Mars: South polar pits and etched terrain

Sharply delineated closed depressions, one-half to tens of kilometers across, with 400 meters estimated maximum depth, are locally abundant in the south polar region. They indent the surface of a massive homogeneous blanket that mantles the cratered bedrock surface. Some pits extend through the blanket exposing the underlying rock floor, and, where the blanket is thin (50–100 meters), its extensive removal exposes large ares of exhumed rock floor producing a terrain described as etched. The blanketing material is speculatively interpreted to be an eolian sedimentary deposit containing a mixture of fine particulate matter, possibly including volcanic ash, and particles of frozen volatiles, principally CO_2and H_2O. Fields of dunes, groups of linear grooves and flutes, and an unusual scoured topography on the surface of layered blanketing material suggest strong wind action. For this reason, deflation by wind, aided by ablation (evaporation) of included frozen volatiles, is regarded as the most likely mechanism for producing the south polar pits and etched terrain. Pitted and etched terrains and the deposits into which they are cut suggest that the south polar region, and presumably the north polar area as well, have experienced alternating episodes of eolian deposition and erosion