A natural satellite or moon is a celestial body that orbits another body (a planet, dwarf planet, or small Solar System body), which is called its primary, and that is not artificial. In the Solar System there are 173 known natural satellites orbiting within 6 planetary satellite systems. In addition, several other planetary-mass objects are known to have satellite systems, including those of the IAU-listed dwarf planets, the moons of Pluto, Haumea and the Eris–Dysnomia systems. As of January 2012, over 200 minor-planet moons have been discovered. There are 76 known objects in the asteroid belt with satellites (five with two each), four Jupiter trojans, 39 near-Earth objects (two with two satellites each), and 14 Mars-crossers. There are also 84 known natural satellites of trans-Neptunian objects. Some 150 additional small bodies have been observed within the rings of Saturn, but only a few were tracked long enough to establish orbits. Planets around other stars are likely to have satellites as well, and although numerous candidates have been detected to date, none have yet been confirmed.... more on Wikipedia.com