By: HISTORY.com Editors

2006

Pluto is demoted

Getty Images / NASA / Handout

Published: June 30, 2022Last Updated: August 25, 2025

In Prague on August 24, 2006, the International Astronomical Union votes to demote Pluto from the ninth planet from the Sun to one of dozens of known dwarf planets.

The vote followed a week of debate by the IAU, who voted on multiple proposals including one that kept not just Pluto as a planet but added two new planets—the asteroid Ceres and Pluto’s moon Charon. The ultimate proposal defined the word “planets” (which comes from the Greek word planets, or “wanderers”) supposedly once and for all: planets are celestial objects large enough to be made rounded by their gravitational orbit around the Sun and to have pushed away nearby planetary objects and debris. Two years later, the IAU decided on a name for dwarf planets similar to Pluto—“plutoid”—grouping Pluto with Eris.

Some influential astronomers were caught off guard by the procedure, questioning the final proposal’s logic and pointing to the low turnout of voters (424 astronomers out of about 10,000 professional astronomers worldwide) at the IAU conference. One astronomer pointed to the contradiction that Earth, Mars, Jupiter and Neptune all have nearby asteroids. “I’m embarrassed for astronomy,” he said. “Less than 5 percent of the world’s astronomers voted.”

This scientific reclassification has had a worldwide cultural impact, as suggested by the American Dialect Society’s choice of “plutoed” as 2006’s Word of the Year—meaning “to demote or devalue someone or something. “Our members believe the great emotional reaction of the public to the demotion of Pluto shows the importance of Pluto as a name,” the society’s president said. Some state legislatures have even named March 13 Pluto Day, in stubborn dismissal of Pluto’s demotion.

The Rise and Fall of Planet Pluto

Look back at the controversial decision to give Pluto the pink slip and shrink the solar system from nine planets to eight.

By: Christopher Klein

Timeline

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Discover more of the major events, famous births, notable deaths and everything else history-making that happened on August 24th

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1814

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1814

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1821

Spain accepts Mexican independence

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1873

Elusive Mount of the Holy Cross photographed

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1914

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1941

Hitler suspends euthanasia program

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1954

Congress passes Communist Control Act

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1969

U.S. unit refuses commander’s order

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1981

John Lennon’s killer sentenced

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2012

Killer in Norway massacre is sentenced

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