Deimos (systematic designation: Mars II)[7] is the smaller and outermost of the two natural satellites of the planet Mars, the other being Phobos. Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars.[2] Deimos is 23,460 km (14,580 mi) from Mars, much further than Mars's other moon, Phobos.[8] It is named for Deimos who in Greek mythology is the twin brother of Phobos, and personifies terror.