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Astronomers divided over "planet" definition

Deutsche Presse Agentur
Published: Tuesday August 22, 2006

Prague- The world's astronomers on Tuesday passionately debated a plan to use roundness as the criteria for defining a "planet," with some experts calling the proposal "reasonable" but others declaring it "bound to fail." Pluto would qualify as a "dwarf planet" distinct from the solar system's eight "classical planets" under the definition presented by a panel at the International Astronomical Union (IAU) conference in Prague.

Yet the special panel also recommended the eight bodies from Mercury to Neptune share the general term "planet" with Pluto and other "trans-Neptunian objects" because they orbit a star and meet gravitational criteria for "hydrostatic equilibrium," which makes them "nearly round."

Moreover, the panel suggested calling Pluto and its space companion Charon a "double planet."

In a non-binding show of hands after a 90-minute debate, IAU members voted "about 50-50" in favour of the proposal's main resolution, said IAU spokesman Lars Christensen. But "a clear majority" opposed two other resolutions.

"But this was just a gauge" before a final conference vote Thursday, Christensen said.

Pluto has been honoured as the ninth planet since its discovery in 1930. Scientists were forced to reconsider its status - and the very definition of a planet - after the 2003 discovery of a larger and more distant object circling the sun called UB313.

Although Pluto's future has captured public attention since the IAU started working on the issue two years ago, most scientists commenting from the conference floor Tuesday focused on technical issues.

Some spoke passionately about the proposed definition's impact on scientists searching for star-orbiting objects outside our solar system.

One astronomer packed his comment with technical jargon and blasted the panel for "committing an offence." Others saw the proposal as "not even premature but dangerous" or "honourable but bound to fail."

At one point, a scientist angrily shouted from his chair and drew applause when the debate moderator, panel member Richard Binzel of the Massachusetts Institute of Technology, cut off discussion to move to another topic.

Implored one astronomer, "We must have a definition that is not politically correct but scientifically accurate."

Defending the plan was panel member Junichi Watanabe, a Japanese astronomer who said "no political or emotional" factors were involved when the panel decided that any star-orbiting body with "a lovely, round shape" should be called a planet.

"It was purely a scientific affair," Watanabe said.

Some critics called for delaying the decision for up to three years, claiming the panel jumped the gun. Binzel replied that "a diverse community" outside the astronomy field is "asking for things to happen."

The panel has already modified the proposal since the conference began last week. Some experts grumbled that the final draft had emerged just an hour before the debate began.

A key modification was to drop a plan to call Pluto and similar objects "plutons."

The change came after geologists around the world criticized IAU last week for neglecting the traditional use of the word "pluton" as the name for an igneous rock.

One panel member quipped that geologists should attack software- maker Microsoft, not astronomers, for the "pluton" oversight because the word did not appear in the panel's spellchecker.

Tuesday's debate ended with the straw poll but was expected to continue in private groups until Thursday, when the conference's 2,300 astronomers were scheduled to vote.

The debate "is still open," Christensen said.

© 2006 DPA - Deutsche Presse-Agenteur