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| January
28, 2001 |
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Space
Center Puts Pluto's Planethood In Doubt
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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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