Astronomers sent into orbit by claim Pluto's not a planet

NEW YORK -- One of the nation's leading science museums has quietly shaken up the universe by suggesting that Pluto is not necessarily a planet at all but just a lump of ice.

The startling suggestion comes from scientists at the Rose Center for Earth and Space, which opened last year at the American Museum of Natural History in New York.

There is a 9-foot-diameter model of Jupiter hanging from the ceiling at the center. There is Saturn with its rings, Mercury, Venus, Earth, Mars, Neptune and Uranus. But what about Pluto, long considered the ninth planet in the solar system?

A solar system display says: "Beyond the outer planets is the Kuiper Belt of comets, a disk of small, icy worlds including Pluto."

"There is no scientific insight to be gained by counting planets," said Neil de Grasse Tyson, director of the Hayden Planetarium, the centerpiece of the Rose Center.

"Eight or nine, the numbers don't matter."

Many astronomers say the museum, the first prominent institution to take this position, has overstepped its bounds.

"Tyson is so far off base with Pluto, it's like he's in a different universe," said David Levy, author of "Clyde Tombaugh, Discoverer of Planet Pluto," about the Kansas farm boy who first spotted Pluto. "The majority of astronomers have said that unless there is definitive evidence to the contrary, Pluto stays a major planet."

The International Astronomical Union calls Pluto one of nine planets in the solar system, and a 1999 proposal to list Pluto as both a planet and a member of the Kuiper Belt was abandoned after it drew strong opposition from astronomers. Pluto has always been a little different: Its composition is like a comet's, and its elliptical orbit is tilted 17 degrees from the orbits of the other planets.

When Pluto was discovered in 1930, it was thought to be about the same size as Earth, but astronomers have now learned that it is only 1,413 miles wide -- smaller than the Earth's moon.

Then, in 1992, astronomers discovered the first Kuiper Belt object, and since then have found hundreds of chunks of rock and ice beyond Neptune, including about 70 that share orbits similar to Pluto's.

The Rose Center said there is no universal definition of a planet and instead divides the solar system into the sun and five families of objects.

There are terrestrial planets, or small, dense rocky objects like Mercury, Venus, Earth and Mars; an asteroid belt consisting of craggy chunks of rock and iron between Mars and Jupiter; the gas giants, which are Jupiter, Saturn, Uranus and Neptune; and two reservoirs of comets, the Oort Cloud and the Kuiper Belt. And Pluto?

"It's in the Kuiper Belt," Tyson said. "What's it made of? It's mostly ice."

On the Net:

Museum: www.amnh.org

Astronomical union: www.iau.org

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