A petition already signed by more than 300 professional researchers is attacking the International Astronomical Union (IAU) decision to expel Pluto from the Solar System's A-list and doom it to the status of "dwarf planet".

"We as planetary scientists and astronomers do not agree with the IAU's definition of a planet, nor will we use it. A better definition is needed," says the protest, placed on the Web.

The petition organiser, Mark Sykes, who is director of the Planetary Science Institute in Tucson, Arizona, said the IAU definition of a planet "does not meet fundamental scientific standards and should be set aside."

"A more open process, involving a broader cross-section of the community engaged in planetary studies of our own Solar System and others should be undertaken," Sykes said.

The British magazine New Scientist said on its website Friday that the rebels intend to stage a conference next year to fix the definition of a planet. As many as 1,000 astronomers will attend, they hope.

A co-sponsor of the petition is Alan Stern, executive director of the Center for Space Exploration Policy Research at the US Southwest Research Institute.

Stern heads NASA's New Horizons mission to Pluto. Its spacecraft -- which also bears some of the ashes of US astronomer Clyde Tombaugh, who discovered Pluto in 1930 -- blasted off in January this year, months before the IAU decision that relegated Pluto's status.

Stern said "only about 428" of the IAU's nearly 10,000 members were involved in the IAU vote in Prague on August 24 that condemned Pluto as a planetary midget.

That tally is barely more than the number of people who signed the protest petition within the first five days of its being launched, he said.

In that landmark general assembly, the IAU declared the Solar System now comprised eight planets: Mercury, Earth, Venus, Mars, Jupiter, Saturn, Uranus and Neptune.

Pluto's status had long been contested by astronomers who said its tiny size, eccentric orbit and orbital plane precluded it from joining the other acknowledged planets.

The IAU assigned Pluto and other large objects to a new category -- "dwarf planet."

By the new IAU yardstick, a planet has "cleared the neighbourhood around its orbit" -- in other words, it is massive enough to wield a gravity that clears rocks and other debris on its orbital path.

Two other objects, 2003 UB313 and the large asteroid Ceres, are already included in the "dwarf" definition. But they could be joined by many large objects believed to be circulating, like 2003 UB313, in the Kuiper Belt which is in Pluto's general vicinity.

The pro-Pluto group says no planet ever fully clears its orbit.

Earth has been catastrophically struck several times in its history by large space rocks and in 1994 even Jupiter, the biggest planet of the Solar System, was wacked by parts of a disintegrating comet, they note.

The planetary club, instead of being reduced to eight, should be enlarged to other planetary-sized objects, they say, an argument that others contest as unwieldy and confusing for the general public.

Named after the god of the underworld in classical mythology, Pluto orbits the Sun at an average distance of 5,906,380,000 kilometers (3,670,050,000 miles), taking 247.9 Earth years to complete a single circuit.

But its orbital plane is a whole 17 degrees off the horizontal plane taken by the eight other planets. In addition, its path around the Sun is so egg-shaped that, for 20 years of its agonisingly long orbit, Pluto tracks inside the orbit of Neptune.

The IAU is, among many other things, the official guardian of the names of celestial objects.

Its next assembly is in 2009, which means a long battle could be in the offing among astronomers, whose quiet and bookish exterior can mask steely resolve when it comes to disputes.

Scientific reputations, history, the teaching of our Solar System and the definition of planets that orbit other stars -- all are at stake in the Pluto debate.

"The only thing missing when (the IAU) announced the decision at their press conference was the 'Mission Accomplished' banner," said University of Colorado researcher Jeffrey Bennett.

"Yes, Im afraid this matter is about as settled as the Iraq war in 2003."

Related Links
Save Our Pluto Petition
Lost Among A Million Outer Planets

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