Translations:Pluto/3/en

The planet Pluto was first discovered in 1930, when it was recognized as the ninth planet of the solar system. However, it differs from the other planets in a number of ways. It has an orbit that is in a different plane, and the orbit is eccentric, with portions inside the orbit of Neptune. It is only slightly larger than the Moon, and its mass is roughly 0.2% of the mass of Earth. These facts, along with the discovery of other similar objects outside the orbit of Neptune, led to the International Astronomical Union in 2006 changing the definition of a planet to exclude Pluto.