NTRS)

Barlow, N. G.

1993-01-01

Depth to diameter ratios for fresh impact craters on Mars are commonly cited as approximately 0.2 for simple craters and 0.1 for complex craters. Recent computation of depth-diameter ratios in the Amazonis-Memnonia region of Mars indicates that craters within the Medusae Fossae Formation deposits found in this region display greater depth-diameter ratios than expected for both simple and complex craters. Photoclinometric and shadow length techniques have been used to obtain depths of craters within the Amazonis-Memnonia region. The 37 craters in the 2 to 29 km diameter range and displaying fresh impact morphologies were identified in the area of study. This region includes the Amazonian aged upper and middle members of the Medusae Fossae Formation and Noachian aged cratered and hilly units. The Medusae Fossae Formation is characterized by extensive, flat to gently undulating deposits of controversial origin. These deposits appear to vary from friable to indurated. Early analysis of crater degradation in the Medusae Fossae region suggested that simple craters excavated to greater depths than expected based on the general depth-diameter relationships derived for Mars. However, too few craters were available in the initial analysis to estimate the actual depth-diameter ratios within this region. Although the analysis is continuing, we are now beginning to see a convergence towards specific values for the depth-diameter ratio depending on geologic unit.

A Comparative Analysis of the Magnetic Field Signals over Impact Structures on the Earth, Mars and the Moon

NASA Technical Reports Server (NTRS)

Isac, Anca; Mandea, Mioara; Purucker, Michael; Langlais, Benoit

2015-01-01

An improved description of magnetic fields of terrestrial bodies has been obtained from recent space missions, leading to a better characterization of the internal fields including those of crustal origin. One of the striking differences in their crustal magnetic field is the signature of large impact craters. A comparative analysis of the magnetic characteristics of these structures can shed light on the history of their respective planetary-scale magnetic dynamos. This has motivated us to identify impact craters and basins, first by their quasi-circular features from the most recent and detailed topographic maps and then from available global magnetic field maps. We have examined the magnetic field observed above 27 complex craters on the Earth, 34 impact basins on Mars and 37 impact basins on the Moon. For the first time, systematic trends in the amplitude and frequency of the magnetic patterns, inside and outside of these structures are observed for all three bodies. The demagnetization effects due to the impact shock wave and excavation processes have been evaluated applying the Equivalent Source Dipole forward modeling approach. The main characteristics of the selected impact craters are shown. The trends in their magnetic signatures are indicated, which are related to the presence or absence of a planetary-scale dynamo at the time of their formation and to impact processes. The low magnetic field intensity at center can be accepted as the prime characteristic of a hypervelocity impact and strongly associated with the mechanics of impact crater formation. In the presence of an active internal field, the process of demagnetization due to the shock impact is associated with post-impact remagnetization processes, generating a more complex magnetic signature.

Exploring Tectonic Activity on Vesta and Ceres

NASA Astrophysics Data System (ADS)

Buczkowski, D.; Scully, J. E. C.; Raymond, C. A.; Russell, C. T.

2017-12-01

Images of Vesta and Ceres taken by the Dawn spacecraft revealed large-scale linear structural features on both asteroids. We evaluate their morphology to determine 1) what processes caused them to form and 2) what implications this has for the history of Vesta and Ceres as planetary bodies. The Divalia Fossae are wide troughs bounded by steep scarps that encircle Vesta roughly aligned with the equator. Fault plane analysis suggests that their formation was triggered by the impact event that formed the Rheasilvia basin. The Saturnalia Fossae extend from Divalia to the northern polar region; fault plane analysis ties their formation to the Veneneia basin impact event. Also, it has been suggested that the elongate hill Brumalia Tholus could have been formed as a magmatic intrusion utilizing the subsurface Albalonga fracture as a conduit to the surface, intruding into and deforming the rock above it. Kilometer-scale linear structures cross much of the eastern hemisphere of Ceres. Many structures appear to be radial to the large craters Urvara and Yalode, and likely formed due to impact processes. However, the Samhain Catenae do not have any obvious relationship to a crater and the lack of raised rims makes it unlikely that these are secondary impacts; they are also crosscut by linear features radial to Urvara and Yalode, indicating they are not fractures formed during those impact events. Instead, the morphology of these structures more closely resembles that of pit crater chains (buried normal faults), and show en echelon orientation and S-shaped linkages. Polygonal craters, which form where there is pervasive subsurface fracturing, are widespread on Ceres, and those polygonal craters proximal to the Samhain Catenae have straight crater rims aligned with the structures. Several craters on Ceres have fractured floors, similar to lunar floor-fractured craters (FFCs), which are theorized to form from floor uplift due to magmatic intrusion. Large (>50 km) Ceres FFCs can have both radial and concentric fractures at the crater center, and/or concentric fractures near the crater wall. Smaller craters have a v-shaped moat separating the wall scarp from the crater interior, but different interior morphologies. A depth vs. diameter analysis shows that the Ceres FFCs are unusually shallow, consistent with the magmatic intrusion models.

Successive Formation of Impact Craters

NASA Image and Video Library

2012-02-16

This image from NASA Dawn spacecraft shows two overlapping impact craters on asteroid Vesta. The rims of the craters are both reasonably fresh but the larger crater must be older because the smaller crater cuts across the larger crater rim.

Constraints on the Formation and Modification of Lobate Debris Aprons Through Categorized Crater Counts

NASA Astrophysics Data System (ADS)

Berman, D. C.; Crown, D. A.; Joseph, E. C. S.

2012-03-01

Compilation of crater counts using CTX images and analysis of SFD, coupled with categorization of crater morphologies, provides important insights into interpretation of the formation and modification of lobate debris aprons.

Floor-Fractured Craters on Ceres and Implications for Internal Composition and Processes

NASA Astrophysics Data System (ADS)

Buczkowski, D.; Schenk, P.; Scully, J. E. C.; Park, R. S.; Preusker, F.; Raymond, C. A.; Russell, C. T.

2016-12-01

Several of the impact craters on Ceres have patterns of fractures on their floors. These fractures appear similar to those found within a class of lunar craters referred to as Floor-Fractured Craters (FFCs) [1]. Lunar FFCs are characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures, and have been classified into crater classes, Types 1 through 6, based on their morphometric properties [1,2]. Models for their formation have included both floor uplift due to magmatic intrusion below the crater or floor shallowing due to viscous relaxation. However, the observation that the depth versus diameter (d/D) relationship of the FFCs is distinctly shallower than the same association for other lunar craters supports the hypotheses that the floor fractures form due to shallow magmatic intrusion under the crater [2]. We have cataloged the Ceres FFCs according to the classification scheme designed for the Moon. Large (>50 km) Ceres FFCs are most consistent with Type 1 lunar FFCs, having deep floors, central peaks, wall terraces, and radial and/or concentric fractures. Smaller craters on Ceres are more consistent with Type 4 lunar FFCs, having less-pronounced floor fractures and v-shaped moats separating the wall scarp from the crater interior. An analysis of the d/D ratio for Ceres craters shows that, like lunar FFCs, the Ceres FFCs are anomalously shallow. This suggests that the fractures on the floor of Ceres FFCs may be due the intrusion of a low-density material below the craters that is uplifting their floors. While on the Moon the intrusive material is hypothesized to be silicate magma, this is unlikely for Ceres. However, a cryovolcanic extrusive edifice has been identified on Ceres [3], suggesting that cryomagmatic intrusions could be responsible for the formation of the Ceres FFCs. References: [1] Schultz P. (1976) Moon, 15, 241-273 [2] Jozwiak L.M. et al (2015) JGR 117, doi: 10.1029/2012JE004134 [3] Ruesch O. et al (2016) Science

Degradation sequence of young lunar craters from orbital infrared survey

NASA Technical Reports Server (NTRS)

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.

Testing models for the formation of the equatorial ridge on Iapetus via crater counting

NASA Astrophysics Data System (ADS)

Damptz, Amanda L.; Dombard, Andrew J.; Kirchoff, Michelle R.

2018-03-01

Iapetus's equatorial ridge, visible in global views of the moon, is unique in the Solar System. The formation of this feature is likely attributed to a key event in the evolution of Iapetus, and various models have been proposed as the source of the ridge. By surveying imagery from the Cassini and Voyager missions, this study aims to compile a database of the impact crater population on and around Iapetus's equatorial ridge, assess the relative age of the ridge from differences in cratering between on ridge and off ridge, and test the various models of ridge formation. This work presents a database that contains 7748 craters ranging from 0.83 km to 591 km in diameter. The database includes the study area in which the crater is located, the latitude and longitude of the crater, the major and minor axis lengths, and the azimuthal angle of orientation of the major axis. Analysis of crater orientation over the entire study area reveals that there is no preference for long-axis orientation, particularly in the area with the highest resolution. Comparison of the crater size-frequency distributions show that the crater distribution on the ridge appears to be depleted in craters larger than 16 km with an abruptly enhanced crater population less than 16 km in diameter up to saturation. One possible interpretation is that the ridge is a relatively younger surface with an enhanced small impactor population. Finally, the compiled results are used to examine each ridge formation hypothesis. Based on these results, a model of ridge formation via a tidally disrupted sub-satellite appears most consistent with our interpretation of a younger ridge with an enhanced small impactor population.

The mechanism of liquid metal jet formation in the cathode spot of vacuum arc discharge

NASA Astrophysics Data System (ADS)

Gashkov, M. A.; Zubarev, N. M.; Mesyats, G. A.; Uimanov, I. V.

2016-08-01

We have theoretically studied the dynamics of molten metal during crater formation in the cathode spot of vacuum arc discharge. At the initial stage, a liquid-metal ridge is formed around the crater. This process has been numerically simulated in the framework of the two-dimensional axisymmetric heat and mass transfer problem in the approximation of viscous incompressible liquid. At a more developed stage, the motion of liquid metal loses axial symmetry, which corresponds to a tendency toward jet formation. The development of azimuthal instabilities of the ridge is analyzed in terms of dispersion relations for surface waves. It is shown that maximum increments correspond to instability of the Rayleigh-Plateau type. Estimations of the time of formation of liquid metal jets and their probable number are obtained.

It Shrinks! It Cracks!

NASA Image and Video Library

2017-04-20

Given enough time, impact craters on Mars tend to fill up with different materials. For instance, some craters on Mars had lakes inside them in the past. When these lakes dried out, they left behind traces of their past existence, such as sedimentary deposits (materials that were carried along with the running water into the lake inside the crater and then settled down). Some craters, especially in high latitudes, contain ice deposits that filled the crater when an earlier ice age allowed ice to extend into the crater's latitude. Here, NASA's Mars Reconnaissance Orbiter spies a crater that lies close to Elysium, a major volcanic system on Mars. The whole region surrounding the crater was at some point covered by lava from the volcano creating vast lava plains, and in the process, flooding impact craters in their way. When the lava eventually cooled down, it solidified and began to shrink in size. This shrinking led to formation of cracks on the surface of the lava that grew in a circular pattern matching the shape of the crater it was filling. Scientists can study these fractures and estimate how much it shrank in volume to better understand the properties of the lava (such as its temperature) during the time it filled the crater. https://photojournal.jpl.nasa.gov/catalog/PIA21596

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

NASA Astrophysics Data System (ADS)

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.

Widespread Magmatism as a Result of Impact Related Decompression Melting on Early Mars

NASA Astrophysics Data System (ADS)

Edwards, C. S.; Bandfield, J. L.; Christensen, P. R.; Rogers, D.

2012-12-01

Flat-floored craters on Mars have been observed since early spacecraft viewed the surface. Early work characterized these craters as infilled by sedimentary materials [e.g. Christensen, 1983] but later work using THEMIS thermal inertia determined these craters contain some of the rockiest materials on the planet and not sedimentary materials [Edwards et al., 2009]. Here we investigate the distribution, physical properties (morphology and thermal inertia), and composition of these craters over the entire planet. We find the majority of rocky crater floors identified (~3300) are concentrated in the low albedo (0.1-0.17), cratered southern highlands. These craters are associated with the highest thermal inertia values (e.g. > 500 to 2000 J m-2 K-1 s-1/2), some of the most mafic materials on the planet (enriched in olivine/pyroxene vs. high-Si phases/plagioclase, often with >10-15% olivine areal abundance), and formed ~3.5 billion years ago. Based on the properties of the crater fill materials described, three mechanisms are considered for the formation of flat-floored, high thermal inertia crater floors on Mars including: 1) the lithification/induration of sediments, 2) the ponding of crustal melt material related to the heat generated during the impact process, and 3) infilling by volcanic materials. We find the only likely scenario is volcanic infilling through fractures created in the impact event. Furthermore, we find the generation of the primitive magma would be directly sourced from the decompression melting of the martian mantle due to the removal of several kilometers of overlying crustal material by the impactor. As the ancient martian crust was likely thin and the geothermal gradients were significantly higher than present day [e.g. Zuber, 2001], the decompression melting of the mantle [Bertka and Holloway, 1994] would be more likely to occur on early Mars then under present day conditions. This is borne out by the ancient ages (~3-4Ga) of the crater floors that indicates their formation early in martian history and not after the crustal thickening of the southern highlands and reduction of the geothermal gradient. Based on the distribution of these crater floors, we find that this process occurred over much of the surface of early Mars, during or shortly thereafter the Late Heavy Bombardment when the crust was still relatively thin and heat flow was high. We have shown that this process was widespread and ubiquitous, responsible for the eruption of significant volumes of primitive mantle material, both inside and outside of craters, and is an important planetary process that has gone previously undocumented. However, this process is likely not unique to Mars and while we have not examined other planetary bodies in detail, craters on Earth's moon and Mercury show distinctive morphologic similarities [e.g. Schultz, 1976] that suggest this process occurred throughout the early solar system on many rocky bodies. References: Bertka, C. M., et al. (1994), Contributions to Mineralogy and Petrology, 115(3), 313-322. Christensen, P. R. (1983), Icarus, 56(3), 496-518. Edwards, C. S., et al. (2009), J. Geophys. Res, 114, E11001. Schultz, P. H. (1976), The Moon, 15, 241-273. Zuber, M. T. (2001), Nature, 412, 220-227.

Fluids during diagenesis and sulfate vein formation in sediments at Gale crater, Mars

NASA Astrophysics Data System (ADS)

Schwenzer, S. P.; Bridges, J. C.; Wiens, R. C.; Conrad, P. G.; Kelley, S. P.; Leveille, R.; Mangold, N.; Martín-Torres, J.; McAdam, A.; Newsom, H.; Zorzano, M. P.; Rapin, W.; Spray, J.; Treiman, A. H.; Westall, F.; Fairén, A. G.; Meslin, P.-Y.

2016-11-01

We model the fluids involved in the alteration processes recorded in the Sheepbed Member mudstones of Yellowknife Bay (YKB), Gale crater, Mars, as revealed by the Mars Science Laboratory Curiosity rover investigations. We compare the Gale crater waters with fluids modeled for shergottites, nakhlites, and the ancient meteorite ALH 84001, as well as rocks analyzed by the Mars Exploration rovers, and with terrestrial ground and surface waters. The aqueous solution present during sediment alteration associated with phyllosilicate formation at Gale was high in Na, K, and Si; had low Mg, Fe, and Al concentrations—relative to terrestrial groundwaters such as the Deccan Traps and other modeled Mars fluids; and had near neutral to alkaline pH. Ca and S species were present in the 10-3 to 10-2 concentration range. A fluid local to Gale crater strata produced the alteration products observed by Curiosity and subsequent evaporation of this groundwater-type fluid formed impure sulfate- and silica-rich deposits—veins or horizons. In a second, separate stage of alteration, partial dissolution of this sulfate-rich layer in Yellowknife Bay, or beyond, led to the pure sulfate veins observed in YKB. This scenario is analogous to similar processes identified at a terrestrial site in Triassic sediments with gypsum veins of the Mercia Mudstone Group in Watchet Bay, UK.

A Lower Limit on the Thickness of Europa's Ice Shell from Numerical Simulations of Impact Cratering

NASA Astrophysics Data System (ADS)

Turtle, E. P.; Ivanov, B. A.

2001-12-01

If Europa has an ice-covered, liquid water ocean, the thickness of the ice shell can be tested by analyzing the impact crater morphologies revealed by Galileo images. Several of Europa's 28 primary impact structures have morphologies typical of complex impact craters on other planetary bodies: terraced rims, flat floors, and central peaks [1]. To constrain the minimum ice thickness necessary to reproduce the observed complex crater morphologies, we have performed numerical simulations, using the modified SALE-2D code [2], of the formation of impact craters in ice layers with thicknesses ranging from 5 to 11 km overlying liquid water. The target ice has ice strength properties from published laboratory data [3] with a gradual decrease towards the base of the ice as the temperature approaches the melting point. The projectile parameters were chosen to produce a 10 km diameter crater in thick ice. We find that ice layers less than 7 km thick are not sufficient to prevent an outburst of liquid water during collapse of the transient cavity. At thicknesses of 8 and 9 km we observe a boundary regime: crater collapse produces a flat or upward-domed floor, however the water under the crater center does not reach the surface. In ice greater than 10 km thick a normal transient cavity forms. These results indicate that the ice thickness, at the times and locations of complex crater formation, must have been comparable to the diameters of the transient craters, the largest of which was between 11.9 and 18.5 km [1]. Implementation of additional mechanisms such as acoustic fluidization and creep may affect the shape of the final crater produced in our simulations: acoustic fluidization can produce central peak and peak-ring craters [4], and creep may result in a flattened crater. We are currently investigating the influence of these processes on the final crater morphology. References: [1] Moore et al., Icarus 151, 2001. [2] Ivanov et al., GSA Spec. Pap., in press. [3] Beeman et al., JGR 93, 1988. [4] Melosh and Ivanov, Ann. Rev. Earth Plan. Sci. 27, 1999.

Mars, Always Cold, Sometimes Wet: New Constraints on Mars Denudation Rates and Climate Evolution from Analog Studies at Haughton Crater, Devon Island, High Arctic

NASA Technical Reports Server (NTRS)

Lee, Pascal; Boucher, M.; Desportes, C.; Glass, B. J.; Lim, D.; McKay, C. P.; Osinski, G. R.; Parnell, J.; Schutt, J. W.

2005-01-01

Analysis of crater modification on Mars and at Haughton Crater, Devon Island, High Arctic, which was recently shown to be significantly older than previously believed (Eocene age instead of Miocene) [1], suggest that Mars may have never been climatically wet and warm for geological lengths of time during and since the Late Noachian. Impact structures offer particularly valuable records of the evolution of a planet s climate and landscape through time. The state of exposure and preservation of impact structures and their intracrater fill provide clues to the nature, timing, and intensity of the processes that have modified the craters since their formation. Modifying processes include weathering, erosion, mantling, and infilling. In this study, we compare the modification of Haughton through time with that of impact craters in the same size class on Mars. We derive upper limits for time-integrated denudation rates on Mars during and since the Late Noachian. These rates are significantly lower than previously published and provide important constraints for Mars climate evolution.

Relative chronology of Martian volcanoes

NASA Technical Reports Server (NTRS)

Landheim, R.; Barlow, N. G.

1991-01-01

Impact cratering is one of the major geological processes that has affected the Martian surface throughout the planet's history. The frequency of craters within particular size ranges provides information about the formation ages and obliterative episodes of Martian geologic units. The Barlow chronology was extended by measuring small craters on the volcanoes and a number of standard terrain units. Inclusions of smaller craters in units previously analyzed by Barlow allowed for a more direct comparison between the size-frequency distribution data for volcanoes and established chronology. During this study, 11,486 craters were mapped and identified in the 1.5 to 8 km diameter range in selected regions of Mars. The results are summarized in this three page report and give a more precise estimate of the relative chronology of the Martian volcanoes. Also, the results of this study lend further support to the increasing evidence that volcanism has been a dominant geologic force throughout Martian history.

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

NASA Astrophysics Data System (ADS)

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 occurs. Penetration is achieved when craters of both sides are connected. Crater diameter on the opposite side is larger than that on the impact side. More fragments are ejected from the opposite side than from the impact side. We present a qualitative explanation for the shapes of Martian deep pit craters.

Remote sensing and geologic studies of the planetary crusts

NASA Technical Reports Server (NTRS)

Hawke, B. R.

1983-01-01

Dark haloed craters and regions of the Moon which were sites of ancient volcanism were remotely sensed as well as KREEP deposits in the Inbrium region. The relationship between geology and geochemistry in the Undarum/Spumans region was also examined. Results are summarized for observations of the Reiner Gamma formation, studies of impact cratering mechanics and processes, spectral variations of asteroidal surfaces, albedo and color variations on Ganymede, and studies of lunar impact structures.

Context of ancient aqueous environments on Mars from in situ geologic mapping at Endeavour Crater

USGS Publications Warehouse

Crumpler, L.S.; Arvidson, R. E.; Bell, J.; Clark, B. C.; Cohen, B. A.; Farrand, W. H.; Gellert, Ralf; Golombek, M.; Grant, J. A.; Guinness, E.; Herkenhoff, Kenneth E.; Johnson, J. R.; Jolliff, B.; Ming, D. W.; Mittlefehldt, D. W.; Parker, T.; Rice, J. W.; Squyres, S. W.; Sullivan, R.; Yen, A. S.

2015-01-01

Using the Mars Exploration Rover Opportunity, we have compiled one of the first field geologic maps on Mars while traversing the Noachian terrain along the rim of the 22 km diameter Endeavour Crater (Latitude −2°16′33″, Longitude −5°10′51″). In situ mapping of the petrographic, elemental, structural, and stratigraphic characteristics of outcrops and rocks distinguishes four mappable bedrock lithologic units. Three of these rock units predate the surrounding Burns formation sulfate-rich sandstones and one, the Matijevic Formation, represents conditions on early Mars predating the formation of Endeavour Crater. The stratigraphy assembled from these observations includes several geologic unconformities. The differences in lithologic units across these unconformities record changes in the character and intensity of the Martian aqueous environment over geologic time. Water circulated through fractures in the oldest rocks over periods long enough that texturally and elementally significant alteration occurred in fracture walls. These oldest pre-Endeavour rocks and their network of mineralized and altered fractures were preserved by burial beneath impact ejecta and were subsequently exhumed and exposed. The alteration along joints in the oldest rocks and the mineralized veins and concentrations of trace metals in overlying lithologic units is direct evidence that copious volumes of mineralized and/or hydrothermal fluids circulated through the early Martian crust. The wide range in intensity of structural and chemical modification from outcrop to outcrop along the crater rim shows that the ejecta of large (>8 km in diameter) impact craters is complex. These results imply that geologic complexity is to be anticipated in other areas of Mars where cratering has been a fundamental process in the local and regional geology and mineralogy.

Global survey of lunar wrinkle ridge formation times

NASA Astrophysics Data System (ADS)

Yue, Z.; Michael, G. G.; Di, K.; Liu, J.

2017-11-01

Wrinkle ridges are a common feature of the lunar maria and record subsequent contraction of mare infill. Constraining the timing of wrinkle ridge formation from crater counts is challenging because they have limited areal extent and it is difficult to determine whether superposed craters post-date ridge formation or have alternatively been uplifted by the deformation. Some wrinkle ridges do allow determination to be made. This is possible where a ridge shows a sufficiently steep boundary or scarp that can be identified as deforming an intersecting crater or the crater obliterates the relief of the ridge. Such boundaries constitute only a small fraction of lunar wrinkle ridge structures yet they are sufficiently numerous to enable us to obtain statistically significant crater counts over systems of structurally related wrinkle ridges. We carried out a global mapping of mare wrinkle ridges, identifying appropriate boundaries for crater identification, and mapping superposed craters. Selected groups of ridges were analyzed using the buffered crater counting method. We found that, except for the ridges in mare Tranquilitatis, the ridge groups formed with average ages between 3.5 and 3.1 Ga ago, or 100-650 Ma after the oldest observable erupted basalts where they are located. We interpret these results to suggest that local stresses from loading by basalt fill are the principal agent responsible for the formation of lunar wrinkle ridges, as others have proposed. We find a markedly longer interval before wrinkle ridge formation in Tranquilitatis which likely indicates a different mechanism of stress accumulation at this site.

Reactive transport and mass balance modeling of the Stimson sedimentary formation and altered fracture zones constrain diagenetic conditions at Gale crater, Mars

NASA Astrophysics Data System (ADS)

Hausrath, E. M.; Ming, D. W.; Peretyazhko, T. S.; Rampe, E. B.

2018-06-01

On a planet as cold and dry as present-day Mars, evidence of multiple aqueous episodes offers an intriguing view into very different past environments. Fluvial, lacustrine, and eolian depositional environments are being investigated by the Mars Science Laboratory Curiosity in Gale crater, Mars. Geochemical and mineralogical observations of these sedimentary rocks suggest diagenetic processes affected the sediments. Here, we analyze diagenesis of the Stimson formation eolian parent material, which caused loss of olivine and formation of magnetite. Additional, later alteration in fracture zones resulted in preferential dissolution of pyroxene and precipitation of secondary amorphous silica and Ca sulfate. The ability to compare the unaltered parent material with the reacted material allows constraints to be placed on the characteristics of the altering solutions. In this work we use a combination of a mass balance approach calculating the fraction of a mobile element lost or gained, τ, with fundamental geochemical kinetics and thermodynamics in the reactive transport code CrunchFlow to examine the characteristics of multiple stages of aqueous alteration at Gale crater, Mars. Our model results indicate that early diagenesis of the Stimson sedimentary formation is consistent with leaching of an eolian deposit by a near-neutral solution, and that formation of the altered fracture zones is consistent with a very acidic, high sulfate solution containing Ca, P and Si. These results indicate a range of past aqueous conditions occurring at Gale crater, Mars, with important implications for past martian climate and environments.

Floor-fractured craters on Ceres and implications for interior processes

NASA Astrophysics Data System (ADS)

Buczkowski, Debra; Schenk, Paul M.; Scully, Jennifer E. C.; Park, Ryan; Preusker, Frank; Raymond, Carol; Russell, Christopher T.

2016-10-01

Several of the impact craters on Ceres have patterns of fractures on their floors. These fractures appear similar to those found within a class of lunar craters referred to as Floor-Fractured Craters (FFCs) [Schultz, 1976].Lunar FFCs are characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures, and have been classified into crater classes, Types 1 through 6, based on their morphometric properties [Schultz, 1976; Jozwiak et al, 2012, 2015]. Models for their formation have included both floor uplift due to magmatic intrusion below the crater or floor shallowing due to viscous relaxation. However, the observation that the depth versus diameter (d/D) relationship of the FFCs is distinctly shallower than the same association for other lunar craters supports the hypotheses that the floor fractures form due to shallow magmatic intrusion under the crater [Jozwiak et al, 2012, 2015].FFCs have also been identified on Mars [Bamberg et al., 2014]. Martian FFCs exhibit morphological characteristics similar to the lunar FFCs, and analyses suggest that the Martian FCCs also formed due to volcanic activity, although heavily influenced by interactions with groundwater and/or ice.We have cataloged the Ceres FFCs according to the classification scheme designed for the Moon. Large (>50 km) Ceres FFCs are most consistent with Type 1 lunar FFCs, having deep floors, central peaks, wall terraces, and radial and/or concentric fractures. Smaller craters on Ceres are more consistent with Type 4 lunar FFCs, having less-pronounced floor fractures and a v-shaped moats separating the wall scarp from the crater interior.An analysis of the d/D ratio for Ceres craters shows that, like lunar FFCs, the Ceres FFCs are anomalously shallow. This suggests that the fractures on the floor of Ceres FFCs may be due the intrusion of a low-density material below the craters that is uplifting their floors. While on the Moon and Mars the intrusive material is hypothesized to be silicate magma, this is unlikely for Ceres. However, a cryovolcanic extrusive edifice has been identified on Ceres [Ruesch et al., 2016], suggesting that cryomagmatic intrusions could be responsible for the formation of the Ceres FFCs.

Gas-emission crater in Central Yamal, West Siberia, Russia, a new permafrost feature

NASA Astrophysics Data System (ADS)

Leibman, Marina; Kizyakov, Alexandr; Khomutov, Artem; Dvornikov, Yury; Streletskaya, Irina; Gubarkov, Anatoly

2016-04-01

The Yamal crater is a hole funnel-shaped on top and cylinder-shaped down to the bottom, surrounded by a parapet. Field study of the crater included size measurements, photo- video-documentation of the feature and the surrounding environment, and geochemical sampling. The upper part of the geological section within the crater consisted of stratified icy sediments, underlain by almost pure stratified ice of nearly vertical orientation of the layers. The volume of discharged material (volume of the void of the crater) was 6 times larger than the volume of material in the parapet. The difference was due to a significant amount of ice exposed in the walls of the crater, emitted to the surface and melted there. Remote sensing data was processes and validated by field observations to reveal the date of crater formation, previous state of the surface, evolution of the crater and environmental conditions of the surrounding area. Crater formed between 9 October and 1 November 2013. The initial size derived from Digital Elevation Model (DEM) had diameter of the vegetated rim 25-29 m. It turned through a sharp bend into a cylinder with close to vertical sides and diameter 15-16 m. Depth of the hole was impossible to estimate from DEM because of no light reaching walls in the narrow hole. By the time of initial observation in July 2014, water was found at the depth exceeding 50 m below the rim. In November 2014 this depth was 26 m. By September 2015 almost all the crater was flooded, with water surface about 5 m below the rim. The plan dimensions of the crater increased dramatically from initial 25-29 to 47-54 m in 2015. Thus, it took two warm seasons to almost entirely fill in the crater. We suppose that during the next 1-2 years parapet will be entirely destroyed, and as a result the crater will look like an ordinary tundra lake. Excluding impossible and improbable versions of the crater's development, the authors conclude that the origin of this crater can be attributed to the air temperature warming trend along with the extreme of 2012. The increased ground temperature and amount of unfrozen water in the permafrost, expanding of cryopegs, formation of a pingo-like mound and its outburst due to high pressure produced by gas hydrate decomposition within permafrost are the main controls. Similar temperature anomalies may increase in number in the future decades, presenting risks for human activities in the region. This conclusion is supported by recent studies of gas-hydrate behavior in the upper permafrost as well as by subsea processes in gas-bearing provinces where analogue mechanism is known to produce pockmarks - subsea depressions. As the crater is surrounded by the parapet, thus is resulting from expulsion of ice and rocks from beneath to the surface and should not be treated as a "sinkhole", "thermokarst" or "collapse".

Crater Formation Above Salt Caverns: Piston vs Hour-glass

NASA Astrophysics Data System (ADS)

Berest, P.

2016-12-01

Conditions leading to crater formation above salt caverns are discussed. In most cases, at the end of leaching, the cavern roof had reached the top of the salt formation, allowing direct contact between brine and marl (or argillite) layers that compose the overburden of the salt formation. These layers are prone to weathering when in contact with saturated brine. Stoping takes place, and the cavern roof rises through the overburden. This process may be several years or dozens of years long. In Lorraine salt formations, stoping stops when the rising cavern top reaches a competent layer, the Beaumont Dolomite. Operators then lower cavern-brine pressure to trigger collapse. A rigid cylinder of rock (a "piston") drops into the cavern, and a crater whose initial edges are vertical is created. Cavern drop is more abrupt when the cavern top is filled partly with air. The contour of the piston is circular, as a circle is the shape such that the ratio between perimeter and area is minimal. In other cases, for instance in Kansas, the cavern rises until the uppermost keystone in the bedrock at shallow depth is breached, permitting loose materials to flow into the cavern through a relatively narrow hole at the bottom of the sink hole, as in an hour glass.

Crater Mound Formation by Wind Erosion on Mars

NASA Astrophysics Data System (ADS)

Steele, L. J.; Kite, E. S.; Michaels, T. I.

2018-01-01

Most of Mars' ancient sedimentary rocks by volume are in wind-eroded sedimentary mounds within impact craters and canyons, but the connections between mound form and wind erosion are unclear. We perform mesoscale simulations of different crater and mound morphologies to understand the formation of sedimentary mounds. As crater depth increases, slope winds produce increased erosion near the base of the crater wall, forming mounds. Peak erosion rates occur when the crater depth is ˜2 km. Mound evolution depends on the size of the host crater. In smaller craters mounds preferentially erode at the top, becoming more squat, while in larger craters mounds become steeper sided. This agrees with observations where smaller craters tend to have proportionally shorter mounds and larger craters have mounds encircled by moats. If a large-scale sedimentary layer blankets a crater, then as the layer recedes across the crater it will erode more toward the edges of the crater, resulting in a crescent-shaped moat. When a 160 km diameter mound-hosting crater is subject to a prevailing wind, the surface wind stress is stronger on the leeward side than on the windward side. This results in the center of the mound appearing to "march upwind" over time and forming a "bat-wing" shape, as is observed for Mount Sharp in Gale crater.

Fluids During Diagenesis and Sulfate Vein Formation in Sediments at Gale Crater, Mars

NASA Technical Reports Server (NTRS)

Schwenzer, S. P.; Bridges, J. C.; Weins, R. C.; Conrad, P. G.; Kelley, S. P.; Leveille, R.; Mangold, N.; Martin-Torres, J.; McAdam, A.; Newsom, H.;

Impact-Induced Clay Mineral Formation and Distribution on Mars

NASA Technical Reports Server (NTRS)

Rivera-Valentin, E. G.; Craig, P. I.

2015-01-01

Clay minerals have been identified in the central peaks and ejecta blankets of impact craters on Mars. Several studies have suggested these clay minerals formed as a result of impact induced hydrothermalism either during Mars' Noachian era or more recently by the melting of subsurface ice. Examples of post-impact clay formation is found in several locations on Earth such as the Mjolnir and Woodleigh Impact Structures. Additionally, a recent study has suggested the clay minerals observed on Ceres are the result of impact-induced hydrothermal processes. Such processes may have occurred on Mars, possibly during the Noachian. Distinguishing between clay minerals formed preor post-impact can be accomplished by studying their IR spectra. In fact, showed that the IR spectra of clay minerals is greatly affected at longer wavelengths (i.e. mid-IR, 5-25 micron) by impact-induced shock deformation while the near-IR spectra (1.0-2.5 micron) remains relatively unchanged. This explains the discrepancy between NIR and MIR observations of clay minerals in martian impact craters noted. Thus, it allows us to determine whether a clay mineral formed from impact-induced hydrothermalism or were pre-existing and were altered by the impact. Here we study the role of impacts on the formation and distribution of clay minerals on Mars via a fully 3-D Monte Carlo cratering model, including impact- melt production using results from modern hydrocode simulations. We identify regions that are conducive to clay formation and the location of clay minerals post-bombardment.

Constraints on the geomorphological evolution of the nested summit craters of Láscar volcano from high spatio-temporal resolution TerraSAR-X interferometry

NASA Astrophysics Data System (ADS)

Richter, Nicole; Salzer, Jacqueline Tema; de Zeeuw-van Dalfsen, Elske; Perissin, Daniele; Walter, Thomas R.

2018-03-01

Small-scale geomorphological changes that are associated with the formation, development, and activity of volcanic craters and eruptive vents are often challenging to characterize, as they may occur slowly over time, can be spatially localized, and difficult, or dangerous, to access. Using high-spatial and high-temporal resolution synthetic aperture radar (SAR) imagery collected by the German TerraSAR-X (TSX) satellite in SpotLight mode in combination with precise topographic data as derived from Pléiades-1A satellite data, we investigate the surface deformation within the nested summit crater system of Láscar volcano, Chile, the most active volcano of the central Andes. Our aim is to better understand the structural evolution of the three craters that comprise this system, to assess their physical state and dynamic behavior, and to link this to eruptive activity and associated hazards. Using multi-temporal SAR interferometry (MT-InSAR) from ascending and descending orbital geometries, we retrieve the vertical and east-west components of the displacement field. This time series indicates constant rates of subsidence and asymmetric horizontal displacements of all summit craters between June 2012 and July 2014, as well as between January 2015 and March 2017. The vertical and horizontal movements that we observe in the central crater are particularly complex and cannot be explained by any single crater formation mechanism; rather, we suggest that short-term activities superimposed on a combination of ongoing crater evolution processes, including gravitational slumping, cooling and compaction of eruption products, as well as possible piston-like subsidence, are responsible for the small-scale geomorphological changes apparent in our data. Our results demonstrate how high-temporal resolution synthetic aperture radar interferometry (InSAR) time series can add constraints on the geomorphological evolution and structural dynamics of active crater and vent systems at volcanoes worldwide.

The indication of Martian gully formation processes by slope-area analysis

USGS Publications Warehouse

Conway, S.J.; Balme, M.R.; Murray, J.B.; Towner, M.C.; Okubo, C.H.; Grindrod, P.M.

2011-01-01

The formation process of recent gullies on Mars is currently under debate. This study aims to discriminate between the proposed formation processes - pure water flow, debris flow and dry mass wasting - through the application of geomorphological indices commonly used in terrestrial geomorphology. High-resolution digital elevation models (DEMs) of Earth and Mars were used to evaluate the drainage characteristics of small slope sections. Data from Earth were used to validate the hillslope, debris-flow and alluvial process domains previously found for large fluvial catchments on Earth, and these domains were applied to gullied and ungullied slopes on Mars. In accordance with other studies, our results indicate that debris flow is one of the main processes forming the Martian gullies that were being examined. The source of the water is predominantly distributed surface melting, not an underground aquifer. Evidence is also presented indicating that other processes may have shaped Martian crater slopes, such as ice-assisted creep and solifluction, in agreement with the proposed recent Martian glacial and periglacial climate. Our results suggest that, within impact craters, different processes are acting on differently oriented slopes, but further work is needed to investigate the potential link between these observations and changes in Martian climate. ?? The Geological Society of London 2011.

Original size of the Vredefort structure, South Africa

NASA Technical Reports Server (NTRS)

Therriault, A. M.; Reid, A. M.; Reimold, W. U.

1993-01-01

The Vredefort structure is located approximately 120 km southwest of Johannesburg, South Africa, and is deeply eroded. Controversies remain on the origin of this structure with the most popular hypotheses being: (1) by impact cratering about 2.0 Ga; (2) as a cryptoexplosion structure about 2.0 Ga; and (3) by purely tectonic processes starting at about 3.0 Ga and ending with the Vredefort event at 2.0 Ga. In view of recent work in which the granophyre dikes are interpreted as the erosional remants of a more extensive impact melt sheet, injected downward into the underlying country rocks, the impact origin hypothesis for Vredefort is adopted. In order to estimate the original dimensions of the Vredefort impact structure, it is assumed that the structure was initially circular, that its predeformation center corresponds to the center of the granitic core, and that the pre-Vredefort geology of the area prior to approximately 2.0 Ga ago is as suggested by Fletcher and Reimold. The spatial relationship between shock metamorphic effects, the shock pressures they record, and the morphological features of the crater were established for a number of large terrestrial craters. The principles of crater formation at large complex impact structures comparable in size to Vredefort were also established, although many details remain unresolved. An important conclusion is that the transient crater, which is formed directly by excavation and displacement by the shock-induced cratering flow-field (i.e., the particle velocity flow field existing in the region of the transient crater but behind the initial outgoing shock front), is highly modified during the late stage processes. The original transient crater diameter lies well within the final rim of the crater, which is established by structural movements during late-stage cavity modification.

Crater Formation Due to Lunar Plume Impingement

NASA Technical Reports Server (NTRS)

Marsell, Brandon

2011-01-01

Thruster plume impingement on a surface comprised of small, loose particles may cause blast ejecta to be spread over a large area and possibly cause damage to the vehicle. For this reason it is important to study the effects of plume impingement and crater formation on surfaces like those found on the moon. Lunar soil, also known as regolith, is made up of fine granular particles on the order of 100 microns.i Whenever a vehicle lifts-off from such a surface, the exhaust plume from the main engine will cause the formation of a crater. This crater formation may cause laterally ejected mass to be deflected and possibly damage the vehicle. This study is a first attempt at analyzing the dynamics of crater formation due to thruster exhaust plume impingement during liftoff from the moon. Though soil erosion on the lunar surface is not considered, this study aims at examining the evolution of the shear stress along the lunar surface as the engine fires. The location of the regions of high shear stress will determine where the crater begins to form and will lend insight into how big the crater will be. This information will help determine the probability that something will strike the vehicle. The final sections of this report discuss a novel method for studying this problem that uses a volume of fluid (VOF)ii method to track the movement of both the exhaust plume and the eroding surface.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morris, A. J. W.; Price, M. C.; Burchell, M. J., E-mail: m.j.burchell@kent.ac.uk

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 consideredmore » 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.« less

Geologic Mapping of the Martian Impact Crater Tooting

NASA Technical Reports Server (NTRS)

Mouginis-Mark, Peter; Boyce, Joseph M.

2008-01-01

Tooting crater is approximately 29 km in diameters, is located at 23.4 deg N, 207.5 deg E and is classified as a multi-layered ejecta crater. Tooting crater is a very young crater, with an estimated age of 700,000 to 2M years. The crater formed on virtually flat lava flows within Amazonis Planitia where there appears to have been no major topographic features prior to the impact, so that we can measure ejecta thickness and cavity volume. In the past 12 months, the authors have: published their first detailed analysis of the geometry of the crater cavity and the distribution of the ejecta layers; refined the geologic map of the interior of Tooting crater through mapping of the cavity at a scale of 1:1100K; and continued the analysis of an increasing number of high resolution images obtained by the CTX and HiRISE instruments. Currently the authors seek to resolve several science issues that have been identified during this mapping, including: what is the origin of the lobate flows on the NW and SW rims of the crater?; how did the ejecta curtain break apart during the formation of the crater, and how uniform was the emplacement process for the ejecta layers; and, can we infer physical characteristics about the ejecta? Future study plans include the completion of a draft geologic map of Tooting crater and submission of it to the U.S. Geological survey for a preliminary review, publishing a second research paper on the detailed geology of the crater cavity and the distribution of the flows on the crater rim, and completing the map text for the 1:100K geologic map description of units at Tooting crater.

Well-Preserved Impact Ejecta and Impact Melt-Rich Deposits in Terra Sabaea

NASA Image and Video Library

2017-01-12

This image of a well-preserved unnamed elliptical crater in Terra Sabaea, is illustrative of the complexity of ejecta deposits forming as a by-product of the impact process that shapes much of the surface of Mars. Here we see a portion of the western ejecta deposits emanating from a 10-kilometer impact crater that occurs within the wall of a larger, 60-kilometer-wide crater. In the central part is a lobe-shaped portion of the ejecta blanket from the smaller crater. The crater is elliptical not because of an angled (oblique) impact, but because it occurred on the steep slopes of the wall of a larger crater. This caused it to be truncated along the slope and elongated perpendicular to the slope. As a result, any impact melt from the smaller crater would have preferentially deposited down slope and towards the floor of the larger crater (towards the west). Within this deposit, we can see fine-scale morphological features in the form of a dense network of small ridges and pits. These crater-related pitted materials are consistent with volatile-rich impact melt-bearing deposits seen in some of the best-preserved craters on Mars (e.g., Zumba, Zunil, etc.). These deposits formed immediately after the impact event, and their discernible presence relate to the preservation state of the crater. This image is an attempt to visualize the complex formation and emplacement history of these enigmatic deposits formed by this elliptical crater and to understand its degradation history. http://photojournal.jpl.nasa.gov/catalog/PIA13078

What can we learn about impact mechanics from large craters on Venus?

NASA Technical Reports Server (NTRS)

Mckinnon, William B.; Alexopoulos, J. S.

1992-01-01

More than 50 unequivocal peak-ring craters and multiringed impact basins have been identified on Venus from Earth-based Arecibo, Venera 15/16, and Magellan radar images. These ringed craters are relatively pristine, and so serve as an important new dataset that will further understanding of the structural and rheological properties of the venusian surface and of impact mechanics in general. They are also the most direct analogues for craters formed on the Earth in Phanerozoic time. Finite-element simulations of basin collapse and ring formation were undertaken in collaboration with V. J. Hillgren (University of Arizona). These calculations used an axisymmetric version of the viscoelastic finite element code TECTON, modeled structures on the scale of Klenova or Meitner, and demonstrated two major points. First, viscous flow and ring formation are possible on the timescale of crater collapse for the sizes of multiringed basins seen on Venus and heat flows appropriate to the plant. Second, an elastic lithosphere overlying a Newtonian viscous asthenosphere results mainly in uplift beneath the crater. Inward asthenospheric flow mainly occurs at deeper levels. Lithospheric response is dominantly vertical and flexural. Tensional stress maxima occur and ring formation by normal faulting is predicted in some cases, but these predicted rings occur too far out to explain observed ring spacings on Venus (or on the Moon). Overall, these estimates and models suggest that multiringed basin formation is indeed possible at the scales observed on Venus. Furthermore, due to the strong inverse dependence of solid-state viscosity on stress, the absence of Cordilleran-style ring faulting in craters smaller than Meitner or Klenova makes sense. The apparent increase in viscosity of shock-fluidized rock with crater diameter, greater interior temperatures accessed by larger, deeper craters, and decreased non-Newtonian viscosity associated with larger craters may conspire to make the transition with diameter from peak-ring crater to Orientale-type multiringed basin rather abrupt.

Vesta and Ceres as Seen by Dawn

NASA Astrophysics Data System (ADS)

Russell, C. T.; Nathues, A.; De Sanctis, M. C.; Prettyman, T. H.; Konopliv, A. S.; Park, R. S.; Jaumann, R.; McSween, H. Y., Jr.; Raymond, C. A.; Pieters, C. M.; McCord, T. B.; Marchi, S.; Schenk, P.; Buczkowski, D.

2015-12-01

Ceres and Vesta are the most massive bodies in the main asteroid belt. They have witnessed 4.6 Ga of solar system history. Dawn's objective is to interview these two witnesses. These bodies are relatively simple protoplanets, with a modest amount of thermal evolution and geochemical alteration. They are our best archetypes of the early building blocks of the terrestrial planets. In particular siderophile elements in the Earth's core were probably first segregated in Vesta-like bodies, and its water was likely first condensed in Ceres-like bodies. Vesta has provided copious meteorites for geochemical analysis. This knowledge was used to infer the constitution of the parent body. Dawn verified that Vesta was consistent with being that body, confirming the geochemical inferences from these samples on the formation and evolution of the solar system. Ceres has not revealed itself with a meteoritic record nor an asteroid family. While the surface is scarred with craters, it is probable that the ejecta from the crater-forming events created little competent material from the icy crust and any such ejected material that reached Earth might have disintegrated upon entry into the Earth's atmosphere. Ceres' surface differs greatly from Vesta's. Plastic or fluidized mass wasting is apparent as are many irregularly shaped craters, including many polygonal crater forms. There are many central-pit craters possibly caused by volatilization of the crust in the center of the impact. There are many central-peak craters but are these due to rebound or pingo-like formation processes? Bright spots, possibly salt deposits, dot the landscape, evidence of fluvial processes beneath the crust. Observations of the largest region of bright spots may suggest sublimation from the surface of the bright area, consistent with Herschel water vapor observations. Ceres is not only the most massive body in the asteroid belt but also possibly the most active occupant of the main belt.

