Scientists gear up for planetary smackdown

By Jeanna Bryner

updated 2:38 p.m. ET Aug. 5, 2008

Top astronomers and other planetary scientists will step into the ring this month to duke it out over a basic, yet controversial, question: What is a planet?

"The Great Planet Debate: Science as Process" conference will be held from Aug. 14-16 at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

Some astronomers see the conference as a way of cleaning up the mess created by the organization that names celestial bodies, the International Astronomical Union (IAU), which in August 2006 voted in a new definition of planet that demoted Pluto to "dwarf planet." (Under a more recent IAU decision, Pluto and similar objects are classified as "plutoids.")

Many planet scientists were disgruntled over the 2006 IAU decision, which they said involved a vote of just 424 astronomers out of some 10,000 professional astronomers around the globe. The most recent decision, to categorize Pluto and such as plutoids, further ticked off many astronomers, who felt the term was developed behind closed doors.

"We're going to do something that the IAU did not, which is discuss what we know about planetary bodies in the solar system and around other stars, and discuss the value of different ways of defining objects as planets and what that means," said Mark V. Sykes, director of the Planetary Science Institute in Tucson, Ariz.

When the dust settles, those involved hope a consensus will stand, a classification scheme for all objects orbiting a star.

"If a new consensus emerges it will easily overturn the IAU. This is not an issue," said Neil deGrasse Tyson, director of the American Museum of Natural History's Hayden Planetarium in New York. "If not, they'll stick with what they've got until something better comes along."

Tyson said he doesn't see the IAU so much as a separate entity, but as part of and a reflection of the astronomical community.

Pluto's part
The planet definition saga began, arguably, when Pluto was discovered in 1930, as this object was an oddball compared with its solar system buddies in its eccentric orbit and small size and low mass (less massive than Earth's moon).

The 2004 discovery of Sedna, an object about three-fourths Pluto's size and about three times as far from the sun, raised some questions about Pluto's planetary status. Then, in 2005, Caltech's Mike Brown announced the discovery of 2003 UB313, and bells rang out of a possible 10th planet in our solar system. The object was round, orbited the sun, and the kicker — it turned out to be larger than our then ninth planet, Pluto. Uh-oh.

Since then, the IAU has labeled Pluto a "dwarf planet" and then later, a "plutoid." But some planetary scientists called foul on the way the IAU voted in the new planet definition or the outcome. In fact some vowed to call Pluto a planet despite the most recent IAU ruling.

And so in addition to scientific sessions, the APL conference will include a Pluto debate between Sykes and Tyson. The debate, Tyson says, will focus on Pluto with regard to the mountain of new information being collected about our solar system and others.

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