EROSION RATES ON MARS INFERRED FROM CRATER STATISTICS

Erosion rates on Mars inferred from crater statistics. B. J. Thomson, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996.

Surface erosion rates on Mars are known to vary in both time and space. Although there have been numerous estimates of present and past erosion rates at landing sites and other specific locations, there has not been a systematic effort to quantify the geographic variation in modern erosion rates planet-wide. Here, we use a gridded array of crater counts (i.e., assessments of the size-frequency distribution of impact structures) to investigate the erosion and removal of craters less than 1 km in diameter. The results clarify and refine expected latitudinal trends in erosion as well as reveal terrain-specific effects.

The results indicate extreme removal of small craters at latitudes above about 40°N and S. The transition diameter (D_t) between resurfaced and normal crater populations is about 500 m in diameter at high latitudes. The erasure of small, high-latitudes craters is consistent with previously observed shallowing of high-latitude craters as measured using depth to diameter ratios, latitudinal trends in sub-km roughness measured by laser altimetry, and observations of dust-mantled-terrain in specific latitude bands. These results suggest that the radiation exposure history of potential sample-return sites is dramatically different depending on the site latitude, a factor that must be accounted for in the search for evidence of past habitability and preservation of organics.