Trails of Martian dust devils, which appear as dark streaks on the light surface, as seen by Mars Reconnaissance Orbiter. Dust devils are strong, well-formed, and relatively long-lived whirlwinds that can form when hot air near the surface rises quickly through a small pocket of cooler, low-pressure air above it. On Mars, dust devils have unexpectedly cleaned the solar panels of the Mars rovers.Photo: NASA/JPL/University of Arizona