Star-gazers puzzled by Pluto


Prague - Scientists who peer under rocks and gaze into space were clashing on Friday over the astronomical question of the year: Is Pluto really a planet?

The unusual dispute between geologists and astronomers has forced a scientific panel to consider scrapping its plan to call Pluto and similar bodies "plutons," said panel member and University of London astronomer Iwan Williams.

Earth-science experts emailed a mountain of objections after the pluton plan was released this week at a Prague conference of 2 500 space scientists with the International Astronomical Union (IAU).

Williams and other members of the IAU panel were scheduled to offer the plan, as part of a new definition of solar system bodies, for a membership vote next week.

The vote will determine the future status of Pluto, a distant world that's been called the ninth planet since its discovery in 1930.

Judging by the news clippings stacked at the conference's press office, the world is watching. And geologists are crying foul.

"The most vociferous reaction (to the proposal) has been against the word 'pluton,'" Williams told Deutsche Presse-Agentur dpa. "Geologists say it's already used.

"In light of the comments received, we might or might not modify (the proposal) a little bit," Williams said. "We're going to try to call them (the proposed plutons) something else."

Among geologists a "pluton" is a traditional term for "any body of igneous rock that solidified below the Earth's surface," according to a University of California web dictionary.

But the IAU panel said this week that, after two years of study, it had coined the word "pluton" to describe a distinctive category of planets. These would include Pluto and at least two other heavenly bodies that orbit the sun beyond Neptune.

Pluto, its companion Charon and a body unofficially called Xena - but scientifically known as 2003 UB313 - would be called "planets" as well as "plutons" as the proposal currently stands. More "plutons" could be found in the future.

In addition, Pluto and Charon would be called a "double planet." No longer would Charon be called Pluto's "moon."

Only Earth and seven other bodies from Mercury to Neptune would qualify as "classical" planets.

"Plutons are distinguished from classical planets in that they reside in orbits around the sun that take longer than 200 years to complete" and have other characteristics that "suggest a different origin than classical planets," according to an IAU circular on the controversial plan.

The proposal would increase the number of all planets - bodies that Williams said have not so far been found outside our solar system - to 12 including the three plutons.

"It's important that our definition is something we can translate to different solar systems in due time" after future astronomical discoveries, Williams said.

He expects bodies orbiting other stars to be found "in the not-too-distant future." And each will have to be categorised.

Williams said a majority of IAU astronomers back the panel's new definition of planets while a minority think neither Pluto nor similar bodies deserve the title for "various reasons."

"Strong views" on the Pluto question have surfaced at least partly because "there is some sort of affection for Pluto," he explained.

But Williams thinks the panel's resolution will be approved after the plan is modified - perhaps in a way that satisfies geologists. IAU members are scheduled to debate the issue Tuesday.

When the dust settles, Williams predicts, Pluto will still be called a planet. - Sapa-dpa


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