Phobos is one of the two moons that revolve around Mars. It’s a lumpy, crater-filled pile of rubble that measures only 10 by 14 by 11 miles (17 by 22 by 18 km). Phobos also orbits closer to Mars than its smaller counterpart, Deimos, at an altitude of only 3,700 miles (6,000 kilometers). This photo was taken by the High-Resolution Stereo Camera on board ESA’s Mars Express in Jan. 2008. Read our full story here: Weird Grooves On Mars’ Moon Phobos Traced to Asteroids