Dinky Pluto Loses Its Status As Planet

These images, released by NASA Thursday, March 6, 1996, show the never-before-seen surface of the planet Pluto as seen fron the Hubble Space Telescope's Faint Object Camera. Leading astronomers approved historic new planet guidelines Thursday, Aug. 24, 2006, downsizing Earth's neighborhood from nine principal heavenly bodies to eight by demoting distant Pluto. (AP Photo/NASA) (AP)

The decision by the IAU, the official arbiter of heavenly objects, restricts membership in the elite cosmic club to the eight classical planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Pluto and objects like it will be known as "dwarf planets," which raised some thorny questions about semantics: If a raincoat is still a coat, and a cell phone is still a phone, why isn't a dwarf planet still a planet?

NASA said Pluto's downgrade would not affect its $700 million New Horizons spacecraft mission, which this year began a 9 1/2-year journey to the oddball object to unearth more of its secrets.

But mission head Alan Stern said he was "embarrassed" by Pluto's undoing and predicted that Thursday's vote would not end the debate. Although 2,500 astronomers from 75 nations attended the conference, only about 300 showed up to vote.

"It's a sloppy definition. It's bad science," he said. "It ain't over."

Under the new rules, two of the three objects that came tantalizingly close to planethood will join Pluto as dwarfs: the asteroid Ceres, which was a planet in the 1800s before it got demoted, and 2003 UB313, an icy object slightly larger than Pluto whose discoverer, Michael Brown of the California Institute of Technology, has nicknamed "Xena." The third object, Pluto's largest moon, Charon, isn't in line for any special designation.

Brown, whose Xena find rekindled calls for Pluto's demise because it showed it isn't nearly as unique as it once seemed, waxed philosophical.

"Eight is enough," he said, jokingly adding: "I may go down in history as the guy who killed Pluto."

Demoting the icy orb named for the Roman god of the underworld isn't personal _ it's just business _ said Jack Horkheimer, director of the Miami Space Transit Planetarium and host of the PBS show "Star Gazer."

"It's like an amicable divorce," he said. "The legal status has changed but the person really hasn't. It's just single again."

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AP Science Writers Alicia Chang in Los Angeles and Seth Borenstein in Washington, and correspondents Sue Leeman in London and Mike Schneider in Cape Canaveral, Fla., contributed to this story.

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On the Net:

International Astronomical Union, http://www.iau.org