MARTIAN IMPACT STRUCTURES EXPOSED IN CROSS-SECTION: WINDOWS INTO THE SUBSURFACE

Using stereo pairs of images from the High Resolution Imaging Science Experiment (HiRISE) camera on MRO, we have conducted a systematic survey of impact craters along the edges of the Valles Marinaris canyon system that have been cut by a combination of tectonism and erosion and are now exposed in cross-section. These ‘cut craters’ permit unique access into the subsurface structure of impact craters, and provide better exposure than is typically available for terrestrial impact structures. Here we directly assess elements of both exterior and interior crater geometry. Quantifiable exterior elements include the radial decay of eject thickness and degree of rim uplift. Exposed interior elements include the depth of layer disruption and nature of crater infill, which is expected to vary in response to the style of sedimentation responsible for the infill (e.g., mass wasting, eolian, or fluvial processes). Results from ejecta measurements are broadly consistent with predictions of a (r / R)^(-3) dependence. Crater interior fill indicates numerous flat-lying layers in some older, larger exposed structures, suggestive of a past epoch of enchanced crater gradation in which fluvial processes may have played a role.