Pluto

Pluto, formal designation 134340 Pluto, is the second-largest known dwarf planet in the Sol System (after Eris) and the tenth-largest body observed directly orbiting the Sun. Classified as a planet, from its discovery in 1930 until 2006, Pluto is now considered a "dwarf planet" along with Eris and Ceres. It is named after the Roman god of the underworld.

Pluto is composed primarily of rock and ice and is relatively small: approximately a fifth the mass of the Earth's Moon and a third of its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU (4.4–7.4 billion km) from the Sun. This causes Pluto to periodically come closer to the Sun than Neptune.