The surface geology and geomorphology of Phobos

We conclude that the surface of Phobos is an arena for a variety of geologic processes. The leading role belongs to impact cratering with associated target destruction, material ejection from the crater and often from Phobos, and subsequent deposition partly with temporary residence in near-martian space. Shaking by impacts and surface stirring by day-night temperature changes cause granular surface material to move down along-slope driven by very low, but nevertheless efficient, surface gravity. A sample return mission is crucially important for a better understanding of the geological processes operating on Phobos. In addition to Phobos material, a returned sample will probably contain pieces of material from Mars. A series of outstanding questions to guide future exploration is listed.