Pluto

Pluto, formally designated 134340 Pluto, is a large trans-Neptunian object in the Kuiper belt. It is the second-most-massive dwarf planet known in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun. Like other Kuiper belt objects, Pluto is composed primarily of rock and ice and is relatively small, approximately one-sixth the mass of the Earth's Moon and one-third 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. As of 2011, it is 32.1 AU from the Sun.