"A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. Formally classified moons include 173 planetary satellites orbiting six of the eight planets,^[and seven orbiting three of the five dwarf planets. As of January 2012, over 200 minor planet moons have been discovered.  There are 76 in the asteroid belt (5 with two satellites), 4 Jupiter trojans, 37 near-Earth objects and 9 Mars-crossers. There are also 76 known moons of trans-Neptunian objects. Some 150 additional small bodies were observed within rings of Saturn, but they were not tracked long enough to establish orbits. Planets around other stars are likely to have natural satellites as well, although none have yet been observed. Of the inner planets, Mercury and Venus have no moons; Earth has one large moon, known as the Moon; and Mars has two tiny moons, Phobos and Deimos. The large gas giants have extensive systems of moons, including half a dozen comparable in size to Earth's moon: the four Galilean moons, Saturn's Titan, and Neptune's Triton. Saturn has an additional six mid-sized moons massive enough to have achieved hydrostatic equilibrium, and Uranus has five. It has been suggested that some satellites may potentially harbour life, though there is currently no direct evidence to support this theory." Source: Wikipedia