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By Katherine Roth - The Associated Press
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 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,''
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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