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At least 37 records · Page 2
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NASA NTRS1977

The effects of target characteristics on fresh crater morphology - Preliminary results for the moon and Mercury

The results are reported of an analysis of the characteristics of fresh crater samples occurring on the two major geologic units on the moon (maria and highlands) and on Mercury (smooth plains and cratered terrain). In particular, the onset diameters and abundances of central peaks and terraces are examined and compared for both geologic units on each planet in order to detect any variations that might be due to geologic unit characteristics. The analysis of lunar crater characteristics is based on information provided in the LPL Catalog of Lunar Craters of Wood and Andersson (1977). The Mercurian data set utilized is related to a program involving the cataloguing of Mercurian craters visible in Mariner 10 photography. It is concluded that the characteristics of the substrate have exerted a measurable influence on the occurrence of central peaks, terraces, and scallops in flash crater samples. Therefore, in order to compare the morphologic characteristics of fresh crater populations between planets, an analysis of possible substrate-related differences must first be undertaken for each planet under consideration. It is suggested that large variations in gravity do not produce major variations in crater wall failure.

Cintala, M. J.↗
NASA NTRS1979

Alphonsus-type dark-halo craters - Morphology, morphometry and eruption conditions

The Alphonsus dark-halo craters are sites of volcanic eruptions with a characteristic crater radius of approximately 1 km. They are characterized by dark haloes ranging from 3 to 4 km, by substantial amounts of nonjuvenile material within the deposits, and by a lack of any associated lava flows or prominent constructional features, such as cones or domes. In the present paper, possible eruption styles are analyzed, using these observational constraints. It is concluded that an eruption process analogous to terrestrial volcanian explosive activity provides the most reasonable explanation for the characteristics of the deposits. The dark-halo craters appear to have formed contemporaneously with the emplacement of lavas in the adjacent Mare Nubium.

Head, J. W., III↗
NASA NTRS1985

Interaction of Martian Flow Ejecta Blankets with Pre-existing Impact Craters: Morphological Observations

The evidence of interaction between impact flow ejecta blankets and pre-existing landforms such as craters, scarps, and wrinkle ridges may yield important clues as to the nature of the ejecta emplacement process. The morphology of flow ejecta blankets and the interactions of these blankets with pre-emplacement impact craters were characterized. About 80 small satellite craters on or in 3 well-expressed low ejecta parent impact craters were recognized. Interaction of the blanket with pre-existing structures was studied, and several types were described. These are: (1) infilling; (2) encroachment; (3) overflow; and (4) breaching. Examination of the overall morphology of three ejecta blankets reveals a range of thickness, from depths sufficient to completely bury craters in the 5 km diameter range in distal areas of the blankets, to very thin blankets which allow subtle pre-existing topography to be visible within a half the diameter of the parent crater. Radial and azimuthal symmetries appear to exist within the blankets over a range of morphologies. It also appears that there is a weak linear correlation between the diameter of craters with nearly 100% infilling and distance from the center of the parent crater.

Pieri, D. C.↗
NASA NTRS1987

Martian rampart craters: Morphologic clues for the physical state of the target at time of impact

Current research attempts to describe morphologic features seen in very high resolution Viking Orbiter images of crater ejecta blankets and interiors, in order to constrain the most likely target properties at the time of crater formation. The Viking Orbiter image data set contains approximately 400 frames at a spatial resolution of better than 10 meters per pixel, and 2,200 frames at a resolution of better than 20 meters per pixel, for which the atmosphere was either clear or only slightly obscured. A search is being conducted of all these images and so far has revealed several examples of both interior and exterior features of impact craters that bear on the nature of the ejecta fluidizing medium. Preliminary observations and speculations on the physical state of the Martian regolith at the time of crater formation are given and briefly discussed.

Mouginis-Mark, Peter J.↗
NASA NTRS1983

Acoustic fluidization and the scale dependence of impact crater morphology

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

Melosh, H. J.↗
NASA NTRS2002

Investigations of Martian Impact Crater Morphologies and Morphometries

We have made substantial progress towards completion of the original objectives and are continuing to include new data from the Mars Global Surveyor MOC and TES instruments as they become available (the MOLA instrument has ceased operation as of 2002). The project funding has been used to provide salary support to the PI and several undergraduate students, cover publication charges for two papers, reimburse travel expenses to conferences and workshops incurred by the PI and students, and cover a number of other expenses such as software upgrades and production costs of slides and color prints. This study is revising the PI's Catalog of Large Martian Impact Craters with information obtained from MGS and is utilizing data in the revised Catalog to investigate which planetary factors (such as location, elevation, terrain type, etc.) primarily affect the formation of specific ejecta morphologies and morphometries.

Barlow, Nadine G.↗
NASA NTRS2015

Crater Morphology in the Phoenix Landing Ellipse: Insights Into Net Erosion and Ice Table Depth

Icebreaker [1] is a Discovery class mission being developed for future flight opportunities. Under this mission concept, the Icebreaker payload is carried on a stationary lander, and lands in the same landing ellipse as Phoenix. Samples are acquired from the subsurface using a drilling system that penetrates into materials which may include loose or cemented soil, icy soil, pure ice, rocks, or mixtures of these. To avoid the complexity of mating additional strings, the drill is single-string, limiting it to a total length of 1 m.

