A solar system object that orbits the Sun at an average distance of 39.5 times the distance between Earth and Sun. Pluto has a mass 0.002 times the mass Earth and a radius 0.18 times the radius of Earth. It is a small body made of water ice, and temperatures there do not rise above –223 degrees Centigrade. Pluto has three moons. Discovered in 1930, it originally was classified as a planet, but was demoted in 2006.
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