Boulders on high

A piece of Mars: Right at the edge of the largest volcano on Mars (Olympus Mons) is a steep cliff. Here, near that edge, are some car-sized boulders poking out from a thick blanket of dust. Strong winds blow down the mountainside (lower right to upper left), leaving behind streamlined hills and grooves. Much of the surface of the volcano looks like this, although the boulders are relatively rare. (ESP_033303_1980, NASA/JPL/Univ. of Arizona)