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'Pluto's changed status no big deal'

Indian astronomers say the demotion is like changing Calcutta to Kolkata and will not affect research in any way.

india Updated: Aug 28, 2006 11:47 IST

Stripping away Pluto's planetary status does not change anything except astronomy textbooks, says astrophysicist Siraj Hasan, who represented India at the International Astronomical Union (IAU) meeting in Prague that took the decision.

But Hasan, director of the Indian Institute of Astrophysics (IIAP), said that while he voted in favour of the change, the manner in which Pluto was dethroned left several astronomers unhappy.

Only around 430 IAU members were present when the resolution on Pluto was put to vote, although some 2,500 had gathered on the opening of the 10-day meeting, he said.

"As voting took place on the last day, many had already left and attendance was poor," Hasan said, adding the group which took part in voting "was not truly representative" of the IAU.

"That something as important as redefinition of planets, on which discussions had been going on for years, was voted by a small number of astronomers was one reason why many were upset," Hasan said. "My own feeling is that the IAU did the right thing and I agree with the resolution."

Under the new ruling, the IAU defines a planet as "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 neighbourhood around its orbit".

Because Pluto does not meet the last criterion (its orbit cuts into that of Neptune), the IAU demoted it to 'dwarf planet' status. The decision leaves the solar system with only eight planets - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Alan Stern, the lead scientist on NASA's robotic New Horizons mission, now on its way to Pluto, and several astronomers of the Johns Hopkins University in the US, were among those who do not approve the new definition.

Johns Hopkins said in a statement that several of its astronomers described the IAU's decision as a "muddled" ruling "that is unlikely to settle ongoing debates over how to define a planet and whether the term should apply to Pluto".

According to BBC News, NASA's Stern slammed Pluto's demotion saying "it is impossible and contrived to put a dividing line between dwarf planets and planets".

Hasan said he found "nothing very profound" in the name change, adding the IAU's ruling was "mainly an attempt to give an objective definition" of a planet.

"Other than rewriting astronomy text books, this is not going to change the way we are looking at Pluto from the point of research," Hasan said.

As S Vishveshwara, former director of the Jawaharlal Nehru Planetarium here pointed out, "It is like changing Calcutta to Kolkata. Nothing more."

Discovered in 1930 by US astronomer Clyde Tombaugh, Pluto's title as planet became controversial especially after the early 1990s when astronomers found several objects comparable to or larger than Pluto in an outer region of the Solar System called the Kuiper Belt. Xena, discovered in 2003, is bigger than Pluto.

"I am sure in the next two or three years we will discover more objects like Xena in the Kuiper belt," said Sujan Sengupta, an astronomer at IIAP who believes Pluto was not born the same way as the other eight planets of the solar system and so cannot claim kinship with them.

"Now that we have a precise definition, we know how to classify the new objects. I am happy that what I have been advocating for years has happened."

Hasan believes the number of planets in the solar system is unlikely to increase beyond the present eight since the new objects to be found will be "trans-Neptunian" objects that would join the class of dwarf planets like Pluto.

"I do not think the new definition of planet will need change unless anything dramatic happens in astronomy research."

First Published: Aug 28, 2006 11:34 IST