Mars has two small satellites, PHOBOS and DEIMOs, . They are irregularly shaped, very dark objects liberally covered with craters . This gives them the appearance of modestly-sized asteriods but their almost circular orbits make it unlikely that they are simply captured asteroids. Several astronomers have suggested that they are the shattered remains of an earlier large single satellite of Mars. Each satellite moves in an orbit remarkably close to the planet and Phobos has the unique distinction of having an orbital period teas than the rotation period of its primary. Because of this, Phobos appears to rise in the west and set in the east and, furthermore, does this twice every martian day. Both satellites are in synchronous rotation, always keeping the same face turned towards Mars.

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