Phobos (pronounced / foŠbYs / RS-bYs, or, as the Greek ¦Ì²¿Â) (systematic name: Mars I) is the largest and closest of two small satellites of Mars, another Deimos. It is named after the Greek god Phobos (which means "fear"), son of Ares (Mars). A small, irregularly shaped object, Phobos orbit about 9377 km (5827 miles) from the center of Mars, closer to its primary than any other planetary moon.