Deimos is Mars' smallest moon with dimensions of just 15 by 12 by 11 km. It orbits Mars once every 30 hours.

Deimos is heavily cratered, but unlike craters on other moons and planets, they do not have ridges. These ridges are usually caused by ejected material falling back down after the impact, but Deimos gravity may be so low, that material just escaped.

It's composition is very similar to that of the asteroids in the nearby asteroid belt, so it is possible that this moon was captured from there.