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For Pluto, a Smaller World After All

Members of the 6th General Assembly of International Astronomic Union vote on a resolution for planet definition
Members of the 6th General Assembly of International Astronomic Union vote on a resolution for planet definition in Prague. The new guidelines made Pluto a dwarf planet rather than a "classical" planet. (Michal Cizek -- AFP/Getty Images)

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By Shankar Vedantam
Washington Post Staff Writer
Friday, August 25, 2006

Pluto the planet is dead.

The baby in the solar system's familiar nine-planet pantheon, a favorite of schoolchildren everywhere, was disowned yesterday by the world's astronomers.

Pluto's failing? It isn't big enough and strong enough to push anyone around.

That's what it takes to be a real planet, the scientists said. Only the eight "classical" planets are large enough to be dominant over smaller bodies in their path.

Pluto's course through the heavens, by contrast, is under the sway of much larger Neptune.

The former planet doesn't have even the consolation of a new title. In a series of votes, the astronomers narrowly decided against calling it a "plutonian object." The term "pluton" was shot down, too. But they insisted that Pluto would still have stature -- it becomes a "dwarf planet" and the prototype of a new, as yet unnamed, subcategory of objects. The scientists said they will seek suggestions for a name from the public.

The fight over Pluto's status at a meeting in Prague of the International Astronomical Union, the body that sets standards for the field, became a vicious battle that ultimately broke along scientific, linguistic and historical lines. The result was hailed by some as a victory of rationality over sentiment, but came as a huge disappointment to others, including the head of a panel charged with coming up with a new definition for "planet."

Owen Gingerich, a Harvard astronomer and historian, said the definition the group ended up with was a perfect example of "a horse designed by a committee." He quoted a colleague in Prague as saying, "It demonstrates how belligerent and self-centered planetary astronomers can be."

The "dwarf planet" classification to which Pluto was relegated will potentially have dozens of members. But the scientists emphasized they were also carving out a subcategory for dwarf planets that orbit beyond Neptune, a group that currently includes Pluto and one other body.

Astronomers acknowledged that one reason to create the special category is public sentiment against dumping Pluto in a large agglomeration of unspectacular objects.

"The message to the public is we recognize Pluto as a prototype of a different kind of object, and that is more exciting than being one of the regular planets," said Ron Ekers, outgoing president of the astronomers union.

That reasoning was not well received in some quarters.


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