Deimos is the smaller of Mars' two moons. Being only 9 by 7 by 6.8 miles in size (15 by 12 by 11 kilometers), Deimos whirls around Mars every 30 hours.
Like Phobos, Deimos is a small and lumpy, heavily cratered object. Its craters are generally smaller than 1.6 miles (2.5 kilometers) in diameter, however, and it lacks the grooves and ridges seen on Phobos. Typically when a meteorite hits a surface, surface material is thrown up and out of the resulting crater. The material usually falls back to the surface surrounding the crater. However, these ejecta deposits are not seen on Deimos, perhaps because the moon's gravity is so low that the ejecta escaped to space. Material does appear to have moved down slopes. Deimos also has a thick regolith, perhaps as deep as 328 feet (100 meters), formed as meteorites pulverized the surface.
Deimos is a dark body that appears to be composed of C-type surface materials, similar to that of asteroids found in the outer asteroid belt.
Deimos was discovered on Aug. 11, 1877 by Asaph Hall.
How Deimos Got its Name
Hall named Mars' moons for the mythological sons of Ares, the Greek counterpart of the Roman god, Mars. Deimos, whose name means dread, is the brother of Phobos.