Surface morphology inside the PSR area of lunar polar crater Shoemaker in comparison with that of the sunlit areas

Abstract

Our study is based on a photogeological analysis of the hill-shade images produced from the LOLA digital terrain models and on a stereometric analysis of LROC NAC images. Our results demonstrate that surface morphology of the permanently shadowed floor of crater Shoemaker is nearly identical to that of the regularly illuminated mare surface at the Lunokhod-2 working area and the surface of the highland plain of the Apollo-16 landing site, being dominated by populations of craters smaller than 1 km in diameters. Craters on the Shoemaker floor have approximately the same depth-to-diameter ratios as those within the Lunokhod-2 and Apollo-16 areas. The observed surface morphology of the Shoemaker floor is the result of meteorite bombardment like in other areas of the Moon. Within the permanently shadowed surface areas we detected no morphological peculiarities that could result from the absence of the diurnal temperature variations that excludes the temperature-related creep component of the downslope material movement. This probably means that in the areas with regular solar illumination, the role of the downslope movement of debris by thermally induced creep mechanisms is secondary compared to shaking by close and distant meteorite impacts and locally by moonquakes.