Poor Pluto

and now this depressing news from the NY times


By DENNIS OVERBYE
Published: August 22, 2006
Pluto was looking more and more like a goner today as astronomers meeting in Prague continued to debate the definition of a planet.


Associated Press/NASA
Pluto, left, with its moons, from left to right, Hydra, Nix and Charon.
Related
Essay: Planets Askew in the Heavens, and Here on Earth, a Mess (August 22, 2006)

For Now, Pluto Holds Its Place in Solar System (August 16, 2006)

“I think that today can go down as the ‘day we lost Pluto,’ ” Jay Pasachoff of Williams College said in an e-mail message from Prague.

Under fire from other astronomers and the public, a committee appointed by the International Astronomical Union revised and then revised again a definition proposed last week that would have expanded the number of official planets to 12, locking in Pluto as well as the newly discovered Xena in the outer solar system, as well as the asteroid Ceres and Pluto’s moon Charon.

The new definition offered today would set up a three-tiered classification scheme with eight “planets”; a group of “dwarf-planets” that would include Pluto, Ceres, Xena and many other icy balls in the outer solar system; and thousands of “smaller solar system bodies,” like comets and asteroids.

The bottom line, said Owen Gingerich, the Harvard astronomer who is chairman of the I.A.U.’s planet definition committee, is that in the new definition, “Pluto is not a planet.”

“There’s not happiness all around, believe me,” he added.

The new proposal was hashed out in a couple of open meetings, the first of which was described by participants as tumultuous, and the second more congenial. Astronomers are supposed to vote on this or some other definition on Thursday, but whether a consensus is emerging depends on whom you talk to. Some astronomers expressed anger that the original definition of planet had been developed in isolation and then dropped on them only a week before the big vote. Others continued to question whether it was so important to decide the question now at all.

Among its defects, some astronomers say, the newer definition abandons any pretense of being applicable to other planetary systems beyond our own solar system.

To many astronomers, Pluto’s tiny size and unusually tilted orbit make it a better match to the icy balls floating in the outskirts of the solar system in what is known as the Kuiper Belt than to the conventional planets like Jupiter and Mars. The issue has been forced on astronomers by the discovery of such a ball even larger than Pluto, nicknamed Xena by its discoverer, Mike Brown of the California Institute of Technology.

If Pluto is a planet, so should be Xena, Dr. Brown has argued.

The committee’s original prime criterion was roundness, meaning that a planet had to be big enough so that gravity would overcome internal forces and squash it into a roughly spherical shape. But a large contingent of astronomers, led by Julio Fernandez of the University of the Republic in Montevideo, Uruguay, has argued that a planet must also be massive enough to clear other objects out of its orbital zone. Dr. Gingerich admitted, “They are in control of things.”

So the newest resolution includes the requirement for orbital dominance as a condition for full-fledged planethood, Dr. Gingerich said. That knocks out Pluto, which crosses the orbit of Neptune, and Xena, which orbits among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt.

“Vociferous objectors have said they could accept this,” Dr. Gingerich said.

Reached in his office at Caltech, Dr. Brown, who as the discoverer of Xena has the most to lose by its and Pluto’s demotion, said he thought he could live with the new proposal. “It essentially demotes Pluto to something other than a real planet, which is reasonable,” he wrote in an e-mail.

Dr. Gingerich cautioned that there were many things still to be sorted out. For example, the International Astronomical Union might consider creating a special name for Pluto and other dwarf-planets, like Xena and others yet to be discovered, that dwell out beyond Neptune. If it did, he said that “plutonians” seemed like a likelier choice than the previous suggestion, “plutons.” That term was protested by geologists, who pointed out that it was already used in earth science for nuggets of molten rock that have solidified and reached the surface.

But with two more days before the scheduled vote, there was no guarantee Pluto would not make a comeback and the definition of planethood be rewritten again.

“Some people think that the astronomers will look stupid if we can’t agree on a definition or if we don’t even know what a planet is,’’ Dr. Pasachoff said. “But someone pointed out that this definition will hold for all time and that it is more important to get it right.”