A Piece of Mars: Sometimes in the floors of small craters, the wind blows in from several directions to produce odd polygon-shaped dunes that look like crochet (maybe Mars is making sweaters for its craters — it is, after all, a cold place). This “sweater” segment is 480×270 m (0.3×0.17 mi) in size (the “stitches” are ~20 m, or 66 ft, across). The smaller interior lines are younger windblown features, that are superposed on the larger structures — their alignment is strongly controlled by the topography of the larger polygonal “stitches”. (HiRISE ESP_017833_1975, NASA/JPL/Univ. of Arizona)

from Welcome to Cosmic Diary bit.ly/2jiFdbK