Karstic terrain in the equatorial layered deposits within a crater in northern Sinus Meridiani, Mars.

NASA Astrophysics Data System (ADS)

Baioni, Davide

2017-04-01

This work investigates the equatorial layered deposits (ELDs) located within a crater located in northern Sinus Meridiani, Mars (4.430 N, 3.320 W), which display traits that are consistent with formation by karst-driven processes. Here, shallow depressions showing a variety of plan forms ranging from rounded, circular, elongated, polygonal and drop-like to elliptical can be observed. The morphologic and morphometric analyses performed, highlight that these depressions display strong morphometric (sizes) and morphologic (shapes, bottoms, walls) similarities with the karst depressions that are common on limestone and evaporite terrains on the Earth and other regions on Mars. On the basis of the characteristics of the investigated landforms and the similarities of features on Earth and Mars, and after discarding other possible origins such as, aeolian, periglacial, volcanic or impact related processes, it has been inferred that the depressions are karstic dolines formed polygenetically by corrosion and solution-related intra-crater processes.

Samples from Martian craters: Origin of the Martian soil by hydrothermal alteration of impact melt deposits and atmospheric interactions with ejecta during crater formation

NASA Technical Reports Server (NTRS)

Newsom, Horton E.

1988-01-01

The origin of the Martian soil is an important question for understanding weathering processes on the Martian surface, and also for understanding the global geochemistry of Mars. Chemical analyses of the soil will provide an opportunity to examine what may be a crustal average, as studies of loess on the Earth have demonstrated. In this regard the origin of the Martian soil is also important for understanding the chemical fractionations that have affected the composition of the soil. Several processes that are likely to contribute to the Martian soil are examined.

Rietveld analysis of X-ray powder diffraction patterns as a potential tool for the identification of impact-deformed carbonate rocks

NASA Astrophysics Data System (ADS)

Huson, S. A.; Foit, F. F.; Watkinson, A. J.; Pope, M. C.

2009-12-01

Previous X-ray powder diffraction (XRD) studies revealed that shock deformed carbonates and quartz have broader XRD patterns than those of unshocked samples. Entire XRD patterns, single peak profiles and Rietveld refined parameters of carbonate samples from the Sierra Madera impact crater, west Texas, unshocked equivalent samples from 95 miles north of the crater and the Mission Canyon Formation of southwest Montana and western Wyoming were used to evaluate the use of X-ray powder diffraction as a potential tool for distinguishing impact deformed rocks from unshocked and tectonically deformed rocks. At Sierra Madera dolostone and limestone samples were collected from the crater rim (lower shock intensity) and the central uplift (higher shock intensity). Unshocked equivalent dolostone samples were collected from well cores drilled outside of the impact crater. Carbonate rocks of the Mission Canyon Formation were sampled along a transect across the tectonic front of the Sevier and Laramide orogenic belts. Whereas calcite subjected to significant shock intensities at the Sierra Madera impact crater can be differentiated from tectonically deformed calcite from the Mission Canyon Formation using Rietveld refined peak profiles, weakly shocked calcite from the crater rim appears to be indistinguishable from the tectonically deformed calcite. In contrast, Rietveld analysis readily distinguishes shocked Sierra Madera dolomite from unshocked equivalent dolostone samples from outside the crater and tectonically deformed Mission Canyon Formation dolomite.

Effects of the Venusian atmosphere on incoming meteoroids and the impact crater population

NASA Technical Reports Server (NTRS)

Herrick, Robert R.; Phillips, Roger J.

1994-01-01

The dense atmosphere on Venus prevents craters smaller than about 2 km in daimater from forming and also causes formation of several crater fields and multiple-floored craters (collectively referred to as multiple impacts). A model has been constructed that simulates the behavior of a meteoroid in a dense planetary atmosphere. This model was then combined with an assumed flux of incoming meteoroids in an effort to reproduce the size-frequency distribution of impact craters and several aspects of the population of the crater fields and multiple-floored craters on Venus. The modeling indicates that it is plausible that the observed rollover in the size-frequency curve for Venus is due entirely to atmospheric effects on incoming meteoroids. However, there must be substantial variation in the density and behavior of incoming meteoroids in the atmosphere. Lower-density meteoroids must be less likely to survive atmospheric passage than simple density differences can account for. Consequently, it is likely that the percentage of craters formed by high-density meteoroids is very high at small crater diameters, and this percentage decreases substantially with increasing crater diameter. Overall, high-density meteoroids created a disproportionately large percentage of the impact craters on Venus. Also, our results indicate that a process such as meteoroid flattening or atmospheric explosion of meteoroids must be invoked to prevent craters smaller than the observed minimum diameter (2 km) from forming. In terms of using the size-frequency distribution to age-date the surface, the model indicates that the observed population has at least 75% of the craters over 32 km in diameter that would be expected on an atmosphereless Venus; thus, this part of the curve is most suitable for comparison with calibrated curves for the Moon.

Mineral abundances at the final four curiosity study sites and implications for their formation

NASA Astrophysics Data System (ADS)

Poulet, F.; Carter, J.; Bishop, J. L.; Loizeau, D.; Murchie, S. M.

2014-03-01

A component of the landing site selection process for the Mars Science Laboratory (MSL) involved the presence of phyllosilicates as the main astrobiological targets. Gale crater was selected as the MSL landing site from among 4 down selected study sites (Gale, Eberswalde and Holden craters, Mawrth Vallis) that addressed the primary scientific goal of assessing the past habitability of Mars. A key constraint on the formation process of these phyllosilicate-bearing deposits is in the precise mineralogical composition. We present a reassessment of the mineralogy of the sites combined with a determination of the modal mineralogy of the major phyllosilicate-bearing deposits of the four final study sites from the modeling of near-infrared spectra using a radiative transfer model. The largest abundance of phyllosilicates (30-70%) is found in Mawrth Vallis, the lowest one in Eberswalde (<25%). Except for Mawrth Vallis, the anhydrous phases (plagioclase, pyroxenes and martian dust) are the dominant phases, suggesting formation conditions with a lower alteration grade and/or a post-formation mixing with anhydrous phases. The composition of Holden layered deposits (mixture of saponite and micas with a total abundance in the range of 25-45%) suggests transport and deposition of altered basalts of the Noachian crust without major chemical transformation. For Eberswalde, the modal mineralogy is also consistent with detrital clays, but the presence of opaline silica indicates that an authigenic formation occurred during the deposition. The overall composition including approximately 20-30% smectite detected by MSL in the rocks of Yellow-knife Bay area interpreted to be material deposited on the floor of Gale crater by channels (http://www.nasa.gov/mission_pages/msl/news/msl20130312.html).

Investigating CO2 Reservoirs at Gale Crater and Evidence for a Dense Early Atmosphere

NASA Technical Reports Server (NTRS)

Niles, P. B.; Archer, P. D.; Heil, E.; Eigenbrode, J.; McAdam, A.; Sutter, B.; Franz, H.; Navarro-Gonzalez, R.; Ming, D.; Mahaffy, P. R.;

On the nature of the Ni-rich component in splash-form Australasian tektites

NASA Astrophysics Data System (ADS)

Goderis, Steven; Tagle, Roald; Fritz, Jörg; Bartoschewitz, Rainer; Artemieva, Natalia

2017-11-01

The Australasian tektite strewn field is exceptional, not only as the largest and most recent, but also as the only strewn field without an identified source impact crater. Therefore, scenarios without the formation of an impact crater, such as a low altitude cometary airburst, have proven hard to discard. Here, new geochemical evidence is presented for mixing of projectile and target material, which implies the formation of an Australasian tektite-related impact crater. First, ninety-two Australasian tektites were grouped according to their Cr, Co and Ni concentrations. Based on this data, Australasian tektites with the highest Ni contents (>200 μg/g) occur more than 1500 km south-southeast (SSE) of the northern Indochina region, with the highest concentration of Ni-rich tektites in South Vietnam, the islands of Borneo, Belitung, and Java, and reports in literature for Ni-rich tektites in central Australia. The tektites with the highest Cr and Ni abundances often also show highly siderophile element (HSE) enrichments of up to 4 ng/g Ir. The most Ni-rich samples exhibit broadly chondrite-relative HSE proportions. However, a chondritic impactor contribution appears to be inconsistent with the observed Ni/Cr, Ni/Co, and Cr/Co ratios. A previously suggested significant terrestrial mantle contribution can also not explain the siderophile element enrichments in combination with relatively low FeOtot (<7 wt.%) and MgO (<4 wt.%) contents. Elemental fractionation during impact cratering or tektite formation by an impactor with a chondritic signature may explain these observations. Alternatively, a projectile component from a primitive achondrite may be advocated, with contribution from a mafic to ultramafic extraterrestrial lithology with a relatively unfractionated HSE signature and Ni/Cr ratio distinctly higher than those of Earth's mantle. Element distribution maps obtained from individual Australasian tektites document complex mingling processes of chemically distinct melt batches, each exhibiting variable contributions from distinct endmember compositions. These texturally recorded mingling processes are consistent with high-resolution numerical models of impact cratering processes that resolve the growth of Kelvin-Helmholtz instabilities at the projectile/target interface during impact, when both materials co-occur at high pressure. These numerical models indicate that Ni-rich tektite populations across the central part of the Australasian tektite strewn field could represent projectile-enriched material preferentially ejected downrange. Continued tracing of this Ni-rich component across the strewn field may help to constrain the location of the yet to be identified source crater of the Australasian (micro)tektites.

Numerical Modelling of the Deep Impact Mission Experiment

NASA Technical Reports Server (NTRS)

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

2005-01-01

NASA s Deep Impact Mission (launched January 2005) will provide, for the first time ever, insights into the interior of a comet (Tempel 1) by shooting a approx.370 kg projectile onto the surface of a comets nucleus. Although it is usually assumed that comets consist of a very porous mixture of water ice and rock, little is known about the internal structure and in particular the constitutive material properties of a comet. It is therefore difficult to predict the dimensions of the excavated crater. Estimates of the crater size are based on laboratory experiments of impacts into various target compositions of different densities and porosities using appropriate scaling laws; they range between 10 s of meters up to 250 m in diameter [1]. The size of the crater depends mainly on the physical process(es) that govern formation: Smaller sizes are expected if (1) strength, rather than gravity, limits crater growth; and, perhaps even more crucially, if (2) internal energy losses by pore-space collapse reduce the coupling efficiency (compaction craters). To investigate the effect of pore space collapse and strength of the target we conducted a suite of numerical experiments and implemented a novel approach for modeling porosity and the compaction of pores in hydrocode calculations.

Interior and Ejecta Morphologies of Impact Craters on Ganymede

NASA Astrophysics Data System (ADS)

Barlow, Nadine G.; Klaybor, K.; Katz-Wigmore, J.

2006-09-01

We are utilizing Galileo SSI imagery of Ganymede to classify impact crater interior and ejecta morphologies. Although we are in the early stages of compiling our Catalog of Impact Craters on Ganymede, some interesting trends are beginning to emerge. Few craters display obvious ejecta morphologies, but 68 craters are classified as single layer ejecta and 3 as double layer ejecta. We see no obvious correlation of layered ejecta morphologies with terrain or latitude. All layered ejecta craters have diameters between 10 and 40 km. Sinuosity ("lobateness") and ejecta extent ("ejecta mobility ratio") of Ganymede layered ejecta craters are lower than for martian layered ejecta craters. This suggests less mobility of ejecta materials on Ganymede, perhaps due to the colder temperatures. Interior structures being investigated include central domes, peaks, and pits. 57 dome craters, 212 central peak craters, and 313 central pit craters have been identified. Central domes occur in 50-100 km diameter craters while peaks are found in craters between 20 and 50 km and central pit craters range between 29 and 74 km in diameter. The Galileo Regio region displays higher concentrations of central dome and central pit craters than other regions we have investigated. 67% of central pit craters studied to date are small pits, where the ratio of pit diameter to crater diameter is <0.2. Craters containing the three interior structures preferentially occur on darker terrain units, suggesting that an ice-silicate composition is more conducive to interior feature formation than pure ice alone. Results of this study have important implications not only for the formation of specific interior and ejecta morphologies on Ganymede but also for analogous features associated with Martian impact craters. This research is funded through NASA Outer Planets Research Program Award #NNG05G116G to N. G. Barlow.

Statistical models of lunar rocks and regolith

NASA Technical Reports Server (NTRS)

Marcus, A. H.

1973-01-01

The mathematical, statistical, and computational approaches used in the investigation of the interrelationship of lunar fragmental material, regolith, lunar rocks, and lunar craters are described. The first two phases of the work explored the sensitivity of the production model of fragmental material to mathematical assumptions, and then completed earlier studies on the survival of lunar surface rocks with respect to competing processes. The third phase combined earlier work into a detailed statistical analysis and probabilistic model of regolith formation by lithologically distinct layers, interpreted as modified crater ejecta blankets. The fourth phase of the work dealt with problems encountered in combining the results of the entire project into a comprehensive, multipurpose computer simulation model for the craters and regolith. Highlights of each phase of research are given.

Impact cratering on porous targets in the strength regime

NASA Astrophysics Data System (ADS)

Nakamura, Akiko M.

2017-12-01

Cratering on small bodies is crucial for the collision cascade and also contributes to the ejection of dust particles into interplanetary space. A crater cavity forms against the mechanical strength of the surface, gravitational acceleration, or both. The formation of moderately sized craters that are sufficiently larger than the thickness of the regolith on small bodies, in which mechanical strength plays the dominant role rather than gravitational acceleration, is in the strength regime. The formation of microcraters on blocks on the surface is also within the strength regime. On the other hand, the formation of a crater of a size comparable to the thickness of the regolith is affected by both gravitational acceleration and cohesion between regolith particles. In this short review, we compile data from the literature pertaining to impact cratering experiments on porous targets, and summarize the ratio of spall diameter to pit diameter, the depth, diameter, and volume of the crater cavity, and the ratio of depth to diameter. Among targets with various porosities studied in the laboratory to date, based on conventional scaling laws (Holsapple and Schmidt, J. Geophys. Res., 87, 1849-1870, 1982) the cratering efficiency obtained for porous sedimentary rocks (Suzuki et al., J. Geophys. Res. 117, E08012, 2012) is intermediate. A comparison with microcraters formed on a glass target with impact velocities up to 14 km s-1 indicates a different dependence of cratering efficiency and depth-to-diameter ratio on impact velocity.

Meteorite crater impact study: a new way to study seismology at school with exciting experiments, and an example of meteorite astroblema in France (Rochechouart)

NASA Astrophysics Data System (ADS)

Carrer, Diane; Berenguer, Jean-Luc; MacMurray, Andrew

2016-04-01

The InSIGHT mission to Mars (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) supported by NASA, IPGP and CNES, is a great opportunity for teachers and pupils to study the Red planet, but also to study other fields of geology at school, such as seismology. With our pupils, we are following the InSight mission and we look forward to analyze seismic data registered by the SEIS seismometer , once it will be available (the InSight mission will launch in 2018 from California, and will land to Mars in 2018 or 2019). As this mission needs meteorite impacts to generate seismic waves ( to discover the Martian interior structure) , we've decided to model those meteorite strikes in the classroom. With our pupils, we've modeled meteorite impact craters with different impactors , such as tennis balls, baseballs, or pingpong balls, and used an analogue substratum made by flour and cocoa. Then, we kept on going our geophysical investigation , studying several parameters. For instance, we've studied the link between size of impactor and size of crater , the link between mass of impactor and Crater Formation, and the link between velocity of impactor and crater formation. In this geophysical approach , potential energy and kinetic energy can be introduced in terms of energy transfer as the impactor falls ( calculation of the velocity of impact and plotting that against crater diameter using v = (2gh)1/2). For each crater formation made in class by students, we have registered seismological data thanks to Audacity software, and study the seismic signal propagation. This exemple of hands-on activity with pupils, and its wide range of geophysical calculation shows how we can do simple experiment modeling meteorite crater impact and exploit registered seismological data at school. We've finaly focused our work with the very famous example of the astroblema of Rochechouart in the South-west of France ( crater formation : - 214 My) , in which it's easy to recognize every typical structure of crater formation (ejecta blankets, overturned crater rim) . In this activity, pupils understand how a model in class can be close to real geological objects.

Noachian and more recent phyllosilicates in impact craters on Mars

PubMed Central

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.

2010-01-01

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. PMID:20616087

Noachian and more recent phyllosilicates in impact craters on Mars.

PubMed

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.

Terrestrial analog field investigations to enable science and exploration studies of impacts and volcanism on the Moon, NEAs, and moons of Mars (Invited)

NASA Astrophysics Data System (ADS)

Heldmann, J. L.; Colaprete, A.; Cohen, B. A.; Elphic, R. C.; Garry, W. B.; Hodges, K. V.; Hughes, S. S.; Kim, K. J.; Lim, D.; McKay, C. P.; Osinski, G. R.; Petro, N. E.; Sears, D. W.; Squyres, S. W.; Tornabene, L. L.

2013-12-01

Terrestrial analog studies are a critical component for furthering our understanding of geologic processes on the Moon, near-Earth asteroids (NEAs), and the moons of Mars. Carefully chosen analog sites provide a unique natural laboratory with high relevance to the associated science on these solar system target bodies. Volcanism and impact cratering are fundamental processes on the Moon, NEAs, and Phobos and Deimos. The terrestrial volcanic and impact records remain invaluable for our understanding of these processes throughout our solar system, since these are our primary source of firsthand knowledge on volcanic landform formation and modification as well as the three-dimensional structural and lithological character of impact craters. Regarding impact cratering, terrestrial fieldwork can help us to understand the origin and emplacement of impactites, the history of impact bombardment in the inner Solar System, the formation of complex impact craters, and the effects of shock on planetary materials. Volcanism is another dominant geologic process that has significantly shaped the surface of planetary bodies and many asteroids. Through terrestrial field investigations we can study the processes, geomorphic features and rock types related to fissure eruptions, volcanic constructs, lava tubes, flows and pyroclastic deposits. Also, terrestrial analog studies have the advantage of enabling simultaneous robotic and/or human exploration testing in a low cost, low risk, high fidelity environment to test technologies and concepts of operations for future missions to the target bodies. Of particular interest is the importance and role of robotic precursor missions prior to human operations for which there is little to no actual mission experience to draw upon. Also critical to understanding new worlds is sample return, and analog studies enable us to develop the appropriate procedures for collecting samples in a manner that will best achieve the science objectives.

Terrestrial Analog Field Investigations to Enable Science and Exploration Studies of Impacts and Volcanism on the Moon, NEAs, and Moons of Mars

NASA Technical Reports Server (NTRS)

Heldmann, Jennifer Lynne; Colaprete, Anthony; Cohen, Barbara; Elphic, Richard; Garry, William; Hodges, Kip; Hughes, Scott; Kim, Kyeon; Lim, Darlene; McKay, Chris;

Asteroid entry in Venusian atmosphere: Pressure and density fields effect on crater formation

NASA Technical Reports Server (NTRS)

Schmidt, Robert

1995-01-01

The objectives are to look at time scales of overpressure compared to cratering and to determine: what are the transient pressure and density due to atmospheric entry; do shock waves evacuate ambient gas; do transient atmospheric disturbances 'settle down' during cratering; can the pressure/density field be approximated as quasi-static; how does disturbance scale with impactor size; and what is the role of atmospheric thickness. The general approach is to perform inexpensive exploratory calculations, perform experiments to validate code and observe crater growth, and to follow up with more realistic coupling calculations. This viewgraph presentation presents progress made with the objective to obtain useful scaling relationships for crater formation when atmospheric effects are important.

Hailar crater - A possible impact structure in Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Xiao, Zhiyong; Chen, Zhaoxu; Pu, Jiang; Xiao, Xiao; Wang, Yichen; Huang, Jun

2018-04-01

Hailar crater, a probable impact structure, is a circular depression about 300 m diameter in Inner Mongolia, northeast China. With broad elevated rims, the present rim-to-floor depth is 8-20 m. Regional geological background and geomorphological comparison suggest that this feature is likely not formed by surface processes such as salt diapir, karst, aeolian, glacial, or volcanic activity. Its unique occurrence in this region and well-preserved morphology are most consistent with it being a Cenozoic impact crater. Two field expeditions in 2016 and 2017 investigated the origin of this structure, recognizing that (1) no additional craters were identified around Hailar crater in the centimeter-scale digital topography models that were constructed using a drone imaging system and stereo photogrammetry; (2) no bedrock exposures are visible within or adjacent to the crater because of thick regolith coverage, and only small pieces of angular unconsolidated rocks are present on the crater wall and the gently-sloped crater rim, suggesting recent energetic formation of the crater; (3) most samples collected from the crater have identical lithology and petrographic characteristics with the background terrain, but some crater samples contain more abundant clasts and silicate hydrothermal veins, indicating that rocks from depths have been exposed by the crater; (4) no shock metamorphic features were found in the samples after thin section examinations; and (5) a systematic sample survey and iron detector scan within and outside of the crater found no iron-rich meteorites larger than 2 cm in size in a depth of 30 cm. Although no conclusive evidence for an impact origin is found yet, Hailar crater was most likely formed by an impact based on its unique occurrence and comparative geomorphologic study. We suggest that drilling in the crater center is required to verify the impact origin, where hypothesized melt-bearing impactites may be encountered.

Chemical transport during formation and alteration of Martian impact and volcanic deposits

NASA Technical Reports Server (NTRS)

Newsom, H. E.

1992-01-01

Much of the surface of Mars, including volcanic and cratered terrains, probably experienced alteration and degassing processes. These processes may have depleted or enriched many important elements in surface materials, including bedrock, dust, and soils. The composition of the martian soil may represent the best estimate, for some elements, of the average composition of the martian crust, similar to the composition of loess created by glacial action on the Earth. The martian soil may represent the only convenient, globally or regionally averaged sample of the martian crust. In order to understand the composition of the source material for the soil, however, we need to understand the contributions of volcanic vs. impact sources for this material and the chemical fractionations involved in its production. The processes to be addressed include degassing of volcanic deposits, as observed in the Valley of Ten Thousand Smokes at Katmai, Alaska, and degassing of meltbearing impact ejecta as inferred for suevite ejecta sheets at the Ries Crater, and alteration or palagonitization of volcanic deposits, as documented for volcanos in British Columbia and many other volcanic terrains, and impact crater deposits. The process of palagonitization has been the subject of several studies with reference to Mars, and palagonite is a good analogue for the spectroscopic properties of the martian dust. The role of impact in cratering has not been as well studied, although other researchers have established that both degassing and alteration are common features of impact crater deposits. Other relevant sources of experimental data include the extensive literature on the corrosion of nuclear waste glass and leaching of shocked materials.

Shatter cones: (Mis)understood?

PubMed

Osinski, Gordon R; Ferrière, Ludovic

2016-08-01

Meteorite impact craters are one of the most common geological features in the solar system. An impact event is a near-instantaneous process that releases a huge amount of energy over a very small region on a planetary surface. This results in characteristic changes in the target rocks, from vaporization and melting to solid-state effects, such as fracturing and shock metamorphism. Shatter cones are distinctive striated conical fractures that are considered unequivocal evidence of impact events. They are one of the most used and trusted shock-metamorphic effects for the recognition of meteorite impact structures. Despite this, there is still considerable debate regarding their formation. We show that shatter cones are present in several stratigraphic settings within and around impact structures. Together with the occurrence of complete and "double" cones, our observations are most consistent with shatter cone formation due to tensional stresses generated by scattering of the shock wave due to heterogeneities in the rock. On the basis of field mapping, we derive the relationship D sc = 0.4 D a, where D sc is the maximum spatial extent of in situ shatter cones, and D a is the apparent crater diameter. This provides an important, new, more accurate method to estimate the apparent diameter of eroded complex craters on Earth. We have reestimated the diameter of eight well-known impact craters as part of this study. Finally, we suggest that shatter cones may reduce the strength of the target, thus aiding crater collapse, and that their distribution in central uplifts also records the obliquity of impact.

Shatter cones: (Mis)understood?

PubMed Central

Osinski, Gordon R.; Ferrière, Ludovic

2016-01-01

Meteorite impact craters are one of the most common geological features in the solar system. An impact event is a near-instantaneous process that releases a huge amount of energy over a very small region on a planetary surface. This results in characteristic changes in the target rocks, from vaporization and melting to solid-state effects, such as fracturing and shock metamorphism. Shatter cones are distinctive striated conical fractures that are considered unequivocal evidence of impact events. They are one of the most used and trusted shock-metamorphic effects for the recognition of meteorite impact structures. Despite this, there is still considerable debate regarding their formation. We show that shatter cones are present in several stratigraphic settings within and around impact structures. Together with the occurrence of complete and “double” cones, our observations are most consistent with shatter cone formation due to tensional stresses generated by scattering of the shock wave due to heterogeneities in the rock. On the basis of field mapping, we derive the relationship Dsc = 0.4 Da, where Dsc is the maximum spatial extent of in situ shatter cones, and Da is the apparent crater diameter. This provides an important, new, more accurate method to estimate the apparent diameter of eroded complex craters on Earth. We have reestimated the diameter of eight well-known impact craters as part of this study. Finally, we suggest that shatter cones may reduce the strength of the target, thus aiding crater collapse, and that their distribution in central uplifts also records the obliquity of impact. PMID:27532050

Major Element Analysis of the Target Rocks at Meteor Crater, Arizona

NASA Technical Reports Server (NTRS)

See, Thomas H.; Hoerz, Friedrich; Mittlefehldt, David W.; Varley, Laura; Mertzman, Stan; Roddy, David

2002-01-01

We collected approximately 400 rock chips in continuous vertical profile at Meteor Crater, Arizona, representing, from bottom to top, the Coconino, Toroweap, Kaibab, and Moenkopi Formations to support ongoing compositional analyses of the impact melts and their stratigraphic source depth(s) and other studies at Meteor Crater that depend on the composition of the target rocks. These rock chips were subsequently pooled into 23 samples for compositional analysis by XRF (x ray fluorescence) methods, each sample reflecting a specific stratigraphic "subsection" approximately 5-10 in thick. We determined the modal abundance of quartz, dolomite, and calcite for the entire Kaibab Formation at vertical resolutions of 1-2 meters. The Coconino Formation composes the lower half of the crater cavity. It is an exceptionally pure sandstone. The Toroweap is only two inches thick and compositionally similar to Coconino, therefore, it is not a good compositional marker horizon. The Kaibab Formation is approximately 80 in thick. XRD (x ray diffraction) studies show that the Kaibab Formation is dominated by dolomite and quartz, albeit in highly variable proportions; calcite is a minor phase at best. The Kaibab at Meteor Crater is therefore a sandy dolomite rather than a limestone, consistent with pronounced facies changes in the Permian of SE Arizona over short vertical and horizontal distances. The Moenkopi forms the 12 in thick cap rock and has the highest Al2O3 and FeO concentrations of all target rocks. With several examples, we illustrate how this systematic compositional and modal characterization of the target ideologies may contribute to an understanding of Meteor Crater, such as the depth of its melt zone, and to impact cratering in general, such as the liberation of CO2 from shocked carbonates.

Effects of Pre-Existing Target Structure on the Formation of Large Craters

NASA Technical Reports Server (NTRS)

Barnouin-Jha, O. S.; Cintala, M. J.; Crawford, D. A.

2003-01-01

The shapes of large-scale craters and the mechanics responsible for melt generation are influenced by broad and small-scale structures present in a target prior to impact. For example, well-developed systems of fractures often create craters that appear square in outline, good examples being Meteor Crater, AZ and the square craters of 433 Eros. Pre-broken target material also affects melt generation. Kieffer has shown how the shock wave generated in Coconino sandstone at Meteor crater created reverberations which, in combination with the natural target heterogeneity present, created peaks and troughs in pressure and compressed density as individual grains collided to produce a range of shock mineralogies and melts within neighboring samples. In this study, we further explore how pre-existing target structure influences various aspects of the cratering process. We combine experimental and numerical techniques to explore the connection between the scales of the impact generated shock wave and the pre-existing target structure. We focus on the propagation of shock waves in coarse, granular media, emphasizing its consequences on excavation, crater growth, ejecta production, cratering efficiency, melt generation, and crater shape. As a baseline, we present a first series of results for idealized targets where the particles are all identical in size and possess the same shock impedance. We will also present a few results, whereby we increase the complexities of the target properties by varying the grain size, strength, impedance and frictional properties. In addition, we investigate the origin and implications of reverberations that are created by the presence of physical and chemical heterogeneity in a target.

Target and Projectile: Material Effects on Crater Excavation and Growth

NASA Technical Reports Server (NTRS)

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.

Inversion of Crater Morphometric Data to Gain Insight on the Cratering Process

NASA Technical Reports Server (NTRS)

Herrick, Robert R.; Lyons, Suzane N.

1998-01-01

In recent years, morphometric data for Venus and several outer planet satellites have been collected, so we now have observational data of complex Craters formed in a large range of target properties. We present general inversion techniques that can utilize the morphometric data to quantitatively test various models of complex crater formation. The morphometric data we use in this paper are depth of a complex crater, the diameter at which the depth-diameter ratio changes, and onset diameters for central peaks, terraces, and peak rings. We tested the roles of impactor velocities and hydrostatic pressure vs. crustal strength, and we tested the specific models of acoustic fluidization (Melosh, 1982) and nonproportional growth (Schultz, 1988). Neither the acoustic fluidization model nor the nonproportional growth in their published formulations are able to successfully reproduce the data. No dependence on impactor velocity is evident from our inversions. Most of the morphometric data is consistent with a linear dependence on the ratio of crustal strength to hydrostatic pressure on a planet, or the factor c/pg.

Collisional and dynamical history of Gaspra

NASA Technical Reports Server (NTRS)

Greenberg, R.; Nolan, M. C.; Bottke, W. F., Jr.; Kolvoord, R. A.

1993-01-01

Interpretation of the impact record on Gaspra requires understanding of the effects of collisions on a target body of Gaspra's size and shape, recognition of impact features that may have different morphologies from craters on larger planets, and models of the geological processes that erase and modify impact features. Crater counts on the 140 sq km of Gaspra imaged at highest resolution by the Galileo spacecraft show a steep size-frequency distribution (cumulative power-law index near -3.5) from the smallest resolvable size (150 m diameter) up through the large feature (1.5 km diameter crater) of familiar crater-like morphology. In addition, there appear to be as many as eight roughly circular concavities with diameters greater than 3 km visible on the asteroid. If we restrict our crater counts to features with traditionally recognized crater morphologies, these concavities would not be included. However, if we define craters to include any concave structures that may represent local or regional damage at an impact size, then the larger features on Gaspra are candidates for consideration. Acceptance of the multi-km features as craters has been cautious for several reasons. First, scaling laws (the physically plausible algorithms for extrapolating from experimental data) indicate that Gaspra could not have sustained such large-crater-forming impacts without being disrupted; second, aside from concavity, the larger structures have no other features (e.g. rims) that can be identified with known impact craters; and third, extrapolation of the power-law size distribution for smaller craters predicts no craters larger than 3 km over the entire surface. On the other hand, recent hydrocode modeling of impacts shows that for given impact (albeit into a sphere), the crater size is much larger than given by scaling laws. Gaspra-size bodies can sustain formation of up to 8-km craters without disruption. Besides allowing larger impact craters, this result doubles the lifetime since the last catastrophic fragmentation event up to one billion years. Events that create multi-km craters also globally damage the material structure, such that regolith is produced, whether or not Gaspra 'initially' had a regolith, contrary to other models in which initial regolith is required in order to allow current regolith. Because the globally destructive shock wave precedes basin formation, crater size is closer to the large size extrapolated from gravity-scaling rather than the strength-scaling that had earlier been assumed for such small bodies. This mechanism may also help explain the existence of Stickney on Phobos. Moreover, rejection of the large concavities as craters based on unfamiliar morphology would be premature, because (aside from Stickney) we have no other data on such large impact structures on such a small, irregular body. The eight candidate concavities cover an area greater than that counted for smaller craters, because they are most apparent where small craters cannot be seen: on low resolution images and at the limb on high resolution images. We estimate that there are at least two with diameter greater than 4 km per 140 sq km, which would have to be accounted for in any model that claims these are impact craters.

The large impact process inferred from the geology of lunar multiring basins

NASA Technical Reports Server (NTRS)

Spudis, Paul D.

1992-01-01

The nature of the impact process has been inferred through the study of the geology of a wide variety of impact crater types and sizes. Some of the largest craters known are the multiring basins found in ancient terrains of the terrestrial planets. Of these features, those found on the Moon possess the most extensive and diverse data coverage, including morphological, geochemical, geophysical, and sample data. The study of the geology of lunar basins over the past 10 years has given us a rudimentary understanding of how these large structures have formed and evolved. The topics covered include basin morphology, basin ejecta, basin excavation, and basin ring formation.

Lunar and Planetary Science XXXV: Impacts: Modeling and Observations

NASA Technical Reports Server (NTRS)

2004-01-01

This document covers the following topics: Cratering on Titan: Projectiles, Craters and Impact Melt; The Cratering Database: Making Code Jockeys Honest; Popigai Impact Structure Modeling: Morphology and Worldwide Ejecta; Anhydrite EOS and Phase Diagram in Relation to Shock Decomposition; Computational Investigations of the Chesapeake Bay Impact Structure; Hydrocode Simulations of the Chesapeake Bay Impact; Lockne Crater as a Result of Oblique Impact; The Influence of a Deep Shelf Sea on the Excavation and Modification of a Marine-Target Crater, the Lockne Crater, Central Sweden; Pre-Drilling Investigation of the Lake Bosumtwi Impact Crater: Constraints from Geophysics and Numerical Modelling; Central Uplift Formation at the Middlesboro Impact Structure, Kentucky, USA; A SRTM Investigation of Serra da Cangalho Impact Structure, Brazil; Brazilian Impact Craters: A Review; Flynn Creek Impact Structure: New Insights from Breccias, Melt Features, Shatter Cones, and Remote Sensing; The Howell Structure, Lincoln County, Tennessee: A Review of Past and Current Research; After the Chicxulub Impact: Control on Depositional and Diagenetic History of the Cenozoic Carbonate Formations of the Northwestern Yucatan Peninsula, Mexico; Ni Contents by Non-Destructive In-Situ XRF Method of Takamatsu-Kagawa Crater District in Japan; and Akiyoshi Limestone Blocks Transported by the P/T Boundary Event to Japan Islands.

Numerical modeling of seismic anomalies at impact craters on a laboratory scale

NASA Astrophysics Data System (ADS)

Wuennemann, K.; Grosse, C. U.; Hiermaier, S.; Gueldemeister, N.; Moser, D.; Durr, N.

2011-12-01

Almost all terrestrial impact craters exhibit a typical geophysical signature. The usually observed circular negative gravity anomaly and reduced seismic velocities in the vicinity of crater structures are presumably related to an approximately hemispherical zone underneath craters where rocks have experienced intense brittle plastic deformation and fracturing during formation (see Fig.1). In the framework of the "MEMIN" (multidisciplinary experimental and modeling impact crater research network) project we carried out hypervelocity cratering experiments at the Fraunhofer Institute for High-Speed Dynamics on a decimeter scale to study the spatiotemporal evolution of the damage zone using ultrasound, acoustic emission techniques, and numerical modeling of crater formation. 2.5-10 mm iron projectiles were shot at 2-5.5 km/s on dry and water-saturated sandstone targets. The target material was characterized before, during and after the impact with high spatial resolution acoustic techniques to detect the extent of the damage zone, the state of rocks therein and to record the growth of cracks. The ultrasound measurements are applied analog to seismic surveys at natural craters but used on a different - i.e. much smaller - scale. We compare the measured data with dynamic models of crater formation, shock, plastic and elastic wave propagation, and tensile/shear failure of rocks in the impacted sandstone blocks. The presence of porosity and pore water significantly affects the propagation of waves. In particular the crushing of pores due to shock compression has to be taken into account. We present preliminary results showing good agreement between experiments and numerical model. In a next step we plan to use the numerical models to upscale the results from laboratory dimensions to the scale of natural impact craters.

Detailed Analysis of the Intra-Ejecta Dark Plains of Caloris Basin, Mercury

NASA Astrophysics Data System (ADS)

Buczkowski, D.; Seelos, K. D.

2010-12-01

The Caloris basin on Mercury is floored by light-toned plains and surrounded by an annulus of dark-toned material interpreted to be ejecta blocks and smooth, dark, ridged plains. Strangely, preliminary crater-counts indicate that these intra-ejecta dark plains are younger than the light-toned plains within the Caloris basin. This would imply a second, younger plains emplacement event, possibly involving lower albedo material volcanics, which resurfaced the original ejecta deposit. On the other hand, the dark plains may be pre-Caloris light plains covered by a thin layer of dark ejecta. Another alternative to the hypothesis of young, dark volcanism is the possibility that previous crater-counts have not thoroughly distinguished between superposed craters (fresh) and partly-buried craters (old) and therefore have not accurately determined the ages of the Caloris units. We here outline the tasks associated with a new mapping project of the Caloris basin, intended to improve our knowledge of the geology and geologic history of the basin, and thus facilitate an understanding of the thermal evolution of this region of Mercury. We will 1) classify craters based on geomorphology and infilling, 2) create a high-resolution map of the intra-ejecta dark plains, 3) perform crater counts of the intra-ejecta dark plains, the ejecta, and the Caloris floor light plains and 4) refine the stratigraphy of Caloris basin units. We will use new high resolution (200-300 m/p) imaging data from the MDIS instrument to create a new geomorphic map of the dark annulus around the Caloris basin. Known Caloris group formations will be mapped where identified and any new units will be defined and mapped as necessary. Specifically, we will delineate hummocks and smooth plains within the Odin formation and map them separately. We will look for unequivocal evidence of volcanic activity within the dark annulus and the Odin Formation, such as vents and flow lobes. The location of any filled craters will be especially noted, to be incorporated into a new crater classification scheme that includes both degradation state and level and type of infilling. We will also distinguish between craters infilled with 1) lava, 2) impact melt and 3) ejecta, based on our interpretation of the MDIS images. We will then determine the crater size-frequency distribution of each geomorphic unit. We will analyze the crater density of the Caloris floor plains unit, the Odin Formation ejecta and the Odin Formation intra-ejecta dark plains. We will do a second count of Caloris floor craters that includes filled craters, to attempt to get a minimum age for the underlying dark basement. Crater counting on any additional geologic units will depend upon results of the geomorphic mapping. Finally, we will refine the stratigraphy of the Caloris basin units. We start in the region where MESSENGER data over-laps Mariner 10 images. By comparing the Caloris group formations mapped in the Tolstoj and Shakespeare quadrangles to the overlapping MDIS images, we determine the distinctive geomorphology of each of these units in the high resolution MESSENGER data. We will then use this as diagnostic criteria as we map the rest of the basin.

The Global Contribution of Secondary Craters on the Icy Satellites

NASA Astrophysics Data System (ADS)

Hoogenboom, T.; Johnson, K. E.; Schenk, P.

2014-12-01

At present, surface ages of bodies in the Outer Solar System are determined only from crater size-frequency distributions (a method dependent on an understanding of the projectile populations responsible for impact craters in these planetary systems). To derive accurate ages using impact craters, the impactor population must be understood. Impact craters in the Outer Solar System can be primary, secondary or sesquinary. The contribution of secondary craters to the overall population has recently become a "topic of interest." Our objective is to better understand the contribution of dispersed secondary craters to the small crater populations, and ultimately that of small comets to the projectile flux on icy satellites in general. We measure the diameters of obvious secondary craters (determined by e.g. irregular crater shape, small size, clustering) formed by all primary craters on Ganymede for which we have sufficiently high resolution data to map secondary craters. Primary craters mapped range from approximately 40 km to 210 km. Image resolution ranges from 45 to 440 m/pixel. Bright terrain on Ganymede is our primary focus. These resurfaced terrains have relatively low crater densities and serve as a basis for characterizing secondary populations as a function of primary size on an icy body for the first time. Although focusing on Ganymede, we also investigate secondary crater size, frequency, distribution, and formation, as well as secondary crater chain formation on icy satellites throughout the Saturnian and Jovian systems principally Rhea. We compare our results to similar studies of secondary cratering on the Moon and Mercury. Using Galileo and Voyager data, we have identified approximately 3,400 secondary craters on Ganymede. In some cases, we measured crater density as a function of distance from a primary crater. Because of the limitations of the Galileo data, it is necessary to extrapolate from small data sets to the global population of secondary craters. Nonetheless, we confirm that secondary craters on Ganymede have narrow size-frequency distributions and that they correlate with primary crater diameter. From these data we will evaluate the contribution of secondary craters over a range of crater diameters.

Geomorphic record of Noachian, Hesperian and Amazonian materials and deposits preserved within Asimov Crater, Mars: A cross-sectional view of the role of volatiles through martian history

NASA Astrophysics Data System (ADS)

Morgan, G. A.; Head, J. W.; Marchant, D. R.

2010-12-01

We describe the geomorphic record preserved within the highly degraded 80 km diameter Asimov impact crater located within Noachis Terra. The crater has been significantly in-filled since its formation in the Noachian, presumably by sedimentary materials similar to units identified elsewhere in Noachian aged craters. In this case the fill is unusual in that there is an annulus of disconnected valleys adjacent to the interior flanks of the crater wall. High-resolution images reveal that Hesperian-aged layered basalt with distinctive columnar jointing caps the interior crater fill and provides a source of debris that via mass wasting, accumulates in the surrounding annular valleys. Models for the formation of the valleys need to account for the removal of large volumes of crater fill material from below the basaltic cap. One distinct possibility is that the fill material originally contained high proportions of volatiles that have since been lost to the atmosphere. We explore this model and others and investigate the surrounding regions to place further constraints on valley formation. The occurrence of steep slopes (>20 °), relatively narrow (sheltered) valleys, and a source of debris have provided favorable conditions for the preservation of late Amazonian shallow-ice deposits. Detailed mapping reveals morphological evidence for viscous ice flow, in the form of several lobate debris tongues (LDT). Superimposed on LDT are a series of fresh-appearing gullies, with typical alcove, channel, and fan morphologies. The shift from ice-rich viscous-flow formation to gully erosion is best explained as a shift in martian climate, from one compatible with excess snowfall and flow of ice-rich deposits, to one consistent with minor snowfall and gully formation. Available dating suggests that the climate transition occurred >8 Ma, prior to the formation of other small-scale ice-rich flow features identified elsewhere on Mars that have been interpreted to have formed during the most recent phases of high obliquity. Taken altogether, Asimov Crater may contain deposits related to volatile accumulation and loss from two distinct epochs of martian history, further supporting the growing evidence of multiple shifts in the martian climate.

Venus: Dating Post-Regional-Plains Formations Through Analysis of Preservation of Crater-Associated Radar-Dark Deposits

NASA Technical Reports Server (NTRS)

Basilevsky, A. T.; Head, J. W., III

2002-01-01

The degree of preservation of crater-associated radar-dark deposits is used to estimate the age of the crater and adjacent deposits. Additional information is contained in the original extended abstract.

Are Floor-Fractured Craters on Ceres Formed by Cryomagmatism?

NASA Astrophysics Data System (ADS)

Buczkowski, D. L.; Sizemore, H. G.; Bland, M. T.; Scully, J. E. C.; Quick, L. C.; Hughson, K. H. G.; Park, R. S.; Preusker, F.; Raymond, C. A.; Russell, C. T.

2018-06-01

Several of the impact craters on Ceres have sets of fractures on their floors, morphologically similar lunar Floor-Fractured Craters. We present a geomorphic and topographic analysis of the cerean FFCs and propose hypotheses for their formation.

Degradation of Endeavour Crater, Mars

NASA Technical Reports Server (NTRS)

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

2015-01-01

The Opportunity rover has traversed portions of two western rim segments of Endeavour, a 22 km-diameter crater in Meridiani Planum, for the past three years. The resultant data enables the evaluation of the geologic expression and degradation state of the crater. Endeavour is Noa-chian-aged, complex in morphology, and originally may have appeared broadly similar to the more pristine 20.5 km-diameter Santa Fe complex crater in Lunae Palus (19.5degN, 312.0degE). By contrast, Endeavour is considerably subdued and largely buried by younger sulfate-rich plains. Exposed rim segments dubbed Cape York (CY) and Solander Point/Murray Ridge/Pillinger Point (MR) located approximately1500 m to the south reveal breccias interpreted as remnants of the ejecta deposit, dubbed the Shoemaker Formation. At CY, the Shoemaker Formation overlies the pre-impact rocks, dubbed the Matijevic Formation.

Relative Ages of the Highlands, Lowlands, and Transition Zone Along a Portion of the Mars Crustal Dichotomy from Densities of Visible and Buried Impact Craters

NASA Technical Reports Server (NTRS)

DeSoto, G. E.; Frey, H. V.

2005-01-01

Understanding the fundamental age relationships of the different parts of the Mars Crustal Dichotomy is essential to fully understanding the events that shaped the early history and formation of the surface of Mars. A dominant question is what are the true relative ages of the Northern Lowlands and the Southern Highlands? Using MOLA data from the Mars Global Surveyor and Viking visual images, a dataset of both buried and visible crater diameters was created over a nine million sq km study area of a section of the dichotomy boundary stretching from Arabia Terra to Utopia Planitia. Cumulative frequency plots on a log-log scale were used to determine the relative ages for the Highlands, the Lowlands, and the Transition Zone, separately for the visible, the buried and the combined total (visible+ buried) populations. We find the overall Highland crater population in this area is slightly older than the Lowlands, consistent with previous global studies, but the Lowlands and Transition Zone are also very old and formed at roughly the same time. It appears that the formation of the Lowlands in this region formed contemporaneously with a large-scale resurfacing event in the Highlands, perhaps caused by the process responsible for the Lowland formation.

