Pluto's New Place in Space Could Be as a 'Pluton'

Graphic shows planetary orbits including that of a proposed 10th planet. (AP Graphic) (AP)

Pluto, another object discovered orbiting it in 1978 called Charon, and a body discovered in 2003 that is slightly farther from the sun -- temporarily named UB313-- would be plutons. A pluton would be any planet beyond Neptune.

"Currently, we know of three, but there are other objects that are close in size to Pluto that will have to go through an evaluation process to determine whether they will be considered plutons," Binzel said. "We fully expect there are even more discoveries to come that are likely to be in this class of plutons."

Binzel and other committee members stressed that categorizing Pluto as a pluton was in no way meant to downgrade its longtime status as the ninth planet.

"We might be demoting it from the list of eight classical planets, but we're promoting it by making it the head of its own special class," said Owen Gingerich of Harvard University, who chaired the panel.

Other astronomers praised the committee for developing a relatively simple but scientifically valid definition to categorize the new objects being discovered, thanks to advances in technology and more powerful telescopes.

"I think the group brilliantly came up with a simple scientific sieve that can be used to decide whether something should be considered a planet," said S. Alan Stern of the Southwest Research Institute in Boulder, Colo., who served on the committee that deadlocked. "I'm very pleased."

But Mike Brown of the California Institute of Technology in Pasadena said he is disappointed, even though the proposal would characterize the object he discovered, UB313, as a planet.

"My first reaction was, 'Wow, this would mean this thing I found is a planet,' which is pretty exciting," Brown said. "Then I started looking at the details, and I don't think they got it quite right."

Brown questioned the caveats in the details of the proposal, which, for example, would make Pluto a planet but not Earth's moon.

"I find the definition oddly inconsistent. It makes no sense to me," Brown said. "They are sort of trying to have things both ways: They want to have a scientific definition, but they also don't want to offend cultural sensibilities."

Brown questioned why a committee would need to vote on what gets planet status.

"That's weird," Brown said. "That's not science."

But the proposal came as welcome news to Neil deGrasse Tyson, director of the Hayden Planetarium in New York. Tyson was inundated with angry and anguished e-mail and letters from schoolchildren when he opened an exhibit that displayed Pluto apart from other planets.

"This is about the only way you could define planethood in a way that would include Pluto. So I find it a little suspicious," Tyson said. "But I'm happy to finally have an unambiguous definition, so I don't have to worry about it after this."