Pluto should get back planet status, say astronomers

By Richard Gray, Science Correspondent

Pluto should have its status as a planet reinstated, leading astronomers have said.

Senior space scientists, including experts from Nasa, will this week attack a controversial decision by the International Astronomical Union, the body responsible for astronomy nomenclature, to redefine what constitutes a planet.

The new definition adopted by the Union saw Pluto demoted to a new kind of celestial underclass now known as "plutoids".

	Too small: Pluto's classification was changed to plutoid by the International Astronomical Union

It had been been known as the furthest planet from the sun since its discovery around 70 years, but saw its status changed because of its small size and remote position in the solar system.

Scientists speaking at a major conference on planets in the Maryland, which starts on Thursday, will call for the icy globe to be reinstated as the ninth planet.

They claim that the revised definitions are confusing and will mean that newly discovered planets in solar systems outside our own can no longer be described as such.

In the current classification, all small and nearly spherical objects orbiting beyond the eighth planet from the sun, Neptune, are now plutoids.

Dr David Morrison, director of the Nasa Lunar Science Institute in California, said: "It has never before been necessary for any organisation to define a word that has been in common every day use so I see no reason why it was necessary on this occasion.

"Astronomers use adjectives such as giant and dwarf to describe different subclasses of objects like planets, stars and galaxies, so why could Pluto not remain as a dwarf planet just as Jupiter is a giant planet.

"Also, around 90 per cent of the planets we know now are outside our solar system, but under the International Astronomical Union’s definition, they cannot be classed as planets."

Scientists speaking at the Great Planet Debate conference will also propose using a simple shape-based mechanism for categorising planets.

Mark Sykes, from the Planetary Science Institute will argue that roundness should be the only category that is applied.

This, he says, will lead to the number of planets in our own solar system increasing to 12.

This has alarmed traditionalists at the International Astronomical Union who fear there will be an ever increasing number of planets in the solar system as more smaller objects are discovered.

Dr Neil deGrasse Tyson, from the American Museum of Natural History, will argue that Pluto does not deserve to be a planet.

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