Now, Pluto's a planet again

February 09, 1999|By BRUCE HAMILTON

Pluto is taking its place among the planets again.

Some scientists want to put Pluto in another category, a move that some saw as a demotion. Last week, the International Astronomical Union opposed the change.

"That settles that for another couple years," said Frank Moon, president of Tri-State Astronomers. "It will come back around again."

So has Pluto. Today it literally reclaims the ninth planetary position.

The interstellar ice ball's orbit brought it closer for several years. Once Pluto passes Neptune, it will again be the farthest planet from the sun.

It was always an outcast. Pluto's properties make it an oddball among the planets. It is neither terrestrial, like Earth, nor Jovian like Jupiter.


Earth's moon is bigger than Pluto, which is the smallest planet. It also has the most eccentric orbit.

"It has been clear for decades that Pluto did not fit in with the pattern of other planets," wrote Mike A'Hearn, a University of Maryland professor, in an Internet statement.

A'Hearn is president of the International Astronomical Union's Planetary Systems Sciences Division. He wanted to categorize Pluto as a "Trans-Neptunian Object."

Other astronomers wanted to assign it a "minor planet number." The union, a nongovernmental organization with some 8,300 members in 83 countries, discussed the issue.

"We got into disputes over what the physical definition of a planet should be," A'Hearn said Monday. The union decided against putting Pluto in the "minor planet" category, he said.

It will officially remain a planet. Although it also might become a "Trans-Neptunian Object," A'Hearn said that is unlikely. "It is no longer viewed as reasonable," he said.

The union's position quells a controversy among those who feared Pluto would lose its status.

"For the foreseeable future, it puts the debate to rest," said A'Hearn.

Some local star-gazers are relieved.

"I'm glad they're not going to demote it," said Rodney Martin, a teacher who runs the Washington County Planetarium.

"It's definitely a different kind of planet," he said. "Who says we can't have icy ones?"

Moon said he's satisfied with the union's decision. To him, it doesn't matter how the object in the outer solar system is classified.

"Whatever happens, Pluto remains Pluto," he said. "Reality plods along in spite of all this stuff."

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