[meteorite-list] Pluto Seems Poised to Lose Its Planet Status

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 22 20:07:48 2006
Message-ID: <200608222344.QAA06592_at_zagami.jpl.nasa.gov>

http://www.nytimes.com/2006/08/22/science/space/22cnd-pluto.html

Pluto Seems Poised to Lose Its Planet Status
By DENNIS OVERBYE
New York Times
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.

"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."
Received on Tue 22 Aug 2006 07:44:20 PM PDT