Pluto, formal designation 134340 Pluto, is the second-largest known dwarf planet in the Solar System (after Eris) and the tenth-largest body observed directly orbiting the Sun. Classified as a planet from its 1930 discovery, in 2006 the International Astronomical Union (IAU) declared it a dwarf planet instead; Pluto is now considered the largest member of a distinct population called the Kuiper belt.