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Pluto, taken by New Horizons' cameras on 14th July 2015Thanks to images sent back by the New Horizons space probe in July 2015, astronomers have discovered much new information about Pluto. Once the smallest and most distant planet in our Solar System, its status was changed in 2006. This was because many objects similar to—or even bigger than—Pluto had been recently discovered in the outer Solar System, notably Eris. So astronomers decided that Pluto, along with Eris, Haumea, Makemake and the largest asteroid Ceres, should all become officially classified as "dwarf planets". 

Clyde Tombaugh


Pluto was first identified in 1930 by the American astronomer Clyde Tombaugh (1906–97). Astronomers had been puzzled over why the orbit of Uranus was not quite as it should be. The only explanation—they thought then—was that there was another planet apart from Neptune farther out from the Sun with a force of gravity strong enough to affect the orbit of Uranus. The hunt was on for the mysterious Planet X. Working at the Lowell Observatory, Arizona, Tombaugh eventually pinpointed Pluto by comparing photographs taken of the same part of the sky six days apart and noticing that a pinprick of light had moved slightly against the background of stars.

The name Pluto was proposed by Venetia Burney, an 11-year-old schoolgirl from Oxford, England. She received £5 as a reward.

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