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POOR, POOR PLUTO

india Updated: Aug 25, 2006 01:46 IST
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THEY WERE supposed to have voted to add three more planets to the solar system. They ended up shrinking it. The International Astronomical Union (IAU) has thrown out poor Pluto which had never quite settled down as the ninth planet. For the record, the solar system now has only eight planets, not nine.

On Thursday, after a tumultuous week of clashing over the essence of the cosmos, leading astronomers stripped Pluto of the planetary status it has held since its discovery in 1930.

But the scientists made clear they're as sentimental as anyone else about the ninth rock from the sun. Jocelyn Bell Burnell - a specialist in neutron stars from Northern Ireland who oversaw the proceedings in Prague - urged those who might be "quite disappointed" to look on the bright side. "It could be argued that we are creating an umbrella called 'planet' under which the dwarf planets exist," she said.

The decision by the international group spells out the basic tests that celestial objects will have to meet before they can be considered for admission to the elite cosmic club.

For now, membership will be restricted to the eight "classical" planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Much-maligned Pluto - named for the Roman god of the underworld - doesn't make the grade under the new rules for a planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit." Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.

Instead, it will be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets." The definition also lays out a third class of lesser objects that orbit the sun - "small solar system bodies," a term that will apply to numerous asteroids, comets and other natural satellites.

The decision at the conference of 2,500 astronomers from 75 countries was a dramatic shift from just a week ago, when the group's leaders floated a proposal that would have reaffirmed Pluto's planetary status and made planets of its largest moon and two other objects.

Now, two of the objects that at one point were cruising toward possible full-fledged planethood will join Pluto as dwarfs: the asteroid Ceres, which was a planet in the 1800s before it got demoted, and 2003 UB313, an icy object slightly larger than Pluto. 

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