Flow

A piece of Mars: Below this ~550 m (0.3 mi) wide crater lies a ~1.3 km (0.8 mi) long “beard”, the wake of an ancient flow around the crater. Based on its location on Mars, I’m guessing the fluid flowing was lava. Inside the (interestingly dual) crater are bedforms, the remnants of more recent fluid flow – but in this case, the fluid is air. (HiRISE ESP_039902_1965, NASA/JPL/Univ. of Arizona)