Moons of Mars 0.07. If viewed from Mars's surface near its equator, full Phobos looks about one third as big as a full moon on Earth. It has an angular diameter of between 8' (rising) and 12' (overhead). Due to its close orbit, it would look smaller when the observer is further away from the Martian equator, and is below the horizon and thus invisible when viewed from Mars's polar ice caps. Deimos looks more like a bright star or planet for an observer on Mars, only slightly bigger than Venus looks from Earth; it has an angular diameter of about 2'. The
Mars mainly phyllosilicates and other minerals known from Mars, point toward an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, similar to the prevailing theory for the origin of Earth's moon. Although the VNIR spectra of the moons of Mars resemble those of outer-belt asteroids, the thermal infrared spectra of Phobos are reported to be inconsistent with chondrites of any class. Mars may have moons smaller than in diameter, and a dust ring is predicted to exist between Phobos and Deimos. Dozens of crewless spacecraft, including orbiters, landers, and rovers, have been sent