Pluto

Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered and is the largest known member of its population. Named after the Roman god of the underworld, Pluto was initially classified as a planet when it was discovered in 1930 but re-classified as a dwarf planet in 2006 following the discovery of Eris. Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice and is relatively small—about two-thirds the diameter of Earth’s moon and one-sixth its mass. It has an eccentric, elliptical orbit that takes it from 30 to 49 AU (4.4–7.4 billion km) from the sun; this range places it outside Neptune’s orbit but closer than Uranus’s. Pluto has five moons: Charon (the largest, with a diameter just over half that of Pluto), Styx, Nix, Kerberos, and Hydra