|Pluto is the second-largest dwarf planet in the solar system. It orbits between 29 and 49 AU from the Sun and was the first Kuiper Belt Object to be discovered. Approximately one-fifth the mass of the Earth's Moon, Pluto is primarily composed of rock and ice. It has an eccentric orbit that is highly inclined with respect to the planets Because its unusual orbit, Pluto comes closer to the Sun than Neptune during a portion of its orbit. Pluto has three moons. The largest, Charon, is nearly equal in size to the planet itself. Pluto's smaller moons, Nix and Hydra, were discovered in 2005.