Icebreaker mission↗
NASA NTRS1977

Lunar Science Conference, 8th, Houston, Tex., March 14-18, 1977, Proceedings. Volume 1 - The moon and the inner solar system. Volume 2 - Petrogenetic studies of mare and highland rocks. Volume 3 - Planetary and lunar surfaces

Solar system processes are considered along with the origin and evolution of the moon, planetary geophysics, lunar basins and crustal layering, lunar magnetism, the lunar surface as a planetary probe, remote observations of lunar and planetary surfaces, earth-based measurements, integrated studies, physical properties of lunar materials, and asteroids, meteorites, and the early solar system. Attention is also given to studies of mare basalts, the kinetics of basalt crystallization, topical studies of mare basalts, highland rocks, experimental studies of highland rocks, geochemical studies of highland rocks, studies of materials of KREEP composition, a consortium study of lunar breccia 73215, topical studies on highland rocks, Venus, and regional studies of the moon. Studies of surface processes, are reported, taking into account cratering mechanics and fresh crater morphology, crater statistics and surface dating, effects of exposure and gardening, and the chemistry of surfaces.

Merril, R. B.↗
NASA NTRS1982

Experimental simulation of impact cratering on icy satellites

Cratering processes on icy satellites were simulated in a series of 102 laboratory impact experiments involving a wide range of target materials. For impacts into homogeneous clay slurries with impact energies ranging from five million to ten billion ergs, target yield strengths ranged from 100 to 38 Pa, and apparent viscosities ranged from 8 to 200 Pa s. Bowl-shaped craters, flat-floored craters, central peak craters with high or little relief, and craters with no relief were observed. Crater diameters increased steadily as energies were raised. A similar sequence was seen for experiment in which impact energy was held constant but target viscosity and strength progressively decreases. The experiments suggest that the physical properties of the target media relative to the gravitationally induced stresses determined the final crater morphology. Crater palimpsests could form by prompt collapse of large central peak craters formed in low target strength materials. Ages estimated from crater size-frequency distributions that include these large craters may give values that are too high.

Greeley, R.↗
NASA NTRS1982

Impact cratering experiments in Bingham materials and the morphology of craters on Mars and Ganymede

Results from a series of laboratory impacts into clay slurry targets are compared with photographs of impact craters on Mars and Ganymede. The interior and ejecta lobe morphology of rampart-type craters, as well as the progression of crater forms seen with increasing diameter on both Mars and Ganymede, are equalitatively explained by a model for impact into Bingham materials. For increasing impact energies and constant target rheology, laboratory craters exhibit a morphologic progression from bowl-shaped forms that are typical of dry planetary surfaces to craters with ejecta flow lobes and decreasing interior relief, characteristic of more volatile-rich planets. A similar sequence is seen for uniform impact energy in slurries of decreasing yield strength. The planetary progressions are explained by assuming that volatile-rich or icy planetary surfaces behave locally in the same way as Bingham materials and produce ejecta slurries with yield strenghs and viscosities comparable to terrestrial debris flows. Hypothetical impact into Mars and Ganymede are compared, and it is concluded that less ejecta would be produced on Ganymede owing to its lower gravitational acceleration, surface temperature, and density of surface materials.

Fink, J. H.↗
NASA NTRS1991

Martian impact crater ejecta morphologies and their potential as indicators of subsurface volatile distribution

Many martian impact craters ejecta morphologies suggestive of fluidization during ejecta emplacement. Impact into subsurface volatile reserviors (i.e., water, ice, CO2, etc.) is the mechanism favored by many scientists, although acceptance of this mechanism is not unanimous. In recent years, a number of studies were undertaken to better understand possible relationships between ejecta morphology and latitude, longitude, crater diameter, and terrain. These results suggest that subsurface volatiles do influence the formation of specific ejecta morphologies and may provide clues to the vertical and horizontal distribution of volatiles in more localized regions of Mars. The location of these volatile reservoirs will be important to humans exploring and settling Mars in the future. Qualitative descriptions of ejecta morphology and quantitative analyses of ejecta sinuosity and ejecta lobe areal extent from the basis of the studies. Ejecta morphology studies indicate that morphology is correlated with crater diameter and latitude, and, using depth-diameter relationships, these correlations strongly suggest that changes in morphology are related to transition among subsurface layers with varying amounts of volatiles. Ejecta sinuosity studies reveal correlations between degree of sinuosity (lobateness) and crater morphology, diameter, latitude, and terrain. Lobateness, together with variations in areal extent of the lobate ejecta blanket with morphology and latitude, probably depends most directly on the ejecta emplacement process. The physical parameters measured here can be compared with those predicted by existing ejecta emplacement models. Some of these parameters are best reproduced by models requiring incorporation of volatiles within the ejecta. However, inconsistencies between other parameters and the models indicate that more detailed modeling is necessary before the location of volatile reservoirs can be confidently predicted based on ejecta morphology studies alone.

