A piece of Mars: Where the wind blows strong and there’s a lot of sand, the surface gets scoured. Some bits of the ground, called yardangs, are more resistant and stick around: they take on shapes elongated in the direction of the wind (in this case, a wind from the lower right). Groups of them are often called “fleets”, as they sometimes look like inverted boat hulls. (993×745 m, ESP_034129_1820, NASA/JPL/Univ. of Arizona)