Are pre-crater mounds gas-inflated?

NASA Astrophysics Data System (ADS)

Leibman, Marina; Kizyakov, Alexandr; Khomutov, Artem; Dvornikov, Yury; Babkina, Elena; Arefiev, Stanislav; Khairullin, Rustam

2017-04-01

Gas-emission craters (GEC) on Yamal peninsula, which occupied minds of researches for the last couple of years since first discovered in 2014, appeared to form on the place of specifically shaped mounds. There was a number of hypotheses involving pingo as an origin of these mounds. This arouse an interest in mapping pingo thus marking the areas of GEC formation risk. Our field research allows us to suggest that remote-sensing-based mapping of pingo may result in mix up of mounds of various origin. Thus, we started with classification of the mounds based on remote-sensing, field observations and survey from helicopter. Then we compared indicators of mounds of various classes to the properties of pre-crater mounds to conclude on their origin. Summarizing field experience, there are three main mound types on Yamal. (1) Outliers (remnant hills), separated from the main geomorphic landform by erosion. Often these mounds comprise polygonal blocks, kind of "baydzherakh". Their indicators are asymmetry (short gentle slope towards the main landform, and steep slope often descending into a small pond of thermokarst-nivation origin), often quadrangle or conic shape, and large size. (2) Pingo, appear within the khasyrei (drain lake basin); often are characterized by open cracks resulting from expansion of polygonal network formed when re-freezing of lake talik prior to pingo formation; old pingo may bear traces of collapse on the top, with depression which differs from the GEC by absence of parapet. (3) Frost-heave mounds (excluding pingo) may form on deep active layer, reducing due to moss-peat formation and forming ice lenses from an active layer water, usually they appear in the drainage hollows, valley bottoms, drain-lake basins periphery. These features are smaller than the first two types of mounds. Their tops as a rule are well vegetated. We were unable to find a single or a set of indicators unequivocally defining any specific mound type, thus indicators of pre-crater mounds are still debatable. Our hypothesis initially does not involve pingo origin of pre-crater mounds for several reasons, among which were the initial depth (70 m) and width (18 m) of the crater void, frozen walls and bottom, no traces of sub-lake talik, an important control for pingo formation, and more. Pre-crater mounds are closer to frost-heave mounds in size (4-7 m high and 30-60 m in diameter). Yet frost-heave mounds like palsa or lithalsa have segregated ice lenses closer to the surface, total thickness of these lenses is equal to the height of the mound. Pre-crater mounds have at least 20 m of tabular ground ice in the section that has no manifestation in the mound height or diameter. All above-mentioned leads to the conclusion that pre-crater mounds form because of gas inflation rather than regular frost heave process involving moisture migration towards the freezing front. This research is supported by Russian Science Foundation Grant 16-17-10203.

Double-layered ejecta craters on Mars: morphology, formation, and a comparison with the Ries ejecta blanket

NASA Astrophysics Data System (ADS)

Kenkmann, Thomas; Wulf, Gerwin; Sturm, Sebastian; Pietrek, Alexa

2015-04-01

The ejecta blankets of impact craters in volatile-rich environments often show characteristic layered ejecta morphologies. The so-called double-layer ejecta (DLE) craters are probably the most confusing crater types showing two ejecta layers with distinct morphologies. A phenomenological ejecta excavation and emplacement model for DLE craters is proposed based on a detailed case study of the Martian crater Steinheim - a textbook like, pristine DLE crater - and studies of other DLE craters [1]. The observations show that DLE craters on Mars are the result of an impact event into a rock/ice mixture that produces large amounts of shock-induced vaporization and melting of ground ice. The deposits of the ejecta curtain are wet in the distal part and dryer in composition in the proximal part. As a result, the outer ejecta layer is emplaced as medial and distal ejecta that propagate outwards in a fluid saturated debris flow mode after landing overrunning previously formed secondary craters. In contrast, the inner ejecta layer is formed by a translational slide of the proximal ejecta deposits. This slide overruns and superimposes parts of the outer ejecta layer. Basal melting of the ice components of the ejecta volumes at the transient crater rim is induced by frictional heating and the enhanced pressure at depth. The results indicate similar processes also for other planetary bodies with volatile-rich environments, such as Ganymede, Europa or the Earth. The Ries crater on Earth has a similar ejecta thickness distribution as DLE craters on Mars [2]. Here basal sliding and fluidization of the ejecta increases outward by the entrainment of locally derived Tertiary sands and clays, that are saturated with groundwater. References: [1] Wulf, G. & Kenkmann, T. (2015) Met. Planet. Sci. (in press); [2] Sturm, S., Wulf. G., Jung, D. & Kenkmann, T. (2013) Geology 41, 531-534.

The Role of Breccia Lenses in Regolith Generation From the Formation of Small, Simple Craters: Application to the Apollo 15 Landing Site

NASA Astrophysics Data System (ADS)

Hirabayashi, M.; Howl, B. A.; Fassett, C. I.; Soderblom, J. M.; Minton, D. A.; Melosh, H. J.

2018-02-01

Impact cratering is likely a primary agent of regolith generation on airless bodies. Regolith production via impact cratering has long been a key topic of study since the Apollo era. The evolution of regolith due to impact cratering, however, is not well understood. A better formulation is needed to help quantify the formation mechanism and timescale of regolith evolution. Here we propose an analytically derived stochastic model that describes the evolution of regolith generated by small, simple craters. We account for ejecta blanketing as well as regolith infilling of the transient crater cavity. Our results show that the regolith infilling plays a key role in producing regolith. Our model demonstrates that because of the stochastic nature of impact cratering, the regolith thickness varies laterally, which is consistent with earlier work. We apply this analytical model to the regolith evolution at the Apollo 15 site. The regolith thickness is computed considering the observed crater size-frequency distribution of small, simple lunar craters (< 381 m in radius for ejecta blanketing and <100 m in radius for the regolith infilling). Allowing for some amount of regolith coming from the outside of the area, our result is consistent with an empirical result from the Apollo 15 seismic experiment. Finally, we find that the timescale of regolith growth is longer than that of crater equilibrium, implying that even if crater equilibrium is observed on a cratered surface, it is likely that the regolith thickness is still evolving due to additional impact craters.

Amorphous and Crystalline H20 Ice at Rhea's Inktomi Crater

NASA Technical Reports Server (NTRS)

Lewis, Emma M.; Dalle Ore, Cristina M.; Cruikshank, Dale P.; White, Oliver L.

2014-01-01

We present the analysis of Cassini spectral data from spectral mapping of Saturnian icy moons Dione and Rhea, to investigate possible effects of impact crater formation on the relative abundances of crystalline and amorphous water ice in the moons' ice crusts. Both moons display morphologically young ray craters as well as older craters. Possible changes in ice properties due to crater formation are conjectured to be more visible in younger craters, and as such Rhea's well imaged ray crater Inktomi is analysed, as are older craters for comparison. We used data from Cassini's Visual and Infrared Mapping Spectrometer (VIMS). For each pixel in the VIMS maps, spectral data were extracted in the near-infrared range (1.75 micrometers less than lambda less than 2.45 micrometers). Analysis was begun by fitting a single Gaussian to the peak in absorption at 2.0 micrometers, which was then subtracted from the data, leaving residuals with a minimum on either side of the original 2.0-micrometers band. The spectra of the individual spatial pixels were then clustered by the differences between these minima, which are sensitive to changes in both ice grain size and crystallinity. This yielded preliminary maps which approximated the physical characteristics of the landscape and were used to identify candidates for further analysis. Spectra were then clustered by the properties of the 1.5-micrometers band, to divide the map into regions based on inferred grain size. For each region, the predicted differences in minima from the Gaussian residuals, over a range of crystallinities, were calculated based on the found grain sizes. This model was used to find the crystallinity of each pixel via grain size and characteristics of the residual function. Preliminary results show a greater degree of crystallization of young crater interiors, particularly in Rhea's ray crater Inktomi, where ice showed crystalline ice abundances between 33 percent and 61 percent. These patterns in ice crystallization are possibly attributable to increased heat generated during crater formation.

Mars Reconnaissance Orbiter and Opportunity observations of the Burns formation: Crater hopping at Meridiani Planum

NASA Astrophysics Data System (ADS)

Arvidson, R. E.; Bell, J. F., III; Catalano, J. G.; Clark, B. C.; Fox, V. K.; Gellert, R.; Grotzinger, J. P.; Guinness, E. A.; Herkenhoff, K. E.; Knoll, A. H.; Lapotre, M. G. A.; McLennan, S. M.; Ming, D. W.; Morris, R. V.; Murchie, S. L.; Powell, K. E.; Smith, M. D.; Squyres, S. W.; Wolff, M. J.; Wray, J. J.

2015-03-01

Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral (1.0-2.65 μm) along-track oversampled observations covering Victoria, Santa Maria, Endeavour, and Ada craters were processed to 6 m/pixel and used in combination with Opportunity observations to detect and map hydrated Mg and Ca sulfate minerals in the Burns formation. The strongest spectral absorption features were found to be associated with outcrops that are relatively young and fresh (Ada) or preferentially scoured of dust, soil, and coatings by prevailing winds. At Victoria and Santa Maria, the scoured areas are on the southeastern rims and walls, opposite to the sides where wind-blown sands extend out of the craters. At Endeavour, the deepest absorptions are in Botany Bay, a subdued and buried rim segment that exhibits high thermal inertias, extensive outcrops, and is interpreted to be a region of enhanced wind scour extending up and out of the crater. Ada, Victoria, and Santa Maria outcrops expose the upper portion of the preserved Burns formation and show spectral evidence for the presence of kieserite. In contrast, gypsum is pervasive spectrally in the Botany Bay exposures. Gypsum, a relatively insoluble evaporative mineral, is interpreted to have formed close to the contact with the Noachian crust as rising groundwaters brought brines close to and onto the surface, either as a direct precipitate or during later diagenesis. The presence of kieserite at the top of the section is hypothesized to reflect precipitation from evaporatively concentrated brines or dehydration of polyhydrated sulfates, in both scenarios as the aqueous environment evolved to very arid conditions.

Mars Reconnaissance Orbiter and Opportunity observations of the Burns formation: crater hopping at Meridiani Planum

USGS Publications Warehouse

R.E. Arvidson,; Bell, J.F.; Catalano, J.G.; Clark, B. C.; Fox, V.K.; Gellert, Ralf; Grotzinger, J.P.; Guinness, E.A.; Herkenhoff, Kenneth E.; Knoll, A.H.; Lapotre, M.G.A.; McLennan, S.M.; Ming, D. W.; Morris, R.V.; Murchie, S.L.; Powell, K. E.; Smith, M.D.; Squyres, S. W.; Wolff, M.J.; J.J. Wray,

2015-01-01

Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral (1.0–2.65 µm) along-track oversampled observations covering Victoria, Santa Maria, Endeavour, and Ada craters were processed to 6 m/pixel and used in combination with Opportunity observations to detect and map hydrated Mg and Ca sulfate minerals in the Burns formation. The strongest spectral absorption features were found to be associated with outcrops that are relatively young and fresh (Ada) or preferentially scoured of dust, soil, and coatings by prevailing winds. At Victoria and Santa Maria, the scoured areas are on the southeastern rims and walls, opposite to the sides where wind-blown sands extend out of the craters. At Endeavour, the deepest absorptions are in Botany Bay, a subdued and buried rim segment that exhibits high thermal inertias, extensive outcrops, and is interpreted to be a region of enhanced wind scour extending up and out of the crater. Ada, Victoria, and Santa Maria outcrops expose the upper portion of the preserved Burns formation and show spectral evidence for the presence of kieserite. In contrast, gypsum is pervasive spectrally in the Botany Bay exposures. Gypsum, a relatively insoluble evaporative mineral, is interpreted to have formed close to the contact with the Noachian crust as rising groundwaters brought brines close to and onto the surface, either as a direct precipitate or during later diagenesis. The presence of kieserite at the top of the section is hypothesized to reflect precipitation from evaporatively concentrated brines or dehydration of polyhydrated sulfates

Exposed Fractured Bedrock in the Central Pit of a Crater

NASA Image and Video Library

2016-11-09

This HiRISE image shows the central pit feature of an approximately 20-kilometer diameter complex crater in located at 304.480 degrees east, -11.860 degrees south, just north of the Valles Marineris. Here we can observe a partial ring of light-toned, massive and fractured bedrock, which has been exposed by the impact-forming event, and via subsequent erosion that typically obscure the bedrock of complex central features. Features such as this one are of particular interest as they provide scientists with numerous exposures of bedrock that can be readily observed from orbit and originate from the deep Martian subsurface. Unlike on Earth, plate tectonics do not appear to be active on Mars. Thus, much of the Martian subsurface is not directly observable through uplift, erosion and exposure of mountain chains, which provide the majority of bedrock exposures on Earth. Exposures of subsurface materials generated by these features provides us with some of the only "windows" into the subsurface geology. This makes the study of impact craters an invaluable source of information when trying to understand, not only the impact process, but also the composition and history of Mars. Although much of what we see here is composed of massive and fractured bedrock, there are zones of rock fragmentation, called "brecciation." These fragmented rocks (a.k.a., breccias) are best viewed in the eastern portion of the central pit, which was captured in a previous HiRISE image. Additionally, we see some occurrences of impact melt-bearing deposits that surround and coat the bedrock exposed within the central pit. Several dunes are on the surface throughout the central pit and surrounding crater floor. The mechanisms behind the formation of central features, particularly central pits, are not completely understood. Geologic mapping of these circumferential "mega" blocks of bedrock indicate radial and concentric fracturing that is consistent with deformation through uplift. The exposed bedrock shows well-expressed lineament features that are likely fractures and faults formed during the uplift process. Studies of the bedrock, and such structures in this image, allows us better to understand the formative events and physical processes responsible for their formation. Current research suggests that their formation is the result of some component of uplift followed by collapse. http://photojournal.jpl.nasa.gov/catalog/PIA21205

Complex crater formation: Insights from combining observations of shock pressure distribution with numerical models at the West Clearwater Lake impact structure

NASA Astrophysics Data System (ADS)

Rae, A. S. P.; Collins, G. S.; Grieve, R. A. F.; Osinski, G. R.; Morgan, J. V.

2017-07-01

Large impact structures have complex morphologies, with zones of structural uplift that can be expressed topographically as central peaks and/or peak rings internal to the crater rim. The formation of these structures requires transient strength reduction in the target material and one of the proposed mechanisms to explain this behavior is acoustic fluidization. Here, samples of shock-metamorphosed quartz-bearing lithologies at the West Clearwater Lake impact structure, Canada, are used to estimate the maximum recorded shock pressures in three dimensions across the crater. These measurements demonstrate that the currently observed distribution of shock metamorphism is strongly controlled by the formation of the structural uplift. The distribution of peak shock pressures, together with apparent crater morphology and geological observations, is compared with numerical impact simulations to constrain parameters used in the block-model implementation of acoustic fluidization. The numerical simulations produce craters that are consistent with morphological and geological observations. The results show that the regeneration of acoustic energy must be an important feature of acoustic fluidization in crater collapse, and should be included in future implementations. Based on the comparison between observational data and impact simulations, we conclude that the West Clearwater Lake structure had an original rim (final crater) diameter of 35-40 km and has since experienced up to 2 km of differential erosion.

Diamond Head Revisited with Ammonium Dichromate.

ERIC Educational Resources Information Center

Arrigoni, Edward

1981-01-01

The classroom demonstration using ammonium dichromate to simulate a volcanic eruption can be modified into a more dramatic and accurate representation of the geologic processes involved in the formation of a volcanic crater. The materials, demonstration setup, safety procedures, and applications to instruction are presented. (Author/WB)

The topography of Ceres and implications for the formation of linear surface structures

NASA Astrophysics Data System (ADS)

Buczkowski, D.; Otto, K.; Ruesch, O.; Scully, J. E. C.; Williams, D. A.; Mest, S. C.; Schenk, P.; Jaumann, R.; Nathues, A.; Preusker, F.; Park, R. S.; Raymond, C. A.; Russell, C. T.

2015-12-01

NASA's Dawn spacecraft began orbiting the dwarf planet Ceres in April 2015. Framing Camera data from the Approach (1.3 km/px) and Survey (415 m/px) orbits include digital terrain models derived from processing stereo images. These models have supported various scientific studies of the surface. The eastern hemisphere of Ceres is topographically higher than the western hemisphere. Some of linear structures on Ceres (which include grooves, pit crater chains, fractures and troughs) appear to be radial to the large basins Urvara and Yalode, and most likely formed due to impact processes. However, set of regional linear structures (RLS) that do not have any obvious relationship to impact craters are found on the eastern hemisphere topographic high region. Many of the longer RLS are comprised of smaller structures that have linked together, suggestive of en echelon fractures. Polygonal craters, theorized to form when pervasive subsurface fracturing affects crater formation [1], are widespread on Ceres [2], and those proximal to the RLS have straight crater rims aligned with the grooves and troughs, suggesting that the RLS are fracture systems. A cross-section of one RLS is displayed in FC images of the Occator crater wall. Comparing these images to the digital terrain models show 1) that the structure dips ~60º and 2) there is downward motion on the hanging wall, implying normal faulting. The digital terrain models also reveal the presence of numerous positive relief features with sub-circular shapes. These dome-like features have been tentatively interpreted as volcanic/magmatic features [3]; other possibilities include salt domes. Analog models of domal uplift in areas of regional extension [4] predict patterns of linear structures similar to those observed in the RLS near Occator. Utilizing topography data provided by the Ceres digital terrain models, we assess the relationship between the RLS and nearby domes and topographic high regions to determine the mechanism by which the RLS may have formed. [1] Thomas, P.C. et al. (1999) Icarus, doi: 10.1006/icar.1999.6121 [2] Otto et al. (2015) EPSC2015-284 [3] Ruesch et al. [this meeting] [4] Sims et al. (2013) AAPG Bulletin, doi: 10.1306/02101209136

Projectile-target mixing in melted ejecta formed during a hypervelocity impact cratering event

NASA Technical Reports Server (NTRS)

Evans, Noreen Joyce; Ahrens, Thomas J.; Shahinpoor, M.; Anderson, W. W.

1993-01-01

Tektites contain little to no projectile contamination while, in contrast, some distal ejecta deposits can be relatively projectile-rich (e.g. the Cretaceous-Tertiary (K-T) boundary clay). This compositional difference motivated an experimental study of hypervelocity target-projectile mixing processes. We hope to scale up the results from these experiments and apply them to terrestrial impact structures like the Chicxulub Crater, Yucutan, Mexico, the leading contender as the site for the impact that caused the mass extinction that marks the K-T boundary. Shock decomposition of the approximately 500m thickness of anhydrite, or greater thickness of limestone, in the target rocks at Chicxulub may have been a critical mechanism for either global cooling via SO3, and subsequently H2SO4, formation, or possibly, global warming via increased CO2 formation. Understanding target-projectile mixing processes during hypervelocity impact may permit more accurate estimates of the amount of potentially toxic, target-derived material reaching stratospheric heights.

Modeling Low Velocity Impacts: Predicting Crater Depth on Pluto

NASA Astrophysics Data System (ADS)

Bray, V. J.; Schenk, P.

2014-12-01

The New Horizons mission is due to fly-by the Pluto system in Summer 2015 and provides the first opportunity to image the Pluto surface in detail, allowing both the appearance and number of its crater population to be studied for the first time. Bray and Schenk (2014) combined previous cratering studies and numerical modeling of the impact process to predict crater morphology on Pluto based on current understanding of Pluto's composition, structure and surrounding impactor population. Predictions of how the low mean impact velocity (~2km/s) of the Pluto system will influence crater formation is a complex issue. Observations of secondary cratering (low velocity, high angle) and laboratory experiments of impact at low velocity are at odds regarding how velocity controls depth-diameter ratios: Observations of secondary craters show that these low velocity craters are shallower than would be expected for a hyper-velocity primary. Conversely, gas gun work has shown that relative crater depth increases as impact velocity decreases. We have investigated the influence of impact velocity further with iSALE hydrocode modeling of comet impact into Pluto. With increasing impact velocity, a projectile will produce wider and deeper craters. The depth-diameter ratio (d/D) however has a more complex progression with increasing impact velocity: impacts faster than 2km/s lead to smaller d/D ratios as impact velocity increases, in agreement with gas-gun studies. However, decreasing impact velocity from 2km/s to 300 m/s produced smaller d/D as impact velocity was decreased. This suggests that on Pluto the deepest craters would be produced by ~ 2km/s impacts, with shallower craters produced by velocities either side of this critical point. Further simulations to investigate whether this effect is connected to the sound speed of the target material are ongoing. The complex relationship between impact velocity and crater depth for impacts occurring between 300m/s and 10 km/s suggests that there might be a larger range of 'pristine' crater depths on Pluto than on bodies with higher mean impact velocity. This might affect our ability to define a pristine crater depth as a starting point for crater infill and relaxation studies.

The structural inventory of a small complex impact crater: Jebel Waqf as Suwwan, Jordan

NASA Astrophysics Data System (ADS)

Kenkmann, Thomas; Sturm, Sebastian; Krüger, Tim; Salameh, Elias; Al-Raggad, Marwan; Konsul, Khalil

2017-07-01

The investigation of terrestrial impact structures is crucial to gain an in-depth understanding of impact cratering processes in the solar system. Here, we use the impact structure Jebel Waqf as Suwwan, Jordan, as a representative for crater formation into a layered sedimentary target with contrasting rheology. The complex crater is moderately eroded (300-420 m) with an apparent diameter of 6.1 km and an original rim fault diameter of 7 km. Based on extensive field work, IKONOS imagery, and geophysical surveying we present a novel geological map of the entire crater structure that provides the basis for structural analysis. Parametric scaling indicates that the structural uplift (250-350 m) and the depth of the ring syncline (<200 m) are anomalously low. The very shallow relief of the crater along with a NE vergence of the asymmetric central uplift and the enhanced deformations in the up-range and down-range sectors of the annular moat and crater rim suggest that the impact was most likely a very oblique one ( 20°). One of the major consequences of the presence of the rheologically anisotropic target was that extensive strata buckling occurred during impact cratering both on the decameter as well as on the hundred-meter scale. The crater rim is defined by a circumferential normal fault dipping mostly toward the crater. Footwall strata beneath the rim fault are bent-up in the down-range sector but appear unaffected in the up-range sector. The hanging wall displays various synthetic and antithetic rotations in the down-range sector but always shows antithetic block rotation in the up-range sector. At greater depth reverse faulting or folding is indicated at the rim indicating that the rim fault was already formed during the excavation stage.

Early Mars: A regional assessment of denudation chronology

NASA Technical Reports Server (NTRS)

Maxwell, T. A.; Craddock, R. A.

1993-01-01

Within the oldest highland units on Mars, the record of crater degradation indicates that fluvial resurfacing was responsible for modifying the Noachian through middle-Hesperian crater population. Based on crater frequency in the Noachian cratered terrain, age/elevation relations suggest that the highest exposures of Noachian dissected and plateau units became stabilized first, followed by successively lower units. In addition, studies of drainage networks indicate that the frequency of Noachian channels is greatest at high elevations. Together, these observations provide strong evidence of atmospheric involvement in volatile recycling. The long time period of crater modification also suggests that dendritic highland drainage was not simply the result of sapping by release of juvenile water, because the varied geologic units as well as the elevation dependence of stability ages makes it unlikely that subsurface recycling could provide a continuous supply of water for channel formation by sapping. While such geomorphic constraints on volatile history have been established by crater counts and stratigraphic relations using the 1:2M photomosaic series, photogeologic age relationships at the detailed level are needed to establish a specific chronology of erosion and sedimentation. Age relations for discrete erosional slopes and depositional basins will help refine ages of fluvial degradation, assess effectiveness of aeolian processes, and provide a regional chronology of fluvial events.

Ancient fluvial processes in the equatorial highlands of Mars

NASA Technical Reports Server (NTRS)

Craddock, Robert A.; Maxwell, Ted A.

1991-01-01

Martian highland craters typically lack ejecta deposits, have no noticeable rim, and are flat floored. In addition, crater size frequency distribution curves show that highland craters have depleted populations less than 20 km in diameter. A variety of processes have been suggested to explain these observations including deposition of aeolian or volcanic materials up to the crater rim crests, thermal creep, terrain softening, and mass wasting. However, none of these processes adequately explains both the crater morphology and population distribution. In order to explain both the Martian highland crater morphology and population distribution, a fluvial process is proposed which is capable of removing the loose crater rim material. The resulting effect is to decrease the crater diameter, thereby causing the population curves to bendover. The eroded material is redistributed, burying or partially burying smaller diameter craters before complete erosion. This material may also be deposited into local topographic lows, creating the depositional basins observed. A fluvial process explains both sets of observations: crater morphology and crater population distribution curves.

A Triple Crater

NASA Image and Video Library

2017-06-01

This image from NASA's Mars Reconnaissance Orbiter shows an elongated depression from three merged craters. The raised rims and ejecta indicate that these are impact craters rather than collapse or volcanic landforms. The pattern made by the ejecta and the craters suggest this was a highly oblique (low angle to the surface) impact, probably coming from the west. There may have been three major pieces flying in close formation to make this triple crater. https://photojournal.jpl.nasa.gov/catalog/PIA21652

Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure

USGS Publications Warehouse

Self-Trail, Jean M.; Edwards, Lucy E.; Litwin, Ronald J.

2009-01-01

Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)–U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of water- saturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dino-flagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As a result, intact Paleogene clasts in Eyreville cores are rare, but clasts of semilithified Potomac Formation silts and clays are common.

Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure

USGS Publications Warehouse

,; Edwards, L.E.; Litwin, R.J.

2009-01-01

Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of watersaturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dinoflagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As a result, intact Paleogene clasts in Eyreville cores are rare, but clasts of semilithified Potomac Formation silts and clays are common. ?? 2009 The Geological Society of America.

A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit

NASA Astrophysics Data System (ADS)

Wilson, Perry B.

2006-11-01

By destructive breakdown we mean a breakdown event that results in surface melting over a macroscopic area in a high E-field region of an accelerator structure. A plasma forms over the molten area, bombarding the surface with an intense ion current (˜108 A/cm2), equivalent to a pressure of about a thousand Atmospheres. This pressure in turn causes molten copper to migrate away from the iris tip, resulting in measurable changes in the iris shape. The breakdown process can be roughly divided into four stages: (1) the formation of "plasma spots" at field emission sites, each spot leaving a crater-like footprint; (2) crater clustering, and the formation of areas with hundreds of overlapping craters; (3) surface melting in the region of a crater cluster; (4) the process after surface melting that leads to destructive breakdown. The physics underlying each of these stages is developed, and a comparison is made between the theory and experimental evidence whenever possible. The key to preventing breakdown lies in stage (3). A single plasma spot emits a current of several amperes, a portion of which returns to impact the surrounding area with a power density on the order 107 Watt/cm2. This power density is not quite adequate to melt the surrounding surface on a time scale short compared to the rf pulse length. In a crater field, however, the impact areas from multiple plasma spots overlap to provide sufficient power density for surface melting over an area on the order of 0.1 mm2 or more. The key to preventing breakdown is to choose an iris tip material that requires the highest power density (proportional to the square of the rf surface field) for surface melting, taking into account the penetration depth of the impacting electrons. The rf surface field required for surface melting (relative to copper) has been calculated for a large number elementary metals, plus stainless-steel and carbon.

Equatorial Layered Deposits in Arabia Terra, Mars: Facies and Process Variability

NASA Astrophysics Data System (ADS)

Pondrelli, M.; Rossi, A.; van Gasselt, S.; Le Deit, L.; Glamoclija, M.; Cavalazzi, B.; Franchi, F.; Fueten, F.; Hauber, E.; Zegers, T.

2012-12-01

Genetic mechanisms proposed to explain Equatorial Layered Deposits (ELDs) formation include subglacial volcanism, aeolian/airfall, lacustrine, lacustrine/volcanic and spring-fed deposition. ELDs have been frequently shown to consist of sulfates (e.g. Gendrin et al., 2005) that might form as a response to evaporation in a playa environment (Hoefen et al., 2003) or during spring precipitation (e.g. Allen and Oehler, 2008; Rossi et al., 2008). The importance of groundwater-dominated hydrological systems was proposed to explain the formation of light-toned deposits in Meridiani Planum and Arabia Terra (e.g. Andrews-Hanna et al. 2007). Additionally, fluid expulsion processes have been invoked to explain the formation of mounds within the light-toned deposits in Arabia Terra (Allen and Oehler, 2008; Rossi et al., 2008; Pondrelli et al., 2011). Potential for habitable conditions of both playa and spring-related settings (Cavalazzi et al., 2007; Glamoclija et al., 2011) coupled with the high preservation potential within sulfates (Panieri et al., 2010), make these deposits a good candidate to understand the potential past habitability of the planet. In order to investigate ELDs genesis, an area in the vicinity of Firsoff crater, where ELDs are present within and outside the craters, was selected for geological mapping and analysis of the landforms and their association using the available dataset, including CRISM in order to infer ELDs composition. Within Firsoff crater, ELDs form a bulge that can be estimated to be at least a few hundred meters thick, while, outside the craters, ELDs form flat-lying deposits. Although heavily eroded by wind and carved by yardangs, several morphologies within the ELDs in the craters seem to be depositional, which would exclude that the entire Firsoff basin had been originally filled by ELDs. Within craters, ELDs consist of roughly meter thick layers draping and onlapping the substratum. They appear affected by polygonal patterns with no evidence of sedimentary structures. Polyhydrated sulfates have been detected. At places, ELDs appear to be linked to and possibly sourced from tectonically controlled lineaments. Large cone-shaped mounds (100 to 500 m) are situated locally on top of ELDs. They consist of boulders embedded in a matrix, and about one-third of them display an orifice at their top. Outside of the craters, ELDs show large-scale cross stratification associated to duneforms, which suggests an aeolian origin possibly associated to playa deposits. We distinguish between fluid expulsion ELDs forming within the crater and aeolian ELDs outside and possibly inside the craters. Fluid expulsion ELDs would result from groundwater upwelling and following evaporitic precipitation, whereas aeolian ELDs would result from reworking and redeposition of the spring ELDs. References Allen and Oehler (2008), Astrobiology, 8, 1093-1112. Andrews-Hanna et al. (2007), Nature, 446, 163-166. Cavalazzi et al. (2007), Sed. Geol., 200, 73-88. Gendrin et al. (2005), Science, 307, 1587. Glamoclija et al. (2011), Geomicrob. J., 29, 733-751. Hoefen et al. (2003), Science, 302, 627-630. Panieri et al. (2010), Geobiology, 8, 101-111. Pondrelli et al. (2011), EPSL, 304, 511-519. Rossi et al. (2008), JGR, 113(8).

Vesta and Ceres by the light of Dawn

NASA Astrophysics Data System (ADS)

Russell, Christopher T.

2015-11-01

Ceres and Vesta are the most massive bodies in the main asteroid belt. They both appear to be intact protoplanets whose growth may have been drastically altered by the concomitant formation of Jupiter.. These two bodies have witnessed 4.6 Ga of solar system history, much, but not all, of which has been recorded in their surfaces. Dawn’s objective is to interview these two witnesses to learn as much as possible about the early epoch. These bodies are protoplanets, our best archetypes of the early building blocks of the terrestrial planets. In particular, siderophile elements in the Earth’s core were probably first segregated in Vesta-like bodies, and its water was likely first condensed in Ceres-like bodies.Many of the basaltic achondrites originated from a common parent body. Dawn verified that Vesta was consistent with that parent body. hence strengthening geochemical inferences from these samples on the formation and evolution of the solar system and supporting hypotheses for their delivery from Vesta to Earth. Ceres has not revealed itself with a meteoritic record. While the surface is scarred with craters, it is probable that the ejecta from the crater-forming event created little competent material from the icy crust and any such ejected projectiles that reached Earth might have disintegrated upon entry into the Earth’s atmosphere.Ceres’ surface differs greatly from Vesta’s. Plastic or fluidized mass wasting is apparent, as are many irregularly shaped craters, including many polygonal crater forms. There are many central-pit craters possibly caused by volatilization of the crust in the center of the impact. There are also many central-peak craters, which were made by rebound or pingo-like formation processes. Bright deposits dot the landscape, which are possibly salt-rich, suggesting fluvial activity beneath the crust. Observations of the brightest spots on Ceres could suggest sublimation from the surface of the bright area, which may be water vapor driven, as Herschel observations suggest. Ceres is not only the most massive body in the asteroid belt but also possibly the most active.

Numerical modeling of Stickney crater and its aftermath

NASA Astrophysics Data System (ADS)

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 Syal, M. et al. (this meeting); [2] Schwartz, S.R. et al. 2012, Granul. Matter 14, 363; [3] Willner, K. et al. 2010, E. Earth Planet. Sci. Lett. 294, 541; [4] Wilson, L. & Head, J.W. 2015, Planet. Space Sci. 105, 26.

Nature of the Martian uplands: Effect on Martian meteorite age distribution and secondary cratering

NASA Astrophysics Data System (ADS)

Hartmann, William K.; Barlow, Nadine G.

2006-10-01

Martian meteorites (MMs) have been launched from an estimated 5-9 sites on Mars within the last 20 Myr. Some 80-89% of these launch sites sampled igneous rock formations from only the last 29% of Martian time. We hypothesize that this imbalance arises not merely from poor statistics, but because the launch processes are dominated by two main phenomena: first, much of the older Martian surface is inefficient in launching rocks during impacts, and second, the volumetrically enormous reservoir of original cumulate crust enhances launch probability for 4.5 Gyr old rocks. There are four lines of evidence for the first point, not all of equal strength. First, impact theory implies that MM launch is favored by surface exposures of near-surface coherent rock (≤102 m deep), whereas Noachian surfaces generally should have ≥102 m of loose or weakly cemented regolith with high ice content, reducing efficiency of rock launch. Second, similarly, both Mars Exploration Rovers found sedimentary strata, 1-2 orders of magnitude weaker than Martian igneous rocks, favoring low launch efficiency among some fluvial-derived Hesperian and Noachian rocks. Even if launched, such rocks may be unrecognized as meteorites on Earth. Third, statistics of MM formation age versus cosmic-ray exposure (CRE) age weakly suggest that older surfaces may need larger, deeper craters to launch rocks. Fourth, in direct confirmation, one of us (N. G. B.) has found that older surfaces need larger craters to produce secondary impact crater fields (cf. Barlow and Block 2004). In a survey of 200 craters, the smallest Noachian, Hesperian, and Amazonian craters with prominent fields of secondaries have diameters of ˜45 km, ˜19 km, and ˜10 km, respectively. Because 40% of Mars is Noachian, and 74% is either Noachian or Hesperian, the subsurface geologic characteristics of the older areas probably affect statistics of recognized MMs and production rates of secondary crater populations, and the MM and secondary crater statistics may give us clues to those properties.

The Chesapeake Bay Impact Crater: An Educational Investigation for Students into the Planetary Impact Process and its Environmental Consequences

NASA Technical Reports Server (NTRS)

Levine, Arlene S.

2008-01-01

Planetary impact craters are a common surface feature of many planetary bodies, including the Earth, the Moon, Mars, Mercury, Venus, and Jupiter s moons, Ganymede and Callisto. The NASA Langley Research Center in Hampton, VA, is located about 5 km inside the outer rim of the Chesapeake Bay Impact Crater. The Chesapeake Bay Impact Crater, with a diameter of 85 km is the sixth largest impact crater on our planet. The U.S. Geological Survey (USGS), in collaboration with the NASA Langley Research Center, the Virginia Department of Environmental Quality (VDEQ), the Hampton Roads Planning District Commission (HRPDC), and the Department of Geology of the College of William and Mary (WM) drilled into and through the crater at the NASA Langley Research Center and obtained a continuous core to a depth of 2075.9 ft (632.73 meters) from the Chesapeake Bay Impact Crater. At the NASA Langley location, the granite basement depth was at 2046 ft (623.87 meters). This collaborative drilling activity provided a unique educational opportunity and ongoing educational partnership between USGS, NASA Langley and the other collaborators. NASA Langley has a decade-long, ongoing educational partnership with the Colonial Coast Council of the Girl Scouts. The core drilling and on site analysis and cataloguing of the core segments provided a unique opportunity for the Girl Scouts to learn how geologists work in the field, their tools for scientific investigation and evaluation, how they perform geological analyses of the cores in an on-site tent and learn about the formation of impact craters and the impact of impacting bodies on the sub-surface, the surface, the oceans and atmosphere of the target body. This was accomplished with a two-part activity. Girl Scout day camps and local Girl Scout troops were invited to Langley Research Center Conference Center, where more than 300 Girl Scouts, their leaders and adult personnel were given briefings by scientists and educators from the USGS, NASA, VDEQ, HRPDC and WM on the principles of geology, the formation of impact craters, the consequences of the impacting body on the atmosphere, ocean, surface and sub-surface, the geological, chemical and biological analyses of the core and the cataloguing and storage of the core segments, etc. After the briefings, the Girl Scouts visited the drilling site where they inspected the core drilling rig, examined the core samples and discussed the drilling procedures, cores and interpretation of the cores with scientists and educators from the organizations conducting the core drilling. Demonstrations at the drilling site included demonstrations of impacting objects hitting multi-colored layered mud targets at different angles of entry. The multi-colored layers of mud were instructive in mapping out the distribution of impact-ejected material around the impact crater. The presentation will include a series of photographs of the Girl Scout participating in activities at the Chesapeake Bay Impact Crater drill site, including retrieving cores from the drilling rig, inspecting the core samples and participating in the impact-crater formation demonstrations.

Crater-associated dark diffuse features on Venus: Properties of surficial deposits and their evolution

NASA Astrophysics Data System (ADS)

Bondarenko, N. V.; Head, J. W.

2009-03-01

In order to assess the nature of crater-associated radar-dark diffuse features (DDFs) on Venus and to understand their formation and evolution, we analyzed Magellan radar roughness, emissivity, and reflectivity data in the vicinity of craters accompanied by these features. Following others, we assumed that DDFs are deposits (mantles) of ejected material emplaced during formation of the impact crater. The majority of radar-dark parabolas (the youngest DDFs) are characterized by a smooth mantle-atmosphere interface having low root-mean-square (rms) slopes on scales of 1-100 m, as derived from Magellan altimeter data. Older DDFs also often have areas with low rms slopes, suggesting that the mantle rms slopes can be preserved for geologically long periods of time. Some parabolas and older DDFs have asymmetric small-scale (decimeter-scale) relief that is interpreted to be dunes that formed as a result of eolian processes. This implies that the mantle material is mobile and can saltate under the influence of wind action. On average, aging of these features is accompanied by a decrease of mantle material dielectric permittivity. The most efficient mechanism for parabola degradation seems to be the removal of mantle material from the site of initial deposition by subsequent winds. We found a few examples of features that could be interpreted to be the result of in situ modification of the primary mantle.

Marine-target craters on Mars? An assessment study

USGS Publications Warehouse

Ormo, J.; Dohm, J.M.; Ferris, J.C.; Lepinette, A.; Fairen, A.G.

2004-01-01

Observations of impact craters on Earth show that a water column at the target strongly influences lithology and morphology of the resultant crater. The degree of influence varies with the target water depth and impactor diameter. Morphological features detectable in satellite imagery include a concentric shape with an inner crater inset within a shallower outer crater, which is cut by gullies excavated by the resurge of water. In this study, we show that if oceans, large seas, and lakes existed on Mars for periods of time, marine-target craters must have formed. We make an assessment of the minimum and maximum amounts of such craters based on published data on water depths, extent, and duration of putative oceans within "contacts 1 and 2," cratering rate during the different oceanic phases, and computer modeling of minimum impactor diameters required to form long-lasting craters in the seafloor of the oceans. We also discuss the influence of erosion and sedimentation on the preservation and exposure of the craters. For an ocean within the smaller "contact 2" with a duration of 100,000 yr and the low present crater formation rate, only ???1-2 detectable marine-target craters would have formed. In a maximum estimate with a duration of 0.8 Gyr, as many as 1400 craters may have formed. An ocean within the larger "contact 1-Meridiani," with a duration of 100,000 yr, would not have received any seafloor craters despite the higher crater formation rate estimated before 3.5 Gyr. On the other hand, with a maximum duration of 0.8 Gyr, about 160 seafloor craters may have formed. However, terrestrial examples show that most marine-target craters may be covered by thick sediments. Ground penetrating radar surveys planned for the ESA Mars Express and NASA 2005 missions may reveal buried craters, though it is uncertain if the resolution will allow the detection of diagnostic features of marine-target craters. The implications regarding the discovery of marine-target craters on Mars is not without significance, as such discoveries would help address the ongoing debate of whether large water bodies occupied the northern plains of Mars and would help constrain future paleoclimatic reconstructions. ?? Meteoritical Society, 2004.

Paleomagnetic and Magnetostratigraphic Studies in Drilling Projects of Impact Craters - Recent Studies, Challenges and Perspectives

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Velasco-Villarreal, M.; Perez-Cruz, L. L.

2013-05-01

Paleomagnetic studies have long been successfully carried out in drilling projects, to characterize the borehole columns and to investigate the subsurface structure and stratigraphy. Magnetic susceptibility logging and magnetostratigraphic studies provide data for lateral correlation, formation evaluation, azimuthal core orientation, physical properties, etc., and are part of the tools available in the ocean and continental drilling programs. The inclusion of continuous core recovery in scientific drilling projects have greatly expanded the range of potential applications of paleomagnetic and rock magnetic studies, by allowing laboratory measurements on core samples. For this presentation, we concentrate on drilling studies of impact structures and their usefulness for documenting the structure, stratigraphy and physical properties at depth. There are about 170-180 impact craters documented in the terrestrial record, which is a small number compared to what is observed in the Moon, Mars, Venus and other bodies of the solar system. Of the terrestrial impact craters, only a few have been studied by drilling. Some craters have been drilled as part of industry exploration surveys and/or academic projects, including notably the Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake and El gygytgyn craters. Drilling of terrestrial craters has proved important in documenting the shallow stratigraphy and structure, providing insight on the cratering and impact dynamics. Questions include several that can only be addressed by retrieving core samples and laboratory analyses. Paleomagnetic, rock magnetic and fabric studies have been conducted in the various craters, which are here summarized with emphasis on the Chicxulub crater and Yucatan carbonate platform. Chicxulub is buried under a kilometer of younger sediments, making drilling an essential tool. Oil exploration included several boreholes, and additionally we have drilled 11 boreholes with continuous core recovery. Contributions and limitations of paleomagnetism for investigating the impact age, crater stratigraphy, cratering, ejecta emplacement, impact dynamics, hydrothermal system and post-impact processes are discussed.

Preliminary Geological Map of the Ac-H-2 Coniraya Quadrangle of Ceres: An Integrated Mapping Study Using Dawn Spacecraft Data

NASA Astrophysics Data System (ADS)

Hiesinger, H.; Pasckert, J. H.; Williams, D. A.; Crown, D. A.; Mest, S. C.; Buczkowski, D.; Schenk, P.; Scully, J. E. C.; Jaumann, R.; Roatsch, T.; Preusker, F.; Platz, T.; Nathues, A.; Hoffmann, M.; Marchi, S.; De Sanctis, M. C.; Russell, C. T.; Raymond, C. A.

2015-12-01

To better understand the geologic history of dwarf planet Ceres, the surface has been divided into 15 quadrangles that are systematically mapped on the basis of images obtained by NASA's Dawn spacecraft, which began orbiting Ceres in April 2015. We will report on preliminary mapping results for the Ac-H-2 Coniraya Quadrangle based on Framing Camera (FC) mosaics from the Dawn Approach (1.3 km/px) and Survey (415 m/px) orbits. This quadrangle is located between 21-66°N and 0-90°E and is dominated by mostly highly degraded impact craters of diameters between 50 and 200 km and clusters of small- to midsize impact craters. Color data show that this quadrangle is generally darker than most regions of the southern hemisphere. Two prominent impact craters in this quadrangle have been named Coniraya and Gaue crater, respectively. Coniraya is the largest more or less intact impact crater with a diameter of 136 km, centered at 65.8°N/40.5°E. It appears shallow and its crater rim is heavily degraded but still continuous. At the current image resolution, textural differences between the interior and exterior of the crater are not visible. With a diameter of 84 km, Gaue crater appears to be the freshest large impact crater in this quadrangle. It is located at the eastern border of the Coniraya Quadrangle with a small central peak at 30°N/85.7°E. The crater rim is quite sharp and the ejecta blanket can be traced around the crater to a distance of ~200km from the crater center. Most of the crater floor around the central peak is covered by a smooth uniform unit with a lower impact crater population than the surrounding surfaces. Color data show that this smooth unit is darker than the surrounding surfaces. A similar unit can be found on the floor of a complex cluster of 10-56 km diameter craters at 32°N/40°E. With upcoming higher resolution data we will refine our geologic map and will specifically investigate possible formation processes of these smooth units.

Excavation of buried hydrated minerals on Mars by impact cratering? (Invited)

NASA Astrophysics Data System (ADS)

Carter, J.; Poulet, F.; Loizeau, D.; Bibring, J.

