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Last Updated: Friday, 23 September 2005, 10:54 GMT 11:54 UK
Bid to solve dispute over planets
Neptune, Nasa
Planets like Neptune would simply be known as gas giants
An expert panel tasked with resolving disagreement over what is and isn't a planet has recommended that astronomers qualify that term with another word.

The panel says astronomers should stop using "planet" on its own, and instead define different "planetary objects".

Under this scheme, Earth and Venus would be known as terrestrial planets, Saturn and Jupiter as gas giants and Pluto as a Trans-Neptunian planet.

The plan was emailed to panel members on 12 September, Nature magazine says.

Old habits die hard
Jacqueline Mitton, astronomy author
The panel of 19 astronomers was convened last year by the International Astronomical Union (IAU) to come up with a solution to the dispute.

The division amongst astronomers over what defines a planet came to the fore this year, with the discovery of a distant object called 2003 UB313.

Cosmic dispute

Members of the team behind the discovery argued that the object, which orbits the Sun near Pluto, qualified as a 10th planet.

Part of their claim rests on 2003 UB313's size - it is as big, if not bigger, than Pluto. And if Pluto qualifies as a planet then surely 2003 UB313 must be one, too.

Others, however, would prefer to lump both in with a group of icy bodies known as Kuiper Belt Objects (KBOs), which orbit 10 billion km from the Sun.

Professor Iwan Williams, chair of the panel and an astronomer at Queen Mary, University of London, told Nature's news pages that the panel hoped to send a final version of the proposal to the IAU in two weeks.

But others disagree with the proposal. Alan Stern, of the Southwest Research Institute in Boulder, Colorado, said astronomers should use properties, not location, as a guide when defining planetary types.

In his view, objects like Pluto and 2003 UB313 would be better known as "ice dwarfs".

Jacqueline Mitton, an astronomy writer from Cambridge, UK, suggested the public and astronomers alike might reject the proposals: "Old habits die hard," she told Nature news.

"Committees can make pronouncements, but they can't always change things."

The term extrasolar planet should be used for planetary objects orbiting stars other than the Sun, the proposal suggests.

Farewell Pluto?
02 Aug 05 |  Magazine
Hubble reveals new map of Pluto
12 Sep 05 |  Science/Nature
Astronomers detect '10th planet'
30 Jul 05 |  Science/Nature
Distant object found orbiting Sun
29 Jul 05 |  Science/Nature

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