CRATER POPULATION AND RESURFACING OF THE MARTIAN NORTH POLAR LAYERED DEPOSITS

The north polar layered deposits (NLPD) at the north pole of Mars are believed to preserve a record of seasonal and climatic cycling of water and dust. The north polar residual cap (NRC) is the uppermost and youngest layer of NPLD material. Understanding its mass-balance in relation to the current climate could provide valuable insight into the climatic record of the NPLD. To quantitatively investigate the recent (10-20 Kyr) mass-balance history of the NPLD, recent orbital solutions can be combined with processes of crater degradation and removal to create landscape evolution models that are constrained by the size-frequency distribution and degradation of the observed crater population. As a first step in this process, a search for craters was conducted within images from the Context Camera (CTX); 184 craters were identified on the NPLD, 103 of which are located within a region estimated to represent recent accumulation. High Resolution Imaging Science Experiment (HiRISE) images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of the processes involved in crater removal; such processes include ice accumulation, sublimation, mass wasting, and eolian deposition and erosion. A classification system for these craters was developed based on the degree of apparent degradation and where possible, depth/diameter (d/D) ratios were determined. Analysis of the spatial distribution of crater degradation and d/D ratios indicates that degradation and infilling may be occurring at uniform rates with perhaps slightly faster rates near the center and edges of our region of interest. From comparison of the size-frequency distribution of these craters with the expected production function for their size range, they are interpreted to be an equilibrium population with an estimated crater lifetime of 30.75*D^(1.14) years. Accumulation rates are derived to be ~8.5*D^(-0.14) mm/year, which corresponds to estimated average values of ~4-5 mm/year. The current NRC crater population is estimated to have accumulated in the last ~2x10^4 years or less.