A Piece of Mars: This field of 2 m wide sand ripples has a dark splotch in the middle (the scene is 300×225 m or 984×738 ft). The splotch is the peak of a low hill that straddles the classification gap between proper dunes and simple drifts of sand. Maybe it was a dune that has been modified down to this bump, or maybe it’s a drift that could grow into a dune, if enough sand blew in and accumulated on it. (HiRISE ESP_038117_1385, NASA/JPL/Univ. of Arizona).