A piece of Mars: Bet you didn’t know there were ribbons on Mars. Long, sweeping, velvety lines, delicately frayed at the ends. These are actually ancient ripples, formed by a wind blowing from right to left. Stripes on the ripples and on the ground between them show the ancient ripple interiors, exposed by erosion. The long ripple in left center is 175 m (574 ft) long. (HiRISE ESP_016136_1525, NASA/JPL/Univ. of Arizona)