Phobos (IPA: systematic designation: Mars I) is the larger and closer of Mars' two moons (the other being Deimos). It is named after the Greek god Phobos (which means "fear"), a son of Ares (Mars). Phobos is one of the smallest moons in the solar system, and orbits about 6000 km (3728 mi) above the surface of Mars, closer to a major planet than any other moon.