Crater wall outcrop analysis for targeting subsurface sampling on Mars

Abstract

Bedrock outcrops were analyzed inside craters on Mars at Meridiani Planum with correlating HiRISE based remote and the Opportunity rover based in-situ images. The aim was to get information on how outcrops could be identified from above in order to help targeting and interpretation of shallow subsurface sampling attempts on Mars by rovers like the planned ExoMars.During the analysis, outcrop indicators, such as albedo differences, rectangular blocks, protruding layers and steep walls were identified inside impact craters. Using shadow length measurements and analyzing density distribution of blocks, nearly vertical walls could also be identified even in images acquired under vertical viewing condition. There is a size dependent tendency in the occurrence of outcrops inside caters. Impact craters with diameters of 5–10m may indicate a subsurface lithology that differs from that visible on the surface, while craters with diameter above 50m may indicate subsurface layering. Many useful large outcrops are present inside craters above diameter of 100m and are possible targets for detailed in-situ analysis. The depth that can be reached by the drill of ExoMars is exhumed by outcrops inside craters above 50–80m diameter.The values presented here are valid only for Terra Meridiani since craters would excavate different subsurface layers in areas with different subsurface lithologies. Although future missions with the aim of subsurface sampling will probably land not at Terra Meridiani, but these terrains could be sedimentary plains too, so the experiences outlined in this work may still be useful there. The identified outcrops may help in the planning of in-situ work and also in the interpretation of results from drill activity.