Will Scientists deep-six Pluto's status as No. 9?
Globe and Mail
The fate of tiny Pluto is hanging in the balance.
Astronomers from around the world are gathering in Prague over the next two weeks to come up with the first official definition of the word planet — and puny Pluto might be considered too small to make the grade.
"We have been living with Pluto as a member of the solar system for 76 years, and school children just love Pluto and we can't take it away from them or they will be broken-hearted," conceded Owen Gingerich, who chaired an International Astronomical Union committee on the matter.
However, last year's discovery in the far fringes of the solar system of an object, nicknamed Xena after the warrior princess from a popular TV show, that is slightly bigger than Pluto has brought the issue to a head.
When Clyde Tombaugh at the Lowell Observatory in Arizona discovered Pluto in 1930, it was touted as being at least as big as Earth.
But by the 1970s, astronomers had figured out that it was much smaller.
It is just 2,270 kilometres in diameter, has just 1/400th the mass of Earth and is substantially smaller than the moon.
Some astronomers have been arguing that Pluto should be stripped of its planetary status. Even so, the IAU, which is responsible for naming planets and other celestial objects, has been reluctant to demote the little world.
If Pluto is big enough to be considered a planet, then the new object Xena should be considered one too, said one of its discoverers, Michael Brown, a professor at the California Institute of Technology in Pasadena.
Others insist that anointing the new find as the 10th planet would be repeating the same mistake made when Pluto was allowed into the planetary club.
What is needed is a clear definition of a planet. So, last year the IAU established a committee of 19 astronomers to do the job. But that cumbersome group became deadlocked. As a result, the organization set up a seven-member subcommittee, which met in Paris at the end of June to sort out the mess.
"We considered a lot of factors and, in the end, we came up with a unanimous recommendation," said Prof. Gingerich, who chaired the subcommittee.
That recommendation will be officially unveiled on Wednesday(Aug. 16) in Prague at a general assembly meeting of the IAU. The astronomers will then debate the proposal and ultimately vote on it. That vote is set for the conference's final day, Aug. 24.
Although Prof. Gingerich is sworn to secrecy about the specific details of the recommendation, he said the committee members are confident they have come up with a suitable compromise.
"We were all very enthusiastic for what we had hammered out because we felt that it was really very defensible scientifically and it also make the proper kind of consideration to the cultural aspects [of Pluto]," he said in a telephone interview from his office at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Still, the existing order of the solar system cannot remain the same for much longer. "I would like to see it admitted that a mistake was made in calling Pluto the ninth planet," says Brian Marsden, an astronomer at the Smithsonian Astrophysical Observatory.
Whatever is decided, it must take into account a continuing gush of astronomical discoveries. New computerized telescopes, which meticulously scan the skies, have identified almost 1,000 bodies in the outer solar system. They range in size from a few kilometres to more than 1,000 kilometres. Many of these icy worlds seem strangely similar to Pluto. (It has even been determined that Pluto has three moons, the largest named Charon.)
Yet when Pluto was first cited in 1930, it didn't seem to fit into the logical order of the solar system, which is make up of four rocky planets (Mercury, Venus, Earth and Mars), followed by four gaseous giants (Jupiter, Saturn, Uranus and Neptune). The ninth planet, diminutive Pluto, seemed alone and oddly out of place.
Now, however, it appears to be part of a distinct region of space crisscrossed with tiny worlds. This emerging swarm is known as the Kuiper Belt and some astronomers believe it may contain up to a million icy bodies. It's possible astronomers will eventually find even more that are larger than Pluto.
Prof. Brown of CalTech, meanwhile, is anxiously waiting to see what happens to his own discovery, Xena, which is clearly bigger than Pluto. It has been given the temporary name of 2003 UB313 as the IAU settles its status.
If 2003 UB313 does gain planetary status, it will be given a proper name likely based on a figure from Greek or Roman mythology.
"What I really hope is that they just make a decision. We have been in limbo for the past year," Prof. Brown said.
He added that the IAU could come up with "perfectly rational reasons for any number of possible solutions." Some astronomers have proposed a new system of ranking the heavenly bodies into groupings of major and minor planets. Others have argued that almost any round body that orbits a star should be deemed a planet.
"The only thing that would really irritate me is a decision of nine planets. That is like saying Pluto is a planet, but anything new we find is not a planet — and that is kind of silly."