2010-12-01

Impact cratering is a key process when studying Mars’s past aqueous environments. It is a widespread and dynamic process which has been active throughout Mars’s history, especially during the Noachian era. Noachian-aged hydrated minerals have been reported on Mars (e.g. [1, 2]) and provide strong constrains on the alleged early wet Martian environment [3]. Our knowledge of this early wet environment will be greatly improved if we understand how hydrated minerals are formed, modified or destroyed by impact processes. One main consequence of impact cratering is the excavation of buried material. Excavated material is found in walls, ejecta and central uplifts in the case of large complex craters. It may originate from the deeply buried crust or subsurface, depending on crater size [4]. In this case craters act as natural boreholes that allow orbital spectroscopic inquiry of otherwise hidden material and is of great importance when investigating the aqueous alteration of Mars. This process has proven particularly useful when studying the northern crust of Mars which is covered by a thick mantling unit [5]. Large craters have penetrated the cover and exhumed buried hydrated crustal material, including the low-grade metamorphic mineral prehnite and there is evidence that the ancient crust has been altered by water down to kilometer depths, both in the northern plains and southern highlands [6]. Using the OMEGA and CRISM [7, 8] near-infrared hyperspectral instruments currently in orbit around Mars we have mapped surface exposures of hydrated minerals and found that many are associated with impact structures [9]. Here we report how detailed analysis of these sites reveal exposures of various hydrated minerals including phyllosilicates, zeolites and sulfates, associated with crater central uplifts, floors, walls, rims and ejecta. We focus on the heavily cratered Tyrrhena Terra region of Mars as well as the large northern plain craters. In both cases, excavation of buried, pre-existing phyllosilicates is thought to be the driving process. Other hydrated mineral formation pathways linked with impact cratering include impact-induced hydrothermal alteration [10-12], shock-induced and post-impact changes to mineral composition. [1]Poulet et al., Nature 438, 623 (2005). [2]Murchie et al., J. Geophys. Res. 114, E00D06 (2009). [3]Bibring et al., Science 312, 5772 (2006). [4]Baratoux et al., J. Geophys. Res. 112, E08S05 (2007). [5]Tanaka et al., J. Geophys. Res. 108, (E4), 8043 (2003). [6]Carter et al., Science 328, 1682 (2010). [7]Bibring et al., Eur. Space Agency Spec. Pub. 1240, 37 (2004). [8]Murchie et al., J. Geophys. Res. 114, E00D07 (2009). [9]Carter et al., Proc. Lunar Planet. Sci. Conf. 40, abstr. 2028 (2009). [10]Abramov and Kring, J. Geophys. Res. 110, (E12), E12S09 (2005). [11]Schwenzer and Kring, Geology 37, 1091 (2009). [12]Marzo et al., Icarus 208, 667-683 (2010).

Impact structures in Africa: A review

PubMed Central

Reimold, Wolf Uwe; Koeberl, Christian

2014-01-01

More than 50 years of space and planetary exploration and concomitant studies of terrestrial impact structures have demonstrated that impact cratering has been a fundamental process – an essential part of planetary evolution – ever since the beginning of accretion and has played a major role in planetary evolution throughout the solar system and beyond. This not only pertains to the development of the planets but to evolution of life as well. The terrestrial impact record represents only a small fraction of the bombardment history that Earth experienced throughout its evolution. While remote sensing investigations of planetary surfaces provide essential information about surface evolution and surface processes, they do not provide the information required for understanding the ultra-high strain rate, high-pressure, and high-temperature impact process. Thus, hands-on investigations of rocks from terrestrial impact craters, shock experimentation for pressure and temperature calibration of impact-related deformation of rocks and minerals, as well as parameter studies pertaining to the physics and chemistry of cratering and ejecta formation and emplacement, and laboratory studies of impact-generated lithologies are mandatory tools. These, together with numerical modeling analysis of impact physics, form the backbone of impact cratering studies. Here, we review the current status of knowledge about impact cratering – and provide a detailed account of the African impact record, which has been expanded vastly since a first overview was published in 1994. No less than 19 confirmed impact structures, and one shatter cone occurrence without related impact crater are now known from Africa. In addition, a number of impact glass, tektite and spherule layer occurrences are known. The 49 sites with proposed, but not yet confirmed, possible impact structures contain at least a considerable number of structures that, from available information, hold the promise to be able to expand the African impact record drastically – provided the political conditions for safe ground-truthing will become available. The fact that 28 structures have also been shown to date NOT to be of impact origin further underpins the strong interest in impact in Africa. We hope that this review stimulates the education of students about impact cratering and the fundamental importance of this process for Earth – both for its biological and geological evolution. This work may provide a reference volume for those workers who would like to search for impact craters and their ejecta in Africa. PMID:27065753

Iapetus: Unique Surface Properties and a Global Color Dichotomy from Cassini Imaging

NASA Astrophysics Data System (ADS)

Denk, Tilmann; Neukum, Gerhard; Roatsch, Thomas; Porco, Carolyn C.; Burns, Joseph A.; Galuba, Götz G.; Schmedemann, Nico; Helfenstein, Paul; Thomas, Peter C.; Wagner, Roland J.; West, Robert A.

2010-01-01

Since 2004, Saturn’s moon Iapetus has been observed repeatedly with the Imaging Science Subsystem of the Cassini spacecraft. The images show numerous impact craters down to the resolution limit of ~10 meters per pixel. Small, bright craters within the dark hemisphere indicate a dark blanket thickness on the order of meters or less. Dark, equator-facing and bright, poleward-facing crater walls suggest temperature-driven water-ice sublimation as the process responsible for local albedo patterns. Imaging data also reveal a global color dichotomy, wherein both dark and bright materials on the leading side have a substantially redder color than the respective trailing-side materials. This global pattern indicates an exogenic origin for the redder leading-side parts and suggests that the global color dichotomy initiated the thermal formation of the global albedo dichotomy.

Iapetus: unique surface properties and a global color dichotomy from Cassini imaging.

PubMed

Denk, Tilmann; Neukum, Gerhard; Roatsch, Thomas; Porco, Carolyn C; Burns, Joseph A; Galuba, Götz G; Schmedemann, Nico; Helfenstein, Paul; Thomas, Peter C; Wagner, Roland J; West, Robert A

2010-01-22

Since 2004, Saturn's moon Iapetus has been observed repeatedly with the Imaging Science Subsystem of the Cassini spacecraft. The images show numerous impact craters down to the resolution limit of approximately 10 meters per pixel. Small, bright craters within the dark hemisphere indicate a dark blanket thickness on the order of meters or less. Dark, equator-facing and bright, poleward-facing crater walls suggest temperature-driven water-ice sublimation as the process responsible for local albedo patterns. Imaging data also reveal a global color dichotomy, wherein both dark and bright materials on the leading side have a substantially redder color than the respective trailing-side materials. This global pattern indicates an exogenic origin for the redder leading-side parts and suggests that the global color dichotomy initiated the thermal formation of the global albedo dichotomy.

Geologic Mapping of the Av-11 Pinaria Quadrangle of Asteroid 4 Vesta

NASA Astrophysics Data System (ADS)

Schenk, P.; Hoogenboom, T.; Williams, D.; Yingst, R. A.; Jaumann, R.; Gaskell, R.; Preusker, F.; Nathues, A.; Roatsch, T.

2012-04-01

As part of the Dawn's orbital mapping investigation of Vesta, the Science Team is conducting geologic mapping of the surface in the form of 15 quadrangle maps, including quadrangle Av-11 (Pinaria). The base map is a monochrome Framing Camera (FC) mosaic at ~70 m/pixel, supplemented by Digital Terrain Models (DTM) and FC color ratio images, both at ~250 m/pixel, slope and contour maps, and Visible and Infrared (VIR) hyperspectral images. Av-11 straddles the 45-degree longitude in the South Polar Region, and is dominated by the rim of the ~505 km south polar topographic feature, Rheasilvia. Sparsely cratered (relatively), Av-11 is dominated by a 20 km high rim scarp (Matronalia Rupes) and by arcuate ridges and troughs forming a radial to spiral pattern across the basin floor. Primary geologic features of Av-11 include the following. Ridge-and-groove terrain radiating arcuately from the central mound unit, interpreted to be structural disruption of the basin floor associated with basin formation. The largest crater in Av-11 is Pinaria (37 km). Mass wasting deposits are observed on its floor. Secondary crater chains and fields are also evident. Mass wasting observed along Rheasilvia rim scarp and in the largest craters indicates scarp failure is a significant process. Parallel fault scarps mark this deposit of slumped debris at the base of 20 km high Matronalia Rupes, which may have formed during or shortly after basin excavation. We interpret most of these deposits as slump material emplaced as a result of the effects of basin formation and collapse. Lobate materials are characterized by lineations and lobate scarps and interpreted as Rheasilvia ejecta deposit outside Rheasilvia rim (the smoothest terrain on Vesta), and are consistent with formation by ejecta. Partial burial of older craters near the edge of these deposits are also observed.

Foraminiferal repopulation of the late Eocene Chesapeake Bay impact crater

USGS Publications Warehouse

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.

Characterizing the Early Impact Bombardment

NASA Technical Reports Server (NTRS)

Bogard, Donald D.

2005-01-01

The early bombardment revealed in the larger impact craters and basins on the moon was a major planetary process that affected all bodies in the inner solar system, including the Earth and Mars. Understanding the nature and timing of this bombardment is a fundamental planetary problem. The surface density of lunar impact craters within a given size range on a given lunar surface is a measure of the age of that surface relative to other lunar surfaces. When crater densities are combined with absolute radiometric ages determined on lunar rocks returned to Earth, the flux of large lunar impactors through time can be estimated. These studies suggest that the flux of impactors producing craters greater than 1 km in diameter has been approximately constant over the past approx. 3 Gyr. However, prior to 3.0 - 3.5 Gyr the impactor flux was much larger and defines an early bombardment period. Unfortunately, no lunar surface feature older than approx. 4 Gyr is accurately dated, and the surface density of craters are saturated in most of the lunar highlands. This means that such data cannot define the impactor flux between lunar formation and approx. 4 Gyr ago.

A meteorite crater on Earth formed on September 15, 2007: The Carancas hypervelocity impact

NASA Astrophysics Data System (ADS)

Tancredi, G.; Ishitsuka, J.; Schultz, P. H.; Harris, R. S.; Brown, P.; Revelle, D. O.; Antier, K.; Le Pichon, A.; Rosales, D.; Vidal, E.; Varela, M. E.; Sánchez, L.; Benavente, S.; Bojorquez, J.; Cabezas, D.; Dalmau, A.

2009-01-01

On September 15, 2007, a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of Lake Titicaca. In the community of Carancas (Peru), a 13.5 m crater and several fragments of a stony meteorite were found close to the site of the impact. The Carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater-forming meteorite impact on Earth. We present several lines of evidence that suggest that the Carancas crater was a hypervelocity impact. An event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the Earth’s atmosphere, therefore it challenges our present models of entry dynamics. We discuss alternatives to explain this particular event. This emphasizes the weakness in the pervasive use of “average” parameters (such as tensile strength, fragmentation behavior and ablation behavior) in current modeling efforts. This underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes.

Calculation of ejecta thickness and structural uplift for Lunar and Martian complex crater rims.

NASA Astrophysics Data System (ADS)

Krüger, Tim; Sturm, Sebastian; Kenkmann, Thomas

2014-05-01

Crater rims of simple and complex craters have an elevation that is formed during the excavation stage of crater formation. For simple crater rims it is believed that the elevation is due to the sum of two equal parts, the thickness of the most proximal impact ejecta blanket (overturned flap) plus the thickness that results from plastic deformation including injection [1, 2, 3]. We intend to measure and quantify the kinematics of mass movements, especially concerning the question why complex impact craters have elevated crater rims like simple craters and precisely constrain the ejecta thickness and structural uplift of Lunar and Martian crater rims to understand what the main contributor to the elevated rim is [4]. We investigated a pristine 16 km-diameter unnamed Martian complex crater (21.52°N, 184.35°) and the lunar complex craters Bessel (21.8°N, 17.9°E) 16 km in diameter and Euler (23.3°N, 29.2°W) 28 km in diameter [5, 6]. In the crater walls of these craters we found columnar lavas on Mars and basaltic layering on the Moon. We used the uppermost layers of these exposed outcrops along the crater wall to determine the dip of the target rocks (Mars) and to distinguish between the bedrock and the overlying ejecta. We precisely measured the structural uplift and ejecta thickness of these complex craters. The unnamed crater on Mars has a mean rim height of 375.75 m, with a structural uplift of 233.88 m (57.44%), exposed as columnar lavas and the superposing ejecta has a height of 141.87 m (43.56%). For the Lunar complex crater Euler the mean total rim height is 790 ± 100 m, with a minimal structural uplift of 475 ± 100 m (60 ± 10 %), exposed as basaltic layers [e.g., 7, 8] and a maximum ejecta thickness of 315 ± 100 m (40 ± 10%). The Lunar complex crater Bessel has a total rim height of 430 ± 15 m , with a minimal structural uplift of 290 ± 15 m (67 ± 3 %), exposed as basaltic layers and a maximum ejecta thickness of 140 ± 115 m (33 ± 3%). For the Martian crater, the calculated structural uplift has a value of 215.83 m [9]. For Euler and Bessel crater calculated values for the structural uplift are 310.76 m and 262.8 m, respectively [10]. The structural uplift of the crater rim only by dike injection and plastic deformation in the underlying target material seems unlikely at distances ~1 km beyond the transient crater cavity. Other mechanisms, like reverse faulting, beginning in the excavation stage of crater formation, could be responsible for additional structural uplift of the crater rim. Nevertheless, our results show that structural uplift is a more dominant effect than ejecta emplacement for complex impact craters. References: [1] Melosh H.J. (1989) Oxford monographs on geology and geophysics, 11, Impact cratering: a geologic process. [2] Poelchau M.H. et al. (2009) JGR, 114, E01006. [3] Shoemaker E. M. (1963) The Solar System, 4, 301-336. [4] Settle M., and Head J.W. (1977) Icarus, v. 31, p. 123. [5] Sturm, S. et al. (2014) LPSC 45, #1801. [6] Krüger T. et al. (2014) LPSC 45, #1834. [7] Hiesinger H. et al. (2002) GRL, 29. [8] Enns A.C. (2013) LPSC XLIV, #2751. [9] Steward S. T. and Valiant G. J. (2006) Meteoritics & Planet. Sci., 41, 1509-1537. [10] Pike R. J. (1974) EPSL, 23, 265-274. [11]Turtle, E. et al. (2005) GSA-SP. 384, 1.

Chemical variations observed on Aeolis Mons in Gale Crater, Mars

NASA Astrophysics Data System (ADS)

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.

Latitude dependence of Martian pedestal craters: Evidence for a sublimation-driven formation mechanism

NASA Astrophysics Data System (ADS)

Kadish, Seth J.; Barlow, Nadine G.; Head, James W.

2009-10-01

We report on the results of a survey to document and characterize pedestal craters on Mars equatorward of ˜60°N and 65°S latitude. The identification of 2696 pedestal craters reveals a strong latitude dependence, with the vast majority found poleward of 33°N and 40°S. This latitudinal extent is correlated with many climate indicators consistent with the presence of an ice-rich substrate and with climate model predictions of where ice is deposited during periods of higher obliquity in the Amazonian. We have measured key physical attributes of pedestal craters, including the farthest radial extents of the pedestals, pedestal heights, and the circularity of the pedestal margins. In conjunction with the geographic distribution, our measurements strongly support a sublimation-related formation mechanism. This is in contrast to previous hypotheses, which have relied on eolian deflation to produce the elevated plateaus. The identification of marginal pits on the scarps of some pedestal craters, interpreted to be sublimation pits, provide direct evidence for the presence of ice-rich material underlying the armored surface of pedestal craters. On the basis of our findings, we propose a formation mechanism whereby projectiles impact into a volatile-rich dust/snow/ice substrate tens to hundreds of meters thick overlying a dominantly fragmental silicate regolith. The area surrounding the resulting crater becomes armored. Pedestals extend to a distance of multiple crater radii, farther than typical ejecta deposits, necessitating an armoring mechanism that is capable of indurating the surface to a distance greater than the reach of the ejecta. Return to low obliquity causes sublimation of the volatile-rich layer from the intercrater plains, lowering the elevation of the regional terrain. This yields generally circular pedestal craters elevated above the surrounding plains. As a result, the armored surfaces of pedestal craters have preserved a significant record of Amazonian climate history in the form of ice-rich deposits.

Discrete curvatures combined with machine learning for automated extraction of impact craters on 3D topographic meshes

NASA Astrophysics Data System (ADS)

Christoff, Nicole; Jorda, Laurent; Viseur, Sophie; Bouley, Sylvain; Manolova, Agata; Mari, Jean-Luc

2017-04-01

One of the challenges of Planetary Science is to estimate as accurately as possible the age of the geological units that crop out on the different space objects in the Solar system. This dating relies on the counting of the impact craters that cover the given outcrop surface. Using this technique, a chronology of the geological events can be determined and their formation and evolution processes can be understood. Over the last decade, several missions to asteroids and planets, such as Dawn to Vesta and Ceres, Messenger to Mercury, Mars Orbiter and Mars Express, produced a huge amount of images, from which equally huge DEMs have been generated. Planned missions, such as BepiColombo, will produce an even larger set of images. This rapidly growing amount of visible images and DEMs makes it more and more fastidious to manually identify craters. Acquisition data will become bigger and this will then require more accurate planetary surface analysis. Because of the importance of the problem, many Crater Detection Algorithm (CDA) were developed and applied onto either image data (2D) or DEM (2D1/5), and rarely onto full 3D data such as 3D topographic meshes. We propose a new approach, based on the detection of crater rim, which form a characteristic round shape. The proposed approach contains two main steps: 1) each vertex is labelled with the values of the mean curvature and minimal curvatures; 2) this curvature map is injected into a Neural Network (NN) to automatically process the region of interest. As a NN approach, it requires a training set of manually detected craters to estimate the optimal weights of the NN. Once trained, the NN can be applied onto the regions of interest for automatically extracting all the craters. As a result, it was observed that detecting forms using a two-dimensional map based on the computation of discrete differential estimators on the 3D mesh is more efficient than using a simple elevation map. This approach significantly reduces the number of false negative detections compared to previous approaches based on 2.5D data processing. The proposed method was validated on a Mars dataset, including a numerical topography acquired by the Mars Orbiter Laser Altimeter (MOLA) instrument and combined with Barlow et al. (2000) crater database. Keywords: geometric modeling, mesh processing, neural network, discrete curvatures, crater detection, planetary science.

Meteor Crater: Energy of formation - Implications of centrifuge scaling

NASA Technical Reports Server (NTRS)

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.

Lunar Floor-Fractured Craters: Classification, Distribution and Implications for Magmatism and Shallow Crustal Structure

NASA Technical Reports Server (NTRS)

Jozwiak, L. M.; Head, J. W.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.

2012-01-01

Floor-fractured craters (FFCs) are a class of lunar craters defined by their distinctly shallow, often plate-like floors, and combinations of radial, con-centric, and polygonal floor-fractures; a variety of other interior features are often observed, such as moats, ridges, small dark-haloed pits, and patches of mare material. They were first classified by Schultz [1] , who recognized eight overall types of floor-fractured crater. These eight subtypes have widely differing appearances, a factor that could provide insight into formation mechanisms (different manifestations of the same mechanism, or indicators of varying formation mechanisms). Two formation mechanisms for FFCs were initially proposed: 1) magmatic intrusion [1], in which magma rising toward the surface in dikes encountered low-density breccia lenses beneath crater floors and spread laterally to form sills, raising and fracturing the crater floor. 2) viscous relaxation [2], in which the properties of the crust permitted viscous flow in the vicinity of the crater, causing long-wavelength relaxation of the topography and uplift and fracturing of the crater floor. Critical to distinguishing between these two end-member hypotheses and identifying others is a quantitative assessment of the topography of FFCs and knowledge of their regional and local settings. The purpose of this study is to use newly available Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) altimeter and Lunar Reconnaissance Orbiter Camera (LROC) image data to provide an updated global catalog of the locations, classes, morphometric and morphologic characteristics of all lunar floor-fractured craters. We use the excellent 8-class system initially described in Schultz [1] as a starting point for classification and the enhanced LOLA/LROC data sets to examine and categorize all FFCs; we found evidence for a new FFC class, discernably different from the previously existing types. Our approach, and the global categorization of all FFCs, permits the spatial distribution of each FFC-subtype to be plotted and assessed allowing for further investigation into FFC formation mechanisms. Upon completion, the data set will be made available on our web site at http://www.planetary.brown.edu/html_pages/data.htm.

Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data

NASA Astrophysics Data System (ADS)

Fassett, C. I.; Head, J. W.; Kadish, S. J.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2012-02-01

Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D ≥ 300 km). These data generally support the widely used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.

Lunar Impact Basins: Stratigraphy, Sequence and Ages from Superposed Impact Crater Populations Measured from Lunar Orbiter Laser Altimeter (LOLA) Data

NASA Technical Reports Server (NTRS)

Fassett, C. I.; Head, J. W.; Kadish, S. J.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2012-01-01

Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D = 300 km). These data generally support the widely used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.

Tektites: Origin as melts produced by the impact of small projectiles onto dry targets

NASA Technical Reports Server (NTRS)

Wasson, John T.

1988-01-01

The formation of tektites in general and layered tektites in particular seems to require a very special kind of cratering event. Evidence for the formation of pools of melt free of unmelted clasts has not been reported for the well-studied terrestrial craters such as Manicouagan or Ries. It is suggested that large amounts of relict-free melt were produced only when a sizeable fraction of the cratered target consisted of dry, high-porosity materials such as aeolian sediments. Since dry, high-porosity target materials are always confined to the outer 100 to 200 m of the Earth, the fraction of melt produced melt is probably higher in small (radius 50 to 500 m) craters than in large (r greater than 1 km) craters. Another reason to infer that the Southeast Asian tektites were produced in a multitude of small craters is the wide distribution of layered tektites. The file spans at least 1200 km, which would require ballistic ejection at velocities greater than 2 km s(-1) if all melt was generated in a single crater. It seems impossible to devise a scenario that would lead to the deposition of primary melt as a crystal-free pool at a distance of 600 km from the crater.

Geomagnetic and morphological signature of small crateriform structures in the Alpine Foreland, Southeast Germany

NASA Astrophysics Data System (ADS)

Neumair, A.; Ernstson, K.

2011-12-01

Lots of rimmed crateriform structures with diameters of the order of meters and ten meters in young fluvial and moraine sediments in Southeast Germany have raised increased interest in the last decade although they have been known since longtime. An anthropogenic origin (for smelting or lime kiln purposes, as prospecting pits, bomb craters, etc) can in most cases be excluded, and the ring walls are speaking against a formation as simple sink holes. Some earlier geomagnetic field and soil susceptibility measurements found anomalies without giving them further enhanced consideration. In a new geomagnetic campaign we exemplarily investigated a few of these craters by fluxgate gradiometer surveys and by magnetic susceptibility measurements of the crater soil and of rock samples digged from the crater underground that also supplied remnant magnetization data. Conspicuously, the craters although morphologically similar, can be subdivided into structures with a clear magnetic signature and ones free of mentionable anomalies. The magnetic signature is expressed by soil susceptibilities up to one order of magnititude higher for the depression and rim area compared to outside the structure, and by an irregular cluster of short-wavelength magnetic anomalies in extreme cases exceding several 1000 nT/m amplitude. Excavations do not show any anthropogenic influence but highly magnetized, frequently strongly fractured cobbles and boulders as the cause. Susceptibilities up to more than 6000 x 10-5 SI and remnant magnetizations of the order of 10 A/m (Koenigsberger ratio Q up to 3.5) were measured. So far enigmatic are very high susceptibilities and remnant magnetizations of limestone clasts. While in general carbonate clasts of the region have susceptibilities of the order of 0.00005 x 10-5 SI and negligible remanence, we measured up to more than 1500 x 10-5 SI and remnant magnetizations of up to 2 A/m (Q up to 3) for limestone samples from the craters. Detailed rock-magnetic studies are ongoing, and, for the moment, we point to new ideas focusing on a formation of at least part of the craters as meteorite craters originating from the recently proposed large Holocene so-called Chiemgau impact event. The magnetic signature as described may prove as a characteristic attribute of identifying respective craters, and thermal effects implying a thermal remnant magnetization are discussed. On the other hand, the highly magnetized carbonate rocks do not show any significant thermal overprint, and a strong shock magnetization debated for some magnetic anomalies in impact craters must seriously be considered. The "magnetic" craters irrespective of their diameters show when appropriately scaled more or less identical diametral cross sections while the craters without magnetic signature have a different profile. Hence, two different processes are suggested to have produced "magnetic" meteorite craters and a second group of craters that may have an endogenetic origin possibly by soil liquefaction sand explosions in the course of the postulated impact event.

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

NASA Astrophysics Data System (ADS)

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.

Diagenetic Crystal Growth in the Murray Formation, Gale Crater, Mars

NASA Technical Reports Server (NTRS)

Kah, L. C.; Kronyak, R. E.; Ming, D. W.; Grotzinger, J. P.; Schieber, J.; Sumner, D. Y.; Edgett, K. S.

2015-01-01

The Pahrump region (Gale Crater, Mars) marks a critical transition between sedimentary environments dominated by alluvial-to-fluvial materials associated with the Gale crater rim, and depositional environments fundamentally linked to the crater's central mound, Mount Sharp. At Pahrump, the Murray formation consists of an approximately 14-meter thick succession dominated by massive to finely laminated mudstone with occasional interbeds of cross-bedded sandstone, and is best interpreted as a dominantly lacustrine environment containing tongues of prograding fluvial material. Murray formation mudstones contain abundant evidence for early diagenetic mineral precipitation and its subsequent removal by later diagenetic processes. Lenticular mineral growth is particularly common within lacustrine mudstone deposits at the Pahrump locality. High-resolution MAHLI images taken by the Curiosity rover permit detailed morphological and spatial analysis of these features. Millimeter-scale lenticular features occur in massive to well-laminated mudstone lithologies and are interpreted as pseudomorphs after calcium sulfate. The distribution and orientation of lenticular features suggests deposition at or near the sediment-water (or sediment-air) interface. Retention of chemical signals similar to host rock suggests that original precipitation was likely poikilotopic, incorporating substantial amounts of the primary matrix. Although poikilotopic crystal growth is common in burial environments, it also occurs during early diagenetic crystal growth within unlithified sediment where high rates of crystal growth are common. Loss of original calcium sulfate mineralogy suggests dissolution by mildly acidic, later-diagenetic fluids. As with lenticular voids observed at Meridiani by the Opportunity Rover, these features indicate that calcium sulfate deposition may have been widespread on early Mars; dissolution of depositional and early diagenetic minerals is a likely source for both calcium and sulfate ion-enrichment in burial fluids that precipitated in ubiquitous late-stage hydrofracture veins

A proposed origin for palimpsests and anomalous pit craters on Ganymede and Callisto

NASA Technical Reports Server (NTRS)

Croft, S. K.

1983-01-01

The hypothesis that palimpsests and anomalous pit craters are essentially pristine crater forms derived from high-velocity impacts and/or impacts into an ice crust with preimpact temperatures near melting is explored. The observational data are briefly reviewed, and an impact model is proposed for the direct formation of a palimpsest from an impact when the modification flow which produces the final crater is dominated by 'wet' fluid flow, as opposed to the 'dry' granular flow which produces normal craters. Conditions of 'wet' modification occur when the volume of impact melt remaining in the transient crater attains a volume comparable to the transient crater. The normal crater-palimpsest transition is found to occur for sufficiently large impacts or sufficiently fast impactors. The range of crater diameters and morphological characteristics inferred from the impact model is consistent with the observed characteristics of palimpsests and anomalous pit craters.

Results of the Mars Exploration Rover Athena science investigation

NASA Astrophysics Data System (ADS)

Squyres, S. W.; Athena Science Team

2004-05-01

The Mars Exploration Rovers ``Spirit" and ``Opportunity" have performed missions of scientific exploration at Gusev Crater and Meridiani Planum on Mars. Their objective is to search for evidence of water activity at the two sites, and to assess the past habitability of the sites. The Gusev Crater site investigated by Spirit is a flat, rock-strewn plain. All rocks at the site investigated to date are olivine basalt. The rover has conducted a radial traverse through the ejecta blanket of the crater Bonneville. After investigation of this crater, the rover will continue its traverse toward the Columbia Hills, a range of hills over 100 m high approximately 2.5 km to the west. To date, no unambiguous evidence of aqueous activity has been found at the Gusev site. The lander carrying Opportunity came to rest in a 20-meter crater in Meridiani Planum. Exposed within this crater is a small outcrop of bedrock. The bedrock outcrop has been studied in detail, and shows compelling evidence for formation and alteration processes involving liquid water. This evidence includes (a) embedded hematite-rich spherules that appear to be concretions, (b) tabular voids with characteristics consistent with those of molds of crystals formed by precipitation from water, (c) extremely high sulfur content, suggesting a compositon of 30-40 salts by weight, (d) significant quantities of jarosite, (e) Cl/Br systematics similar to those of terrestrial evaporites, and (f) cross stratification indicative of deposition in a moving fluid environment, probably water. Precipitated minerals at the Meridiani site could be very effective at preserving evidence of conditions and processes in the aqueous environment there, making them an attractive potential target for future study.

Martian Cratering 7: The Role of Impact Gardening

NASA Astrophysics Data System (ADS)

Hartmann, William K.; Anguita, Jorge; de la Casa, Miguel A.; Berman, Daniel C.; Ryan, Eileen V.

2001-01-01

Viking-era researchers concluded that impact craters of diameter D<50 m were absent on Mars, and thus impact gardening was considered negligible in establishing decameter-scale surface properties. This paper documents martian crater populations down to diameter D˜11 m and probably less on Mars, requiring a certain degree of impact gardening. Applying lunar data, we calculate cumulative gardening depth as a function of total cratering. Stratigraphic units exposed since Noachian times would have experienced tens to hundreds of meters of gardening. Early Amazonian/late Hesperian sites, such as the first three landing sites, experienced cumulative gardening on the order of 3-14 m, a conclusion that may conflict with some landing site interpretations. Martian surfaces with less than a percent or so of lunar mare crater densities have negligible impact gardening because of a probable cutoff of hypervelocity impact cratering below D˜1 m, due to Mars' atmosphere. Unlike lunar regolith, martian regolith has been affected, and fines removed, by many processes. Deflation may have been a factor in leaving widespread boulder fields and associated dune fields, observed by the first three landers. Ancient regolith provided a porous medium for water storage, subsurface transport, and massive permafrost formation. Older regolith was probably cemented by evaporites and permafrost, may contain interbedded sediments and lavas, and may have been brecciated by later impacts. Growing evidence suggests recent water mobility, and the existence of duricrust at Viking and Pathfinder sites demonstrates the cementing process. These results affect lander/rover searches for intact ancient deposits. The upper tens of meters of exposed Noachian units cannot survive today in a pristine state. Intact Noachian deposits might best be found in cliffside strata, or in recently exhumed regions. The hematite-rich areas found in Terra Meridiani by the Mars Global Surveyor are probably examples of the latter.

Wind-related processes detected by the Spirit rover at Gusev crater, Mars

USGS Publications Warehouse

Greeley, R.; Squyres, S. W.; Arvidson, R. E.; Bartlett, P.; Bell, J.F.; Blaney, D.; Cabrol, N.A.; Farmer, J.; Farrand, B.; Golombek, M.P.; Gorevan, S.P.; Grant, J. A.; Haldemann, A.F.C.; Herkenhoff, K. E.; Johnson, J.; Landis, G.; Madsen, M.B.; McLennan, S.H.; Moersch, J.; Rice, J. W.; Richter, L.; Ruff, S.; Sullivan, R.J.; Thompson, S.D.; Wang, A.; Weitz, C.M.; Whelley, P.

2004-01-01

Wind-abraded rocks, ripples, drifts, and other deposits of windblown sediments are seen at the Columbia Memorial Station where the Spirit rover landed. Orientations of these features suggest formative winds from the north-northwest, consistent with predictions from atmospheric models of afternoon winds in Gusev Crater. Cuttings from the rover Rock Abrasion Tool are asymmetrically distributed toward the south-southeast, suggesting active winds from the north-northwest at the time (midday) of the abrasion operations. Characteristics of some rocks, such as a two-toned appearance, suggest that they were possibly buried and exhumed on the order of 5 to 60 centimeters by wind deflation, depending on location.

Craters near the south pole of Callisto

NASA Technical Reports Server (NTRS)

1997-01-01

This image of the south polar region of the Jovian satellite Callisto was taken in twilight by the Galileo spacecraft on its eighth orbit around Jupiter. Craters ranging in size from 60 kilometers (36 miles) down to the limit of resolution are visible in this image. Scientists count the number of craters on a planetary surface to estimate its relative (and sometimes absolute) age. Note that many of the craters are not as sharp in appearance as the two large craters near the bottom of the image. This is an indication that some process has eroded the craters since their formation.

This image is centered at 82.5 south latitude and 62.6 west longitude, and covers an area approximately 370 kilometers (220 miles) by 280 kilometers (170 miles). North is toward the top of the image. This image was taken on May 6, 1997 by the Solid State Imaging system (CCD) on board NASA's Galileo spacecraft at a resolution of 676 meters (417 feet) per picture element.

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://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

Patterned surfaces in the drying of films composed of water, polymer, and alcohol

NASA Astrophysics Data System (ADS)

Fichot, Julie; Heyd, Rodolphe; Josserand, Christophe; Chourpa, Igor; Gombart, Emilie; Tranchant, Jean-Francois; Saboungi, Marie-Louise

2012-12-01

A study of the complex drying dynamics of polymeric mixtures with optical microscopy and gravimetric measurement is presented. Droplet formation is observed, followed by a collapse that leads to the residual craters in the dried film. The process is followed in situ under well-defined temperature and hygrometric conditions to determine the origin and nature of these droplets and craters. The drying process is usually completed within 1 h. The observations are explained using a simple diffusion model based on experimental results collected from mass and optical measurements as well as Raman confocal microspectrometry. Although the specific polymeric mixtures used here are of interest to the cosmetic industry, the general conclusions reached can apply to other polymeric aqueous solutions with applications to commercial and artistic painting.

Some implications of large impact craters and basins on Venus for terrestrial ringed craters and planetary evolution

NASA Technical Reports Server (NTRS)

Mckinnon, W. B.; Alexopoulos, J. S.

1994-01-01

Approximately 950 impact craters have been identified on the surface of Venus, mainly in Magellan radar images. From a combination of Earth-based Arecibo, Venera 15/1, and Magellan radar images, we have interpreted 72 as unequivocal peak-ring craters and four as multiringed basins. The morphological and structural preservation of these craters is high owing to the low level of geologic activity on the venusian surface (which is in some ways similar to the terrestrial benthic environment). Thus these craters should prove crucial to understanding the mechanics of ringed crater formation. They are also the most direct analogs for craters formed on the Earth in Phanerozoic time, such as Chicxulub. We summarize our findings to date concerning these structures.

Alteration Effects at Gale and Gusev Craters

NASA Image and Video Library

2015-12-17

This graph shows the ratio of concentrations of several elements in four different pairs of targets examined by Alpha Particle X-ray Spectrometer (APXS) instruments on NASA Mars rovers Curiosity and Spirit. For each pair of targets, one shows evidence of mineral alteration and the other is an unaltered counterpart. The first three pairs (with ratios shown by green, blue and red lines) are targets in Gale Crater analyzed by Curiosity's APXS. The fourth pair (with ratio shown by the black line) is in Gusev Crater and was analyzed by Spirit's APXS. Similar profiles are observed, suggesting the possibility of related formation processes. As with examples of silica enrichment found by Curiosity, the origin of high-silica nodular deposits found by Spirit also remains unresolved: Either acidic weathering or silica addition could be responsible. It is clear, however, that liquid water was involved in either alteration scenario. http://photojournal.jpl.nasa.gov/catalog/PIA20276

Eruption of magmatic foams on the Moon: Formation in the waning stages of dike emplacement events as an explanation of ;irregular mare patches;

NASA Astrophysics Data System (ADS)

Wilson, Lionel; Head, James W.

2017-04-01

Volcanic eruptions on the Moon take place in conditions of low gravity and negligible atmospheric pressure, very different from those on Earth. These differences lead to characteristic lunar versions of hawaiian and strombolian explosive activity, and to the production of unusual eruption products neither predicted nor observed on Earth in the terminal stages of eruptions. These include the unusual mounds and rough (hummocky, blocky) floors of some small-shield summit pit crater floors, elongate depressions and mare flows (similar to those named ;irregular mare patches;, IMPs, by Braden et al., 2014). We examine the ascent and eruption of magma in the waning stages of the eruptive process in small-shield summit pit crater floors and show that many IMP characteristics can be plausibly explained by basaltic magma behavior as the rise rate of the ascending magma slows to zero, volatiles exsolve in the dike and lava lake to form a very vesicular foam, and the dike begins to close. Stresses in the very vesicular and porous lava lake crust produce fractures through which the foam extrudes at a rate determined by its non-Newtonian rheology. Waning-stage extrusion of viscous magmatic foams to the surface produces convex mounds whose physical properties inhibit typical impact crater formation and regolith development, creating an artificially young crater retention age. This mechanism for the production and extrusion of very vesicular magmatic foams is also applicable to waning-stage dike closure associated with pit craters atop dikes, and fissure eruptions in the lunar maria, providing an explanation for many irregular mare patches. This mechanism implies that IMPs and associated mare structures (small shields, pit craters and fissure flows) formed synchronously billions of years ago, in contrast to very young ages (less than 100 million years) proposed for IMPs by some workers.

Ejecta- and Size-Scaling Considerations from Impacts of Glass Projectiles into Sand

NASA Technical Reports Server (NTRS)

Anderson J. L. B.; Cintala, M. J.; Siebenaler, S. A.; Barnouin-Jha, O. S.

2007-01-01

One of the most promising means of learning how initial impact conditions are related to the processes leading to the formation of a planetary-scale crater is through scaling relationships.1,2,3 The first phase of deriving such relationships has led to great insight into the cratering process and has yielded predictive capabilities that are mathematically rigorous and internally consistent. Such derivations typically have treated targets as continuous media; in many, cases, however, planetary materials represent irregular and discontinuous targets, the effects of which on the scaling relationships are still poorly understood.4,5 We continue to examine the effects of varying impact conditions on the excavation and final dimensions of craters formed in sand. Along with the more commonly treated variables such as impact speed, projectile size and material, and impact angle,6 such experiments also permit the study of changing granularity and friction angle of the target materials. This contribution presents some of the data collected during and after the impact of glass spheres into a medium-grained sand.

Lunar and Planetary Science XXXV: Martian Aeolian and Mass Wasting Processes: Blowing and Flowing

NASA Technical Reports Server (NTRS)

2004-01-01

The session Martian Aeolian and Mass Wasting Processes: BLowing and Flowing included the following topics: 1) Three Decades of Martian Surface Changes; 2) Thermophysical Properties of Isidis Basin, Mars; 3) Intracrater Material in Eastern Arabia Terra: THEMIS, MOC, and MOLA Analysis of Wind-blown Deposits and Possible High-Inertia Source Material; 4) Thermal Properties of Sand from TES and THEMIS: Do Martian Dunes Make a Good Control for Thermal Inertia Calculations? 5) A Comparative Analysis of Barchan Dunes in the Intra-Crater Dune Fields and the North Polar Sand Sea; 6) Diluvial Dunes in Athabasca Valles, Mars: Morphology, Modeling and Implications; 7) Surface Profiling of Natural Dust Devils; 8) Martian Dust Devil Tracks: Inferred Directions of Movement; 9) Numerical Simulations of Anastomosing Slope Streaks on Mars; 10) Young Fans in an Equatorial Crater in Xanthe Terra, Mars; 11) Large Well-exposed Alluvual Fans in Deep Late-Noachian Craters; 12) New Evidence for the Formation of Large Landslides on Mars; and 13) What Can We Learn from the Ages of Valles Marineris Landslides on Martian Impact History?

Mercury

NASA Technical Reports Server (NTRS)

Vilas, Faith (Editor); Chapman, Clark R. (Editor); Matthews, Mildred Shapley (Editor)

1988-01-01

Papers are presented on future observations of and missions to Mercury, the photometry and polarimetry of Mercury, the surface composition of Mercury from reflectance spectrophotometry, the Goldstone radar observations of Mercury, the radar observations of Mercury, the stratigraphy and geologic history of Mercury, the geomorphology of impact craters on Mercury, and the cratering record on Mercury and the origin of impacting objects. Consideration is also given to the tectonics of Mercury, the tectonic history of Mercury, Mercury's thermal history and the generation of its magnetic field, the rotational dynamics of Mercury and the state of its core, Mercury's magnetic field and interior, the magnetosphere of Mercury, and the Mercury atmosphere. Other papers are on the present bounds on the bulk composition of Mercury and the implications for planetary formation processes, the building stones of the planets, the origin and composition of Mercury, the formation of Mercury from planetesimals, and theoretical considerations on the strange density of Mercury.

Investigation of Charon's Craters With Abrupt Terminus Ejecta, Comparisons With Other Icy Bodies, and Formation Implications

NASA Astrophysics Data System (ADS)

Robbins, Stuart J.; Runyon, Kirby; Singer, Kelsi N.; Bray, Veronica J.; Beyer, Ross A.; Schenk, Paul; McKinnon, William B.; Grundy, William M.; Nimmo, Francis; Moore, Jeffrey M.; Spencer, John R.; White, Oliver L.; Binzel, Richard P.; Buie, Marc W.; Buratti, Bonnie J.; Cheng, Andrew F.; Linscott, Ivan R.; Reitsema, Harold J.; Reuter, Dennis C.; Showalter, Mark R.; Tyler, G. Len; Young, Leslie A.; Olkin, Catherine B.; Ennico, Kimberly S.; Weaver, Harold A.; Stern, S. Alan

2018-01-01

On the moon and other airless bodies, ballistically emplaced ejecta transitions from a thinning, continuous inner deposit to become discontinuous beyond approximately one crater radius from the crater rim and can further break into discrete rays and secondary craters. In contrast, on Mars, ejecta often form continuous, distinct, and sometimes thick deposits that transition to a low ridge or escarpment that may be circular or lobate. The Martian ejecta type has been variously termed pancake, rampart, lobate, or layered, and in this work we refer to it as "abrupt termini" ejecta (ATE). Two main formation mechanisms have been proposed, one requiring interaction of the ejecta with the atmosphere and the other mobilization of near-surface volatiles. ATE morphologies are also unambiguously seen on Ganymede, Europa, Dione, and Tethys, but they are not as common as on Mars. We have identified up to 38 craters on Charon that show signs of ATE, including possible distal ramparts and lobate margins. These ejecta show morphologic and morphometric similarities with other moons in the solar system, which are a subset of the properties observed on Mars. From comparison of these ejecta on Charon and other solar system bodies, we find the strongest support for subsurface volatile mobilization and ejecta fluidization as the main formation mechanism for the ATE, at least on airless, icy worlds. This conclusion comes from the bodies on which they are found, an apparent preference for certain terrains, and the observation that craters with ATE can be near to similarly sized craters that only have gradational ejecta.

Relative crater production rates on planets

NASA Technical Reports Server (NTRS)

Hartmann, W. K.

1977-01-01

The relative numbers of impacts on different planets, estimated from the dynamical histories of planetesimals in specified orbits (Wetherill, 1975), are converted by a described procedure to crater production rates. Conversions are dependent on impact velocity and surface gravity. Crater retention ages can then be derived from the ratio of the crater density to the crater production rate. The data indicate that the terrestrial planets have crater production rates within a factor ten of each other. As an example, for the case of Mars, least-squares fits to crater-count data suggest an average age of 0.3 to 3 billion years for two types of channels. The age of Olympus Mons is discussed, and the effect of Tharsis volcanism on channel formation is considered.

The Structure of the Kaali Impact Crater (Estonia) based on 3D Laser Scanning, Photogrammetric Modelling and Strike and Dip Measurements

NASA Astrophysics Data System (ADS)

Zanetti, Michael; Wilk, Jakob; Joeleht, Argo; Välja, Rudolf; Losiak, Anna; Wisniowski, Tomek; Huber, Matthew; Pavel, Kristiina; Kriiska, Aivar; Plado, Jüri; Geppert, Wolf Dietrich; Kukko, Antero; Kaartinen, Harri

2015-04-01

Introduction: The Kaali Impact Crater on the island of Saaremaa, Estonia (58.37° N, 22.67° E) is part of a crater-strewn-field consisting of nine identified craters, ranging in size from 110m (Kaali Main) to a few meters in diameter [1-3]. The strewn field was formed by the breakup of an IAB iron meteorite during atmospheric entry [4]. The main crater is due to its size an important crater to study the effects of small asteroidal impacts on terrestrial planets. Despite some anthropomorphic changes, the crater is well preserved. During a scientific expedition in August 2014, we mapped the crater in unprecedented detail using 3D laser scanning tools and made detailed strike and dip measurements of all outcrops. Additional measurements using ground-penetrating radar and electro-resistivity tomography we also conducted to further refine the subsurface crater morphology. The results include a high resolution topographic map of the crater, previously unreported observations of overturned ejecta, and refined morphometric estimates of the crater. Additionally, research conducted as part of the expedition has provided a new, best-estimate for the formation of the crater (3200a +/- 30 BP) based on 14C AMS dating of charcoal from within the ejecta blanket [Losiak et al., 2015, this conference]. Structural Mapping: Although Kaali Main has been the subject of previous investigation (e.g. [2,5,6]), most of the structural descriptions of the crater pre-date modern crater investigations. Strongly inclined blocks were previously considered being affected by erosion and slope processes, our new observations show that most high dip-angle features fit well with overall dip-angle systematics. The existence of the overturned flap can be demonstrated in at least four areas around the crater. 3D Laser Scanning: A point cloud containing 16 million data points was created using 43 individual scans from a tripod mounted Faro 3D 330x laser scanner. Scans were processed using Trimble Realworks software. A DEM, Hillshade, Slope Map and Contour Map were created in ESRI ArcScene software. Photogrammetry: Photogrammetric techniques from images of key outcrops were used to create texture, photorealistic 3D representations using Agisoft PhotoScan software. Acknowledgements: We extend our sincerest gratitude to the Estonian National Heritage Board for permission to dig and make measurements at the crater. References: [1] I.Kolkun (1922) Üldine geologia. Tallin, 170. [2] J. A.Reinwald (1933) Publications of the Geological Institution of the University of Tartu, 30:1-20. [3] J.A.Reinwald (1928) thesis; Univ of Tartu [4] L.J.Spencer (1938) Miner. Mag., 25:75-80. [5] A.Aaloe (1959) ENSV TA Geoloogia Instituudi Uurimused, 2:105-117. [6] A.Raukas et al. (2002) Impact Studies 2005, 341-355.

The 45th Annual Meteoritical Society Meeting

NASA Technical Reports Server (NTRS)

Jones, P. (Compiler); Turner, L. (Compiler)

1982-01-01

Impact craters and shock effects, chondrite formation and evolution, meteorites, chondrules, irons, nebular processes and meteorite parent bodies, regoliths and breccias, antarctic meteorite curation, isotopic studies of meteorites and lunar samples, organics and terrestrial weathering, refractory inclusions, cosmic dust, particle irradiations before and after compaction, and mineralogic studies and analytical techniques are discussed.

An Assessment of Regional Variations in Martian Modified Impact Crater Morphology

NASA Astrophysics Data System (ADS)

Craddock, Robert A.; Bandeira, Lourenço.; Howard, Alan D.

