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Planet issue embroils scientists
By Jeffrey White (staff writer/ The Prague Post)
This article first appeared in The Prague Post on August 26, 2006. This article is republished with friendly permission of The Prague Post. Visit The Prague Post at )

Posted August 30, 2006

[Since the article's first appearance, Pluto was stripped of its status as a planet and redefined as a "dwarf planet," leaving just eight classical planets in the solar system. European Weekly]

Sharp divisions in opinion among some of the world's top astronomers about how to define a planet could scuttle more than a week's worth of debate and proposals on how to settle an issue that has divided the field for years.

Puny Pluto's status as a planet, a frequent matter of debate, looked no closer to resolution Aug. 22 as astronomers of the International Astronomical Union's (IAU's) triennial convention packed into a large hall of Prague's Congress Center and failed to endorse a draft resolution defining what a planet is.

The committee wants to define a planet as a celestial body that has enough self-gravity to pull itself into a round shape and orbits a star rather than another object. Moreover, the committee recommends categorizing Pluto and three other new planets as "dwarf planets."

The full assembly of the IAU, more than 2,500 astronomers, will vote on the matter Aug. 25. If approved, three new planets — Charon, a moon of Pluto; Ceres, a large asteroid; and a newly discovered body known as Xena — will join our solar system.

But during more than an hour of heated debate, it became clear that warring disciplines within astronomy, mostly between gravitational physicists and dynamic physicists, are making it hard to produce a simple resolution.

"This is not a scientific issue of what is correct," said IAU President Ron Eckers. "There is no correct answer to this issue. This is about a compromise that will work."

Still, a growing number of astronomers called on the IAU to put off the issue for another three years, when the general assembly reconvenes in Rio de Janeiro.

One astronomer screamed into a microphone that the committee's failure to take into account quantum dynamics in its definition was "an insult to the entire astronomical community."

Dominant issue

International media has focused on Prague's Congress Center in Vyšehrad for more than a week, and the planet issue has cast a shadow over what scientists say are a lot more important concerns for the field of astronomy.

"It's what everybody's talking about," one astronomer said.

Of course, many are surprised that in a field as complex as astronomy, a collection of some of its most brilliant practitioners are still debating what a planet is.

"It never mattered before," said Virginia Trimble, of the University of Maryland.

But then came Xena — or, officially, 2003 UB313 — which California Institute of Technology Astronomer Mike Brown discovered in 2003 well beyond Pluto. Careful measurements revealed that it was indeed bigger than Pluto, a conclusion confirmed earlier this year by a team at the University of Bonn in Germany.

"It was the first object that was larger than Pluto," said Frank Bertoldi, the team's leader. "The issue was acute. It had to be dealt with."

After two years of failing to define a planet, the IAU convened a new committee in Paris in June. During the course of a few sleepless nights, in the words of one member, the group reached consensus.

Owen Gingerich, a Harvard professor who chaired the IAU's recent "definition committee" said Pluto was the "elephant in the parlor" throughout the process.

Pluto's status has been debated since the planet's discovery in 1930, and, despite what millions learn in school, astronomers long ago concluded that it's not really a planet: Its orbit is too different, its size — one-quarter of 1 percent as massive as Earth — is too small.

To make matters worse, it has remained largely a mystery, hard to observe at some 40 times further from the sun than Earth (which is itself 93 million miles, or 150 million kilometers, from the sun).

Still, Pluto has a strong lobby supporting it.

"People like Pluto in the same way they tend to favor the underdog," said Richard Binzel, an astronomer at the Massachusetts Institute of Technology. "There is an emotional attachment to Pluto that is uncommon in the world of science."

Keeping it simple

Debate among astronomers is settling not so much on Pluto, but on how to find a definition that is not too simple, but not too complex either.

"People want an easy definition, but I don't think a lot of this stuff is easy to explain," said David Morrison, who writes astronomy textbooks.

In the end, the recommendation on the table defines a planet in both intrinsic and extrinsic ways: Shape, size and orbit are broad enough to understand, but leave enough room to get specific.

Still, at press time, e-mails were pouring into the IAU with alternate suggestions on how to best fine-tune the definition of "planet." At the Aug. 22 debate, several new ideas were floated, and it was unclear what kind of airing they would get.

One overall concern was that defining a planet broadly flings open the door to literally millions of potential other bodies.

"The proposal I actually favor is to say that everybody on this planet has grown up with the idea that there are nine planets. ... Sorry, all you other guys, you just don't make it," said Paul Weissman of NASA's Jet Propulsion Laboratory.

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