Geology of the Melas Chasma landing site for the Mars Exploration Rover mission

Abstract

The Melas Chasma landing site was considered a high‐priority site for the Mars Exploration Rover (MER) mission because of the opportunity to land on and study potential layered sedimentary deposits. Though no longer considered a candidate site because of safety concerns, the site remains a scientifically interesting area that provides insight into the geologic history of Valles Marineris. Within the landing ellipse are dunes, landslide material, and unusual blocky deposits. The blocky deposits are composed of rounded blocks, some of which have meter‐scale layering, and they show evidence of ductile deformation, including bending and distortion of coherent blocks around each other. The morphologic characteristics of the blocks are unique, and they appear to have no terrestrial analogue. However, the gross morphology of these blocky deposits and their superposition on adjacent wallrock is consistent with the blocks having been transported downslope. Given the existence of other large mass failures in the area, we propose the blocky deposits may also have originated from mass movement events. The size of the blocks coupled with the distances they traveled indicates high mobility. The distances the blocks were transported and their rounded, irregular shapes suggest either water in the source material or deposition in a subaqueous environment. The source for the main blocky deposit inside the landing ellipse is considered to be the wallrock to the south, while the other two blocky deposits have source regions along the northern canyon walls. The southern wallrock of Melas Chasma contains numerous valleys not seen elsewhere in Valles Marineris. The identification of valley networks along the southern wallrock suggests that a source of water existed below the surface of the plateau and produced the valleys after intersecting the edge of the exposed canyon walls.