2018-03-01

Impact craters on Mars have been extensively modified by ancient geologic processes that may have included rainfall and surface runoff, snow and ice, denudation by lava flows, burial by eolian material, or others. Many of these processes can leave distinct signatures on the morphometry of the modified impact crater as well as the surrounding landscape. To look for signs of potential regional differences in crater modification processes, we conducted an analysis of different morphometric parameters related to modified impact craters located in the Margaritifer Sinus, Sinus Sabaeus, Iapygia, Mare Tyrrhenum, Aeolis, and Eridania quadrangles, including depth, crater wall slope, crater floor slope, the curvature between the interior wall and the crater floor slope, and the curvature between the interior wall and surrounding landscape. A Welch's t test analysis comparing these parameters shows that fresh impact craters (Type 4) have consistent morphologies regardless of their geographic location examined in this study, which is not unexpected. Modified impact craters both in the initial (Type 3) and terminal stages (Type 1) of modification also have statistically consistent morphologies. This would suggest that the processes that operated in the late Noachian were globally ubiquitous, and that modified craters eventually reached a stable crater morphology. However, craters preserved in advanced (but not terminal) stages of modification (Type 2) have morphologies that vary across the quadrangles. It is possible that these variations reflect spatial differences in the types and intensity of geologic processes that operated during the Noachian, implying that the ancient climate also varied across regions.

Formation (and dating) of small impact craters on Earth as an analogue for Mars (Ilumetsa Craters Estonia)

NASA Astrophysics Data System (ADS)

Losiak, Anna; Jõeleht, Argo; Plado, Juri; Szyszka, Mateusz; Wild, Eva Maria; Bronikowska, Malgorzata; Belcher, Claire; Kirsimäe, Kalle; Steier, Peter

2017-04-01

Crater-strewn-fields are present on planetary bodies with an atmosphere such as Earth and Mars, but the process of their formation is still not fully understood. For example, a recent discovery of small pieces of impact-produced-charcoal within the ejecta blanket of 100 m in diameter Kaali crater (Losiak et al. 2016) may suggest existence of very local ( 10 cm thick layer in the distance of 10 m from the rim), short lived ( hours) thermal anomalies ( 300°C) in the ejecta blanket of even small craters. Ilumetsa in SE Estonia is an atypical example of crater-strewn-field consisting of only two relatively large, rimmed structures with diameters of 75-80 m (Ilumetsa Large: IL) and 50 m (Ilumetsa Small: IS) with true depths of about 8 and 3.5 m, respectively (Plado 2012 MAPS). Structures were previously dated by the 14C analysis of gyttja from the bottom of IL (Liiva et al. 1979 Eesti Loodus) to be 7170-6660 cal. BP. About 600 years older age (7570-7320 cal. BC: Raukas et al. 2001, MAPS) was proposed based on dated layer of peat in which glassy spherules, interpreted as dissipated melt or condensed vapor (however their chemical composition was not reported). Ilumetsa is listed as a proven meteorite impact in the Earth Impact Database, but neither remnants of the projectile nor other identification criteria (e.g., PDFs) have been found up to this point. The aim of this study was to search for possible impact related charcoals in order to determine the size and extend of thermal anomalies around small impact craters, as well as to determine how this atypical strew field was formed. Additionally, we hoped to determine/confirm the age of those structures. We have found charcoal in a similar geological setting as in Kaali Main crater in both Ilumetsa structures. The calibrated (95,4% probability) time ranges of four dated samples from IL and one sample of IS span the time interval from 7670-6950 cal. BP (consistent with previous dating). One sample from IS is younger (4830-4580 cal. BP) - it was found less deep than other charcoals found within the same trench, and it may be interpreted as a remnant of a "recent" forest fire, later buried within the sediment derived from the erosion of the raised rim. The second sample is older (8540-8400 cal. BP). It was found on a greater depth than most of the samples and may represent an older plant material that was buried within the sediments before the impact happened. More 14C dating will be performed. Chemical analyses of sediments exposed in profiles did not reveal any specific enrichment with respect the host rocks in elements (Ni, Cr) that could be related to extraterrestrial material. INAA measurements will be performed. Field search for metal-containing meteorites was inconclusive (until now nothing was found), but preliminary studies on the atmospheric entry modeling of the Ilumetsa meteoroid shows that using standard value of strength (4.4e6 - 4.4e7 N/kg) for a stony meteoroid, cannot lead to reproduction of the Ilumetsa craters formation due to cascade fragmentation specific for such weak bodies. In conclusion: the Ilumetsa structures were formed around 7000 cal. BP, but a clear proof of their impact origin is still missing. More analysis is being currently performed. Understanding formation of small terrestrial impact craters will lead to better understanding formation of similar structures on other planetary bodies, and their influence on their environment.

Magma genesis at Gale Crater: Evidence for Pervasive Mantle Metasomatism

NASA Astrophysics Data System (ADS)

Filiberto, J.

2017-12-01

Basaltic rocks have been analyzed at Gale Crater with a larger range in bulk chemistry than at any other landing site [1]. Therefore, the rocks may have experienced significantly different formation conditions than those experienced by magmas at Gusev Crater or Meridiani Planum. Specifically, the rocks at Gale Crater have higher potassium than other Martian rocks, with a potential analog of the Nakhlite parental magma, and are consistent with forming from a metasomatized mantle source [2-4]. Mantle metasomatism would not only affect the bulk chemistry but mantle melting conditions, as metasomatism fluxes fluids into the source region. Here I will combine differences in bulk chemistry between Martian basalts to calculate formation conditions in the interior and investigate if the rocks at Gale Crater experienced magma genesis conditions consistent with metasomatism - lower temperatures and pressures of formation. To calculate average formation conditions, I rely on experimental results, where available, and silica-activity and Mg-exchange thermometry calculations for all other compositions following [5, 6]. The results show that there is a direct correlation between the calculated mantle potential temperature and the K/Ti ratio of Gale Crater rocks. This is consistent with fluid fluxed metasomatism introducing fluids to the system, which depressed the melting temperature and fluxed K but not Ti to the system. Therefore, all basalts at Gale Crater are consistent with forming from a metasomatized mantle source, which affected not only the chemistry of the basalts but also the formation conditions. References: [1] Cousin A. et al. (2017) Icarus. 288: 265-283. [2] Treiman A.H. et al. (2016) Journal of Geophysical Research: Planets. 121: 75-106. [3] Treiman A.H. and Medard E. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10.1130/abs/2016AM-285851. [4] Schmidt M.E. et al. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10.1130/abs/2016AM-285651. [5] Filiberto J. and Dasgupta R. (2011) Earth and Planetary Science Letters. 304: 527-537. [6] Filiberto J. and Dasgupta R. (2015) Journal of Geophysical Research: Planets. 120: DOI: 10.1002/2014JE004745.

Impact Cratering Calculations

NASA Technical Reports Server (NTRS)

Ahrens, Thomas J.

2002-01-01

Many Martian craters are surrounded by ejecta blankets which appear to have been fluidized forming lobate and layered deposits terminated by one or more continuous distal scarps, or ramparts. One of the first hypotheses for the formation of so-called rampart ejecta features was shock-melting of subsurface ice, entrainment of liquid water into the ejecta blanket, and subsequent fluidized flow. Our work quantifies this concept. Rampart ejecta found on all but the youngest volcanic and polar regions, and the different rampart ejecta morphologies are correlated with crater size and terrain. In addition, the minimum diameter of craters with rampart features decreases with increasing latitude indicating that ice laden crust resides closer to the surface as one goes poleward on Mars. Our second goal in was to determine what strength model(s) reproduce the faults and complex features found in large scale gravity driven craters. Collapse features found in large scale craters require that the rock strength weaken as a result of the shock processing of rock and the later cratering shear flows. In addition to the presence of molten silicate in the intensely shocked region, the presence of water, either ambient, or the result of shock melting of ice weakens rock. There are several other mechanisms for the reduction of strength in geologic materials including dynamic tensile and shear induced fracturing. Fracturing is a mechanism for large reductions in strength. We found that by incorporating damage into the models that we could in a single integrated impact calculation, starting in the atmosphere produce final crater profiles having the major features found in the field measurements (central uplifts, inner ring, terracing and faulting). This was accomplished with undamaged surface strengths (0.1 GPa) and in depth strengths (1.0 GPa).

Landing site selection for Luna-Glob mission in crater Boguslawsky

NASA Astrophysics Data System (ADS)

Ivanov, M. A.; Hiesinger, H.; Abdrakhimov, A. M.; Basilevsky, A. T.; Head, J. W.; Pasckert, J.-H.; Bauch, K.; van der Bogert, C. H.; Gläser, P.; Kohanov, A.

2015-11-01

Boguslawsky crater (72.9°S, 43.3°E, ~100 km in diameter) is a primary target for the Luna-Glob mission. The crater has a morphologically smooth (at the resolution of WAC images), flat, and horizontal floor, which is about 55-60 km in diameter. Two ellipses were selected as specific candidate landing areas on the floor: the western ellipse is centered at 72.9°S, 41.3°E and the eastern ellipse is centered at 73.9°S, 43.9°E. Both ellipses represent areas from which Earth is visible during the entire year of 2016 and lack permanently shadowed areas. Boguslawsky crater is located on or near the rim of the South Pole-Aitken basin, which provides the unique possibility to sample some of the most ancient rocks on the Moon that probably pre-date the SPA impact event. The low depth/diameter ratio of Boguslawsky suggests that the crater has been partly filled after its formation. Although volcanic flooding of the crater cannot be ruled out, the more likely process of filling of Boguslawsky is the emplacement of ejecta from nearby and remote large craters/basins. Three morphologically distinctive units are the most abundant within the selected landing ellipses: rolling plains (rpc), flat plains (fp), and ejecta from crater Boguslawsky-D (ejf), which occurs on the eastern wall of Boguslawsky. The possible contribution of materials from unknown sources makes the flat and rolling plains less desirable targets for landing. In contrast, ejecta from Boguslawsky-D represents local materials re-distributed by the Boguslawsky-D impact from the wall onto the floor of Boguslawsky. Thus, this unit, which constitutes about 50% of the eastern landing ellipse, represents a target of clearer provenance and a higher scientific priority.

Duginavi and Oxo

NASA Image and Video Library

2017-12-01

This image taken by NASA's Dawn spacecraft shows Duginavi Crater, a large (96 miles, 155 kilometers in diameter) crater on Ceres. Duginavi's degraded rim barely stands out in this picture, which indicates this feature is very old. There are several factors that alter and eventually erase the shapes of geological features on bodies that do not have an atmosphere. These include gravity, which is responsible for landslides and scarps. The formation of newer craters, and the material that gets ejected in the process, has smoothed over craters such as Duginavi. Duginavi hosts the small Oxo Crater, recognizable by its bright rim and ejecta. Oxo is the first site at which ice was discovered on Ceres. Duginavi is named for an agriculture god of the Kogi people of northern Colombia. Oxo bears the name of the god of agriculture in Afro-Brazilian beliefs of Yoruba derivation. These features can be found on the global map of Ceres. Dawn took this image on October 8, 2015, from its high-altitude mapping orbit, at a distance of about 915 miles (1,470 kilometers) above the surface. It has a resolution of 450 feet (140 meters) per pixel. The center coordinates of this image are 39 degrees north latitude, 8 degrees east longitude. https://photojournal.jpl.nasa.gov/catalog/PIA21912

Between Two Lakes: Opportunities for the Inception of Life in Gale Crater, Mars

NASA Astrophysics Data System (ADS)

Heydari, E.; Calef, F.; Schroeder, J.; van Beek, J.; Parker, T. J.; Rowland, S. K.; Fairén, A. G.; Hallet, B.

2017-12-01

Many lakes may have existed in Gale crater, Mars. Five years of investigations by the Curiosity Rover has revealed clear sedimentological evidence for the presence of at least two in the rover's landing ellipse. They are here named the first lake and the last lake. The first lake formed soon after the formation of the crater and was previously introduced by Grotzinger et al. (2015). Water rushed into the crater from its northern rim inundating the crater quickly. Physical evidence for the presence of the first lake includes 300 m of mudstone of the Murray formation exposed in the foothills of Mt. Sharp. Abundance of fine-grained lithologies, dominance of laminations, absence of features suggestive of sedimentation in shallow-waters, and the lack of indicators of an ice-covered lake, all suggest that the Murray formation was deposited at the bottom of a lake that was kilometers deep and was not frozen. The first lake eventually dried up and about 3 km of sediments whose characteristics are known only from orbital images filled Gale crater (Malin and Edgett, 2000). A sediment-filled Gale crater was later exhumed from its margins, leading to the emergence of Mt. Sharp at the crater center. Afterwards, water flowed into the crater, this time from the south, forming a100 m - 200 m deep lake in the vicinity of the landing ellipse: the last lake. The evidence for the last lake is sedimentological record of two to three river deltas preserved in the Rugged Terrain Unit. These deltas prograded rapidly from south to north depositing a 5 m-thick layer over all previously deposited strata. The first lake established the potential conditions for life to begin in Gale crater. They continued until the last lake dried up and Mars became permanently cold. The duration is not well known, but it may have endured for millions of years. Sedimentological evidence provided by the Curiosity rover suggests that multitude of opportunities existed for the inception of life between the two lakes. These include diverse shallow- and deep-water environments hospitable to life, abundant supply of liquid waters of varied geochemical characteristics, and favorable climate conditions.

From lakes to sand seas: a record of early Mars climate change explored in northern Gale crater, Mars

NASA Astrophysics Data System (ADS)

Gupta, S.; Banham, S.; Rubin, D. M.; Watkins, J. A.; Edgett, K. S.; Sumner, D. Y.; Grotzinger, J. P.; Lewis, K. W.; Edgar, L. A.; Stack, K.; Day, M.; Lapôtre, M. G. A.; Bell, J. F., III; Ewing, R. C.; Stein, N.; Rivera-Hernandez, F.; Vasavada, A. R.

2017-12-01

While traversing the northern flank of Aeolis Mons, Gale crater, Mars Science Laboratory rover Curiosity encountered a decametre-thick sandstone unit unconformably overlying the lacustrine Murray formation. This sandstone contains cross-bed sets on the order of 1 m thick, composed of uniform mm-thick laminations of uniform thickness, and lacks silt- or mud-grade sediments. Cross sets are separated by sub-horizontal bounding surfaces which extend for tens of metres across outcrops. Dip-azimuths of cross-laminations are predominantly toward the north-east, which is oblique to the north-west slope of the unconformity on which the sandstone accumulated. This sandstone was designated the Stimson formation after Mt. Stimson, where it was delineated from the Murray formation. Textural analysis of this sandstone revealed a bi-modal sorting with well-rounded grains, typical of particles transported by aeolian processes. Stacked cross-bedded sets, representing the migration of aeolian dune-scale bedforms, combined with the absence of finer-grained facies characteristic of interdune deposits, suggest that the Stimson accumulated by aerodynamic processes and that the depositional surface was devoid of moisture which could have attracted dust to form interdune deposits. Reconstruction of this "dry" dune-field based on architectural measurements suggest that cross sets were emplaced by the migration of dunes with minimum heights of 10m, that were spaced 160 m apart. The dune field covered an area of 30-45 km2, and was confined to the break-in-slope at the base of Aeolis Mons. Cross-set dips suggest that the palaeowind drove these dunes toward the north east, oblique to the slope of the unconformity on which these sandstones accumulated. Construction of a dry dune field in Gale crater required an environment of extreme aridity with absence of water at the surface and within the shallow sub-surface. This is in stark contrast to the lacustrine environment in which the underlying Murray formation accumulated. The contrast in depositional environments between these units suggest that the prevailing climate in Gale crater changed, at least temporarily, from a humid environment with surface water that had potential for sustaining life, to a barren desert with reduced potential for habitability at the surface.

The cratering record in the inner solar system: Implications for earth

NASA Technical Reports Server (NTRS)

Barlow, N. G.

1988-01-01

Internal and external processes have reworked the Earth's surface throughout its history. In particular, the effect of meteorite impacts on the early history of the earth is lost due to fluvial, aeolian, volcanic and plate tectonic action. The cratering record on other inner solar system bodies often provides the only clue to the relative cratering rates and intensities that the earth has experienced throughout its history. Of the five major bodies within the inner solar system, Mercury, Mars, and the Moon retain scars of an early episode of high impact rates. The heavily cratered regions on Mercury, Mars, and the Moon show crater size-frequency distribution curves similar in shape and crater density, whereas the lightly cratered plains on the Moon and Mars show distribution curves which, although similar to each other, are statistically different in shape and density from the more heavily cratered units. The similarities among crater size-frequency distribution curves for the Moon, Mercury, and Mars suggest that the entire inner solar system was subjected to the two populations of impacting objects but Earth and Venus have lost their record of heavy bombardment impactors. Thus, based on the cratering record on the Moon, Mercury, and Mars, it can be inferred that the Earth experienced a period of high crater rates and basin formation prior to about 3.8 BY ago. Recent studies have linked mass extinctions to large terrestrial impacts, so life forms were unable to establish themselves until impact rates decreased substantially and terrestrial conditions became more benign. The possible periodicity of mass extinctions has led to the theory of fluctuating impact rates due to comet showers in the post heavy bombardment period. The active erosional environment on the Earth complicates attempts to verify these showers by erasing geological evidence of older impact craters. The estimated size of the impactor purportedly responsible for the Cretaceous-Tertiary mass extinctions is 10 km in diameter. Thus impactors greater than or equal to the size postulated for K-T impactor are rare within the inner solar system since the end of heavy bombardment.

Syn- and posteruptive hazards of maar diatreme volcanoes

NASA Astrophysics Data System (ADS)

Lorenz, Volker

2007-01-01

Maar-diatreme volcanoes represent the second most common volcano type on continents and islands. This study presents a first review of syn- and posteruptive volcanic and related hazards and intends to stimulate future research in this field. Maar-diatreme volcanoes are phreatomagmatic monogenetic volcanoes. They may erupt explosively for days to 15 years. Above the preeruptive surface a relatively flat tephra ring forms. Below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone-shaped diatreme and its root zone. During activity both the maar-crater and the diatreme grow in depth and diameter. Inside the diatreme, which may penetrate downwards for up to 2.5 km, fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits. Ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside, thus the diatreme represents a kind of growing sinkhole. Due to the subsidence of the diatreme underneath, the maar-crater is a subsidence crater and also grows in depth and diameter with ongoing activity. As long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle. Syneruptive hazards of maar-diatreme volcanoes are earthquakes, eruption clouds, tephra fall, base surges, ballistic blocks and bombs, lahars, volcanic gases, cutting of the growing maar crater into the preeruptive ground, formation of a tephra ring, fragmentation of country rocks, thus destruction of area and ground, changes in groundwater table, and potential renewal of eruptions. The main hazards mostly affect an area 3 to possibly 5 km in radius. Distal effects are comparable to those of small eruption clouds from polygenetic volcanoes. Syneruptive effects on infrastructure, people, animals, vegetation, agricultural land, and drainage are pointed out. Posteruptive hazards concern erosion and formation of lahars. Inside the crater a lake usually forms and diverse types of sediments accumulate in the crater. Volcanic gases may be released in the crater. Compaction and other diagenetic processes within the diatreme fill result in its subsidence. This posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time. It may last millions of years. Various studies and monitoring are suggested for syn- and posteruptive activities of maar-diatreme volcanoes erupting in the future. The recently formed maar-diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic, limnic, and biologic evolution, and potential posteruptive hazards. For future maar-diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km. Areas that are potentially endangered by maar-diatreme eruptions in the future are pointed out.

Categorized Crater Counts on Martian Lobate Debris Aprons

NASA Astrophysics Data System (ADS)

Berman, D. C.; Crown, D. A.; Joseph, E. C.

2015-05-01

We have developed a new approach for analyzing crater size-frequency distributions designed to interpret formation and modification ages from complex geologic surfaces, such as those of ice-rich debris aprons.

A newly discovered impact crater in Titan's Senkyo: Cassini VIMS observations and comparison with other impact features

USGS Publications Warehouse

Buratti, B.J.; Sotin, Christophe; Lawrence, K.; Brown, R.H.; Le, Mouelic S.; Soderblom, J.M.; Barnes, J.; Clark, R.N.; Baines, K.H.; Nicholson, P.D.

2012-01-01

Senkyo is an equatorial plain on Titan filled with dunes and surrounded by hummocky plateaus. During the Titan targeted flyby T61 on August 25, 2009, the Cassini Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft observed a circular feature, centered at 5.4?? N and 341??W, that superimposes the dune fields and a bright plateau. This circular feature, which has been named Paxsi by the International Astronomical Union, is 120??10 km in diameter (measured from the outer edge of the crater rim) and exhibits a central bright area that can be interpreted as the central peak or pit of an impact crater. Although there are only a handful of certain impact craters on Titan, there are two other craters that are of similar size to this newly discovered feature and that have been studied by VIMS: Sinlap (Le Mou??lic et al, 2008) and Selk (Soderblom et al, 2010). Sinlap is associated with a large downwind, fan-like feature that may have been formed from an impact plume that rapidly expanded and deposited icy particles onto the surface. Although much of the surrounding region is covered with dunes, the plume region is devoid of dunes. The formation process of Selk also appears to have removed (or covered up) dunes from parts of the adjacent dune-filled terrain. The circular feature on Senkyo is quite different: there is no evidence of an ejecta blanket and the crater itself appears to be infilled with dune material. The rim of the crater appears to be eroded by fluvial processes; at one point the rim is breached. The rim is unusually narrow, which may be due to mass wasting on its inside and subsequent infill by dunes. Based on these observations, we interpret this newly discovered feature to be a more eroded crater than both Sinlap and Selk. Paxsi may have formed during a period when Titan was warmer and more ductile than it is currently. ?? 2011 Elsevier Ltd. All rights reserved.

Magma ascent and magmatism controlled by cratering on the Moon

NASA Astrophysics Data System (ADS)

Michaut, C.; Pinel, V.

2016-12-01

The lunar primary crust was formed by flotation of light plagioclase minerals on top of the lunar magma ocean, resulting in a relatively light and thick crust. This crust acted as a barrier for the denser primary mantle melts: mare basalts erupted primarily within large impact basins where at least part of this crust was removed. Thus, lunar magmas likely stored at the base of or deep in the lunar crust and the ascent of magma to shallow depths probably required local or regional tensional stresses. On the Moon, evidences of shallow sites of magmatism are mostly concentrated within old and degraded simple and complex craters that surround the Mare basalts. Impacts, that were numerous in the early times of the Moon, created depressions at the lunar surface that induced specific states of stress. Below a crater, magma ascent is helped by the tensional stresses caused by the depression up to a depth that is close to the crater radius. However, many craters that are the sites of shallow magmatism are less than 10 to 20 km in radius and are equally situated in regions of thin (i.e. 20 km) or thick (i.e. 60km) crust suggesting that the depression, although significant enough to control magma emplacement, was not large enough to induce it. Since the sites of magmatism surround the mare basalts, we explore the common idea that the weight of the Mare induced a tensile state of stress in the surrounding regions. We constrain the regional state of stress that was necessary to help magma ascent to shallow depths but was low enough for the local depression due to a crater to control magma emplacement. This state of stress is consistent with a relatively thin but extended mare load. We also show that the depression due to the crater probably caused the horizontalization and hence the storage of the magmatic intrusion at shallow depth below the crater. In the end, because of the neutral buoyancy of magmas in the crust and the lack of tectonic processes, impact processes largely controlled magma transport and secondary crust formation on the Moon.

Topographic Evaluation of Mars 2001 Candidate Landing Sites: A MGS-Viking Synergistic Study

NASA Technical Reports Server (NTRS)

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

1999-01-01

One of the greatest unresolved issues concerns the evolution of Mars early in its history; during the time period that accretion was winding down but the frequency of impacting debris was still heavy. Ancient cratered terrain that has only been moderately modified since the period of heavy bombardment covers about a quarter of the planet's surface but the environment during its formation is still uncertain. This terrain was dominantly formed by cratering. But unlike on the airless Moon, the impacting craters were strongly modified by other contemporary surface processes that have produced distinctive features such as 1) dendritic channel networks, 2) rimless, flatfloored craters, 3) obliteration of most craters smaller than a few kilometers in diameter (except for post heavy-bombardment impacts), and 4) smooth intercrater plains. The involvement of water in these modification processes seems unavoidable, but interpretations of the surface conditions on early Mars range from the extremes of 1) the "cold" model which envisions a thin atmosphere and surface temperatures below freezing except for local hydrothermal springs; and 2) the "warm" model, which invokes a thick atmosphere, seasonal temperatures above freezing in temperate and equatorial regions, and at least occasional precipitation as part of an active hydrological cycle. The nature of hydrologic cycles, if they occurred on Mars, would have been critically dependent on the environment. The resolution of where along this spectrum the actual environment of early Mars occurred is clearly a major issue, particularly because the alternate scenarios have much different implications about the possibility that life might have evolved on Mars.

Topographic Analysis of the Asymmetric Ejecta of Zunil Crater, Mars

NASA Astrophysics Data System (ADS)

Mouginis-Mark, P. J.; Sharpton, V. L.

2016-12-01

The 10.1 km diameter crater Zunil (7.7oN, 166.2oE) has many of the attributes of a fresh impact crater on Mars, including pitted material on the crater floor, an extensive field of secondary craters, as well as thermally-distinct crater rays. But unlike most craters of this size and location, Zunil crater displays a striking azimuthal variation in ejecta deposits with both fluidized and ballistic ejecta. Here we investigate the geometric attributes of the crater cavity and rim to try to identify the cause of this ejecta asymmetry, as well as the possible explanation for the formation of the ballistic ejecta. To accomplish this, we have created a digital elevation model (DEM) from stereo Context Camera (CTX) images, using the Ames Stereo Pipeline software. We used CTX frames F06_038250_1877 and G05_020211_1877 to produce a DEM with a nominal spatial resolution of 24 m/pixel, and use this DEM to conduct a detailed morphometric analysis of the crater in order to ascertain the nature of this "lobate-ballistic ejecta dichotomy", as well as derive new information on local target properties and the nature of the impact process itself. Measuring the rim height and radius at one-degree increments of azimuth, we find there are numerous places on the rim crest that are both higher and wider, or lower and narrower, than is typical for Zunil crater. There are places where rim height and radius are both close to average, while in other places both the rim height and radius are larger or smaller than the average. There is also a lack of consistency between the geometry of the crater and the type of ejecta; namely no direct correlation between rim height, crater radius, and ejecta type, but a slight negative correlation between radius and rim height for parts of the crater which possess ballistic ejecta. We find good circumstantial evidence that some of the target rock within which Zunil crater formed may have been dry at the time of impact compared to other craters of this size, latitude and elevation. We speculate that this lack of volatiles most likely arose from the drainage of water to depths greater than the excavation depth of Zunil crater. The asymmetric nature of the ejecta blanket argues strongly against the notion that the Martian atmosphere was partially responsible for ejecta fluidization.

In Situ Sedimentological Evidence for Climate Change in Early Mars Provided by the Curiosity Rover in Gale Crater

NASA Astrophysics Data System (ADS)

Heydari, Ezat; Fairen, Alberto G.

2016-10-01

The Striated formation is one of the rock units that was deposited in Gale crater, Mars, during the Late Noachian to Hesperian time (4.2 to 3.6 billion years ago). It crops out for 3 km along the Curiosity's traverse. The Striated formation strikes N65○E and has a depositional dip of 10○ - 20○ to SE. It consists of 500 m to 1000 m of highly rhythmic layers each 1 m to 4 m in thickness. Study of MAHLI and MastCam images provided by the Curiosity Rover indicates that layers form fining-upward cycles consisting of thick-bedded to massive conglomerate at the base that grades upward to thinly bedded conglomerate, then to pebbly sandstone, and topped by laminated, fine grained sandstone. Layers show slump folds, soft sediment deformation, and cross-beddings.The highly rhythmic occurrence and the fining-upward grain size characteristic indicate that each layer within the Striated formation is a coarse-grained turbidite: a type of rock that forms when sediments move down-hill by gravity-driven turbidity flows and deposit in deep waters. We propose that turbidite layers of the Striated formation are related to delivery of sediments to Gale crater by megafloods through its northern rim. Upon entering Gale crater, sediments moved down-hill and deposited as turbidite layers when the crater may have been filled to the rim with water. About 1000 to 3000 turbidite layers are present suggesting the occurrences of as many megafloods during hothouse climatic intervals when Mars was warmer than the Present and had plenty of liquid water. Floods were generated by one or a combination of the following processes: (1) torrential rain along the margins of Mars's Northern Ocean, 500 km to 1000 km to the north, (2) rapid melting of ice in highland areas, and (3) tsunamis formed by impacts on the Northern Ocean. Cold and/or dry climate of icehouse intervals may have followed each warming episode. Mars's climate forcing mechanism and periodicities of climate change are not clear at this point. However, the highly regular and rhythmic nature of turbidite layers point to an orbital triggering mechanism, possibly driven by changes in obliquity.

The Geographic Distribution of Boulder Halo Craters at Mid-to-High Latitudes on Mars

NASA Technical Reports Server (NTRS)

Rader, L. X.; Fassett, C. I.; Levy, J. S.; King, I. R.; Chaffey, P. M.; Wagoner, C. M.; Hanlon, A. E.; Watters, J. L.; Kreslavsky, M. A.; Holt, J. W.;

Intercrater Plains and Heavily Cratered Terrain

NASA Image and Video Library

2000-08-05

This image, from NASA Mariner 10 spacecraft which launched in 1974, shows intercrater plains and heavily cratered terrain typical of much of Mercury outside the area affected by the formation of the Caloris basin.

An Impact Ejecta Behavior Model for Small, Irregular Bodies

NASA Technical Reports Server (NTRS)

Richardson, J. E.; Melosh, H. J.; Greenberg, R.

2003-01-01

In recent years, spacecraft observations of asteroids 951 Gaspra, 243 Ida, 253 Mathilde, and 433 Eros have shown the overriding dominance of impact processes with regard to the structure and surface morphology of these small, irregular bodies. In particular, impact ejecta play an important role in regolith formation, ranging from small particles to large blocks, as well as surface feature modification and obscuration. To investigate these processes, a numerical model has been developed based upon the impact ejecta scaling laws provided by Housen, Schmidt, and Holsapple, and modified to more properly simulate the late-stage ejection velocities and ejecta plume shape changes (ejection angle variations) shown in impact cratering experiments. A target strength parameter has also been added to allow the simulation of strength-dominated cratering events in addition to the more familiar gravity-dominated cratering events. The result is a dynamical simulation which models -- via tracer particles -- the ejecta plume behavior, ejecta blanket placement, and impact crater area resulting from a specified impact on an irregularly shaped target body, which is modeled in 3-dimensional polygon fashion. This target body can be placed in a simple rotation state about one of its principal axes, with the impact site and projectile/target parameters selected by the user. The gravitational force from the irregular target body (on each tracer particle) is determined using the polygonized surface (polyhedron) gravity technique developed by Werner.

On the nature and rate of resurfacing of Venus

NASA Technical Reports Server (NTRS)

Arvidson, Raymond E.; Grimm, Robert E.; Phillips, Roger J.; Schaber, Gerald G.; Shoemaker, Eugene M.

1990-01-01

Crrater production and obliteration are modeled for the plains of Venus, using (1) the observed distribution of Venus-crossing asteroids and comets; (2) viscous relaxation of crater topography; and (3) erosion and burial by atmospheric, volcanic, and tectonic processes. Crater lifetimes are assumed to be proportional to crater depths for both classes of obliterative processes although the individual criteria vary. An average crater retention age between 0.4 to 2.0 Gyr is estimated for plains, under the assumption that craters are produced and not removed. The range is driven by uncertainty in identifying degraded impact as opposed to volcanic craters. On the other hand, crater retention ages greater than about 1.6 Gyr are unlikely if viscous relaxation operates without loading of crater floor by burial. The preferred model has plains subject to crater production and obliteration processes that vary over both space and time.

Martian planetwide crater distributions: Implications for geologic history and surface processes

USGS Publications Warehouse

Soderblom, L.A.; Condit, C.D.; West, R.A.; Herman, B.M.; Kreidler, T.J.

1974-01-01

Population-density maps of craters in three size ranges (0.6 to 1.2 km, 4 to 10 km, and >20 km in diameter) were compiled for most of Mars from Mariner 9 imagery. These data provide: historical records of the eolian processes (0.6 to 1.2 km craters); stratigraphic, relative, and absolute timescales (4 to 10 km craters); and a history of the early postaccretional evolution of the uplands (> 20 km craters). Based on the distribution of large craters (>20 km diameters), Mars is divisible into two general classes of terrain, densely cratered and very lightly cratered-a division remarkably like the uplands-maria dichotomy of the moon. It is probable that this bimodal character in the density distribution of large craters arose from an abrupt transition in the impact flux rate from an early intense period associated with the tailing off of accretion to an extended quiescent epoch, not from a void in geological activity during much of Mars' history. Radio-isotope studies of Apollo lunar samples show that this transition occurred on the moon in a short time. The intermediate-sized craters (4 to 10 km diameter) and the small-sized craters (0.6 to 1.2 km diameter) appear to be genetically related. The smaller ones are apparently secondary impact craters generated by the former. Most of the craters in the larger of these two size classes appear fresh and uneroded, although many are partly buried by dust mantles. Poleward of the 40?? parallels the small fresh craters are notably absent owing to these mantles. The density of small craters is highest in an irregular band centered at 20??S. This band coincides closely with (1) the zone of permanent low-albedo markings; (2) the "wind equator" (the latitude of zero net north or south transport at the surface); and (3) a band that includes a majority of the small dendritic channels. Situated in the southermost part of the equatorial unmantled terrain which extends from about 40??N to 40??S, this band is apparently devoid of even a thin mantle. Because this belt is also coincident with the latitutde of maximum solar insolation (periapsis occurs near summer solstice), we suggest that this band arises from the asymmetrical global wind patterns at the surface and that the band probably follows the latitude of maximum heating which migrates north and south from 25??N to 25??S within the unmantled terrain on a 50,000 year timescale. The population of intermediate-sized craters (4-10 km diameter) appears unaffected by the eolian mantles, at least within the ??45?? latitudes. Hence the local density of these craters is probably a valid indicator of the relative age of surfaces generated during the period since the uplands were intensely bombarded and eroded. It now appears that the impact fluxes at Mars and the moon have been roughly the same over the last 4 b.y. because the oldest postaccretional, mare-like surfaces on Mars and the moon display about the same crater density. If so, the nearness of Mars to the asteroid belt has not generated a flux 10 to 25 times greater than the lunar flux. Whereas the lunar maria show a variation of about a factor of three in crater density from the oldest to the youngest major units, analogous surfaces on Mars show a variation between 30 and 50. This implies that periods of active eolian erosion, tectonic evolution, volcanic eruption, and possibly fluvial modification have been scattered throughout Martian history since the formation and degradation of the martian uplands and not confined to small, ancient or recent, epochs. These processes are surely active on the planet today. ?? 1974.

Distribution and Orientation of Alluvial Fans in Martian Craters

NASA Technical Reports Server (NTRS)

Kraal, E. R.; Moore, J. M.; Howard, A. D.; Asphaug, E. I.

2005-01-01

We present the results of the complete survey of Martian alluvial fans from 0-30 S, initiated by Moore and Howard. Nineteen impact craters contain alluvial fans. They are regionally grouped into three distinct areas. We present our initial results regarding their distribution and orientation in order to understand what controls their formation. Since alluvial fans are formed by water transport of sediment, these features record wetter episodes of Martian climate. In addition, their enigmatic distribution (in regional groups and in some craters, but not similar adjacent ones) needs to be understood, to see how regional geology, topographic characteristics, and/or climate influence their formation and distribution.

Landform degradation on Mercury, the moon, and Mars - Evidence from crater depth/diameter relationships

NASA Technical Reports Server (NTRS)

Malin, M. C.; Dzurisin, D.

1977-01-01

Craters on Mercury, the moon, and Mars were classified into two groups, namely, fresh and degraded craters, on the basis of qualitative visual degradation as revealed by degree of rim crispness, terraced interior walls, slumping from crater walls, etc., and the depth/diameter relationship of craters was studied. Lunar and Mercurian crater populations indicate the existence of terrain-correlated degradational phenomena. The depth/diameter relations for Mercury and the moon display remarkably similar forms, suggesting similar degrees of landform degradation. Depth/diameter curves display a break in slope, dividing two distinct crater populations. Mars craters show few of the trends of those of Mercury and the moon. The depth/diameter curve has no definite break in slope, though there is considerable depth variation. The role of nonballistic degradation in connection with the early formation of large expanses of intercrater plains is discussed.

Formation of lunar basin rings

USGS Publications Warehouse

Hodges, C.A.; Wilhelms, D.E.

1978-01-01

The origin of the multiple concentric rings that characterize lunar impact basins, and the probable depth and diameter of the transient crater have been widely debated. As an alternative to prevailing "megaterrace" hypotheses, we propose that the outer scarps or mountain rings that delineate the topographic rims of basins-the Cordilleran at Orientale, the Apennine at Imbrium, and the Altai at Nectaris-define the transient cavities, enlarged relatively little by slumping, and thus are analogous to the rim crests of craters like Copernicus; inner rings are uplifted rims of craters nested within the transient cavity. The magnitude of slumping that occurs on all scarps is insufficient to produce major inner rings from the outer. These conclusions are based largely on the observed gradational sequence in lunar central uplifts:. from simple peaks through somewhat annular clusters of peaks, peak and ring combinations and double ring basins, culminating in multiring structures that may also include peaks. In contrast, belts of slump terraces are not gradational with inner rings. Terrestrial analogs suggest two possible mechanisms for producing rings. In some cases, peaks may expand into rings as material is ejected from their cores, as apparently occurred at Gosses Bluff, Australia. A second process, differential excavation of lithologically diverse layers, has produced nested experimental craters and is, we suspect, instrumental in the formation of terrestrial ringed impact craters. Peak expansion could produce double-ring structures in homogeneous materials, but differential excavation is probably required to produce multiring and peak-in-ring configurations in large lunar impact structures. Our interpretation of the representative lunar multiring basin Orientale is consistent with formation of three rings in three layers detected seismically in part of the Moon-the Cordillera (basin-bounding) ring in the upper crust, the composite Montes Rook ring in the underlying, more coherent "heald" crust, and an innermost, 320-km ring at the crust-mantle interface. Depth-diameter ratios of 1 10to 1 15 are consistent with this interpretation and suggest that volumes of transient cavities and hence of basin ejecta may be considerably greater than commonly assumed. ?? 1978.

Tafoni - A Llink Between Mars and Earth

NASA Astrophysics Data System (ADS)

Iacob, R. H.; Iacob, C. E.

2013-12-01

Remarkable rock erosion structures on the planetary surface, tafoni represent an important instrument for investigating the specific environmental conditions causing such rock formations. From simple cavities to refined honeycomb or other intricate patterns, tafoni are a reflection of the complex interaction between the rock structure and the environmental factors. On the genesis of tafoni, there is no unique breakdown mechanism at work, but a multitude of physical and chemical processes developing over time. However, some of these formation mechanisms are typically predominant. Tafoni can be found on a variety of rock substrates, from sandstone and vesicular lava rocks to granite and basalt, and in a variety of environments, from wet coastal areas to the extreme dry zones of hot deserts, high plateaus or frozen lands of Antarctica. During various NASA missions, tafoni were also identified on rock formations on Mars. Comparative study of the environmental conditions leading to the formation of tafoni on Earth and Mars can help explain past and present surface erosion mechanisms on the Red Planet. The mechanisms responsible for tafoni formation on Earth include wind erosion, exfoliation, frost shattering, and, in the majority of cases, salt weathering. Microclimate variations of temperature, evaporation of salt water, disaggregation of mineral grains, as well as sandblasting, are among most common contributors that initiate the pitting of the rock surface, giving way to further development of tafoni alveoli, cavities and other erosion patterns. Dissolution of calcium carbonates and siliceous cements, or hydration of feldspars, are representative examples of tafoni erosion involving rain water, sea water or air moisture. Live organisms and biochemical processes are significant contributors to the formation and evolution of tafoni, especially in humid or water reach environments. In many instances, tafoni reflect erosion mechanism specific to environmental conditions that no longer exist. NASA's current Mars Science Laboratory mission offers exceptional opportunities to perform a comparative study between tafoni formations on Mars and those on Earth. The present mission of Curiosity at Gale Crater, benefiting not only from the most advanced technology for in-situ investigations but also from a terrain rich in rock breakdown features, was able to reveal new tafoni formations. Gale Crater's landscape presents a variety of surface erosion elements, witnesses of major planetary transformations suffered by Mars during the past 3 billion years. While the wind and sand-blasting erosion are the most recent causes of the surface erosion at Gale Crater, leading to the smoothing, thinning, exfoliation and piercing of various rock layers, other geological formations such as alluvial fans, moat areas, gravel sediments, round shaped mounds and toadstool formations demonstrate that liquid water was vigorously shaping the surface of Mars billions of years ago. In such a context, the study of tafoni formations revealed during Curiosity's trek from Bradbury Landing through the Glenelg area of Gale Crater, will help advance the understanding of the Martian past and present environment, providing scenarios for the evolution of the Red Planet. The presentation contains various images of tafoni samples from Mars and Earth, explaining by similitude presumptive weathering mechanisms on Mars.

Preservation of layered paleodeposits in high-latitude pedestal craters on Mars

NASA Astrophysics Data System (ADS)

Kadish, Seth J.; Head, James W.

2011-06-01

An outstanding question in Mars' climate history is whether or not pedestal craters represent the armored remnants of ice-rich paleodeposits. We address this question using new high-resolution images; in a survey of several hundred high-latitude pedestal craters, we have identified 12 examples in which visible and/or topographically expressed layers are exposed on the marginal scarp of the pedestal. One example, located on the south polar layered deposits, preserves ice-rich layers that have otherwise been completely removed from the polar cap. These observations provide empirical evidence that the pedestal crater formation mechanism is capable of armoring and preserving ice-rich layered paleodeposits. Although layered exposures have not yet been observed in mid-latitude pedestal craters, high-latitude instances of discontinuous, partially covered layers suggest that layers can be readily concealed, likely through mantling and/or mass wasting processes along the marginal scarp. This interpretation is supported by the observation that high-latitude pedestals with exposed layers along their margins are, on average, taller than mid-latitude examples, and have larger, steeper marginal scarps, which may help to maintain layer exposures. These observations favor the interpretation that mid- to high-latitude pedestal craters represent the armored remnants of ice- and dust-rich paleodeposits, which occurred transiently due to changes in the climate regime. Preservation of fine-scale layering of ice and dust at these latitudes implies that the climate change did not involve regional melting conditions.

Crater Retention Ages from (4) Vesta Matching Independent Ar-Ar Ages of HED Meteorites

NASA Astrophysics Data System (ADS)

Schmedemann, Nico; Kneissl, Thomas; Ivanov, Boris A.; Michael, Gregory G.; Neukum, Gerhard; Nathues, Andreas; Sierks, Holger; Wagner, Roland; Krohn, Katrin; Le Corre, Lucille; Reddy, Vishnu; Ruesch, Ottaviano; Hiesinger, Harald; Jaumann, Ralf; Raymond, Carol A.; Russell, Christopher T.

2013-04-01

In July 2012 the Dawn spacecraft completed its mapping task of the Main Belt asteroid Vesta with a second high altitude mapping orbit. Dawn is now on its way to the dwarf planet (1) Ceres, where it will perform a similar mapping campaign like that at Vesta [1]. The Main Belt is the source region of most impactors in the inner solar system [2,3,4], making it a key region for understanding the early history of our Solar System. In order to determine absolute surface ages from Vesta we derived a crater production function and a chronology function for Vesta. We derived these functions from the respective lunar functions [2] and scaled [5] them to the impact conditions on Vesta [6]. In general we find good agreement between the derived crater production function and the measured crater distribution. However, we also find disagreement between 8 and 15 km crater size, on areas older ~2.2 Ga. Older areas show a steep (~-6 cumulative) slope, which we link to a decaying influence of the vestan collisional family (Vestoids). The lower boundary of 8 km crater size may be explained by fast ejected small spalls and/or a more efficient Yarkovsky effect [7]. This influence is not observed for instance inside the large Rheasilvia basin, which we date with ~2.2 Ga. Since the formation of this basin is believed to be a major source of replenishment of the Vestoids, it's currently observed cratering record is not indicative for the basin formation age in contrast to [8]. The young interior of the Rheasilvia basin is likely a result of repeated resets of the crater retention age due to mass wasting processes on the basin walls. We use topographic heights, which are less affected by mass wasting such as the top of the central peak of the basin as well as proximal ejecta blankets outside the basin to date the formation age of Rheasilvia. For the central peak we derive a surface age of 3.59 (+0.079/-0.18) Ga. The proximal ejecta blanket at the Oppia crater is dated with 3.62 (+0.054/-0.087) Ga and 3.63 (+0.058/-0.096) Ga. We also find seismic (miniscule ejecta blanket from Rheasilvia) resurfacing events in the time frame of ~3.56 to ~3.59 Ga at several areas in the northern hemisphere, indicative for a major seismic activity probably connected to the Rheasilvia formation. An antipodal activity is also suggested by hydrocode modeling [9]. By summation of age probability curves of measurements we link to the Rheasilvia formation, we find 3.58 (+0.07/-0.12) Ga. Using a similar attempt we find 3.75 (+0.05/-0.21) Ga for the Veneneia formation. Both crater retention ages correspond within the error bars with prominent peaks of independent Ar-Ar ages of Vesta related HED meteorites [10]. Acknowledgement: This work has been supported by the German Space Agency (DLR) on behalf of the Federal Ministry of Economics and Technology, grants 50OW1101(NS,TK), 50QM1001 (GM) and 50OW1102 (OR,HH). References: [1] Russell et al. (2007): Advances in Space Research 40(2): pp193-201, 2007. [2] Neukum and Ivanov: In: Gehrels T (ed) "Hazards due to comets and asteroids". University of Arizona Press, Tucson, 359-416, 1994. [3] O'Brien and Greenberg (2005): Icarus 178(1): 179-212. [4] Nesvorny et al. (2009): Icarus 200(2): 698-701. [5] Ivanov (2001): Chronology and Evolution of Mars 96, 87-104, 2001. [6] Schmedemann et al. (2012): 43.LPSC, The Woodlands, #1659. [7] Morbidelli et al. (2003): Icarus 162, 328-336. [8] Marchi et al. (2012): Science 336, 690. [9] Bowling et al. (2012): 75th Annual Meeting of the Meteoritical Society, 2012, Cairns, Australia. Meteoritics and Planetary Science Supplement, id.5256. [10] Bogard, D. D. (2011): Chemie der Erde - Geochemistry, vol. 71, issue 3: 207-226.

