This means that Pluto periodically comes closer to the Sun than Neptune, but a stable orbital resonance with Neptune prevents them from colliding. It has a moderately eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU (4.4–7.4 billion km) from the Sun. Like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small-one-sixth the mass of the Moon and one-third its volume. It is the largest known trans-Neptunian object by volume but is less massive than Eris. Pluto is the ninth-largest and tenth-most- massive known object directly orbiting the Sun. This led the International Astronomical Union (IAU) in 2006 to formally define the term planet -excluding Pluto and reclassifying it as a dwarf planet. Beginning in the 1990s, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt and the scattered disc, including the dwarf planet Eris. It was the first and the largest Kuiper belt object to be discovered.Īfter Pluto was discovered in 1930, it was declared to be the ninth planet from the Sun. Pluto ( minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. Pluto compared in size to the Earth and Moon
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