Mars has two very small satellites orbiting it, Phobos and Deimos. Scientists believe that both moons are actually asteroids captured via Mars's gravitational field. Made of dark rock that includes a great deal of carbon, both satellites have many craters due to collisions with debris.
Phobos, with a 13-mile radius, is the larger of the two moons, and it is 5,830 miles from Mars. It circles Mars three times per day. Deimos has a radius of eight miles, and it is 14,580 miles from Mars. It circles Mars once very 30 hours.
Asaph Hall discovered both moons in 1877. He named them after the sons of the Greek god Ares whose Roman counterpart is Mars.