Using the Bombardment History of the Moon to Understand Planet Formation

NASA Astrophysics Data System (ADS)

Bottke, W. F.; NASA/NLSI CenterLunar Origin; Evolution (CLOE)

2011-12-01

The Moon is unique. It is the only object that is both relatively accessible and still bears scars from practically every epoch of solar system formation. This is both a challenge and a blessing. It is a challenge because to understand the Moon's complex bombardment history, we need to understand the formation and evolution of the solar system as a whole. It is a blessing because the Moon is an irreplaceable resource for the study of events that have shaped the Earth and other planets. For example, we can now show the Moon's bombardment history can be broken into several episodes defined by planet formation processes. The earliest phase lasts for several hundreds of My after the first solids form. Here many planets grow via a new process called "planetesimal-driven migration", with embryos moving outward in the disk by gravitationally-scattering planetesimals. This mobility assists accretion and may explain the interesting properties of certain worlds (e.g., Mars). In the outer solar system, the giant planets form on different orbits than their observed ones via a variety of processes that we are still struggling to understand. The evidence they had a different configuration, however, can be found in (i) the orbital distribution of the asteroid belt, with particular unusual asteroids residing where Jupiter used to have its mean motion resonances, and (ii) in the lunar crater record, with the oldest craters formed at half the impact velocity than more recent ones. The lunar impact flux over this interval constrains how these worlds evolved. The second episode occurred near 4.1 Ga and is often called the "Nice model". It was triggered by a dynamical instability taking place among the giant planets, who quickly moved to their current orbits via interactions with both themselves and comet-like planetesimals scattered out of a disk residing beyond 12 AU. A by-product of this planetary reconfiguration was the ejection of comets and asteroids from stable reservoirs across this solar system. Some hit the Moon and produced the so-called lunar "cataclysm", with impact velocities nearly the same as current values. This velocity change allows us to use craters to predict that this episode started near the formation time of lunar basin Nectaris. The episode's end is often thought to be marked across the solar system by the formation of the last lunar basin Orientale near 3.7 Ga. However, basin-forming projectiles liberated by this event continued to hit Earth throughout the Archean and likely persisted until ~2.5 Ga. The implications of this for the history of our biosphere are likely to be profound. The final episode, which lasted billions of years, is defined by collision events in the asteroid belt, which deliver impactors to the inner solar system via dynamical processes. This period likely contains both "lulls" and intervals of steeply higher impact rates via asteroid showers. While the history of this period is still poorly understood, correlations between the lunar crater record and family-forming events in the main belt suggest impacts have influenced, perhaps significantly, the evolution of life on Earth.

Reports of planetary geology program, 1976 - 1977. [abstracts

NASA Technical Reports Server (NTRS)

Arvidson, R. (Compiler); Wahmann, R. (Compiler); Howard, J. H., III

1977-01-01

One hundred seventeen investigations undertaken in the NASA Planetary Geology Program in 1976-1977 are reported in abstract form. Topics discussed include solar system formation; planetary interiors; planetary evolution; asteroids, comets and moons; cratering; volcanic, eolian, fluvial and mass wasting processes; volatiles and the Martian regolith; mapping; and instrument development and techniques. An author index is provided.

The Explorer's Guide to Impact Craters

NASA Technical Reports Server (NTRS)

Chuang, F.; Pierazzo, E.; Osinski, G.

2005-01-01

Impact cratering is a fundamental geologic process of our solar system. It competes with other processes, such as plate tectonics, volcanism, fluvial, glacial and eolian activity, in shaping the surfaces of planetary bodies. In some cases, like the Moon and Mercury, impact craters are the dominant landform. On other planetary bodies impact craters are being continuously erased by the action of other geological processes, like volcanism on Io, erosion and plate tectonics on the Earth, tectonic and volcanic resurfacing on Venus, or ancient erosion periods on Mars. The study of crater populations is one of the principal tools for understanding the geologic history of a planetary surface. Among the general public, impact cratering has drawn wide attention through its portrayal in several Hollywood movies. Questions that are raised after watching these movies include: How do scientists learn about impact cratering? , and What information do impact craters provide in understanding the evolution of a planetary surface? Fundamental approaches used by scientists to learn about impact cratering include field work at known terrestrial craters, remote sensing studies of craters on various solid surfaces of solar system bodies, and theoretical and laboratory studies using the known physics of impact cratering.

Ceres' intriguing Occator crater and its faculae: formation and evolution

NASA Astrophysics Data System (ADS)

Buczkowski, D.; Scully, J. E. C.; Bowling, T.; Bu, C.; Castillo, J. C.; Jaumann, R.; Longobardo, A.; Nathues, A.; Neesemann, A.; Palomba, E.; Platz, T.; Quick, L. C.; Raponi, A.; Raymond, C. A.; Ruesch, O.; Russell, C. T.; Schenk, P.; Stein, N.

2017-12-01

Since March 2015, the Dawn spacecraft has orbited and explored Ceres, which is a dwarf planet and the largest object in the asteroid belt (radius 470 km). One of the most intriguing features on Ceres' surface is Occator crater, a 92-km-diameter impact crater that contains distinctive bright spots, called faculae, within its floor (Nathues et al., 2015; Russell et al., 2016; Schenk et al., 2017). Occator crater has been dated to 20-30 million years old (Nathues et al., 2017; Neesemann et al., 2017). The single scattering albedo of Occator's faculae is 0.67-0.80, which is greater than Ceres' average single scattering albedo of 0.09-0.11 (Li et al., 2016). The central facula is named Cerealia Facula, and is located in a 9 km wide and 700 m deep pit. There are also multiple additional faculae in the eastern crater floor, which are named the Vinalia Faculae. The faculae are mostly composed of sodium carbonate, are distinct from Ceres' average surface composition and are proposed to be the solid residues of crystallized brines (De Sanctis et al., 2016). The presence of such bright, apparently fresh, material on the surface of a dwarf planet that is billions of years old is intriguing, and indicates that active processes involving brines occurred within the geologically recent past. The Dawn Science Team has investigated whether the processes that formed the crater and the faculae are entirely endogenic, entirely exogenic or a combination of both. For example, the extensive lobate materials within the crater floor have been proposed to be impact melt, mass wasting deposits or cryolava flows (e.g. Buczkowski et al., 2017; Jaumann et al., 2017; Nathues et al., 2017; Schenk et al., 2017). Each possibility has the potential to provide fascinating insights into Ceres' evolution, including the potential for liquids within Ceres' interior today. The team's in-depth investigation of Occator crater will be presented in an upcoming special issue of the journal Icarus. This special issue will include analyses of Occator and the faculae based on Dawn data, modeling studies, laboratory experiments, and studies comparing Occator and the faculae to other impact craters and bright deposits. In this presentation we will preview and summarize these results.

Ground Truthing Orbital Clay Mineral Observations with the APXS Onboard Mars Exploration Rover Opportunity

NASA Technical Reports Server (NTRS)

Schroeder, C.; Gellert, R.; VanBommel, S.; Clark, B. C.; Ming, D. W.; Mittlefehldt, D. S.; Yen, A. S.

2016-01-01

NASA's Mars Exploration Rover Opportunity has been exploring approximately 22 km diameter Endeavour crater since 2011. Its rim segments predate the Hesperian-age Burns formation and expose Noachian-age material, which is associated with orbital Fe3+-Mg-rich clay mineral observations [1,2]. Moving to an orders of magnitude smaller instrumental field of view on the ground, the clay minerals were challenging to pinpoint on the basis of geochemical data because they appear to be the result of near-isochemical weathering of the local bedrock [3,4]. However, the APXS revealed a more complex mineral story as fracture fills and so-called red zones appear to contain more Al-rich clay minerals [5,6], which had not been observed from orbit. These observations are important to constrain clay mineral formation processes. More detail will be added as Opportunity is heading into her 10th extended mission, during which she will investigate Noachian bedrock that predates Endeavour crater, study sedimentary rocks inside Endeavour crater, and explore a fluid-carved gully. ESA's ExoMars rover will land on Noachian-age Oxia Planum where abundant Fe3+-Mg-rich clay minerals have been observed from orbit, but the story will undoubtedly become more complex once seen from the ground.

Amazonian mid- to high-latitude glaciation on Mars: Supply-limited ice sources, ice accumulation patterns, and concentric crater fill glacial flow and ice sequestration

NASA Astrophysics Data System (ADS)

Fastook, James L.; Head, James W.

2014-02-01

Concentric crater fill (CCF) occurs in the interior of impact craters in mid- to high latitudes on Mars and is interpreted to have formed by glacial ice flow and debris covering. We use the characteristics and orientation of deposits comprising CCF, the thickness of pedestal deposits in mid- to high-latitude pedestal craters (Pd), the volumes of the current polar caps, and information about regional slopes and ice rheology to address questions about (1) the maximum thickness of regional ice deposits during the Late Amazonian, (2) the likelihood that these deposits flowed regionally, (3) the geological regions and features most likely to induce ice-flow, and (4) the locations and environments in which ice is likely to have been sequestered up to the present. We find that regional ice flow under Late Amazonian climate conditions requires ice thicknesses exceeding many hundreds of meters for slopes typical of the vast majority of the surface of Mars, a thickness for the mid-latitudes that is well in excess of the total volume available from polar ice reservoirs. This indicates that although conditions for mid- to high-latitude glaciation may have persisted for tens to hundreds of millions of years, the process is “supply limited”, with a steady state reached when the polar ice cap water ice supply becomes exhausted. Impact craters are by far the most abundant landform with associated slopes (interior wall and exterior rim) sufficiently high to induce glacial ice flow under Late Amazonian climate conditions, and topographic slope data show that Amazonian impact craters have been clearly modified, undergoing crater interior slope reduction and floor shallowing. We show that these trends are the predictable response of ice deposition and preferential accumulation and retention in mid- to high-latitude crater interiors during episodes of enhanced spin-axis obliquity. We demonstrate that flow from a single episode of an inter-crater terrain layer comparable to Pedestal Crater deposit thicknesses (~50 m) cannot fill the craters in a time period compatible with the interpreted formation times of the Pedestal Crater mantled ice layers. We use a representative obliquity solution to drive an ice flow model and show that a cyclical pattern of multiply recurring layers can both fill the craters with a significant volume of ice, as well as transport debris from the crater walls out into the central regions of the craters. The cyclical pattern of waxing and waning mantling layers results in a rippled pattern of surface debris extending out into the crater interiors that would manifest itself as an observable concentric pattern, comparable in appearance to concentric crater fill. In this scenario, the formation of mantling sublimation till layers seals the accumulating ice and sequesters it from significant temperature variations at diurnal, annual and spin-axis/orbital cycle time scales, to produce ancient ice records preserved today below CCF crater floors. Lack of meltwater features associated with concentric crater fill provides evidence that the Late Amazonian climate did not exceed the melting temperature in the mid- to high-latitudes for any significant period of time. Continued sequestration of ice with time in CCF and related deposits (lobate debris aprons and lineated valley fill) further reduces the already supply-limited polar ice sources, suggesting that there has been a declining reservoir of available ice with each ensuing glacial period. Together, these deposits represent a candidate library of climate chemistry and global change dating from the Late Amazonian, and a non-polar water resource for future exploration.

Constraints on the Martian cratering rate imposed by the SNC meteorites and Vallis Marineris layered deposits

NASA Technical Reports Server (NTRS)

Brandenburg, J. E.

1993-01-01

Following two independent lines of evidence -- estimates of the age and formation time of a portion of the Martian geologic column exposed in the layered deposits and the crystallization and ejection ages of the SNC meteorites -- it appears that the Martian cratering rate must be double the lunar rate or even higher. This means models such as NHII or NHIII (Neukum and Hiller models II and III), which estimate the Martian cratering rate as being several times lunar are probably far closer to reality on Mars than lunar rates. The effect of such a shift is profound: Mars is transformed from a rather Moon-like place into a planet with vigorous dynamics, multiple large impacts, erosion, floods, and volcanism throughout its history. A strong shift upward in cratering rates on Mars apparently solves some glaring problems; however, it creates others. The period of time during which Earth-like atmospheric conditions existed, the liquid water era on Mars, persists in NHIII up to only 0.5 b.y. ago. Scenarios of extended Earth-like conditions on Mars have been discounted in the past because they would have removed many of the craters from the early bombardment era found in the south. It does appear that some process of crater removal was quite vigorous in the north during Mars' past. Evidence exists that the northern plains may have been the home of long-lived seas or perhaps even a paleo-ocean, so models exist for highly localized destruction of craters in the north. However, the question of how the ancient crater population could be preserved in the south under a long liquid-water era found in any high-cratering-rate models is a serious question that must be addressed. It does appear to be a higher-order problem because it involves low-energy dynamics acting in localized areas, i.e., erosion of craters in the south of Mars, whereas the two problems with the low-cratering-rate models involve high-energy events acting over large areas: the formation of the Vallis Marineris, the SNC ejecting impacts, and the global atmospheric pressure and temperature conditions that allow liquid water to exist as a robust entity anywhere on the Martian surface. In any case, it appears Mars is a more complex and dynamic planet than previously supposed. It has canyons dating from the middle to late period of its history that contain apparent lake sediments bedded deeper than most sediments on Earth. Recent multiple, violent impacts on Mars have apparently provided us with multiple random samples of its surface that all crystallized less than 1.5 b.y. ago. These things cannot be accommodated in our present cratering chronologies of Mars, based on 1x lunar cratering rates, without great difficulties. These difficulties suggest that a new chronology, probably based on NHII or even NHIII, should be adopted; this new chronology will provide us with a new view of Mars as a dynamic planet of rich history.

The formation of peak rings in large impact craters.

PubMed

Morgan, Joanna V; Gulick, Sean P S; Bralower, Timothy; Chenot, Elise; Christeson, Gail; Claeys, Philippe; Cockell, Charles; Collins, Gareth S; Coolen, Marco J L; Ferrière, Ludovic; Gebhardt, Catalina; Goto, Kazuhisa; Jones, Heather; Kring, David A; Le Ber, Erwan; Lofi, Johanna; Long, Xiao; Lowery, Christopher; Mellett, Claire; Ocampo-Torres, Rubén; Osinski, Gordon R; Perez-Cruz, Ligia; Pickersgill, Annemarie; Poelchau, Michael; Rae, Auriol; Rasmussen, Cornelia; Rebolledo-Vieyra, Mario; Riller, Ulrich; Sato, Honami; Schmitt, Douglas R; Smit, Jan; Tikoo, Sonia; Tomioka, Naotaka; Urrutia-Fucugauchi, Jaime; Whalen, Michael; Wittmann, Axel; Yamaguchi, Kosei E; Zylberman, William

2016-11-18

Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust. Copyright © 2016, American Association for the Advancement of Science.

Two astroblems in Ukraine - witnesses of the last days of dinosaurs

NASA Astrophysics Data System (ADS)

Vidmachenko, A. P.

2017-05-01

Moor then 65 million years ago an asteroid with a few kilometers in size with mass of 1 trillion tons created a crater Chicxulub with a diameter of 170 km on the Yucatán Peninsula in Mexico. Then the dinosaurs died out. The largest of Ukrainian astroblems is Manevichska, located in Volyn region. It has a diameter of 45 km and occurred about 65 million years ago too. In the central part of Ukraine on the border of Kirovograd and Cherkassy regions, there is Boltyshka astrobleme. The crater has diameter 25 km and depth of more than 1 km. Boltyshka crater also appeared more than 65 million years ago. These dating of the occurrence of astroblems indicates the close age of these two craters with formation of Chicxulub. If almost coinciding formation time of two or more impact structures, it is significantly increases the effect of impact on the environment and living beings.

Numerical modelling of impact crater formation associated with isolated lunar skylight candidates on lava tubes

NASA Astrophysics Data System (ADS)

Martellato, E.; Foing, B. H.; Benkhoff, J.

2013-09-01

Skylights are openings on subsurface voids as lava tubes and caves. Recently deep hole structures, possibly skylights, were discovered on lunar photo images by the JAXA SELenological and ENgineering Explorer (SELENE)-Kaguya mission, and successively confirmed by the NASA Lunar Reconnaissance Orbiter (LRO) mission. Vertical hole structures and possibly underlying subsurface voids have high potential as resources for scientific study, and future unmanned and manned activities on the Moon. One mechanism proposed for their formation is impact cratering. The collapse of craters is due to the back spallation phenomena on the rear surface of the lava tube roofs. Previous analysis in this topic was based on small-scales laboratory experiments. These have pointed out that (i) the target thickness-to-crater diameter ratio is 0.7, and (ii) the projectile diameter-to-target thickness ratio is 0.16, at the ballistic limit once extrapolated to planetary conditions.

Characteristic properties of laser ablation of translucent targets

NASA Astrophysics Data System (ADS)

Platonov, V. V.; Kochurin, E. A.; Osipov, V. V.; Lisenkov, V. V.; Zubarev, N. M.

2018-07-01

This study reveals the characteristic features of the laser ablation of the solid Nd:Y2O3 targets, such as the dynamics of the laser plume, the crater depth, and the weight and size distribution of liquid melt droplets. The ablation was initiated by the ytterbium fiber laser radiation pulses with constant energy (0.67 J) and with different power densities. The dependence on the power density of such parameters as the injection time of drops, mass distribution of drops, crater depth, and productivity of synthesis of nonopowder was revealed. To explain the formation of deep craters a model was proposed, stating that the formation of liquid droplets is a consequence of the Kelvin–Helmholtz instability’s appearing and developing on the border between the liquid melt on the crater’s wall and the vapor flow from the crater. The increment of this instability and its characteristic size was determined.

A cold-wet middle-latitude environment on Mars during the Hesperian-Amazonian transition: Evidence from northern Arabia valleys and paleolakes

NASA Astrophysics Data System (ADS)

Wilson, Sharon A.; Howard, Alan D.; Moore, Jeffrey M.; Grant, John A.

2016-09-01

The growing inventory of post-Noachian fluvial valleys may represent a late, widespread episode of aqueous activity on Mars, contrary to the paradigm that fluvial activity largely ceased around the Noachian-Hesperian boundary. Fresh shallow valleys (FSVs) are widespread from ~30 to 45° in both hemispheres with a high concentration in northern Arabia Terra. Valleys in northern Arabia Terra characteristically start abruptly on steeper slopes and terminate in topographic depressions at elevations corresponding to model-predicted lake levels. Longer valley systems flowed into and out of chains of paleolakes. Minimum discharges based on the dimensions of the incised channel assuming medium to coarse sand-size grains ranges from tens to hundreds of m3 s-1, respectively, consistent with formation via snowmelt from surface or sub-ice flows. Hydrologic calculations indicate the valleys likely formed in hundreds of years or less, and crater statistics constrain the timing of fluvial activity to between the Hesperian and middle Amazonian. Several craters with channels extending radially outward supports evidence for overflow of interior crater lakes possibly fed by groundwater. Most FSVs occur away from young impact craters which make an association with impact processes improbable. The widespread occurrence of FSVs along with their similar morphology and shared modest state of degradation is consistent with most forming during a global interval of favorable climate, perhaps contemporaneous with alluvial fan formation in equatorial and midlatitudes. Evidence for a snowmelt-based hydrology and considerable depths of water on the landscape in Arabia supports a cold, wet, and possibly habitable environment late in Martian history.

Geologic Mapping of the Ac-H-6 Quadrangle of Ceres from Nasa's Dawn Mission: Compositional Changes

NASA Astrophysics Data System (ADS)

Krohn, Katrin; Jaumann, Ralf; Tosi, Federico; Nass, Andrea; Otto, Katharina A.; Schulzeck, Franziska; Stephan, Katrin; Wagner, Roland J.; Williams, David A.; Buczkowski, Debra L.; Mest, Scott C.; Scully, Jennifer E. C.; von der Gathen, Isabel; Kersten, Elke; Matz, Klaus-Dieter; Pieters, Carle M.; Preusker, Frank; Roatsch, Thomas; De Sanctis, Maria Cristina; Zambon, Francesca

2016-04-01

Cereś surface is affected by numerous impact craters and some of them show features such as channels or multiple flow events forming a smooth, less cratered surface, indicating possible post-impact resurfacing [1,2]. Flow features occur on several craters on Ceres such as Haulani, Ikapati, Occator, Jarimba and Kondos in combination with smooth crater floors [3,4], appearing as extended plains, ponded material, lobate flow fronts and in the case of Haulani lobate flows originating from the crest of the central ridge [3] partly overwhelming the mass wasting deposits from the rim. Haulanís crater flanks are also affected by multiple flow events radiating out from the crater and partly forming breakages. Flows occur as fine-grained lobes with well-defined margins and as smooth undifferentiated streaky flows covering the adjacent surface. Thus, adjacent craters are covered by flow material. Occator also exhibits multiple flows but in contrast to Haulani, the flows originating from the center overwhelm the mass wasting deposits from the rim [4]. The flows have a "bluish" signature in the FC color filters ratio. Channels occur at relatively fresh craters. They also show the "bluish" signature like the flows and plains. Only few channels occur at older "reddish" craters. They are relatively fresh incised into flow features or crater ejecta. Most are small, narrow and have lobated lobes with predominant distinctive flow margins. The widths vary between a few tens of meters to about 3 km. The channels are found on crater flanks as well as on the crater floors. The occurrence of flow features indicates viscous material on the surface. Those features could be formed by impact melt. However, impact melt is produced during the impact, assuming similar material properties as the ejecta it is expected to have nearly the same age as the impact itself, but the flows and plains are almost free of craters, thus, they seem to be much younger than the impact itself. In addition, the source of impact melt flows is diffusely distributed but many of the observed flows originate from district sources in the crater interior and the flows, however, are well defined. The compositional differences derived from the color ratio and possible time variable effects related to cryo-processes either volcanic or glacial [1,2]. Furthermore, the suggestion of an occurrence ice within the Cerean crust [5] as well as possible salts incorporated into a regolith layer [4,5,6] indicates similar geological processes as seen on other icy bodies. Some lobate flow-like deposits on Ganymede such as at Sippar Sulcus are suggested to be formed by volcanic eruptions creating a channel and flow, and cutting down into the surface forming a depression. Thus, an endogenic formation process cannot be excluded. References: [1] Jaumann R. et al. (2015) EPSC X, Abstract #2015-83. [2] Jaumann R. et al. (2015) AGU, Abstract #P42A-05. [3] Krohn K. et al. (2016) LPSC XLVII, this issue. [4] Jaumann R. et al. (2016) LPSC XLVII, this issue. [5] McCord T.B. and Sotin C. (2005) J. Geophys. Res., 110, E05009. [6] Castillo-Rogez J.C. and McCord T.B. (2010) Icarus 203, 443-459.

Morphology of Cryogenic Flows and Channels on Dwarf Planet Ceres

NASA Astrophysics Data System (ADS)

Krohn, Katrin; Jaumann, Ralf; Otto, Katharina A.; von der Gathen, Isabel; Matz, Klaus-Dieter; Buczkowski, Debra L.; Williams, David A.; Pieters, Carle M.; Preusker, Frank; Roatsch, Thomas; Stephan, Katrin; Wagner, Roland J.; Russell, Christopher T.; Raymond, Carol A.

2016-04-01

Cereś surface is affected by numerous impact craters and some of them show features such as channels or multiple flow events forming a smooth, less cratered surface, indicating possible post-impact resurfacing [1,2]. Flow features occur on several craters on Ceres such as Haulani, Ikapati, Occator, Jarimba and Kondos in combination with smooth crater floors [3,4], appearing as extended plains, ponded material, lobate flow fronts and in the case of Haulani lobate flows originating from the crest of the central ridge [3] partly overwhelming the mass wasting deposits from the rim. Haulanís crater flanks are also affected by multiple flow events radiating out from the crater and partly forming breakages. Flows occur as fine-grained lobes with well-defined margins and as smooth undifferentiated streaky flows covering the adjacent surface. Thus, adjacent craters are covered by flow material. Occator also exhibits multiple flows but in contrast to Haulani, the flows originating from the center overwhelm the mass wasting deposits from the rim [4]. The flows have a "bluish" signature in the FC color filters ratio. Channels occur at relatively fresh craters. They also show the "bluish" signature like the flows and plains. Only few channels occur at older "reddish" craters. They are relatively fresh incised into flow features or crater ejecta. Most are small, narrow and have lobated lobes with predominant distinctive flow margins. The widths vary between a few tens of meters to about 3 km. The channels are found on crater flanks as well as on the crater floors. The occurrence of flow features indicates viscous material on the surface. Those features could be formed by impact melt. However, impact melt is produced during the impact, assuming similar material properties as the ejecta it is expected to have nearly the same age as the impact itself, but the flows and plains are almost free of craters, thus, they seem to be much younger than the impact itself. In addition, the source of impact melt flows is diffusely distributed but many of the observed flows originate from district sources in the crater interior and the flows, however, are well defined. The compositional differences derived from the color ratio and possible time variable effects related to cryo-processes either volcanic or glacial [1,2]. Furthermore, the suggestion of an occurrence ice within the Cerean crust [5] as well as possible salts incorporated into a regolith layer [4,5,6] indicates similar geological processes as seen on other icy bodies. Some lobate flow-like deposits on Ganymede such as at Sippar Sulcus are suggested to be formed by volcanic eruptions creating a channel and flow, and cutting down into the surface forming a depression. Thus, an endogenic formation process cannot be excluded. References: [1] Jaumann R. et al. (2015) EPSC X, Abstract #2015-83. [2] Jaumann R. et al. (2015) AGU, Abstract #P42A-05. [3] Krohn K. et al. (2016) LPSC XLVII, this issue. [4] Jaumann R. et al. (2016) LPSC XLVII, this issue. [5] McCord T.B. and Sotin C. (2005) J. Geophys. Res., 110, E05009. [6] Castillo-Rogez J.C. and McCord T.B. (2010) Icarus 203, 443-459.

Small Rayed Crater Ejecta Retention Age Calculated from Current Crater Production Rates on Mars

NASA Technical Reports Server (NTRS)

Calef, F. J. III; Herrick, R. R.; Sharpton, V. L.

2011-01-01

Ejecta from impact craters, while extant, records erosive and depositional processes on their surfaces. Estimating ejecta retention age (Eret), the time span when ejecta remains recognizable around a crater, can be applied to estimate the timescale that surface processes operate on, thereby obtaining a history of geologic activity. However, the abundance of sub-kilometer diameter (D) craters identifiable in high resolution Mars imagery has led to questions of accuracy in absolute crater dating and hence ejecta retention ages (Eret). This research calculates the maximum Eret for small rayed impact craters (SRC) on Mars using estimates of the Martian impactor flux adjusted for meteorite ablation losses in the atmosphere. In addition, we utilize the diameter-distance relationship of secondary cratering to adjust crater counts in the vicinity of the large primary crater Zunil.

Impact cratering in viscous targets - Laboratory experiments

NASA Technical Reports Server (NTRS)

Greeley, R.; Fink, J.; Snyder, D. B.; Gault, D. E.; Guest, J. E.; Schultz, P. H.

1980-01-01

To determine the effects of target yield strength and viscosity on the formation and morphology of Martian multilobed, slosh and rampart-type impact craters, 75 experiments in which target properties and impact energies were varied were carried out for high-speed motion picture observation in keeping with the following sequence: (1) projectile initial impact; (2) crater excavation and rise of ejecta plume; (3) formation of a transient central mound which generates a surge of material upon collapse that can partly override the plume deposit; and (4) oscillation of the central mound with progressively smaller surges of material leaving the crater. A dimensional analysis of the experimental results indicates that the dimensions of the central mound are proportional to (1) the energy of the impacting projectile and (2) to the inverse of both the yield strength and viscosity of the target material, and it is determined that extrapolation of these results to large Martian craters requires an effective surface layer viscosity of less than 10 to the 10th poise. These results may also be applicable to impacts on outer planet satellites composed of ice-silicate mixtures.

Structure, stratigraphy, and origin of Husband Hill, Columbia Hills, Gusev Crater, Mars

USGS Publications Warehouse

McCoy, T.J.; Sims, M.; Schmidt, M.E.; Edwards, L.; Tornabene, L.L.; Crumpler, L.S.; Cohen, B. A.; Soderblom, L.A.; Blaney, D.L.; Squyres, S. W.; Arvidson, R. E.; Rica, J.W.; Treguier, E.; d'Uston, C.; Grant, J. A.; McSween, H.Y.; Golombek, M.P.; Haldemann, A.F.C.; de Souza, P.A.

2008-01-01

The strike and dip of lithologic units imaged in stereo by the Spirit rover in the Columbia Hills using three-dimensional imaging software shows that measured dips (15-32??) for bedding on the main edifice of the Columbia Hill are steeper than local topography (???8-10??). Outcrops measured on West Spur are conformable in strike with shallower dips (7-15??) than observed on Husband Hill. Dips are consistent with observed strata draping the Columbia Hills. Initial uplift was likely related either to the formation of the Gusev Crater central peak or ring or through mutual interference of overlapping crater rims. Uplift was followed by subsequent draping by a series of impact and volcaniclastic materials that experienced temporally and spatially variable aqueous infiltration, cementation, and alteration episodically during or after deposition. West Spur likely represents a spatially isolated depositional event. Erosion by a variety of processes, including mass wasting, removed tens of meters of materials and formed the Tennessee Valley primarily after deposition. This was followed by eruption of the Adirondack-class plains basalt lava flows which embayed the Columbia Hills. Minor erosion, impact, and aeolian processes have subsequently modified the Columbia Hills. Copyright 2008 by the American Geophysical Union.

Proceedings of the 38th Lunar and Planetary Science Conference

NASA Technical Reports Server (NTRS)

2007-01-01

The sessions in the conference include: Titan, Mars Volcanism, Mars Polar Layered Deposits, Early Solar System Isotopes, SPECIAL SESSION: Mars Reconnaissance Orbiter: New Ways of Studying the Red Planet, Achondrites: Exploring Oxygen Isotopes and Parent-Body Processes, Solar System Formation and Evolution, SPECIAL SESSION: SMART-1, . Impact Cratering: Observations and Experiments, SPECIAL SESSION: Volcanism and Tectonism on Saturnian Satellites, Solar Nebula Composition, Mars Fluvial Geomorphology, Asteroid Observations: Spectra, Mostly, Mars Sediments and Geochemistry: View from the Surface, Mars Tectonics and Crustal Dichotomy, Stardust: Wild-2 Revealed, Impact Cratering from Observations and Interpretations, Mars Sediments and Geochemistry: The Map View, Chondrules and Their Formation, Enceladus, Asteroids and Deep Impact: Structure, Dynamics, and Experiments, Mars Surface Process and Evolution, Martian Meteorites: Nakhlites, Experiments, and the Great Shergottite Age Debate, Stardust: Mainly Mineralogy, Astrobiology, Wind-Surface Interactions on Mars and Earth, Icy Satellite Surfaces, Venus, Lunar Remote Sensing, Space Weathering, and Impact Effects, Interplanetary Dust/Genesis, Mars Cratering: Counts and Catastrophes?, Chondrites: Secondary Processes, Mars Sediments and Geochemistry: Atmosphere, Soils, Brines, and Minerals, Lunar Interior and Differentiation, Mars Magnetics and Atmosphere: Core to Ionosphere, Metal-rich Chondrites, Organics in Chondrites, Lunar Impacts and Meteorites, Presolar/Solar Grains, Topics for Print Only papers are: Outer Planets/Satellites, Early Solar System, Interplanetary Dust, Comets and Kuiper Belt Objects, Asteroids and Meteoroids, Chondrites, Achondrites, Meteorite Related, Mars Reconnaissance Orbiter, Mars, Astrobiology, Planetary Differentiation, Impacts, Mercury, Lunar Samples and Modeling, Venus, Missions and Instruments, Global Warming, Education and Public Outreach, Poster sessions are: Asteroids/Kuiper Belt Objects, Galilean Satellites: Geology and Mapping, Titan, Volcanism and Tectonism on Saturnian Satellites, Early Solar System, Achondrite Hodgepodge, Ordinary Chondrites, Carbonaceous Chondrites, Impact Cratering from Observations and Interpretations, Impact Cratering from Experiments and Modeling, SMART-1, Planetary Differentiation, Mars Geology, Mars Volcanism, Mars Tectonics, Mars: Polar, Glacial, and Near-Surface Ice, Mars Valley Networks, Mars Gullies, Mars Outflow Channels, Mars Sediments and Geochemistry: Spirit and Opportunity, Mars Reconnaissance Orbiter: New Ways of Studying the Red Planet, Mars Reconnaissance Orbiter: Geology, Layers, and Landforms, Oh, My!, Mars Reconnaissance Orbiter: Viewing Mars Through Multicolored Glasses; Mars Science Laboratory, Phoenix, and ExoMars: Science, Instruments, and Landing Sites; Planetary Analogs: Chemical and Mineral, Planetary Analogs: Physical, Planetary Analogs: Operations, Future Mission Concepts, Planetary Data, Imaging, and Cartography, Outer Solar System, Presolar/Solar Grains, Stardust Mission; Interplanetary Dust, Genesis, Asteroids and Comets: Models, Dynamics, and Experiments, Venus, Mercury, Laboratory Instruments, Methods, and Techniques to Support Planetary Exploration; Instruments, Techniques, and Enabling Techologies for Planetary Exploration; Lunar Missions and Instruments, Living and Working on the Moon, Meteoroid Impacts on the Moon, Lunar Remote Sensing, Lunar Samples and Experiments, Lunar Atmosphere, Moon: Soils, Poles, and Volatiles, Lunar Topography and Geophysics, Lunar Meteorites, Chondrites: Secondary Processes, Chondrites, Martian Meteorites, Mars Cratering, Mars Surface Processes and Evolution, Mars Sediments and Geochemistry: Regolith, Spectroscopy, and Imaging, Mars Sediments and Geochemistry: Analogs and Mineralogy, Mars: Magnetics and Atmosphere, Mars Aeolian Geomorphology, Mars Data Processing and Analyses, Astrobiology, Engaging Student Educators and the Public in Planetary Science,

Impact crater morphology and the Central Pit/Dome of Occator: Ceres as an Ice-rich Body

NASA Astrophysics Data System (ADS)

Schenk, P.; Marchi, S.; O'Brien, D. P.; Platz, T.; Bland, M. T.; Buczkowski, D.; Scully, J. E. C.; Ammannito, E.; Raymond, C. A.; Russell, C. T.

2016-12-01

Pristine crater morphologies on Ceres (at D <40 km) are astonishingly similar to those on midsize icy bodies (e.g., moons of Saturn) but very different from those on silicate-rich Vesta. All these bodies have similar gravity and broadly similar impact velocities, and these patterns reveal that the upper 10s of km of Ceres are much weaker than on silicate-rich Vesta. This stands in contrast to the lack of viscous relaxation (Bland et al., 2016), which implies an upper layer on Ceres capable of resisting flow despite the relatively high surface temperatures. This can be explained as distinct responses of an outer layer partially composed of weak ices and strong silicates that fail during high-strain impact processes (which are apparently controlled by the weak phase) but does not flow under low-strain creep (which is apparently controlled more by the strong phase). Furthermore, comparison with Martian craters indicates that, in contrast to Ceres, the amount of water ice in the crust of Mars results in hybrid morphologies only midway between silicate and ice worlds, indicating that the upper layers of Ceres must have more ice than does Mars. The presence of apparent impact melt deposits and central pits in larger craters (D>40 km and D>75 km, respectively) on Ceres implies either warmer conditions than at Saturn, or the presence of a deeper layer enriched in (weaker) ice at comparable depths, also consistent with partial relaxation in larger craters. The formation of a fractured dome 3-km-wide and 0.75-km-high within recently formed Occator crater may be due to refreezing of a water zone melted after impact, or mobilization of carbonates or ice in the crater center, possibly from such deeper layers.

Ernst Julius Öpik's (1916) note on the theory of explosion cratering on the Moon's surface—The complex case of a long-overlooked benchmark paper

NASA Astrophysics Data System (ADS)

Racki, Grzegorz; Koeberl, Christian; Viik, Tõnu; Jagt-Yazykova, Elena A.; Jagt, John W. M.

2014-10-01

High-velocity impact as a common phenomenon in planetary evolution was ignored until well into the twentieth century, mostly because of inadequate understanding of cratering processes. An eight-page note, published in Russian by the young Ernst Julius Öpik, a great Estonian astronomer, was among the key selenological papers, but due to the language barrier, it was barely known and mostly incorrectly cited. This particular paper is here intended to serve as an explanatory supplement to an English translation of Öpik's article, but also to document an early stage in our understanding of cratering. First, we outline the historical-biographical background of this benchmark paper, and second, a comprehensive discussion of its merits is presented, from past and present perspectives alike. In his theoretical research, Öpik analyzed the explosive formation of craters numerically, albeit in a very simple way. For the first time, he approximated relationships among minimal meteorite size, impact energy, and crater diameter; this scaling focused solely on the gravitational energy of excavating the crater (a "useful" working approach). This initial physical model, with a rational mechanical basis, was developed in a series of papers up to 1961. Öpik should certainly be viewed as the founder of the numerical simulation approach in planetary sciences. In addition, the present note also briefly describes Nikolai A. Morozov as a remarkable man, a forgotten Russian scientist and, surprisingly, the true initiator of Öpik's explosive impact theory. In fact, already between 1909 and 1911, Morozov probably was the first to consider conclusively that explosion craters would be circular, bowl-shaped depressions even when formed under different impact angles.

Mapping Variability in the Medusae Fossae Formation: Yardang Morphologies, Fluvial Reworking, and Crater Depth to Diameter Ratios

NASA Astrophysics Data System (ADS)

Khuller, A. R.; Kerber, L.

2017-12-01

The Medusae Fossae Formation (MFF) is a voluminous, fine-grained deposit thought to be of pyroclastic origin. While it contains widespread, well-preserved inverted fluvial features, its pervasive cover of dust means that little is known about its composition, and indirect means must be used to characterize its material properties. This project aims to correlate fluvial features in the Western MFF with other indicators of material strength: yardang morphology and crater depth-to-diameter ratios. For this work, Context Camera (CTX) images were used to map features of fluvial origin (inverted channels, sinuous ridges, alluvial fans). The presence of rounded, meso-yardangs in close proximity to fluvial features was also mapped. Crater depth-diameter (d/D) ratios (for craters 1-512km) were analyzed using a global Mars crater database (Robbins and Hynek, 2012) as a proxy for material strength. Approximately 1400 fluvial segments were mapped, with the most populous cluster located in Aeolis and Zephyria Plana. Rounded meso-yardangs were found to be common in areas that also have fluvial features. In agreement with previous work (Barlow, 1993), MFF craters were found to have a greater d/D ratio (0.0523) than the global mean (0.0511). Ratios between MFF lobes differ significantly, providing insight into the heterogeneity of induration within the formation. The deepest craters are found in Eumenides Dorsum and the shallowest in Aeolis Planum, consistent with a greater degree of induration and reworking in the western part of the formation where the fluvial features and "salt-playa" meso-yardangs are found. It also suggests that Eumenides, which is the tallest MFF outcrop, could also be the least compacted. The presence of long, complex, and sometimes overlapping branching networks imply multiple relative episodes of channel formation. Rounded meso-yardangs, which are associated with salt playa surfaces on Earth, provide additional evidence for the presence of liquid water during the history of the MFF. The preservation of fluvial activity, through inversion and negative relief as well as the `protection' provided by the layers of friable MFF deposits indicates that some of the most well-preserved stratigraphy could perhaps be accessed by future Martian surface exploration missions within the MFF.

Ballistic Performance Model of Crater Formation in Monolithic, Porous Thermal Protection Systems

NASA Technical Reports Server (NTRS)

Miller, J. E.; Christiansen, E. L.; Deighton, K. D.

2014-01-01

Porous monolithic ablative systems insulate atmospheric reentry vehicles from reentry plasmas generated by atmospheric braking from orbital and exo-orbital velocities. Due to the necessity that these materials create a temperature gradient up to several thousand Kelvin over their thickness, it is important that these materials are near their pristine state prior to reentry. These materials may also be on exposed surfaces to space environment threats like orbital debris and meteoroids leaving a probability that these exposed surfaces will be below their prescribed values. Owing to the typical small size of impact craters in these materials, the local flow fields over these craters and the ablative process afford some margin in thermal protection designs for these locally reduced performance values. In this work, tests to develop ballistic performance models for thermal protection materials typical of those being used on Orion are discussed. A density profile as a function of depth of a typical monolithic ablator and substructure system is shown in Figure 1a.

Styles of crater gradation in Southern Ismenius Lacus, Mars

NASA Technical Reports Server (NTRS)

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

1991-01-01

Preserved morphology around selected impact craters together with results from study of long term gradational evolution are used to assess processes responsible for crater modification in southern Ismenius Lacus. Results are compared with the gradational styles of selected terrestrial craters. Although most craters in the region display complex primary morphologies, some first order comparisons with the gradational styles around simple terrestrial craters may be valid. Nearly complete high resolution coverage provides a basis for studying morphologic features at scales comparable to those observed in LANDSAT TM images of terrestrial craters. It is concluded that the relative importance of gradational processes differs around the terrestrial and Martian craters considered here: Martian rimless morphologies are produced by mass wasting, eolian deposition/erosion, and limited fluvial incisement resulting in downwasting and significant backwasting of crater walls.

Intercrater Plains and Heavily Cratered Terrain - First Encounter

NASA Image and Video Library

2000-01-18

Intercrater plains and heavily cratered terrain typical of much of Mercury outside the area affected by the formation of the Caloris basin are shown in this image taken during the NASA Mariner 10 first encounter with Mercury in 1974.

The Topography and Basin Deposits of the Equatorial Highlands: A MGS-Viking Synergistic Study

NASA Technical Reports Server (NTRS)

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

1999-01-01

One of the greatest unresolved issues concerns the evolution of Mars early in its history; during the time period that accretion was winding down but the frequency of impacting debris was still heavy. Ancient cratered terrain that has only been moderately modified since the period of heavy bombardment covers about a quarter of the planet's surface but the environment during its formation is still uncertain. This terrain was dominantly formed by cratering. But unlike on the airless Moon, the impacting craters were strongly modified by other contemporary surface processes that have produced distinctive features such as: 1) dendritic channel networks, 2) rimless, flatfloored craters, 3) obliteration of most craters smaller than a few kilometers in diameter (except for post heavy-bombardment impacts), and 4) smooth intercrater plains. The involvement of water in these modification processes seems unavoidable, but interpretations of the surface conditions on early Mars range from the extremes of: 1) the "cold" model which envisions a thin atmosphere and surface temperatures below freezing except for local hydrothermal springs; and 2) the "warm" model, which invokes a thick atmosphere, seasonal temperatures above freezing in temperate and equatorial regions, and at least occasional precipitation as part of an active hydrological cycle. The nature of hydrologic cycles, if they occurred on Mars, would have been critically dependent on the environment. The resolution of where along this spectrum the actual environment of early Mars occurred is clearly a major issue, particularly because the alternate scenarios have much different implications about the possibility that life might have evolved on Mars. Additional information is contained in the original extended abstract.

­­­­High-Resolution Mapping of Kick`em Jenny Submarine Volcano and Associated Landslides

NASA Astrophysics Data System (ADS)

Ruchala, T. L.; Carey, S.; Hart, L.; Chen, M.; Scott, C.; Tominaga, M.; Dondin, F. J. Y.; Fujii, M.

2016-02-01

To understand the physical and geological processes that drive the volcanism and control the morphology of Kick`em Jenny (KEJ) volcano, the only active submarine volcano in the in the Lesser Antilles volcanic arc, we conducted near-source, high-resolution mapping of KEJ and its subsurface using the Remotely Operated Vehicle (ROV) Hercules during cruise NA054 of the E/V Nautilus (Sept.-Oct. 2014). Shipboard bathymetric data (EM302 system) and slope analysis maps were used to decipher the detailed seafloor morphology surrounding KEJ. Multiple generations of submarine landslides and canyons were observed, suggesting the area has been hosting dynamic sediment transport systems at multiple scales over time. Some of them might have been associated by past eruptions. Clear contacts between partially lithified carbonate sediments and volcanic formations were identified from ROV videos at the middle of the landslide slope face. Detailed observations of facies on these exposures provide constraints on the time intervals between landslide events along the western slope of KEJ. ROV video imagery also identified outcrops of columnar basalts located in the middle of the landslide deposits. These are similar in appearance to those observed in the KEJ crater during previous ROV dives, indicating a possible travel distance of volcanic materials from the crater region along landslide path. High-resolution photo mosaics, bathymetry, and magnetic data acquired by ROV Hercules were used to investigate geological processes and the possible volcanic source of landslide material within the KEJ crater. Mapping in the northwestern part of the crater floor revealed distinctive regions, including (i) microbial mats, (ii) active hydrothermal vent sites; (iii) landforms curved by channelized bottom current where seafloor is outcropped; and (iv) coarse scree the distribution of which may correlate with the distance from the crater rim. Near-bottom magnetic profiles show coherent magnetic signatures with correlatable high amplitude anomalies located in the middle of the KEJ crater.

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

NASA Astrophysics Data System (ADS)

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 results are that the Chicxulub peak ring is formed from fractured basement rocks that may host a subsurface biosphere. The impactite layer overlying the peak ring in turn provides insight into resurge and tsunami processes, while the Paleogene sediments contain the record of the recovery of life after the mass extinction event.

Shallow magma diversions during explosive diatreme-forming eruptions.

PubMed

Le Corvec, Nicolas; Muirhead, James D; White, James D L

2018-04-13

The diversion of magma is an important mechanism that may lead to the relocation of a volcanic vent. Magma diversion is known to occur during explosive volcanic eruptions generating subterranean excavation and remobilization of country and volcanic rocks. However, feedbacks between explosive crater formation and intrusion processes have not been considered previously, despite their importance for understanding evolving hazards during volcanic eruptions. Here, we apply numerical modeling to test the impacts of excavation and subsequent infilling of diatreme structures on stress states and intrusion geometries during the formation of maar-diatreme complexes. Explosive excavation and infilling of diatremes affects local stress states which inhibits magma ascent and drives lateral diversion at various depths, which are expected to promote intra-diatreme explosions, host rock mixing, and vent migration. Our models demonstrate novel mechanisms explaining the generation of saucer-shaped sills, linked with magma diversion and enhanced intra-diatreme explosive fragmentation during maar-diatreme volcanism. Similar mechanisms will occur at other volcanic vents producing crater-forming eruptions.

