A piece of Mars: The blue structures are rippled dunes found not far from the south polar cap of Mars. They are probably partially active, enough to create the fine ripples found on and between the dunes. But the steeper bluish slopes on the right are pitted and rough, which is not characteristic of actively migrating dunes. Ice in the dunes probably keeps them from being mobilized by the wind. (ESP_031749_1080, NASA/JPL/University of Arizona).