The Mars Orbiter Laser Altimeter (MOLA) acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of Mars during the Fall of 1997. It sampled 98 minimally degraded impact craters between the latitudes of 80°N and 12°S The best fitting depth (d) versus diameter (D) power‐law relationship for these craters is: d = 0.14 D 0.90 for simple varieties, and d = 0.25 D 0.49 for complex structures. The simple‐to‐complex transition diameter is 8 km (+/−0.5 km). The cross‐sectional “shape” of the crater cavities was determined by fitting a power‐function to each profile. Variation in the exponent (n) suggest the craters flatten with increasing diameter and impact energy. The ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for Mars in most cases.
Introduction: The Lunar Reconnaissance Orbiter spacecraft (LRO) Lunar Exploration Neutron Detector (LEND) permits analysis of the neutron flux [1] for landforms with reasonably well-established surface ages, such as impact craters. In addition, thanks to LRO observations of crater geometric properties that are formation-age dependent, additional factors can be analyzed. Using LEND neutron counting statistics acquired between September 2009 and December 2010 from the primary LRO mapping orbit, we have analyzed the neutron flux signature of a population of fresh Copernican age craters in comparison with a set of “control” craters with greater formation ages (Eratosthenian). Best-available crater age data from published literature [2] has been utilized together with a set of crater geometric properties measured from released LOLA gridded data [3]. The primary objective is to test the hypothesis that neutron flux (and hence bulk Hydrogen content) signatures are related to crater formation ages, at least for impact events in some specific geological settings. Thanks to the high spatial resolving power of current LEND measurements (10-20 km), craters and their surrounding ejecta blankets can be assessed at scales not possible with Lunar Prospector LPNS data. A set of 24 impact crater targets was selected (Table 1) on the basis of crater age, morphology, and LEND sampling statistics. We fully recognize that continuously improving LEND counting statistics as well as calibrations will lead to a continual refinement of these preliminary results. Nonetheless, we believe that the basic trends established herein are noteworthy. LRO LEND Observations: Table 1 illustrates the reference set of 24 impact features selected for analysis. It includes mostly fresh Copernican craters (FCC) with a few Eratosthenian craters as controls. Table 1 highlights the key parameters for each crater from LEND and those derived from geometric analysis of LOLA gridded data using methods developed by Garvin for Mars and Earth [4]. On the basis of the results in [1], LEND neutron flux values < 4.96 counts per second (cps) are associated with appreciable concentrations of hydrogen in the regolith, with values as high as 4 wt. % if a dry layer mantles the underlying H-bearing regolith. On the basis of preliminary analysis, there is no first-order statistical correlation of LEND neutron flux (or related H concentration) and first-order crater age. Young features such as Giordano Bruno and Aristarchus, for example, display neutron flux values that range from 4.98 cps to 5.10 cps, while much older (Eratosthenian) craters have values in a similar range. Thus, exposure of fresh regolith, whether in the mare or the highlands, does not appear to reflect local H concentration, at least in the regions sampled by the 24 craters evaluated in this study (Fig. 1). Some of the most recent but smaller complex craters evaluated, however, do show the greatest level of neutron suppression, suggesting the possibility of enhanced regolith hydrogen (e.g., Kepler, Godin).
The record of large-scale cratering on Earth is scant, and the only currently 'proven' 100-km-class impact structure known to have formed within the Cenozoic is Popigai, located in the Siberian Arctic at 71.5 deg N, 111 deg E. Popigai is clearly a multiringed impact basin formed within the crystalline shield rocks (Anabar) and platform sediments of the Siberian taiga, and estimates of the volume of preserved impact melt typically exceed 1700 cu km, which is within a factor of 2-3 of what would be predicted using scaling relationships. We present the preliminary results of an analysis of the present-day topography of the Popigai structure, together with refined absolute age estimates, in order to reconstruct the pre-erosional morphology of the basin, as well as to quantify the erosion or sediment infill rates in the Popigai region.
Initial, science-directed human exploration of Mars will benefit from capabilities in which human explorers remain in orbit to control telerobotic systems on the surface (Figure 1). Low-latency, high-bandwidth telerobotics (LLT) from Mars orbit offers opportunities for what the terrestrial robotics community considers to be high-quality telepresence. Such telepresence would provide high quality sensory perception and situation awareness, and even capabilities for dexterous manipulation as required for adaptive, informed selection of scientific samples [1]. Astronauts on orbit in close communication proximity to a surface exploration site (in order to minimize communication latency) represent a capability that would extend human cognition to Mars (and potentially for other bodies such as asteroids, Venus, the Moon, etc.) without the challenges, expense, and risk of putting those humans on hazardous surfaces or within deep gravity wells. Such a strategy may be consistent with goals for a human space flight program that, are currently being developed within NASA.
Abstract— Small terrestrial hypervelocity impact craters have a bowl‐shaped form and are partially filled by an interior breccia lens, roughly parabolic in cross‐section, of allochthonous material. This interior breccia volume is geometrically modelled as the volume of material slumped off the interior wall of the transient cavity during late stage crater modification. This model is tested by comparing the estimated volume of the breccia lens based on observational data with the calculated volume of slump material based on known dimensional parameters. The model fits well for Meteor Crater and Brent and is highly sensitive to changes in input parameters ( e.g. , a 10% increase in the input diameter for Meteor Crater produces an almost 200% increase in the model breccia lens volume). Further testing of the model with less constrained data from West Hawk Lake and Lonar leads to reasonable fits, given the sensitivity of the model to input parameters. Fits to other craters: Aouelloul, Tenoumer and Wolf Creek, where previous depth data are constrained only by gravity data, are unsatisfactory. However, revised depths can be obtained that fit both the gravity data and the model. While these tests do not provide unqualified support for the model, they do suggest that it may represent a good first order approximation. More and better quality dimensional data are required for more rigorous testing.
