The Modification of Circumpolar Craters in the Martian Cryosphere

Understanding the evolution of the Martian cryosphere is of fundamental climatological significance due to the potential ramifications of its volatility. MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) and SHARAD (Shallow Radar) observations indicate that the two largest near-surface cryospheric reservoirs – the North and South Polar Layered Deposits (NPLD and SPLD) – exhibit large-scale similarities, as both are comprised of nearly pure (> 90%) water ice deposits over their 2-4 km thicknesses. However, there are important compositional differences, as the NPLD exhibits a surface comprised mostly of water ice and it partially overlies a lithic-rich basal unit whereas the SPLD exhibits a surface that is primarily dust-rich and there is no evidence of
a basal unit. Additionally, cratering statistics indicate that the surface of the NPLD is orders of magnitude younger than that of the SPLD, thereby implying dramatically higher resurfacing rates in the NPLD.

Recently created 3D SHARAD data volumes of the NPLD and SPLD have identified previously unknown buried craters with no surface expression. We propose to systematically study the modification of surface and buried craters in the NPLD, SPLD, and adjacent cryospheric terrains using these radar volumes together with other datasets. Our planned investigation will involve three primary tasks (a) 3D radar volume mapping and (b) radar dielectric property estimation of the subsurface stratigraphy associated with surface and buried craters, and (c) landform evolution modeling of crater modification via erosion, deposition, and viscous flow.

The main research objectives of this proposal are to: (1) assess how NPLD and SPLD resurfacing processes have varied both spatially and temporally by looking at the stratigraphy of radar-detected layers above buried craters and below surface craters – do craters act as localized depocenters that drive further accumulation?; (2) ascertain whether preservation of various crater types (e.g., buried craters and pedestal craters) is due to armoring that may be correlated with radar-derived crater composition; and (3) determine whether different populations of northern and southern circumpolar craters exhibit similar crater modification histories, which would strongly imply a common origin: Did the north and south circumpolar deposit complexes both form more than several hundred million or perhaps even over a billion years ago?

We will employ a variety of publicly released SHARAD, MARSIS, MOLA (Mars Orbiter Laser Altimeter), HRSC (High Resolution Stereo Camera), CTX (Context Camera), and HiRISE (High Resolution Imaging Science Experiment) data to constrain circumpolar crater modification. In accordance with the stated goals of the Mars Data Analysis Program (MDAP) to enhance the scientific return from missions to Mars conducted by NASA and other space agencies, our proposed data synthesis and analysis of Martian radar, altimetry, and imagery datasets will more precisely characterize the extent and composition of both surface ice and buried ice deposits, thereby providing key insights into the long-term evolution of the Martian circumpolar deposits.