Small lunar craters at the Apollo 16 and 17 landing sites - morphology and degradation

NASA Astrophysics Data System (ADS)

Mahanti, P.; Robinson, M. S.; Thompson, T. J.; Henriksen, M. R.

2018-01-01

New analysis and modeling approaches are applied to high-resolution images and topography of the Apollo 16 and 17 landing sites to investigate the morphology and estimate degradation of small lunar craters (SLCs; 35 to 250 m diameter). We find SLCs at the two sites are mostly degraded with an average depth-diameter ratio (d/D) < 0.1 , resulting in a landscape dominated by shallow, inverted cone-shaped craters. An improved standardized morphological classification and a novel set of quantitative shape indicators are defined and used to compare SLCs between the two sites. Our classification methodology allows morphological class populations to be designated with minimal (and measurable) ambiguity simplifying the study of SLC degradation at different target regions. SLC shape indicators are computationally obtained from topography, further facilitating a quantitative and repeatable comparison across study areas. Our results indicate that the interior slopes of SLCs evolve faster and through different processes relative to larger craters ( > 500 m). Assuming SLCs are formed with large initial depth-to-diameter ratio (d/D ≥ 0.2), our observation that even the fresher SLCs are relatively shallow imply that a faster mass wasting process post-formation stabilizes the crater walls and eventually slows down degradation. We also found that the Apollo 16 Cayley plains have a higher percentage of fresh craters than the Apollo 17 Taurus Littrow (TL) plains. A combination of a less-cohesive target material and/or seismic shaking resulting from moonquakes or the impact of Tycho crater secondaries was likely responsible for a higher degradation rate in the TL-plains compared to the Cayley plains. This study explores the relationship between the symmetry and probability densities of key morphological traits like d/D, mean wall slope and rate of degradation. We show that the shape of d/D probability density function of SLCs in a study area encodes their rate of degradation. Comparison of power-law fitting and probabilistic modeling of depth-diameter relations shows that probabilistic methods complement regression models and are necessary for robust prediction of SLC depths from diameter (and vice versa) for different geological targets.

Meteorite impact in the ocean

NASA Technical Reports Server (NTRS)

Strelitz, R.

1979-01-01

In the present study, the dynamic of hypervelocity impacts and crater formation in water are examined with allowance for the unique properties of water. More precisely, the transient crater calculated is permitted to relax and act as a source of oceanic surface waves.

The Enigmatic Bench Unit of Endeavour Crater Rim in Meridiani Planum, Mars

NASA Astrophysics Data System (ADS)

Ruff, S. W.

2013-12-01

For the first 2680 sols of its mission, the Mars Exploration Rover Opportunity traversed across essentially the same rocks: sulfur-rich sandstones known as the Burns formation. On August 8, 2011 Opportunity completed a ~21 km traverse from Victoria crater to the rim of the ~22 km diameter Endeavour crater where it crossed a slightly raised smooth bench unit that surrounds an interior core of higher standing and more rugged terrain on a rim segment named Cape York. As recognized by its distinctive morphologic character evident in orbital images, the inward sloping bench feature is found associated with portions of other segments of the discontinuous raised rim of Endeavour crater. Viewed by Opportunity, it appears as platy, fractured, relatively light-toned outcrop that is fine-grained, lacks hematite concretions and in places hosts veins of Ca- and S-rich composition, likely due to precipitation of gypsum in fractures that cut the bench unit (1). The bench outcrop target named Grasberg included a grind using the Rock Abrasion Tool (RAT) to obtain a cleaner surface for the Alpha Particle X-ray Spectrometer chemistry measurement compared with the initially investigated target named Deadwood. In addition to its greater strength than Burns formation as determined by the RAT grind operation, Grasberg and other examples of the bench unit have lower S, higher Cl and other elemental characteristics that depart from typical Burns formation. Thus the 'Grasberg unit' clearly represents a distinct rock type compared to the Meridiani plains. A second unit makes up the exposed core of the Cape York rim segment. Known as Shoemaker formation, it is composed of breccias that are recognized as a suevite deposit produced from the Endeavour impact event (1). The Shoemaker formation appears to be onlapped by the Grasberg unit with Burns formation onlapping it (1). However, a well-exposed section observed in a wedge-shaped fracture known as Whim Creek on the northeast portion of the Cape York bench clearly presents Grasberg rocks above Burns rocks. Erosion of a plunging synclinal form could explain this apparent inverted relationship, or it reveals that the Grasberg unit is younger than Burns formation. But this latter interpretation implies that Grasberg rocks, which have been observed only at the Endeavour rim, have been stripped off of Burns formation everywhere else. The Grasberg bench unit has recently been encountered in an isthmus setting between two low knobs of presumed Shoemaker formation called Nobbys Head and Sutherland Point just south of Cape York. The isthmus also presents Grasberg as topographically elevated above the Burns formation rocks. Despite its broad, smooth exposure, no remnants of Burns formation have been found on top of Grasberg at this location or anywhere on the Cape York bench. So the stratigraphic relationship between Grasberg and Burns rocks remains enigmatic. At the time of writing, Opportunity is at the edge of Solander Point, another bench feature on the northern tip of a rim segment known as Cape Tribulation. The erosional expression of this example appears different from those examined previously and perhaps offers the best chance to understand stratigraphic relationships. 1. S. W. Squyres et al., Ancient impact and aqueous processes at Endeavour Crater, Mars. Science 336, 570 (2012).

Morphology and composition of the surface of Mars: Mars Odyssey THEMIS results.

PubMed

Christensen, Philip R; Bandfield, Joshua L; Bell, James F; Gorelick, Noel; Hamilton, Victoria E; Ivanov, Anton; Jakosky, Bruce M; Kieffer, Hugh H; Lane, Melissa D; Malin, Michael C; McConnochie, Timothy; McEwen, Alfred S; McSween, Harry Y; Mehall, Greg L; Moersch, Jeffery E; Nealson, Kenneth H; Rice, James W; Richardson, Mark I; Ruff, Steven W; Smith, Michael D; Titus, Timothy N; Wyatt, Michael B

2003-06-27

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.

Global stratigraphy. [of planet Mars

NASA Technical Reports Server (NTRS)

Tanaka, Kenneth L.; Scott, David H.; Greeley, Ronald

1992-01-01

Attention is given to recent major advances in the definition and documentation of Martian stratigraphy and geology. Mariner 9 provided the images for the first global geologic mapping program, resulting in the recognition of the major geologic processes that have operated on the planet, and in the definition of the three major chronostratigraphic divisions: the Noachian, Hesperian, and Amazonian Systems. Viking Orbiter images permitted the recognition of additional geologic units and the formal naming of many formations. Epochs are assigned absolute ages based on the densities of superposed craters and crater-flux models. Recommendations are made with regard to future areas of study, namely, crustal stratigraphy and structure, the highland-lowland boundary, the Tharsis Rise, Valles Marineris, channels and valley networks, and possible Martian oceans, lakes, and ponds.

Morphology and composition of the surface of Mars: Mars Odyssey THEMIS results

USGS Publications Warehouse

Christensen, P.R.; Bandfield, J.L.; Bell, J.F.; Gorelick, N.; Hamilton, V.E.; Ivanov, A.; Jakosky, B.M.; Kieffer, H.H.; Lane, M.D.; Malin, M.C.; McConnochie, T.; McEwen, A.S.; McSween, H.Y.; Mehall, G.L.; Moersch, J.E.; Nealson, K.H.; Rice, J. W.; Richardson, M.I.; Ruff, S.W.; Smith, M.D.; Titus, T.N.; Wyatt, M.B.

2003-01-01

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.

Expanded Craters on Mars: Implications for Shallow, Mid-latitude Excess Ice

NASA Astrophysics Data System (ADS)

Viola, Donna

Understanding the age and distribution of shallow ice on Mars is valuable for interpreting past and present climate conditions, and has implications on habitability and future in situ resource utilization. Many ice-related features, such as lobate debris aprons and concentric crater fill, have been studied using a range of remote sensing techniques. Here, I explore the distribution of expanded craters, a form of sublimation thermokarst where shallow, excess ice has been destabilized and sublimated following an impact event. This leads to the collapse of the overlying dry regolith to produce the appearance of diameter widening. The modern presence of these features suggests that excess ice has remained preserved in the terrain immediately surrounding the craters since the time of their formation in order to maintain the surface. High-resolution imagery is ideal for observing thermokarst features, and much of the work described here will utilize data from the Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO). Expanded craters tend to be found in clusters that emanate radially from at least four primary craters in Arcadia Planitia, and are interpreted as secondary craters that formed nearly simultaneously with their primaries. Crater age dates of the primaries indicate that the expanded secondaries, as well as the ice layer into which they impacted, must be at least tens of millions of years old. Older double-layer ejecta craters in Arcadia Planitia commonly have expanded craters superposed on their ejecta - and they tend to be more expanded (with larger diameters) in the inner ejecta layer. This has implications on the formation mechanisms for craters with this unique ejecta morphology. Finally, I explore the distribution of expanded craters south of Arcadia Planitia and across the southern mid-latitudes, along with scalloped depressions (another form of sublimation thermokarst), in order to identify the modern excess ice boundary in this region and any longitudinal variations. This study identifies some potential low-latitude locations with patchy excess ice, possibly preserved during a past climate. Through these studies, I will infer regions that contain abundant ice today and consider the implications that this ice has on both the martian climate and future exploration.

Global maps of anhydrous minerals at the surface of Mars from OMEGA/MEx

NASA Astrophysics Data System (ADS)

Ody, A.; Poulet, F.; Langevin, Y.; Bibring, J.-P.; Bellucci, G.; Altieri, F.; Gondet, B.; Vincendon, M.; Carter, J.; Manaud, N.

2012-09-01

We here reassess the global distribution of several key mineral species using the entire OMEGA/Mars Express VIS-NIR imaging spectrometer data set, acquired from orbit insertion in January 2004 to August 2010. Thirty-two pixels per degree global maps of ferric oxides, pyroxenes and olivines have been derived. A significant filtering process was applied in order to exclude data acquired with unfavorable observation geometries or partial surface coverage with water and CO2 frosts. Because of strong atmospheric variations over the 3.6 Martian years of observations primarily due to the interannual variability of the aerosol opacity, a new filter based on the atmospheric dust opacity calibrated by the Mars Exploration Rovers measurements has also been implemented. The Fe3+ absorption features are present everywhere on the surface, with a variety of intensities indicating distinct formation processes. The pyroxene-bearing regions are localized in low albedo regions, while the bright regions are spectrally comparable to anhydrous nanophase ferric oxides. The expanded data set increases by a factor of about 2, the number of olivine detections reported in previous OMEGA-based studies. Olivine is mainly detected in three types of areas over the Martian surface: discontinuous patches on the terraces of the three main basins; smooth inter-crater plains and smooth crater floors throughout the southern highlands; and crater sand dunes, crater ejectas and extended bedrock exposures in the northern plains. Olivine is also detected in the low albedo pyroxene-bearing dunes surrounding the northern polar cap.

Impact craters on Titan

USGS Publications Warehouse

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.

Impact craters on Titan

USGS Publications Warehouse

Wood, C.A.; Lorenz, R.; Kirk, R.; Lopes, R.; Mitchell, Ken; Stofan, E.

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. ?? 2009 Elsevier Inc.

Ray craters on Ganymede: Implications for cratering apex-antapex asymmetry and surface modification processes

NASA Astrophysics Data System (ADS)

Xu, Luyuan; Hirata, Naoyuki; Miyamoto, Hideaki

2017-10-01

As the youngest features on Ganymede, ray craters are useful in revealing the sources of recent impactors and surface modification processes on the satellite. We examine craters with D > 10 km on Ganymede from images obtained by the Voyager and Galileo spacecraft to identify ray craters and study their spatial distributions. Furthermore, we carefully select images of appropriate solar and emission angles to obtain unbiased ray crater densities. As a result, we find that the density of large ray craters (D > 25 km) on the bright terrain exhibits an apex-antapex asymmetry, and its degree of asymmetry is much lower than the theoretical estimation for ecliptic comets. For large craters (D > 25 km), ecliptic comets ought to be less important than previously assumed, and a possible explanation is that nearly isotropic comets may play a more important role on Ganymede than previously thought. We also find that small ray craters (10 km < D < 25 km) on the bright terrain and ray craters (D > 10 km) on the dark terrain show no apex-antapex asymmetry. We interpret that the distribution difference between the terrain types comes from preferential thermal sublimation on the dark terrain, while the distribution difference between large and small ray craters suggests that rays of small craters are more readily erased by some surface modification processes, such as micrometeorite gardening.

The Carancas meteorite impact crater, Peru: Geologic surveying and modeling of crater formation and atmospheric passage

NASA Astrophysics Data System (ADS)

Kenkmann, T.; Artemieva, N. A.; Wünnemann, K.; Poelchau, M. H.; Elbeshausen, D.; Núñez Del Prado, H.

2009-08-01

The recent Carancas meteorite impact event caused a worldwide sensation. An H4-5 chondrite struck the Earth south of Lake Titicaca in Peru on September 15, 2007, and formed a crater 14.2 m across. It is the smallest, youngest, and one of two eye-witnessed impact crater events on Earth. The impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters. Fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight. The small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters. The Carancas cratering event, however, demonstrates that meter-sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances. We present results of a detailed geologic survey of the crater and its ejecta. To constrain the possible range of impact parameters we carried out numerical models of crater formation with the iSALE hydrocode in two and three dimensions. Depending on the strength properties of the target, the impact energies range between approximately 100-1000 MJ (0.024- 0.24 t TNT). By modeling the atmospheric traverse we demonstrate that low cosmic velocities (12- 14 kms-1) and shallow entry angles (<20°) are prerequisites to keep aerodynamic stresses low (<10 MPa) and thus to prevent fragmentation of stony meteoroids with standard strength properties. This scenario results in a strong meteoroid deceleration, a deflection of the trajectory to a steeper impact angle (40-60°), and an impact velocity of 350-600 ms-1, which is insufficient to produce a shock wave and significant shock effects in target minerals. Aerodynamic and crater modeling are consistent with field data and our microscopic inspection. However, these data are in conflict with trajectories inferred from the analysis of infrasound signals.

Monte Carlo calculations of lunar regolith thickness distributions.

NASA Technical Reports Server (NTRS)

Oberbeck, V. R.; Quaide, W. L.; Mahan, M.; Paulson, J.

1973-01-01

It is pointed out that none of the existing models of lunar regolith evolution take into account the relationship between regolith thickness, crater shape, and volume of debris ejected. The results of a Monte Carlo computer simulation of regolith evolution are presented. The simulation was designed to consider the full effect of the buffering regolith through calculation of the amount of debris produced by any given crater as a function of the amount of debris present at the site of the crater at the time of crater formation. The method is essentially an improved version of the Oberbeck and Quaide (1968) model.

Acidic Fluids Across Mars: Detections of Magnesium-Nickel Sulfates

NASA Technical Reports Server (NTRS)

Yen, A. S.; Ming, D. W.; Gellert, R.; Mittlefehldt, D. W.; Rampe, E. B.; Vaniman, D. T.; Thompson, L. M.; Morris, R. V.; Clark, B. C.; VanBommel, S. J.

2017-01-01

Calcium, magnesium and ferric iron sulfates have been detected by the instrument suites on the Mars rovers. A subset of the magnesium sulfates show clear associations with nickel. These associations indicate Ni(2+) co-precipitation with or substitution for Mg(2+) from sulfate-saturated solutions. Nickel is ex-tracted from primary rocks almost exclusively at pH values less than 6, constraining the formation of these Mg-Ni sulfates to mildly to strongly acidic conditions. There is clear evidence for aqueous alteration at the rim of Endeavour Crater (Meridiani Planum), in the Murray formation mudstone (Gale Crater), and near Home Plate (Gusev Crater). The discovery of Mg-Ni sulfates at these locations indicates a history of fluid-rock interactions at low pH.

Evolved Gas Analyses of the Murray Formation in Gale Crater, Mars: Results of the Curiosity Rover's Sample Analysis at Mars (SAM) Instrument

NASA Technical Reports Server (NTRS)

Sutter, B.; McAdam, A. C.; Rampe, E. B.; Thompson, L. M.; Ming, D. W.; Mahaffy, P. R.; Navarro-Gonzalez, R.; Stern, J. C.; Eigenbrode, J. L.; Archer, P. D.

2017-01-01

The Sample Analysis at Mars (SAM) instrument aboard the Mars Science Laboratory rover has analyzed 13 samples from Gale Crater. All SAM-evolved gas analyses have yielded a multitude of volatiles (e.g., H2O, SO2, H2S, CO2, CO, NO, O2, HCl) [1- 6]. The objectives of this work are to 1) Characterize recent evolved SO2, CO2, O2, and NO gas traces of the Murray formation mudstone, 2) Constrain sediment mineralogy/composition based on SAM evolved gas analysis (SAM-EGA), and 3) Discuss the implications of these results relative to understanding the geological history of Gale Crater.

Distribution, morphology, and origins of Martian pit crater chains

NASA Astrophysics Data System (ADS)

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 trends. The information collected in the study was then compared with non-Martian examples of pit chains and physical analog models. We evaluated the various mechanisms for pit chain development based on the data collected and conclude that dilational normal faulting and sub-vertical fissuring provide the simplest and most comprehensive mechanisms to explain the regional associations, detailed geometry, and progression of pit chain development.

Pacific Enewetak Atoll Crater Exploration (PEACE) program, Enewetak Atoll, Republic of the Marshall Islands; Part 1, Drilling operations and descriptions of boreholes in vicinity of KOA and OAK craters

USGS Publications Warehouse

Henry, T.W.; Wardlaw, B.R.; Skipp, Betty; Major, R. P.; Tracey, J.I.

1986-01-01

Evidence of a post-Cretaceous uplift of the Sioux Quartzite ridge in southeastern South Dakota consists of deformation of the Dakota Formation, Graneros Shale, Greenhorn Limestone, Carlile Shale, and Niobrara Formation of Cretaceous age. The Greenhorn is warped upward about 400 ft on the Sioux Quartzite with a formation dip ranging from 30-50 ft/mi. Elsewhere in eastern South Dakota the dip of the Greenhorn ranges from 3-8 ft/mi. (Author 's abstract)

Formation and disruption of aquifers in southwestern Chryse Planitia, Mars

USGS Publications Warehouse

Rodriguez, J.A.P.; Tanaka, K.L.; Kargel, J.S.; Dohm, J.M.; Kuzmin, R.; Fairen, A.G.; Sasaki, S.; Komatsu, G.; Schulze-Makuch, D.; Jianguo, Y.

2007-01-01

We present geologic evidence suggesting that after the development of Mars' cryolithosphere, the formation of aquifers in southwestern Chryse Planitia and their subsequent disruption led to extensive regional resurfacing during the Late Hesperian, and perhaps even during the Amazonian. In our model, these aquifers formed preferentially along thrust faults associated with wrinkle ridges, as well as along fault systems peripheral to impact craters. The characteristics of degraded wrinkle ridges and impact craters in southwestern Chryse Planitia indicate a profound role of subsurface volatiles and especially liquid water in the upper crust (the upper one hundred to a few thousands of meters). Like lunar wrinkle ridges, the martian ones are presumed to mark the surface extensions of thrust faults, but in our study area the wrinkle ridges are heavily modified. Wrinkle ridges and nearby plains have locally undergone collapse, and in other areas they are associated with domical intrusions we interpret as mud volcanoes and mud diapirs. In at least one instance, a sinuous valley emanates from a modified wrinkle ridge, further indicating hydrological influences on these thrust-fault-controlled features. A key must be the formation of volatile-rich crust. Primary crustal formation and differentiation incorporated juvenile volatiles into the global crust, but the crustal record here was then strongly modified by the giant Chryse impact. The decipherable rock record here begins with the Chryse impact and continues with the resulting basin's erosion and infilling, which includes outflow channel activity. We propose that in Simud Vallis surface flow dissection into the base of the cryolithosphere-produced zones where water infiltrated and migrated along SW-dipping strata deformed by the Chryse impact, thereby forming an extensive aquifer in southwestern Chryse Planitia. In this region, compressive stresses produced by the rise of Tharsis led to the formation of wrinkle ridges. Zones of high fracture density within the highly strained planes of the thrust faults underlying the wrinkle ridges formed regions of high permeability; thus, groundwater likely flowed and gathered along these tectonic structures to form zones of elevated permeability. Volatile depletion and migration within the upper crustal materials, predominantly along fault systems, led to structurally controlled episodic resurfacing in southwestern Chryse Planitia. The erosional modification of impact craters in this region is linked to these processes. This erosion is scale independent over a range of crater diameters from a few hundred meters to tens of kilometers. According to our model, pressurized water and sediment intruded and locally extruded and caused crustal subsidence and other degradational activity across this region. The modification of craters across this wide range of sizes, according to our model, implies that there was intensive mobilization of liquid water in the upper crust ranging from about one hundred to several thousand meters deep. ?? 2007 Elsevier Inc. All rights reserved.

Evidence for self-secondary cratering of Copernican-age continuous ejecta deposits on the Moon

NASA Astrophysics Data System (ADS)

Zanetti, M.; Stadermann, A.; Jolliff, B.; Hiesinger, H.; van der Bogert, C. H.; Plescia, J.

2017-12-01

Crater size-frequency distributions on the ejecta blankets of Aristarchus and Tycho Craters are highly variable, resulting in apparent absolute model age differences despite ejecta being emplaced in a geologic instant. Crater populations on impact melt ponds are a factor of 4 less than on the ejecta, and crater density increases with distance from the parent crater rim. Although target material properties may affect crater diameters and in turn crater size-frequency distribution (CSFD) results, they cannot completely reconcile crater density and population differences observed within the ejecta blanket. We infer from the data that self-secondary cratering, the formation of impact craters immediately following the emplacement of the continuous ejecta blanket by ejecta from the parent crater, contributed to the population of small craters (< 300 m diameter) on ejecta blankets and must be taken into account if small craters and small count areas are to be used for relative and absolute model age determinations on the Moon. Our results indicate that the cumulative number of craters larger than 1 km in diameter per unit area, N(1), on the continuous ejecta blanket at Tycho Crater, ranges between 2.17 × 10-5 and 1.0 × 10-4, with impact melt ponds most accurately reflecting the primary crater flux (N(1) = 3.4 × 10-5). Using the cratering flux recorded on Tycho impact melt deposits calibrated to accepted exposure age (109 ± 1.5 Ma) as ground truth, and using similar crater distribution analyses on impact melt at Aristarchus Crater, we infer the age of Aristarchus Crater to be ∼280 Ma. The broader implications of this work suggest that the measured cratering rate on ejecta blankets throughout the Solar System may be overestimated, and caution should be exercised when using small crater diameters (i.e. < 300 m on the Moon) for absolute model age determination.

Hydrated Sulfates in the Southern High Latitudes of Mars

NASA Astrophysics Data System (ADS)

Ackiss, S. E.; Wray, J. J.

2012-12-01

Sulfates on Mars appear largely concentrated in sedimentary rocks dating to the Late Noachian or Hesperian [e.g., 1], but they are also abundant in Amazonian sand dunes around the north polar cap [2]. The gypsum in those dunes derives from the polar layered deposits [e.g., 3], where it may form when sunlight causes minor melting and weathering of embedded dust. We are investigating whether such processes might have also contributed to sulfate formation elsewhere, specifically in regions surrounding the south polar terrain. Our study regions to date include the Sisyphi Montes (20W-40E and 55-75S) and other mountainous areas near the Thyles Rupes (110-140E and 55-75S), the Ulyxis Rupes (150-180E and 55-70S), and Chamberlin Crater (110-150W and 55-75S). We searched for sulfates using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). TRR3 images were evaluated using standard CRISM procedures, including the "volcano scan" atmospheric correction. We used spectral parameters to identify regions of interest, from which we extracted spectra, which we divided by spectrally neutral regions in the same scene to remove systematic artifacts. The resulting ratio spectra were visually compared to library spectra to identify possible hydrated mineral constituents. Some sulfates in the southern high latitudes appear localized to mountains of the Sisyphi Montes, which have been interpreted as volcanoes that erupted under a Hesperian ice sheet [4]. These sulfates might have formed via volcanic hydrothermal or acid fog alteration. We found that nearly 50% of the images on putative volcanoes in the Sisyphi Montes show a 1.9 μm absorption consistent with hydration. The percentage for images on the plains between volcanoes is actually higher; i.e., hydration is not unique to the volcanoes. Nevertheless, the three locations at which we found the strongest absorptions are all on volcanoes. In the Thyles Rupes region, 25% of the images on putative volcanoes are hydrated with a broad band at ~1.92 μm. Roughly 45% of the images off volcanoes are hydrated with the majority of them being located inside a crater, on a crater rim, or in the plains. Nearly 80% of hydrated images near the Ulyxis Rupes are also located either on a crater rim or inside a crater. Twenty percent of the images near the Chamberlin Crater are hydrated and mostly located in the plains or on a crater rim. Their spectra show consistent absorptions around 1.9 and 2.5 μm. The concentration of hydrated sulfates inside and on the rims of craters in all three of these regions suggests that the sulfates may be relatively old, and were exposed when the surface was impacted. Our results substantially expand the number of known areas in the southern high latitudes exhibiting hydration. The fact that hydration is found in all the regions we studied suggests an ubiquitous process for hydrated mineral formation, possibly similar to icy weathering processes proposed for the north polar region. References: [1] Bibring J.-P. et al. (2006) Science, 312, 400-404. [2] Langevin Y. et al. (2005) Science, 307, 1584-1586. [3] Massé M. et al. (2010) Icarus, 209, 434-451. [4] Ghatan G. and Head J. (2002) JGR, 107, 5048

Processing Images of Craters for Spacecraft Navigation

NASA Technical Reports Server (NTRS)

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.

The role of igneous sills in shaping the Martian uplands

NASA Technical Reports Server (NTRS)

Wilhelms, D. E.; Baldwin, R. J.

1989-01-01

Relations among geologic units and landforms suggest that igneous sills lie beneath much of the intercrater and intracrater terrain of the Martian uplands. The igneous rocks crop out along the upland-lowland front and in crater floors and other depressions that are low enough to intersect the sill's intrusion horizons. It is suggested that heat from the cooling sills melted some of the ice contained in overlying fragmental deposits, creating valley networks by subsurface flow of the meltwater. Terrains with undulatory, smooth surfaces and softened traces of valleys were created by more direct contact with the sills. Widespread subsidence following emplacement of the sills deformed both them and the nonvolcanic deposits that overlie them, accounting for the many structures that continue from ridged plains into the hilly uplands. Crater counts show that the deposit that became valleyed, softened, and ridged probably began to form (and to acquire interstitial ice) during or shortly after the Middle Noachian Epoch, and continued to form as late as the Early Hesperian Epoch. The upper layers of this deposit, many of the visible valleys, and the ridged plains and postulated sills all have similar Early Hesperian ages. Continued formation of valleys is indicated by their incision of fresh-appearing crater ejecta. The dependence of valley formation on internal processes implies that Mars did not necessarily have a dense early atmosphere or warm climate.

Terrestrial analogs to lunar sinuous rilles - Kauhako Crater and channel, Kalaupapa, Molokai, and other Hawaiian lava conduit systems

NASA Technical Reports Server (NTRS)

Coombs, C. R.; Hawke, B. R.; Wilson, L.

1990-01-01

Two source vents, one explosive and one effusive erupted to form a cinder cone and low lava shield that together compose the Kalaupapa peninsula of Molokai, Hawaii, A 50-100-m-wide channel/tube system extends 2.3 km northward from kauhako crater in the center of the shield. Based on modeling, a volume of up to about 0.2 cu km of lava erupted at a rate of 260 cu m/sec to flow through the Kauhako conduit system in one of the last eruptive episodes on the peninsula. Channel downcutting by thermal erosion occurred at a rate of about 10 micron/sec to help form the 30-m-deep conduit. Two smaller, secondary tube systems formed east of the main lava channel/tube. Several other lava conduit systems on the islands of Oahu and Hawaii were also compared to the Kauhako and lunar sinuous rille systems. These other lava conduits include Whittington, Kupaianaha, and Mauna Ulu lava tubes. Morphologically, the Hawaiian tube systems studied are very similar to lunar sinuous rilles in that they have deep head craters, sinuous channels, and gentle slopes. Thermal erosion is postulated to be an important factor in the formation of these terrestrial channel systems and by analogy is inferred to be an important process involved in the formation of lunar sinuous rilles.

Terrestrial analogs to lunar sinuous rilles - Kauhako Crater and channel, Kalaupapa, Molokai, and other Hawaiian lava conduit systems

NASA Astrophysics Data System (ADS)

Coombs, C. R.; Hawke, B. R.; Wilson, L.

Two source vents, one explosive and one effusive erupted to form a cinder cone and low lava shield that together compose the Kalaupapa peninsula of Molokai, Hawaii, A 50-100-m-wide channel/tube system extends 2.3 km northward from kauhako crater in the center of the shield. Based on modeling, a volume of up to about 0.2 cu km of lava erupted at a rate of 260 cu m/sec to flow through the Kauhako conduit system in one of the last eruptive episodes on the peninsula. Channel downcutting by thermal erosion occurred at a rate of about 10 micron/sec to help form the 30-m-deep conduit. Two smaller, secondary tube systems formed east of the main lava channel/tube. Several other lava conduit systems on the islands of Oahu and Hawaii were also compared to the Kauhako and lunar sinuous rille systems. These other lava conduits include Whittington, Kupaianaha, and Mauna Ulu lava tubes. Morphologically, the Hawaiian tube systems studied are very similar to lunar sinuous rilles in that they have deep head craters, sinuous channels, and gentle slopes. Thermal erosion is postulated to be an important factor in the formation of these terrestrial channel systems and by analogy is inferred to be an important process involved in the formation of lunar sinuous rilles.

Geomorphology and Geology of the Southwestern Margaritifer Sinus and Argyre Regions of Mars. Part 4: Flow Ejecta Crater Distribution

NASA Technical Reports Server (NTRS)

Parker, T. J.; Pieri, D. C.

1985-01-01

Flow ejecta craters - craters surrounded by lobate ejecta blankets - are found throughout the study area. The ratio of the crater's diameter to that of the flow ejecta in this region is approximately 40 to 45%. Flow ejecta craters are dominantly sharply defined craters, with slightly degraded craters being somewhat less common. This is probably indicative of the ejecta's relatively low resistence to weathering and susceptibility to burial. Flow ejecta craters here seem to occur within a narrow range of crater sizes - the smallest being about 4km in diameter and the largest being about 27km in diameter. Ejecta blankets of craters at 4km are easily seen and those of smaller craters are simply not seen even in images with better than average resolution for the region. This may be due to the depth of excavation of small impacting bodies being insufficient to reach volatile-rich material. Flow ejecta craters above 24km are rare, and those craters above 27km do not display flow ejecta blankets. This may be a result of an excavation depth so great that the volatile content of the ejecta is insufficient to form a fluid ejecta blanket. The geomorphic/geologic unit appears also to play an important role in the formation of flow ejecta craters. Given the typical size range for the occurrence of flow ejecta craters for most units, it can be seen that the percentage of flow ejecta craters to the total number of craters within this size range varies significantly from one unit to the next. The wide variance in flow ejecta crater density over this relatively small geographical area argues strongly for a lithologic control of their distribution.

Spatial distribution of impact craters on Deimos

NASA Astrophysics Data System (ADS)

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.

Surface ages of mid-size saturnian satellites

NASA Astrophysics Data System (ADS)

Di Sisto, Romina P.; Zanardi, Macarena

2016-01-01

The observations of the surfaces of the mid-sized saturnian satellites made by Cassini-Huygens mission have shown a variety of features that allows study of the processes that took place and are taking place on those worlds. Research of the saturnian satellite surfaces has clear implications not only for Saturn's history and Saturn's surroundings, but also for the Solar System. Crater counting from high definition images is very important and could serve for the determination of the age of the surfaces. In a recent paper, we have calculated the production of craters on the mid-sized saturnian satellites by Centaur objects considering the current configuration of the Solar System. Also, we have compared our results with crater counts from Cassini images by other authors and we have noted that the number of observed small craters is less than our calculated theoretical number. In this paper we estimate the age of the surface for each observed terrain on each mid-sized satellite of Saturn. All the surfaces analyzed appear to be old with the exception of Enceladus. However, we have noticed that since there are less observed small craters than calculated (except on Iapetus), this results in younger ages than expected. This could be the result of efficient endogenous or exogenous process(es) for erasing small craters and/or crater saturation at those sizes. The size limit from which the observed number of smaller craters is less than the calculated is different for each satellite, possibly indicating processes that are unique to each, but other potential common explanations for this paucity of small craters would be crater saturation and/or deposition of E-ring particles. These processes are also suggested by the findings that the smaller craters are being preferentially removed, and the erasure process is gradual. On Enceladus, only mid and high latitude plains have remnants of old terrains; the other regions could be young. In particular, the regions near the South Polar Terrain could be as young as 50 Myr old. On the contrary for Iapetus, all the surface is old and it notably registers a primordial source of craters. As the crater size is decreased, it would be perceived to approach saturation until D≲ 2 km-craters, where saturation is complete.

Experimental hypervelocity impact into quartz sand - Distribution and shock metamorphism of ejecta

NASA Technical Reports Server (NTRS)

Stoeffler, D.; Gault, D. E.; Wedekind, J.; Polkowski, G.

1975-01-01

Results are presented for vertical impacts of 0.3-g cylindrical plastic projectiles into noncohesive quartz sand in which vertical and horizontal reference strate were employed by using layers of colored sand. The impacts were performed at velocities of 5.9-6.9 km/sec with a vertical gun ballistic range. The craters, 30-33 cm in diameter, reveal a radial decay of the ejecta mass per unit area with a power of -2.8 to -3.5. Material displaced from the upper 15% of the crater depth d is represented within the whole ejecta blanked, material from deeper than 28% of d is deposited inside 2 crater radii, and no material from deeper than 33% of d was ejected beyond the crater rim. Shock-metamorphosed particles (glassy agglutinates, cataclastic breccias, and comminuted quartz) amount to some 4% of the total displaced mass and indicate progressive zones of decay of shock intensity from a peak pressure of 300 kbar. The shock-metamorphosed particles and the shock-induced change in the grain size distribution of ejected samples have close analogies to the basic characteristics of the lunar regolith. Possible applications to regolith formation and to ejecta formations of large-scale impact craters are discussed.

Significant results from Apollo 14 lunar orbital photography.

NASA Technical Reports Server (NTRS)

El-Baz, F.; Roosa, S. A.

1972-01-01

Apollo 14 obtained 950 photographs from lunar orbit using the Hasselblad and Hycon cameras. The photographs reveal a number of new geologic features as well as previously unrecognized details of the morphology, structure, and stratigraphy of lunar surface units. The primary result is the verification of the extensive role of volcanism in the formation and modification of the lunar highlands, especially on the far side. Terra volcanism appears to be manifest in the formation of (1) constructional units of hilly and furrowed materials of regional extent as in the Kant Plateau in the central near-side highlands and northwest of the crater Pasteur near the eastern limb of the moon; (2) somewhat viscous lava flows and pools associated with fracture systems and/or what appear to be volcanic craters; (3) craters, crater chains, and irregular depressions, particularly on the lunar far side. The first photographs of a flow channel, a leveed sinuous rille that apparently originated by lava flowage on the surface, were obtained by Apollo 14. Another first is a high-resolution photograph of the interior of what appears to be the youngest lunar crater yet photographed in the 20- 40-km size range.

Sporadic Groundwater Upwelling in Deep Martian Craters: Evidence for Lacustrine Clays and Carbonates

NASA Technical Reports Server (NTRS)

Michalski, J. R.; Rogers, A. D.; Wright, S. P.; Niles, P.; Cuadros, J.

2012-01-01

While the surface of Mars may have had an active hydrosphere early in its history [1], it is likely that this water retreated to the subsurface early on due to loss of the magnetic field and early atmosphere [2]. This likely resulted in the formation of two distinct aqueous regimes for Mars from the Late Noachian onward: one dominated by redistribution of surface ice and occasional melting of snow/ice [3], and one dominated by groundwater activity [4]. The excavation of alteration minerals from deep in the crust by impact craters points to an active, ancient, deep hydrothermal system [5]. Putative sapping features [6] may occur where the groundwater breached the surface. Upwelling groundwater may also have played a critical role in the formation of massive, layered, cemented sediments in Sinus Meridiani [7,8], in the Valles Marineris [9], and possibly in Gale Crater [10], where the Curiosity Rover will land later this year. Understanding the past distribution, geochemistry, and significance of groundwater on Mars is critical to untangling the origins of deep alteration minerals, Hesperian sulfate deposits, and crater fill deposits at Gale Crater or in other locations.

First natural occurrence of coesite

USGS Publications Warehouse

Chao, E.C.T.; Shoemaker, E.M.; Madsen, B.M.

1960-01-01

Coesite, the high-pressure polymorph of SiO2, hitherto known only as a synthetic compound, is identified as an abundant mineral in sheared Coconino sandstone at Meteor Crater, Arizona. This natural occurrence has important bearing on the recognition of meteorite impact craters in quartz-bearing geologic formations.

Bunte Breccia of the Ries - Continuous deposits of large impact craters

NASA Technical Reports Server (NTRS)

Horz, F.; Ostertag, R.; Rainey, D. A.

1983-01-01

The 26-km-diameter Ries impact crater in south Germany and the mechanism of ejection and emplacement associated with its formation about 15 Myr ago are discussed in detail, and the implications of the findings for models of crater formation on earth, moon, and planets are considered. Field observations and laboratory tests on 560-m core materials from nine locations are reported. The continuous deposits (Bunte Breccia) are found to be a chaotic mixture resulting from deposition at ambient temperatures in a highly turbulent environment, probably in the ballistic scenario proposed by Oberbeck et al. (1975), with an emplacement time of only about 5 min. Further impact parameters are estimated using the 'Z model' of Maxwell (1977): initial radius = 6.5 km, excavation depth = 1650 m, excavation volume = 136 cu km, and transient cavity volume = 230 cu km. The interpretation of lunar and planetary remote-sensing and in situ evidence from impact craters is reviewed in the light of the Ries findings. Numerous photographs, maps, diagrams, and tables illustrate the investigation.

The Formation and Erosion History of Mt. Sharp

NASA Technical Reports Server (NTRS)

Allen, Carlton C.; Dapremont, Angela M.

2014-01-01

The Curiosity rover is exploring 155 km diameter Gale crater and Mt. Sharp, Gale's 5 km high central mound (Fig. 1). This study addresses the formation and erosion history of Mt. Sharp. Gale lies on the topographic dichotomy between the southern highlands and the northern plains - a drop of over 2 km [1,2]. Altitude differences between the north and south rim reflect this regional slope, as do altitude differences between the deep annulus north of Mt. Sharp and the southern crater floor. Orbiter and rover images demonstrate that most exposed areas on Mt. Sharp consist of thin, sub-parallel units interpreted as sedimentary layers [3]. Gale is typical of the 50 large martian craters that have been totally or partially filled with such layers [4,5]. In many craters these sediments have been deeply eroded. Central Peak and Peak Ring: The highest point on Mt. Sharp, near the crater's center, is interpreted as a central peak [6]. The peak has a massive lower portion and a thin, smooth capping deposit (Fig. 2). Gale's size is transitional between martian craters with single central peaks and craters with peak rings approximately half the crater's diameter [2,6]. The boundaries of Mt. Sharp, as well as an arc of hills to the southeast of the mountain, closely match a circle approximately 80 km in diameter (Fig. 3). This morphology suggests that the Gale impact may have formed both a central peak and a partial peak ring, which is covered by the sediments of Mt. Sharp in the north and possibly exposed in the arc of eroded hills in the southeast quadrant (Figs. 3,4).

Formation and mantling ages of lobate debris aprons on Mars: Insights from categorized crater counts

NASA Astrophysics Data System (ADS)

Berman, Daniel C.; Crown, David A.; Joseph, Emily C. S.

2015-06-01

Lobate debris aprons in the Martian mid-latitudes offer important insights into the history of the Martian climate and the role of volatiles in Martian geologic activity. Here we present the results of counts of small impact craters, categorized by morphology, on debris aprons in the Deuteronilus Mensae region and the area east of Hellas basin. Mars Reconnaissance Orbiter (MRO) ConTeXt Camera (CTX) images were used to document crater populations on the apron surfaces. Each crater was assessed and categorized according to its morphological characteristics (fresh, degraded, or filled). Fresh and most degraded craters likely superpose recent mantling deposits, whereas filled craters contain mantling deposits and thus indicate a minimum formation age for the apron (i.e., the age since stabilization of the debris apron surface following some modification but prior to mantling). Size-frequency distributions (SFDs) were compiled using established methodologies and plotted to assess their fit to the isochrons. The range or ranges in crater diameter over which each distribution paralleled the isochrons was determined by visual inspection, and general age constraints were noted from SFDs for all craters on a given surface and from each morphological class. The diameter range of each SFD segment observed to parallel an isochron was then input into the Craterstats2 analysis tool to calculate specific age estimates. The aprons were assessed both individually and as regional populations, which improved interpretation of the results and demonstrated the value and limitations of both approaches. The categorized counts reveal three groups of ages: (a) filled impact craters at larger diameters (>~500 m) typically show the oldest ages, between ~300 Ma and 1 Ga, (b) smaller diameter filled and degraded craters reveal ages of resurfacing events between ~10 Ma and 300 Ma, and (c) fresh crater populations (<~100 m diameter) indicate mantling deposits of less than ~10 Ma in age. These results indicate that the lobate debris apron populations formed (or their surfaces became stable) in the Early to Middle Amazonian Epochs, and were subsequently subjected to complex degradation by erosion and sublimation and/or melting of contained ice, culminating in episodes of deposition of ice-rich mantles in the Late Amazonian Epoch.

Martian planetwide crater distributions - Implications for geologic history and surface processes

NASA Technical Reports Server (NTRS)

Soderblom, L. A.; Condit, C. D.; West, R. A.; Herman, B. M.; Kreidler, T. J.

1974-01-01

Three different diameter size ranges are considered in connection with the Martian crater distribution, taking into account small craters from 0.6 to 1.2 km, intermediate-sized craters from 4 to 10 km, and large craters with diameters exceeding 20 km. One of the objectives of the investigation reported is to establish the effects of eolian processes in the modification of craters in the different size ranges. Another objective is concerned with a description of the genetic relationships among the three size ranges of craters. Observables related to the relative age of geologic provinces are to be separated from observables related to geographic variations in eolian transport and deposition. Lunar and Martian cratering histories are compared as a basis for establishing relative and absolute time scales for the geological evolution of Mars.

Filled Crater and Scallops

NASA Image and Video Library

2015-01-28

In this observation from NASA Mars Reconnaissance Orbiter made for a study of ancient craters, we see the craters filled with smooth material that has subsequently degraded into scallops. These formations might be possibly due to ground ice sublimation. High resolution can help to estimate any differences in roughness on the smoother main mantle and in the eroded hollows. With the enhanced color swath, we might be able to view composition variations of the material. http://photojournal.jpl.nasa.gov/catalog/PIA19288

The Explorer's Guide to Impact Craters

NASA Astrophysics Data System (ADS)

Pierazzo, E.; Osinski, G.; Chuang, F.

2004-12-01

Impact cratering is a fundamental geologic process of our solar system. It competes with other processes, such as plate tectonics, volcanism, or fluvial, glacial and eolian activity, in shaping the surfaces of planetary bodies. In some cases, like the Moon and Mercury, impact craters are the dominant landform. On other planetary bodies impact craters are being continuously erased by the action of other geological processes, like volcanism on Io, erosion and plate tectonics on the Earth, tectonic and volcanic resurfacing on Venus, or ancient erosion periods on Mars. The study of crater populations is one of the principal tools for understanding the geologic history of a planetary surface. Among the general public, impact cratering has drawn wide attention through its portrayal in several Hollywood movies. Questions that are raised after watching these movies include: ``How do scientists learn about impact cratering?'', and ``What information do impact craters provide in understanding the evolution of a planetary surface?'' Fundamental approaches used by scientists to learn about impact cratering include field work at known terrestrial craters, remote sensing studies of craters on various solid surfaces of solar system bodies, and theoretical and laboratory studies using the known physics of impact cratering. We will provide students, science teachers, and the general public an opportunity to experience the scientific endeavor of understanding and exploring impact craters through a multi-level approach including images, videos, and rock samples. This type of interactive learning can also be made available to the general public in the form of a website, which can be addressed worldwide at any time.

Synthesis of Akaganeite in the Presence of Sulfate: Implications for Akaganeite Formation in Yellowknife Bay, Gale Crater, Mars

NASA Technical Reports Server (NTRS)

Peretyazhko, T. S.; Fox, A.; Sutter, B.; Niles, P. B.; Adams, M.; Morris, R. V.; Ming, D. W.

2016-01-01

Akaganeite (beta-FeOOH) is an Fe(III) (hydr)oxide with a tunnel structure usually occupied by chloride. Akaganeite has been recently discovered in a mudstone on the surface of Mars by the Chemistry and Mineralogy (CheMin) and Sample Analysis at Mars (SAM) instruments onboard the Mars Science Laboratory (MSL) Curiosity Rover in Gale crater [1, 2]. Akaganeite was detected together with sulfate minerals [anhydrite (CaSO4) and basanite (2CaSO4·2H2O)] in the drilled Cumberland and John Clein mudstone samples at Yellowknife Bay [2]. Discovery of akaganeite and sulfates in the same samples suggests that sulfate ions could be present in aqueous solution during akaganeite formation. However, mechanism and aqueous environmental conditions of akaganeite formation (e.g., pH and range of sulfate concentration) in Yellowknife Bay remain unknown. The objective of our work was to perform synthesis of akaganeite without or with sulfate addition at variable pHs in order to constrain formation conditions of akaganeite in Yellowknife Bay, Gale crater on Mars.