Barlow, Nadine G.↗
NASA NTRS1987

Effects of elevation and ridged plains thicknesses on Martian crater ejecta morphology

Relationships between the distribution of Martian crater ejecta morphologies and both the elevation and ridged plains thicknesses were investigated using individual Viking Orbiter images of 383 craters with uneroded ejecta termini located between +/- 25 deg latitude. Only a slight correlation was found between elevation and the distribution of ejecta types for the ridged plains. A stronger correlation was identified between the thicknesses of Lunae and Hesperia Plana and the complexity of ejecta morphologies. For a given crater size range, the complexity of the ejecta increases with decreasing thicknesses of the ridged plains. Possible explanations for the observed phenomena are discussed.

Horner, V. M.↗
NASA NTRS1998

Mid-Latitude versus Polar-Latitude Transitional Impact Craters: Geometric Properties from Mars Orbiter Laser Altimeter (MOLA) Observations and Viking Images

One intriguing aspect of martian impact crater morphology is the change of crater cavity and ejecta characteristics from the mid-latitudes to the polar regions. This is thought to reflect differences in target properties such as an increasing presence of ice in the polar regions. Previous image-based efforts concerning martian crater morphology has documented some aspects of this, but has been hampered by the lack of adequate topography data. Recent Mars Orbiter Laser Altimeter (MOLA) topographic profiles provide a quantitative perspective for interpreting the detailed morphologies of martian crater cavities and ejecta morphology. This study is a preliminary effort to quantify the latitude-dependent differences in morphology with the goal of identifying target-dependent and crater modification effects from the combined of images and MOLA topography. We combine the available MOLA profiles and the corresponding Viking Mars Digital Image Mosaics (MDIMS), and high resolution Viking Orbiter images to focus on two transitional craters; one on the mid-latitudes, and one in the North Polar region. One MOLA pass (MGS Orbit 34) traverses the center of a 15.9 km diameter fresh complex crater located at 12.8degN 83.8degE on the Hesperian ridge plains unit (Hvr). Viking images, as well as MOLA data, show that this crater has well developed wall terraces and a central peak with 429 m of relative relief. Three MOLA passes have been acquired for a second impact crater, which is located at 69.5degN 41degE on the Vastitas Borealis Formation. This fresh rampart crater lacks terraces and central peak structures and it has a depth af 579 m. Correlation between images and MOLA topographic profiles allows us to construct basic facies maps of the craters. Eight main units were identified, four of which are common on both craters.

Matias, A.↗
NASA NTRS1991

Ancient fluvial processes in the equatorial highlands of Mars

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.

Craddock, Robert A.↗
NASA NTRS1987

Crater ejecta morphology and the presence of water on Mars

The possible effects of projectile, target, and environment on the cratering process is reviewed. It is suggested that contradictions in interpreting Martian crater ejecta morphologies reflect over simplifying the process as a singular consequence of buried water. It seem entirely possible that most ejecta facies could be produced without the presence of liquid water. However, the combination of extraordinary ejecta fluidity, absence of secondaries, and high ejection angles all would point to the combined effects of atmosphere and fluid rich substrates. Moreover, recent experiments revealing the broad scour zone associated with rapid vapor expansion may account for numerous craters in the circumpolar regions with subtle radial grooving extending 10 crater radii away with faint distal ramparts. Thus certain crater ejecta morphologies may yet provide fundamental clues for the presence of unbound water.

Schultz, P. H.↗
NASA NTRS2018

P43K-3884 Characterizing Martian Crater Circulations with the NASA Ames Mars GCM

Observations made in Gale Crater by instruments on the MSL Curiosity Rover show that the diurnal amplitude of the surface pressure is increased and the depth of the Convective Boundary Layer (CBL) is decreased relative to other lander locations on flatter regions of Mars (Haberle et al., 2014; Moores et al., 2015). Mesoscale modeling studies of Gale Crater suggest that crater circulations produce these effects. Tyler & Barnes (2013) show that local upslope/downslope flows along the crater rim and Mt. Sharp amplify the diurnal pressure cycle. These same flows are thought to be at least partly responsible for the suppression of the CBL because upward air flow at the rim and in the center (due to Mt. Sharp) forces subsidence over the lowest regions of the crater during the day. Regional flows, largely due to the location of Gale near the dichotomy boundary, may also play a role in shaping the circulation internal to the crater. Whether the behavior of the CBL and the amplified diurnal pressure cycle are phenomena observed in craters morphologically different from Gale (i.e. bowl-shaped, irregular, degraded) is not yet understood. We will explore these questions by characterizing the behavior of these processes as they are shaped by the morphology of craters greater than 100 km in diameter. We use the NASA Ames Mars Global Circulation Model (GCM) that now utilizes the NOAA/GFDL cubed-sphere finite-volume dynamical core to examine ~100 craters of varying size and shape from a database of known Martian craters (Robbins & Hynek, 2014). Run at 7.5 km resolution, the GCM is capable of resolving surface winds, temperature, and pressure inside craters of this size allowing for the analysis of dozens of craters simulated at various seasons and within the context of synoptic and global-scale phenomena.

Batterson, Courtney MaryLou↗