NEW YORK (AP)
-- 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 smallish 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 no Pluto, even though it
has long been 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,"
says 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," says 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 who did not want to diminish
Pluto's status.
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 says 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 says. "What's it made of? It's
mostly ice."
Tyson says there is a precedent to demoting planets: Ceres was
called a planet in 1801 and later demoted. Critics counter that
Ceres, which is only 580 miles wide, was only considered a planet
for a year, while Pluto has been a major planet for more than
70 years. In addition, they say, there was consensus among astronomers
in the case of Ceres.
Still, others praise the museum for its bold move.
"People just don't like the idea that you can change the number
of planets," says David Jewit, a professor at the University of
Hawaii who co-discovered the first Kuiper Belt object. "The Rose
Center is just slightly ahead of its time."
Jane Levenson, an "explainer" at the Rose center, says visitors
-- mostly kids -- sometimes ask about the missing Pluto.
"We just explain that there are five types of objects that circle
the sun," she says. "We don't make a big deal about Pluto."
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