Pluto
Pluto is a dwarf planet in the Kuiper Belt, about 2,377 kilometres across, with ice mountains and a thin atmosphere.
Pluto was discovered in 1930 by Clyde Tombaugh at the Lowell Observatory in Arizona and was counted as the ninth planet for 76 years. It was named after the Roman god of the underworld, a name suggested by an 11-year-old English girl, Venetia Burney. In 2006 the International Astronomical Union reclassified it as a dwarf planet, after the discovery of other similar bodies beyond Neptune.
Pluto is about 2,377 kilometres across, smaller than our Moon. It orbits the Sun every 248 years and has five known moons, the largest of which, Charon, is about half Pluto's size.
When New Horizons flew past in 2015, it revealed a surprisingly active world, with glaciers of nitrogen ice, mountains of water ice several kilometres high and a thin, hazy atmosphere. Pluto shows that even small, cold bodies far from the Sun can stay geologically alive for billions of years.
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