Craters and Resurfacing of the Martian North Polar Cap

Details Craters and Resurfacing of the Martian North Polar Cap Craters and Resurfacing of the Martian North Polar Cap

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p41b1360g&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P41B-1360

Mathematics

Logic

5422 Ices, 5462 Polar Regions, 6022 Impact Phenomena (5420, 8136), 6225 Mars, 8136 Impact Phenomena (5420, 6022)

Scientific paper

The north polar residual cap (NRC), which covers the north polar layered deposits (NPLD), is about 1m thick and composed of large-grained, dust-poor water ice. The lack of dust accumulation indicates that this material accumulated recently; however, paradoxically, the exposure of large-grained (old) ice indicates a current state of net ablation. The NRC is often considered to be new NPLD material, thus understanding its mass-balance and relationship to the current climate could provide a key to reading the climatic record of the NPLD. Previous studies of the NRC cratering record (Herkenhoff and Plaut, Icarus, 2000; Tanaka, Nature, 2005) concluded a resurfacing age of only 10-100 Kyr; however, these conclusions were based on 0-2 craters. In order to constrain the processes and rates of NRC resurfacing we undertook a search for craters within the CTX (MRO's context camera) dataset. CTX data released to date provide almost complete coverage of the NRC with pixel scales of ~6m. This search increased the number of known craters on the NRC and NPLD from 4 to ~100 with crater diameters ranging from ~20 to ~400m. We then followed up on specific craters with observations by HiRISE (MRO's High Resolution Imaging Science Experiment) with pixel scales of ~30cm, acquiring ~50 of these targets. HiRISE observations reveal that craters are the sites of preferential ice accumulation (which gradually infills the crater cavity), while ablation and wind action combine to remove the crater rim. A morphologic sequence of degradation states (including depths from shadows) allows for a qualitative understanding of the processes involved in converting fresh craters (measured depth/diameter ~0.23) to craters currently almost unidentifiable. Variation in the argument of perihelion affects polar climate over the lifetime of these craters. We are combining recent orbital solutions (Laskar et al., Icarus, 2004) with the processes described above to create landscape evolution models that quantifiably investigate the recent (10-100 Kyr) mass-balance history of the NRC and which are constrained by the size-frequency and degradation of the observed crater population.

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