Pluto

Article By:

Stern, S. Alan Space Science and Engineering Division, Southwest Research Institute, Boulder, Colorado.

Last reviewed:May 2021

DOI:https://doi.org/10.1036/1097-8542.529400

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• Pluto, published August 2018:Download PDF Get Adobe Acrobat Reader
• Pluto, published May 2017:Download PDF Get Adobe Acrobat Reader
• Pluto, published June 2014:Download PDF Get Adobe Acrobat Reader

The largest dwarf planet in the solar system and a member of the Kuiper Belt of icy objects mostly beyond the orbit of Neptune. Pluto (Fig. 1) was discovered on February 18, 1930, by U.S. astronomer Clyde W. Tombaugh at the Lowell Observatory in Flagstaff, Arizona. Tombaugh discovered Pluto on photographic plates taken with a special astronomical camera as part of a systematic search. Pluto's name was suggested later in 1930 by Venetia Burney, an English schoolgirl. At the time and until 2006, Pluto was considered the ninth planet of the solar system in orbit around the Sun. However, in 2006, the International Astronomical Union reclassified Pluto as a dwarf planet, along with fellow Kuiper belt member Eric, discovered in 2003, and Ceres in the asteroid belt, among numerous other bodies. The population of dwarf planets far outnumbers the population of large planets, suggesting that solar system formation predominantly creates small planets, not large planets, as has been thought. See also: Kuiper Belt; Planet; Solar system; Sun

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