Processes Modifying Cratered Terrains on Pluto

NASA Technical Reports Server (NTRS)

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.

Impact craters: their importance in geologic record and implications for natural resource development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levie, D. Jr.

1986-05-01

Impacting bodies of sufficient size traveling at hypervelocities carry tremendous potential energy. This relatively infrequent process results in the instantaneous formation of unique structures that are characterized by extensive fracturing and brecciation of the target material. Impacts onto continental shield areas can create rich ore deposits, such as the Sudbury mining district in Canada. Impacts into the sedimentary column can instantaneously create hydrocarbon reservoirs out of initially nonporous rocks, such as at Red Wing Creek and Viewfield in the Williston basin. Associated reservoirs are usually limited to a highly deformed central uplift in larger craters, or to the fractured rimmore » facies in smaller craters. The presence of reservoirs and trapping mechanisms is largely dependent, however, upon the preservation state of the crater in the subsurface. A catastrophic extraterrestrial event (a large asteroid impact) has also been suggested as the cause for the extinction of the dinosaurs, but the latest theory proposes a companion star with a 26 m.y. periodicity as the cause for numerous lifeform extinctions over a similar time interval. Regardless of their magnitude and distribution over the earth, it is clear that catastrophic extraterrestrial events have been responsible for altering the geologic column locally, regionally, and quite possibly on a global scale.« less

Interpretations of family size distributions: The Datura example

NASA Astrophysics Data System (ADS)

Henych, Tomáš; Holsapple, Keith A.

2018-04-01

Young asteroid families are unique sources of information about fragmentation physics and the structure of their parent bodies, since their physical properties have not changed much since their birth. Families have different properties such as age, size, taxonomy, collision severity and others, and understanding the effect of those properties on our observations of the size-frequency distribution (SFD) of family fragments can give us important insights into the hypervelocity collision processes at scales we cannot achieve in our laboratories. Here we take as an example the very young Datura family, with a small 8-km parent body, and compare its size distribution to other families, with both large and small parent bodies, and created by both catastrophic and cratering formation events. We conclude that most likely explanation for the shallower size distribution compared to larger families is a more pronounced observational bias because of its small size. Its size distribution is perfectly normal when its parent body size is taken into account. We also discuss some other possibilities. In addition, we study another common feature: an offset or "bump" in the distribution occurring for a few of the larger elements. We hypothesize that it can be explained by a newly described regime of cratering, "spall cratering", which controls the majority of impact craters on the surface of small asteroids like Datura.

HiRISE observations of new impact craters exposing Martian ground ice

USGS Publications Warehouse

Dundas, Colin M.; Byrne, Shane; McEwen, Alfred S.; Mellon, Michael T.; Kennedy, Megan R.; Daubar, Ingrid J.; Saper, Lee

2014-01-01

Twenty small new impact craters or clusters have been observed to excavate bright material inferred to be ice at mid and high latitudes on Mars. In the northern hemisphere, the craters are widely distributed geographically and occur at latitudes as low as 39°N. Stability modeling suggests that this ice distribution requires a long-term average atmospheric water vapor content around 25 precipitable microns, more than double the present value, which is consistent with the expected effect of recent orbital variations. Alternatively, near-surface humidity could be higher than expected for current column abundances if water vapor is not well-mixed with atmospheric CO2, or the vapor pressure at the ice table could be lower due to salts. Ice in and around the craters remains visibly bright for months to years, indicating that it is clean ice rather than ice-cemented regolith. Although some clean ice may be produced by the impact process, it is likely that the original ground ice was excess ice (exceeding dry soil pore space) in many cases. Observations of the craters suggest small-scale heterogeneities in this excess ice. The origin of such ice is uncertain. Ice lens formation by migration of thin films of liquid is most consistent with local heterogeneity in ice content and common surface boulders, but in some cases nearby thermokarst landforms suggest large amounts of excess ice that may be best explained by a degraded ice sheet.

Impacts into quartz sand: Crater formation, shock metamorphism, and ejecta distribution in laboratory experiments and numerical models

NASA Astrophysics Data System (ADS)

Wünnemann, Kai; Zhu, Meng-Hua; Stöffler, Dieter

2016-10-01

We investigated the ejection mechanics by a complementary approach of cratering experiments, including the microscopic analysis of material sampled from these experiments, and 2-D numerical modeling of vertical impacts. The study is based on cratering experiments in quartz sand targets performed at the NASA Ames Vertical Gun Range. In these experiments, the preimpact location in the target and the final position of ejecta was determined by using color-coded sand and a catcher system for the ejecta. The results were compared with numerical simulations of the cratering and ejection process to validate the iSALE shock physics code. In turn the models provide further details on the ejection velocities and angles. We quantify the general assumption that ejecta thickness decreases with distance according to a power-law and that the relative proportion of shocked material in the ejecta increase with distance. We distinguish three types of shock metamorphic particles (1) melt particles, (2) shock lithified aggregates, and (3) shock-comminuted grains. The agreement between experiment and model was excellent, which provides confidence that the models can predict ejection angles, velocities, and the degree of shock loading of material expelled from a crater accurately if impact parameters such as impact velocity, impactor size, and gravity are varied beyond the experimental limitations. This study is relevant for a quantitative assessment of impact gardening on planetary surfaces and the evolution of regolith layers on atmosphereless bodies.

Crater topography on Titan: Implications for landscape evolution

NASA Astrophysics Data System (ADS)

Neish, C.; Kirk, R.; Lorenz, R.; Bray, V.; Schenk, P.; Stiles, B.; Turtle, E.; Cassini Radar Team

2012-04-01

Unique among the icy satellites, Titan’s surface shows evidence for extensive modification by fluvial and aeolian erosion, which act to change the topography of its surface over time. Quantifying the extent of this landscape evolution is difficult, since the original, ‘non-eroded’ surface topography is generally unknown. However, fresh craters on icy satellites have a well-known shape and morphology, which has been determined from extensive studies on the airless worlds of the outer solar system (Schenk et al., 2004). By comparing the topography of craters on Titan to similarly sized, pristine analogues on airless bodies, we can obtain one of the few direct measures of the amount of erosion that has occurred on Titan. Cassini RADAR has imaged >30% of the surface of Titan, and more than 60 potential craters have been identified in this data set (Wood et al., 2010; Neish and Lorenz, 2012). Topographic information for these craters can be obtained from a technique known as ‘SARTopo’, which estimates surface heights by comparing the calibration of overlapping synthetic aperture radar (SAR) beams (Stiles et al., 2009). We present topography data for several craters on Titan, and compare the data to similarly sized craters on Ganymede, for which topography has been extracted from stereo-derived digital elevation models (Bray et al., 2012). We find that the depths of craters on Titan are generally within the range of depths observed on Ganymede, but several hundreds of meters shallower than the average (Fig. 1). A statistical comparison between the two data sets suggests that it is extremely unlikely that Titan’s craters were selected from the depth distribution of fresh craters on Ganymede, and that is it much more probable that the relative depths of Titan are uniformly distributed between ‘fresh’ and ‘completely infilled’. This is consistent with an infilling process that varies linearly with time, such as aeolian infilling. Figure 1: Depth of craters on Titan (gray diamonds) compared to similarly sized, fresh craters on Ganymede (central peaks, +; central pits, *) and a handful of relaxed craters (black squares) from Bray et al. (2012). References: Bray, V., et al.: "Ganymede crater dimensions - implications for central peak and central pit formation and development". Icarus, Vol. 217, pp. 115-129, 2012. Neish, C.D., Lorenz, R.D.: "Titan’s global crater population: A new assessment". Planetary and Space Science, Vol. 60, pp. 26-33, 2012. Schenk, P.M., et al.: "Ages and interiors: the cratering record of the Galilean satellites". In: Bagenal, F., McKinnon, W.B. (Eds.), Jupiter: The Planet, Satellites, and Magnetosphere, Cambridge University Press, Cambridge, UK, pp. 427-456, 2004. Stiles, B.W., et al.: "Determining Titan surface topography from Cassini SAR data". Icarus, Vol. 202, pp. 584-598, 2009. Wood, C.A., et al.: "Impact craters on Titan". Icarus, Vol. 206, pp. 334-344, 2010.

Geologic implications of the Apollo 14 Fra Mauro breccias and comparison with ejecta from the Ries Crater, Germany

USGS Publications Warehouse

Chao, E.C.T.

1973-01-01

On the basis of petrographic and laboratory and active seismic data for the Fra Mauro breccias, and by comparison with the nature and distribution of the ejecta from the Ries crater, Germany, some tentative conclusions regarding the geologic significance of the Fra Mauro Formation on the moon can be drawn. The Fra Mauro Formation, as a whole, consists of unwcldcd, porous ejecta, slightly less porous than the regolith. It contains hand-specimen and larger size clasts of strongly annealed complex breccias, partly to slightly annealed breccias, basalts, and perhaps spherule-rich breccias. These clasts are embedded in a matrix of porous aggregate dominated by mineral and breccia fragments and probably largely free of undevitrified glass. All strongly annealed hand-specimen-size breccias are clasts in the Fra Mauro Formation. To account for the porous, unwelded state of the Fra Mauro Formation, the ejecta must have been deposited at a temperature below that required for welding and annealing. Large boulders probably compacted by the Cone crater event occur near the rim of the crater. They probably consist of a similar suite of fragments, but are probably less porous than the formation. The geochronologic clocks of fragments in the Fra Mauro Formation, with textures ranging from unannealed to strongly annealed, were not reset or strongly modified by the Imbrian event. Strongly annealed breccia clasts and basalt clasts are pre-Imbrian, and probably existed as ejecta mixed with basalt flows in the Imbrium Basin prior to the Imbrian event. The Imbrian event probably occurred between 3.90 or 3.88 and 3.65 b.y. ago.

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

NASA Technical Reports Server (NTRS)

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.

ARC-1965-A-33996

NASA Image and Video Library

1965-02-17

30 calibabor Vertical Gun Range in horizontal loading position. Dr. William Quaide and Donald Gault of Ames planetology branch used this gun range to study the formation of impact craters on the Moon. N-204A Verticle Gun is used to simulate the physics and mechanics of planetaryimpact cratering phenomena.

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

NASA Astrophysics Data System (ADS)

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.

The missing large impact craters on Ceres.

PubMed

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

2016-07-26

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.

Origin of the outer layer of martian low-aspect ratio layered ejecta craters

NASA Astrophysics Data System (ADS)

Boyce, Joseph M.; Wilson, Lionel; Barlow, Nadine G.

2015-01-01

Low-aspect ratio layered ejecta (LARLE) craters are one of the most enigmatic types of martian layered ejecta craters. We propose that the extensive outer layer of these craters is produced through the same base surge mechanism as that which produced the base surge deposits generated by near-surface, buried nuclear and high-explosive detonations. However, the LARLE layers have higher aspect ratios compared with base surge deposits from explosion craters, a result of differences in thicknesses of these layers. This characteristics is probably caused by the addition of large amounts of small particles of dust and ice derived from climate-related mantles of snow, ice and dust in the areas where LARLE craters form. These deposits are likely to be quickly stabilized (order of a few days to a few years) from eolian erosion by formation of duricrust produced by diffusion of water vapor out of the deposits.

The missing large impact craters on Ceres

USGS Publications Warehouse

Marchi, S.; Ermakov, A.; Raymond, C.A.; Fu, R.R.; O'Brien, D.P.; Bland, Michael T.; 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.

Lunar floor-fractured craters: Modes of dike and sill emplacement and implications of gas production and intrusion cooling on surface morphology and structure

NASA Astrophysics Data System (ADS)

Wilson, Lionel; Head, James W.

2018-05-01

Lunar floor-fractured craters (FFCs) represent the surface manifestation of a class of shallow crustal intrusions in which magma-filled cracks (dikes) rising to the surface from great depth encounter contrasts in host rock lithology (breccia lens, rigid solidified melt sheet) and intrude laterally to form a sill, laccolith or bysmalith, thereby uplifting and deforming the crater floor. Recent developments in the knowledge of lunar crustal thickness and density structure have enabled important revisions to models of the generation, ascent and eruption of magma, and new knowledge about the presence and behavior of magmatic volatiles has provided additional perspectives on shallow intrusion processes in FFCs. We use these new data to assess the processes that occur during dike and sill emplacement with particular emphasis on tracking the fate and migration of volatiles and their relation to candidate venting processes. FFCs result when dikes are capable of intruding close to the surface, but fail to erupt because of the substructure of their host impact craters, and instead intrude laterally after encountering a boundary where an increase in ductility (base of breccia lens) or rigidity (base of solidified melt sheet) occurs. Magma in dikes approaching the lunar surface experiences increasingly lower overburden pressures: this enhances CO gas formation and brings the magma into the realm of the low pressure release of H2O and sulfur compounds, both factors adding volatiles to those already collected in the rising low-pressure part of the dike tip. High magma rise velocity is driven by the positive buoyancy of the magma in the part of the dike remaining in the mantle. The dike tip overshoots the interface and the consequent excess pressure at the interface drives the horizontal flow of magma to form the intrusion and raise the crater floor. If sill intrusion were controlled by the physical properties at the base of the melt sheet, dikes would be required to approach to within ∼300 m of the surface, and thus eruptions, rather than intrusions, would be very likely to occur; instead, dynamical considerations strongly favor the sub-crustal breccia lens as the location of the physical property contrast localizing lateral intrusion, at a depth of several kilometers. The end of lateral and vertical sill growth occurs when the internal magma pressure equals the external pressure (the intrusion just supports the weight of the overlying crust). Dynamical considerations lead to the conclusion that dike magma volumes are up to ∼1100 km3, and are generally insufficient to form FFCs on the lunar farside; the estimated magma volumes available for injection into sills on the lunar nearside (up to ∼800 km3) are comparable to the observed floor uplift in many smaller FFCs, and thus consistent with these FFCs forming from a single dike emplacement event. In contrast, the thickest intrusions in the largest craters imply volumes requiring multiple dike contributions; these are likely to be events well-separated in time, rather than injection of new magma into a recently-formed and still-cooling intrusion. We present a temporal sequence of 1) dike emplacement, 2) sill formation and surface deformation, 3) bubble rise, foam layer formation and collapse, 4) intrusion cooling, and a synthesis of predicted deformation sequence and eruption styles. Initial lateral injection of the sill at a depth well below the upper dike tip initiates upbowing of the overburden, leveraging deformation of the crater floor melt sheet above. This is followed by lateral spreading of the sill toward the edges of the crater floor, where crater wall and rim deposit overburden inhibit further lateral growth, and the sill grows vertically into a laccolith or bysmalith, uplifting the entire floor above the intrusion. Subsidiary dikes can be emplaced in the fractures at the uplift margins and will rise to the isostatic level of the initial dike tip; if these contain sufficient volatiles to decrease magma density, eruptions can also occur. This initial phase of intrusion, sill lateral spreading and floor uplift occurs within a few hours after initial dike emplacement. During the subsequent cooling of the sill, bubbles can rise hundreds of meters to the top of the intrusion to create a foam layer; when drainage of gas bubble wall magma occurs in the foam layer, a continuous gas layer forms above the foam. Gas formation and upward migration produces an increase in sill thickness, while subsequent cooling and solidification cause a thickness decreases and subsidence. The total topographic evolution history, following an initial 2 km thick sill intrusion and floor uplift (hours), includes further floor uplift by gas formation and migration (decades; ∼30 m), followed by cooling, solidification and subsidence (∼a century; ∼350 m). An initial 2 km thick sill is predicted to have a final thickness of ∼1.7 km. This predicted sequence of events can be compared with the sequence of floor deformation and volcanism in FFCs in order to test and refine this model.

A possible formation mechanism of rampart-like ejecta pattern in a laboratory

NASA Astrophysics Data System (ADS)

Suzuki, A.; Kadono, T.; Nakamura, A. M.; Arakawa, M.; Wada, K.; Yamamoto, S.

2011-12-01

The ejecta morphologies around impact craters represent highly diverse appearance on the surface of solid bodies in our Solar System. It is considered that the varied ejecta morphologies result from the environments such as the atmospheric pressure, the volatile content in the subsurface, because they affect the emplacement process of the ejecta. Clarifying the relationships between the ejecta morphologies and the formation processes and environments could constrain the ancient surface environment and the evolution of the planets. We have investigated the ejecta patterns around the impact craters which formed on a glass beads layer in a laboratory, and found that the patterns depend on impact velocity, atmospheric pressure, and initial state of packing of the target [Suzuki et al., 2010, JpGU abstract]. Now, we focus on one of the ejecta patterns which has a petal-like (or sometimes concentric) ridges on the distal edge of the continuous ejecta. This ejecta pattern looks very similar to the rampart ejecta morphology observed around Martian impact craters [e.g. Barlow et al., 2000]. The experiments are conducted with the small light gas gun placed in Kobe University, Japan. The projectile is a cylinder with a diameter of 10 mm and a height of 10 mm, and is made of aluminum, nylon, or stainless. The target is a layer of glass beads (nearly uniform diameter) in a tub with ~28 cm in diameter. The bulk density is about 1.7 g/cm^3. The following three parameters are varied: 1) the diameter of the target glass beads (50, 100, 420 microns), 2) the ambient atmospheric pressure in the chamber (from ~500 Pa to atmospheric pressure), 3) the impact velocity of the projectile (from a few to ~120 m/s). In our experiments, the rampart-like ridged patterns are observed within the following conditions: 1) the diameter of the target glass beads is 50 and 100 microns, 2) the ambient pressure in the chamber is higher than ~10^4 Pa, and 3) the impact velocity is higher than 16 m/s. Eventually, we have succeeded to capture the formation of the rampart-like ridges with high-speed video camera. Our experiments clarify that the rampart-like ridges are formed by the thin, radial ejecta flow that originates around the crater rim, other than the sedimentation of ejecta decelerated by the ambient atmosphere. A wake of the projectile going through the atmosphere might be responsible for the crater rim collapsed, which results in initiating the radial ejecta flow. Additionally, it is found that erodible surface (i.e. a particle layer in this case) is essential to produce the rampart-like ridges.

Lunar History

NASA Technical Reports Server (NTRS)

Edmunson, Jennifer E.

2009-01-01

This section of the workshop describes the history of the moon, and offers explanations for the importance of understanding lunar history for engineers and users of lunar simulants. Included are summaries of the initial impact that is currently in favor as explaining the moon's formation, the crust generation, the creation of craters by impactors, the era of the lunar cataclysm, which some believe effected the evolution of life on earth, the nature of lunar impacts, crater morphology, which includes pictures of lunar craters that show the different types of craters, more recent events include effect of micrometeorites, solar wind, radiation and generation of agglutinates. Also included is a glossary of terms.

Recharge from a subsidence crater at the Nevada test site

USGS Publications Warehouse

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.

Is There any Relationship Between the Santa Elena Depression and Chicxulub Impact Crater, Northwestern Yucatan Peninsula, Mexico?

NASA Astrophysics Data System (ADS)

Lefticariu, L.

2005-05-01

The Terminal Cretaceous Chicxulub Impact Crater had a strong control on the depositional and diagenetic history of the northern Yucatan Platform during most of the Cenozoic Era. The Chicxulub Sedimentary Basin (henceforth Basin), which approximately coincides with the impact crater, is circumscribed by a concentration of karstic sinkholes known as the Ring of Cenotes. Santa Elena Depression (henceforth Depression) is the name proposed for the bowl-shaped buried feature, first contoured by geophysical studies, immediately south of the Basin, in the area where the Ticul 1 and UNAM 5 wells were drilled. Lithologic, petrographic, and biostratigraphic data on PEMEX, UNAM, and ICDP cores show that: 1) Cenozoic deposits are much thicker inside the Basin than inside the Depression, 2) in general, the Cenozoic formations from inside the Depression are the thickest among those outside the Basin, 3) variably dolomitized pelagic or outer-platform wackestone or mudstone occur both inside the Basin and Depression, 4) the age of the deeper-water sedimentary carbonate rocks is Paleocene-Eocene inside the Basin and Paleocene?-Early Eocene inside the Depression, 5) the oldest formations that crop out are of Middle Eocene age at the edge of the Basin and Early-Middle Eocene age inside the Depression, 6) saline lake deposits, that consist chiefly of anhydrite, gypsum, and fine carbonate, and also contain quartz, chert, clay, zeolite, potassium feldspar, pyrite, and fragments of wood, are present in the Cenozoic section of the UNAM 5 core between 282 and 198 m below the present land surface, 7) the dolomite, subaerial exposure features (subaerial crusts, vugs, karst, dedolomite), and vug-filling cement from the Eocene formations are more abundant inside the Depression than inside the Basin. The depositional environments that are proposed for explaining the Cenozoic facies succession within the Santa Elena Depression are: 1) deeper marine water (Paleocene?-Early Eocene), 2) relatively isolated saline lake (Middle Eocene), and 3) shallow marine water (Middle-Late Eocene?). In places, the deeper-water facies are similar to those within the Chicxulub Sedimentary Basin. The shallow-water facies is similar to those occurring outside the Basin. In general, quartz and silicates are rare in the Cenozoic sedimentary carbonate of the northwestern Yucatan Peninsula. Therefore, their presence in the UNAM 5 core could be attributed to either impact breccia reworking or silicic volcanic processes. Quartz, chert, zeolite, and clay also are common in the suevite breccia of both Yax-1 and UNAM 5 cores. The fact that the Santa Elena Depression was a distinct sedimentary basin during much of the Paleogene could be explained by any or a combination of the following hypotheses: 1) In spite of being located outside the cenote ring, the Depression is a sub-basin of the larger and deeper Chicxulub Sedimentary Basin and is therefore located within the Chicxulub Impact Crater, 2) the Depression coincides with an impact crater distinct from the Chicxulub Impact Crater, 3) the Depression formed after the Chicxulub bolide impact due to slumping, crater wall failure, or larger-scale tectonic processes. The lack of conclusive evidence for multiple impact breccia layers in the northwestern Yucatan Peninsula, corroborated with the presence on top of the impact breccia from UNAM 5 core of deeper-water limestone similar to that of Late Paleocene-Early Eocene age from Yax-1 core, would be more consistent with either the first or third hypothesis.

Diatremes and craters attributed to natural explosions

USGS Publications Warehouse

Shoemaker, Eugene Merle

1956-01-01

Diatremes - volcanic pipes attributed to explosion - and craters have been studied to infer the ultimate causes and physical conditions attending natural explosive processes. Initial piercement of diatremes on the Navajo reservation, Arizona was probably along a fracture propagated by a high-pressure aqueous fluid. Gas rising at high velocity along the fracture would become converted to a gas-solid fluidized system by entrainment of wall- rock fragments. The first stages of widening of the vent are probably accomplished mainly by simple abrasion of the high-velocity fluidized system on the walls of the fracture. As the vent widens, its enlargement may be accelerated by inward spalling of the walls. The inferred mechanics of the Navajo-Hopi diatremes is used to illustrate the possibility of diatreme formation over a molten salt mass.

In plain sight: the Chesapeake Bay crater ejecta blanket

NASA Astrophysics Data System (ADS)

Griscom, D. L.

2012-02-01

The discovery nearly two decades ago of a 90 km-diameter impact crater below the lower Chesapeake Bay has gone unnoted by the general public because to date all published literature on the subject has described it as "buried". To the contrary, evidence is presented here that the so-called "upland deposits" that blanket ∼5000 km2 of the U.S. Middle-Atlantic Coastal Plain (M-ACP) display morphologic, lithologic, and stratigraphic features consistent with their being ejecta from the 35.4 Ma Chesapeake Bay Impact Structure (CBIS) and absolutely inconsistent with the prevailing belief that they are of fluvial origin. Specifically supporting impact origin are the facts that (i) a 95 %-pure iron ore endemic to the upland deposits of southern Maryland, eastern Virginia, and the District of Columbia has previously been proven to be impactoclastic in origin, (ii) this iron ore welds together a small percentage of well-rounded quartzite pebbles and cobbles of the upland deposits into brittle sheets interpretable as "spall plates" created in the interference-zone of the CBIS impact, (iii) the predominantly non-welded upland gravels have long ago been shown to be size sorted with an extreme crater-centric gradient far too large to have been the work of rivers, but well explained as atmospheric size-sorted interference-zone ejecta, (iv) new evidence is provided here that ~60 % of the non-welded quartzite pebbles and cobbles of the (lower lying) gravel member of the upland deposits display planar fractures attributable to interference-zone tensile waves, (v) the (overlying) loam member of the upland deposits is attributable to base-surge-type deposition, (vi) several exotic clasts found in a debris flow topographically below the upland deposits can only be explained as jetting-phase crater ejecta, and (vii) an allogenic granite boulder found among the upland deposits is deduced to have been launched into space and sculpted by hypervelocity air friction during reentry. An idealized calculation of the CBIS ejecta-blanket elevation profile minutes after the impact was carried out founded on well established rules for explosion and impact-generated craters. This profile is shown here to match the volume of the upland deposits ≥170 km from the crater center. Closer to the crater, much of the "postdicted" ejecta blanket has clearly been removed by erosion. Nevertheless the Shirley and fossil-free Bacons Castle Formations, located between the upland deposits and the CBIS interior and veneering the present day surface with units ∼10-20 m deep, are respectively identified as curtain- and excavation-phase ejecta. The neritic-fossil-bearing Calvert Formation external to the crater is deduced to be of Eocene age (as opposed to early Miocene as currently believed), preserved by the armoring effects of the overlying CBIS ejecta composed of the (distal) upland deposits and the (proximal) Bacons Castle Formation. The lithofacies of the in-crater Calvert Formation can only have resulted from inward mass wasting of the postdicted ejecta blanket, vestiges of which (i.e. the Bacons Castle and Shirley Formations) still overlap the crater rim and sag into its interior, consistent with this expectation. Because there appear to be a total of ∼10 000 km2 of CBIS ejecta lying on the present-day surface, future research should center the stratigraphic, lithologic, and petrologic properties of these ejecta versus both radial distance from the crater center (to identify ejecta from different ejection stages) and circumferentially at fixed radial distances (to detect possible anisotropies relating the impact angle and direction of approach of the impactor). The geological units described here may comprise the best preserved, and certainly the most accessible, ejecta blanket of a major crater on the Earth's surface and therefore promise to be a boon to the field of impact geology. As a corollary, a major revision of the current stratigraphic column of the M-ACP will be necessary.

The Amorphous Composition of Three Mudstone Samples from Gale Crater: Implications for Weathering and Diagenetic Processes on Mars

NASA Technical Reports Server (NTRS)

Achilles, C. N.; Downs, R. T.; Rampe, E. B.; Morris, R. V.; Bristow, T. F.; Ming, D. W.; Blake, D. F.; Vaniman, D. T.; Morrison, S. M.; Sutter, B.;

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

NASA Astrophysics Data System (ADS)

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 and its extrusive equivalent dome 31, we infer that the stratigraphic position of the ca. 32 ka Auckland/Mono Lake geomagnetic excursion, if recorded in beds of the Wilson Creek formation, is between Ashes 7 and 8. Accordingly, the prominent geomagnetic excursion bisected by Ash 15 lower in the section is the ca. 41 ka global Laschamp event.

Investigating Weathering of Basaltic Materials in Gale Crater, Mars: A Combined Laboratory, Modeling and Terrestrial Field Approach

NASA Technical Reports Server (NTRS)

Hausrath, Elisabeth; Ralston, Stephanie J.; Bamisile, Toluwalope; Ming, Douglas; Peretyazhko, Tanya; Rampe, Elizabeth; Gainey, Seth

2017-01-01

Recent observations from Gale Crater, Mars document past aqueous alteration both in the formation of the Stimson sandstone unit, as well as in the formation of altered fractures within that unit. Geochemical and mineralogical data from Curiosity also suggest Fe-rich amorphous weathering products are present in most samples measured to date. Here we interpret conditions of possible past weathering in Gale Crater using a combination of field, laboratory, and modeling work. In order to better understand secondary Fe-rich phases on Mars, we are examining formation of weathering products in high Fe and Mg and low Al serpentine soils in the Klamath Mountains, CA. We have isolated potential weathering products from these soils, and are analyzing them using synchrotron µXRF and µXRD as well as FullPat for a direct comparison to analyses from Gale Crater. In order to interpret the implications of the persistence of potential secondary Fe-containing phases on Mars, we are also measuring the dissolution rates of the secondary weathering products allophane, Fe-rich allophane, and hisingerite. Ongoing dissolution experiments of these materials suggest that they dissolve significantly more rapidly than more crystalline secondary minerals with similar chemical compositions. Finally, to quantify the specific conditions of past aqueous alteration in Gale Crater we are performing reactive transport modeling of a range of possible past environmental conditions. Specifically, we are testing the conditions under which a Stimson unit-like material forms from a parent material similar to Rocknest or Bagnold eolian deposits, and the conditions under which observed altered fracture zones form from a Stimson unit-like parent material. Our modeling results indicate that the formation of the Stimson unit is consistent with leaching of an eolian deposit with a solution of pH = 6-8, and that formation of the altered fracture zones is consistent with leaching with a very acidic (pH = 2-3) high sulfate solution containing Ca. These results suggest circumneutral pH conditions during authigenesis or early diagenesis in the Stimson formation sediments followed by diagenetic alteration by very acidic solutions along fracture zones.

A Massive Central Peak and a Low Peak Ring in Gale Crater - Important Influences on the Formation of Mt. Sharp

NASA Technical Reports Server (NTRS)

Allen, Carlton C.

2015-01-01

The Curiosity rover is exploring 155 km diameter Gale crater and Mt. Sharp, Gale's high central mound. This study addresses the central peak and proposed peak ring, and their influence on the overall morphology of the mountain.

Lunar and Planetary Science XXXV: Mars: Hydrology, Drainage, and Valley Systems

NASA Technical Reports Server (NTRS)

2004-01-01

The titles in this section include: 1) Analysis of Orientation Dependence of Martian Gullies; 2) A Preliminary Relationship between the Depth of Martian Gullies and the Abundance of Hydrogen on Near-Surface Mars; 3) Water Indicators in Sirenum Terra and around the Argyre Impact Basin, Mars; 4) The Distribution of Gullies and Tounge-shaped Ridges and Their Role in the Degradation of Martian Craters; 5) A Critical Evaluation of Crater Lake Systems in Memnonia Quadrangle, Mars; 6) Impact-generated Hydrothermal Activity at Gusev Crater: Implications for the Spirit Mission; 7) Characterization of the Distributary Fan in Holden NE Crater using Stereo Analysis; 8) Computational Analysis of Drainage Basins on Mars: Appraising the Drainage Density; 9) Hypsometric Analyses of Martian Basins: A Comparison to Terrestrial, Lunar, and Venusian Hypsometry; 10) Morphologic Development of Harmakhis Vallis, Mars; 11) Mangala Valles, Mars: Investigations of the source of Flood Water and Early Stages of Flooding; 12) The Formation of Aromatum Chaos and the Water Discharge Rate at Ravi Vallis; 13) Inferring Hydraulics from Geomorphology for Athabasca Valles, Mars; 14) The Origin and Evolution of Dao Vallis: Formation and Modification of Martian Channels by Structural Collapse and Glaciation; 15) Snowmelt and the Formation of Valley Networks on Martian Volcanoes; 16) Extent of Floating Ice in an Ancient Echus Chasma/Kasei Valley System, Mars.

Deformed barchans under alternating flows: Flume experiments and comparison with barchan dunes within Proctor Crater, Mars

NASA Astrophysics Data System (ADS)

Taniguchi, Keisuke; Endo, Noritaka

2007-10-01

It is generally considered that barchans, isolated crescentic-shaped dunes, develop where wind is unidirectional and the available sand is insufficient to cover the entire dune field; however, Bishop [Bishop, M.A., 2001. Seasonal variation of crescentic dune morphology and morphometry, Strzelecki Simpson desert, Australia. Earth Surface Process and Landforms 26, 783 791.] observed barchans that developed in areas where winds blow seasonally in opposite directions and described a peculiar deformation feature, the “rear slipface,” that is not found in ordinary barchans. Barchans under such bidirectional flows are poorly understood, and it is necessary to study barchans that formed under many different flow conditions. We conducted flume experiments to investigate the deformation of barchans under alternating water flow, and observed new deformation features in addition to rear slipfaces. We conclude that the deformation of barchans can be categorized into four types, one of which shows morphologies similar to barchans within Proctor Crater, Mars. The deformation type depends on the strength of the reverse flow relative to the forward flow and the absolute velocity of the forward flow. Comparison of our results with barchan dunes within Proctor Crater enable us to qualitatively estimate the wind strength and direction related to dune formation on Mars. These results are in agreement with those of Fenton et al. [Fenton, L.K., Toigo, A.D., Richardson, M.I., 2005. Aeolian processes in Proctor Crater on Mars: Mesoscale modeling of dune-forming winds. Journal of Geophysical Research 110 (E6), E06005.].

Lava heating and loading of ice sheets on early Mars: Predictions for meltwater generation, groundwater recharge, and resulting landforms

NASA Astrophysics Data System (ADS)

Cassanelli, James P.; Head, James W.

2016-06-01

Recent modeling studies of the early Mars climate predict a predominantly cold climate, characterized by the formation of regional ice sheets across the highland areas of Mars. Formation of the predicted "icy highlands" ice sheets is coincident with a peak in the volcanic flux of Mars involving the emplacement of the Late Noachian - Early Hesperian ridged plains unit. We explore the relationship between the predicted early Mars "icy highlands" ice sheets, and the extensive early flood volcanism to gain insight into the surface conditions prevalent during the Late Noachian to Early Hesperian transition period. Using Hesperia Planum as a type area, we develop an ice sheet lava heating and loading model. We quantitatively assess the thermal and melting processes involved in the lava heating and loading process following the chronological sequence of lava emplacement. We test a broad range of parameters to thoroughly constrain the lava heating and loading process and outline predictions for the formation of resulting geological features. We apply the theoretical model to a study area within the Hesperia Planum region and assess the observed geology against predictions derived from the ice sheet lava heating and loading model. Due to the highly cratered nature of the Noachian highlands terrain onto which the volcanic plains were emplaced, we predict highly asymmetrical lava loading conditions. Crater interiors are predicted to accumulate greater thicknesses of lava over more rapid timescales, while in the intercrater plains, lava accumulation occurs over longer timescales and does not reach great thicknesses. We find that top-down melting due to conductive heat transfer from supraglacial lava flows is generally limited when the emplaced lava flows are less than ∼10 m thick, but is very significant at lava flow thicknesses of ∼100 m or greater. We find that bottom-up cryosphere and ice sheet melting is most likely to occur within crater interiors where lavas accumulate to a sufficient thickness to raise the ice-melting isotherm to the base of the superposed lavas. In these locations, if lava accumulation occurs rapidly, bottom-up melting of the ice sheet can continue, or begin, after lava accumulation has completed in a process we term "deferred melting". Subsurface mass loss through melting of the buried ice sheets is predicted to cause substantial subsidence in the superposed lavas, leading to the formation of associated collapse features including fracture systems, depressions, surface faulting and folding, wrinkle-ridge formation, and chaos terrain. In addition, if meltwater generated from the lava heating and loading process becomes trapped at the lava flow margins due to the presence of impermeable confining units, large highly pressurized episodic flooding events could occur. Examination of the study area reveals geological features which are generally consistent with those predicted to form as a result of the ice sheet lava heating and loading process, suggesting the presence of surface snow and ice during the Late Noachian to Early Hesperian period.

Lunar and Planetary Science Conference, 15th, Houston, TX, March 12-16, 1984, Proceedings. Part 2

NASA Technical Reports Server (NTRS)

Ryder, G. (Editor); Schubert, G. (Editor)

1985-01-01

Subjects of lunar petrology are discussed, taking into account Apollo 14 aluminous mare basalts and their possible relationship to KREEP, the petrology and geochemistry of clasts from consortium breccia, the depths of the mare basalt source region, the origin of olivine at Copernicus, a transient heating event in the history of a highlands troctolite from Apollo 12 soil, and the composition and evolution of the lunar crust in the Descartes highlands. Other topics explored are related to early earth and magmatic processes, differentiated meteorites, chondritic meteorites, other planets and remote sensing, and cratering. Attention is given to the gravity field of Venus at constant altitude and comparison with earth, a spectral analog of Martian soil, dark halo craters and the thickness of grooved terrain on Ganymede, the geomorphology of Rhea, a Monte Carlo model of lunar megaregolith development, the scaling of complex craters, crustal radiogenic heat production and the selective survival of ancient continental crust, and the formation of an impact-generated H2O atmosphere and its implications for the early thermal history of the earth.

Experimental impact cratering provides ground truth data for understanding planetary-scale collision processes

NASA Astrophysics Data System (ADS)

Poelchau, Michael H.; Deutsch, Alex; Kenkmann, Thomas

2013-04-01

Impact cratering is generally accepted as one of the primary processes that shape planetary surfaces in the solar system. While post-impact analysis of craters by remote sensing or field work gives many insights into this process, impact cratering experiments have several advantages for impact research: 1) excavation and ejection processes can be directly observed, 2) physical parameters of the experiment are defined and can be varied, and 3) cratered target material can be analyzed post-impact in an unaltered, uneroded state. The main goal of the MEMIN project is to comprehensively quantify impact processes by conducting a stringently controlled experimental impact cratering campaign on the meso-scale with a multidisciplinary analytical approach. As a unique feature we use two-stage light gas guns capable of producing impact craters in the decimeter size-range in solid rocks that, in turn, allow detailed spatial analysis of petrophysical, structural, and geochemical changes in target rocks and ejecta. In total, we have carried out 24 experiments at the facilities of the Fraunhofer EMI, Freiburg - Germany. Steel, aluminum, and iron meteorite projectiles ranging in diameter from 2.5 to 12 mm were accelerated to velocities ranging from 2.5 to 7.8 km/s. Targets were solid rocks, namely sandstone, quartzite and tuff that were either dry or saturated with water. In the experimental setup, high speed framing cameras monitored the impact process, ultrasound sensors were attached to the target to record the passage of the shock wave, and special particle catchers were positioned opposite of the target surface to capture the ejected target and projectile material. In addition to the cratering experiments, planar shock recovery experiments were performed on the target material, and numerical models of the cratering process were developed. The experiments resulted in craters with diameters up to 40 cm, which is unique in laboratory cratering research. Target porosity exponentially reduces crater volumes and cratering efficiency relative to non-porous rocks, and also yields less steep ejecta angles. Microstructural analysis of the subsurface shows a zone of pervasive grain crushing and pore space reduction. This is in good agreement with new mesoscale numerical models, which are able to quantify localized shock pressure behavior in the target's pore space. Planar shock recovery experiments confirm these local pressure excursions, based on microanalysis of shock metamorphic features in quartz. Saturation of porous target rocks with water counteracts many of the effects of porosity. Post-impact analysis of projectile remnants shows that during mixing of projectile and target melts, the Fe of the projectile is preferentially partitioned into target melt to a greater degree than Ni and Co. We plan to continue evaluating the experimental results in combination with numerical models. These models help to quantify and evaluate cratering processes, while experimental data serve as benchmarks to validate the improved numerical models, thus helping to "bridge the gap" between experiments and nature. The results confirm and expand current crater scaling laws, and make an application to craters on planetary surfaces possible.

Icy Islands reveal similar volatile behavior on Pluto and Mars

NASA Astrophysics Data System (ADS)

Sori, M.; Bapst, J.; Byrne, S.

2017-12-01

Ice deposits on planetary surfaces may hold paleoclimate records and elucidate important geologic processes involving volatiles, atmospheres, topography, and climate. Sputnik Planitia on Pluto and the well-studied north and south polar layered deposits (NPLD and SPLD) of Mars are examples. Ice peripheral to these main deposits may be even more sensitive to climatic changes. At northern martian latitudes, 18 outlying H2O ice mounds have previously been mapped within impact craters (Fig. 1a) near the NPLD. Here, we use remote sensing observations from New Horizons and Mars orbital spacecraft to study similar features in craters near Sputnik Planitia and the SPLD. We identify tens of outlying topographic mounds in craters near the SPLD (Fig. 1b) and five bright albedo features in craters near Sputnik Planitia (Fig. 1c). We assess the possibility that these deposits are analogous to the H2O ice mounds at northern martian polar latitudes. The southern martian deposits are physically diverse, but always include convex topography and host craters >15 km in diameter. We interpret at least some of them to be composed of H2O ice like their northern counterparts. The five features on Pluto are located in similarly sized craters and have corresponding spectral detections of N2 ice. One (Fig. 1c) has topography very similar to martian ice mounds, including a convex shape up to 160 m thick. We conclude it is an N2 ice mound, equivalent to Mars' H2O ice mounds in that crater topography provides a favorable microclimate for volatiles. The mound may preserve a paleoclimate record that would be erased in Sputnik Planitia by convection. Using a finite element model, we estimate flow velocities of this N2 ice mound to be 1 cm/yr, implying it may be younger than the other four which could have topography subdued by viscous relaxation. We compare the properties and possible formation mechanisms of these features to test the hypothesis that Pluto's ice cycle is similar to Mars' in certain periods of its orbital history. Figure 1. THEMIS images of ice mounds in the martian craters (a) Louth and (b) Deseado near the NPLD and SPLD, with extracted MOLA topographic profiles. (c) New Horizons base map of the five outlying volatile deposits in craters on Pluto, with extracted topographic profile from crater 3 and corresponding ice flow simulation.

The Lacustrine Upper Brushy Basin Member of the Morrison Formation, Four Corners Region, Usa: a Lithological and Mineralogical Terrestrial Analog for Gale Crater, Mars

NASA Astrophysics Data System (ADS)

Potter-McIntyre, S. L.; Chan, M. A.; McPherson, B. J.

2013-12-01

The upper part of the Jurassic Brushy Basin Member of the Morrison Formation is an iron- and clay-rich volcaniclastic shale deposited in an ephemeral alkaline saline lake system. Sedimentary rocks exposed in Gale Crater consist of similar non-acidic clays, possibly of lacustrine origin. Three primary clastic lithofacies are present in both the Brushy Basin Member and at Gale Crater: silt-/claystone, sandstone, and conglomerate. Both the terrestrial and martian silt-/claystone lithofacies are interpreted as lacustrine depositional environments due to features such as parallel laminated and massive sedimentary structures. Vugs are present in the siltstone/claystone facies on both the Colorado Plateau and at Gale Crater. Fluvial features are also observed in both examples such as cross-bedded sandstones and imbricated conglomerates. Concretions are present in both the Colorado Plateau and Gale Crater units. The vugs in the Brushy Basin Member preserve algal forms with cellular elaboration and are interpreted as charophyte molds. Two distinct suites of elements (1. C, Fe, As, P and, 2. C, S, Se, P) are associated with the microbial fossils and may be potential markers for biosignatures. Vugs at Gale Crater are a potential target to investigate the possibility of preserved microbial (algal) life where early analyses show the presence of the elements capable of supporting life. The Brushy Basin Member is composed predominately of quartz, feldspars, zeolites and altered volcanic ash. The abundant clay minerals in both the terrestrial and martian examples are hypothesized to have formed due to partial alteration of volcanic minerals in alkaline fluid. Similarly, concretions present in the terrestrial unit exhibit a diverse range of mineralogies likely due to alkaline fluid chemistries interacting with reactive volcaniclastic sediments. Terrestrial concretion mineralogy is diverse even within an outcrop or stratigraphic horizon which suggests reactants to precipitate concretions are being sourced from diagenetic micorenvironments. Similar diagenetic microenvironments may be preserved at Gale Crater due to the fine-grained, volcaniclastic (reactive) rocks. The Brushy Basin Member is a valuable analog because comparative iron-and clay-rich compositions help to: 1) understand diagenetic processes in a non-acidic, saline lacustrine environment, 2) document specific sedimentary structures and lithofacies associations to interpret depositional environment, 3) document specific biomediated features (e.g., textures, morphologies, chemistries), and 4) demonstrate how these features might persist or respond to diagenesis over time.

The Transition from Complex Crater to Peak-Ring Basin on the Moon: New Observations from the Lunar Orbiter Laser Altimeter (LOLA) Instrument

NASA Technical Reports Server (NTRS)

Baker, David M. H.; Head, James W.; Fassett, Caleb I.; Kadish, Seth J.; Smith, Dave E.; Zuber, Maria T.; Neumann, Gregory A.

2012-01-01

Impact craters on planetary bodies transition with increasing size from simple, to complex, to peak-ring basins and finally to multi-ring basins. Important to understanding the relationship between complex craters with central peaks and multi-ring basins is the analysis of protobasins (exhibiting a rim crest and interior ring plus a central peak) and peak-ring basins (exhibiting a rim crest and an interior ring). New data have permitted improved portrayal and classification of these transitional features on the Moon. We used new 128 pixel/degree gridded topographic data from the Lunar Orbiter Laser Altimeter (LOLA) instrument onboard the Lunar Reconnaissance Orbiter, combined with image mosaics, to conduct a survey of craters >50 km in diameter on the Moon and to update the existing catalogs of lunar peak-ring basins and protobasins. Our updated catalog includes 17 peak-ring basins (rim-crest diameters range from 207 km to 582 km, geometric mean = 343 km) and 3 protobasins (137-170 km, geometric mean = 157 km). Several basins inferred to be multi-ring basins in prior studies (Apollo, Moscoviense, Grimaldi, Freundlich-Sharonov, Coulomb-Sarton, and Korolev) are now classified as peak-ring basins due to their similarities with lunar peak-ring basin morphologies and absence of definitive topographic ring structures greater than two in number. We also include in our catalog 23 craters exhibiting small ring-like clusters of peaks (50-205 km, geometric mean = 81 km); one (Humboldt) exhibits a rim-crest diameter and an interior morphology that may be uniquely transitional to the process of forming peak rings. Comparisons of the predictions of models for the formation of peak-ring basins with the characteristics of the new basin catalog for the Moon suggest that formation and modification of an interior melt cavity and nonlinear scaling of impact melt volume with crater diameter provide important controls on the development of peak rings. In particular, a power-law model of growth of an interior melt cavity with increasing crater diameter is consistent with power-law fits to the peak-ring basin data for the Moon and Mercury. We suggest that the relationship between the depth of melting and depth of the transient cavity offers a plausible control on the onset diameter and subsequent development of peak-ring basins and also multi-ring basins, which is consistent with both planetary gravitational acceleration and mean impact velocity being important in determining the onset of basin morphological forms on the terrestrial planets.

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

NASA Astrophysics Data System (ADS)

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.