Geometric properties of Martian impact craters: Preliminary results from the Mars Orbiter Laser Altimeter

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 crat ers between the latitudes of 80 degrees N and 12 degrees 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 stru ctures. 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 thic kness is skewed suggesting that use of existing empirical expressions for t he expected radial decay of ejecta thickness is inappropriate for Mars in m ost cases.