Third Rock's Astronomers 'Dwarf' Pluto's Status in the Solar System
Posted on: Friday, 25 August 2006, 06:00 CDT
By Dan Vergano
Astronomers gave Pluto the Mickey Mouse treatment Thursday, classifying the world a "dwarf" rather than a full-fledged planet.
Like its cartoon counterpart, the orb became a sidekick when the International Astronomical Union (IAU) meeting in Prague took a hand vote and decided to downsize the solar system to eight planets.
"Pluto is still Pluto; it is still the same scientifically interesting object at the edge of the solar system," says astronomer Richard Binzel of the Massachusetts Institute of Technology, a member of the IAU's planet definition committee. "Science has advanced to the point where we realize there are lots of Plutos out there."
Last year's announcement that a world larger than Pluto had been detected -- named UB 313 and nicknamed "Xena" by discovery team leader Mike Brown of the California Institute of Technology -- put pressure on the IAU to redefine planets, says planetary scientist Will Grundy of the Lowell Observatory in Flagstaff, Ariz. Over the past decade, some science museums and astronomers had removed tiny Pluto, which is smaller than Earth's moon, from the list of planets.
The IAU's new definition of a planet is that it must:
*Orbit the sun.
*Be big enough for its own gravity to compact it into a ball.
*Have "cleared the neighborhood around its orbit," meaning it is not surrounded by objects of similar size and characteristics.
The last condition was added to a draft planet definition proposed by the committee last week that would have added three more planets to the solar system immediately: UB 313, Pluto's moon Charon, and the asteroid Ceres, along with dozens more in the Kuiper comet belt in the next decade.
Instead, the orbit-clearing requirement means Pluto, Ceres and UB 313 become "dwarf planets" under a second resolution also adopted. None has cleared its orbital belt of similar-size objects. The new definition passed with 95% of the votes, the IAU's Lars Lindberg Christensen says.
"I'm of course disappointed that Xena will not be the 10th planet, but I definitely support the IAU in this difficult and courageous decision," Brown says. Others were less enthusiastic. "I think this is utter nonsense. How can we ever say whether something has cleared out its orbit?" asks astronomer Sanjay Limaye of the University of Wisconsin-Madison.
Meanwhile, textbook and encyclopedia writers, including publishers of the 2007 World Book Encyclopedia, have been awaiting the new definition. Says Editor in Chief Paul Kobasa: "I suspect kids are going to be more interested in Pluto now than before."
(c) Copyright 2005 USA TODAY, a division of Gannett Co. Inc.
Source: USA TODAY
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