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AP) - The universe really is expanding -
astronomers are proposing to rewrite the textbooks to say that our
solar system has 12 planets rather than the nine memorized by
generations of schoolchildren.

      Much-maligned Pluto would remain a planet - and its largest moon
plus two other heavenly bodies would join Earth's neighborhood -
under a draft resolution to be formally presented Wednesday to the
International Astronomical Union, the arbiter of what is and isn't
a planet.

      "Yes, Virginia, Pluto is a planet," quipped Richard Binzel, a
professor of planetary science at the Massachusetts Institute of
Technology.

      The proposal could change, however: Binzel and the other nearly
2,500 astronomers from 75 nations meeting in Prague to hammer out a
universal definition of a planet will hold two brainstorming
sessions before they vote on the resolution next week. But the
draft comes from the IAU's executive committee, which only submits
recommendations likely to get two-thirds approval from the group.

      Besides reaffirming the status of puny Pluto - whose detractors
insist it shouldn't be a planet at all - the new lineup would
include 2003 UB313, the farthest-known object in the solar system
and nicknamed Xena; Pluto's largest moon, Charon; and the asteroid
Ceres, which was a planet in the 1800s before it got demoted.

      The panel also proposed a new category of planets called
"plutons," referring to Pluto-like objects that reside in the
Kuiper Belt, a mysterious, disc-shaped zone beyond Neptune
containing thousands of comets and planetary objects. Pluto itself
and two of the potential newcomers - Charon and 2003 UB313 - would
be plutons.

      Astronomers also were being asked to get rid of the term "minor
planets," which long has been used to collectively describe
asteroids, comets and other non-planetary objects. Instead, those
would become collectively known as "small solar system bodies."

      If the resolution is approved, the 12 planets in our solar
system listed in order of their proximity to the sun would be
Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus,
Neptune, Pluto, Charon, and the provisionally named 2003 UB313. Its
discoverer, Michael Brown of the California Institute of
Technology, nicknamed it Xena after the warrior princess of TV
fame, but it likely would be rechristened something else later, the
panel said.

      The galactic shift would force publishers to update
encyclopedias and school textbooks, and elementary school teachers
to rejigger the planet mobiles hanging from classroom ceilings. Far
outside the realm of science, astrologers accustomed to making
predictions based on the classic nine might have to tweak their
formulas.

      Even if the list of planets is officially lengthened when
astronomers vote on Aug. 24, it's not likely to stay that way for
long: The IAU has a "watchlist" of at least a dozen other
potential candidates that could become planets once more is known
about their sizes and orbits.

      "The solar system is a middle-aged star, and like all
middle-aged things, its waistline is expanding," said Jack
Horkheimer, director of the Miami Space Transit Planetarium in the
United States and host of Public Broadcasting's Stargazer
television show.

      Opponents of Pluto, which was named a planet in 1930, still
might spoil for a fight. Earth's moon is larger; so is 2003 UB313
(Xena), about 70 miles wider.

      But the IAU said Pluto meets its proposed new definition of a
planet: any round object larger than 800 kilometers (nearly 500
miles) in diameter that orbits the sun and has a mass roughly
one-12,000th that of Earth. Moons and asteroids will make the grade
if they meet those basic tests.

      Roundness is key, experts said, because it indicates an object
has enough self-gravity to pull itself into a spherical shape. Yet
Earth's moon wouldn't qualify because the two bodies' common center
of gravity lies below the surface of the Earth.

      "People were probably wondering: If they take away Pluto, is
Rhode Island next?" Binzel quipped. "There are as many opinions
about Pluto as there are astronomers. But Pluto has gravity on its
side. By the physics of our proposed definition, Pluto makes it by
a long shot."

      IAU President Ronald D. Ekers said the draft definition, two
years in the making, was an attempt to reach a cosmic consensus and
end decades of quarreling. "We don't want an American version, a
European version and a Japanese version" of what constitutes a
planet, he said.

      Neil deGrasse Tyson, director of the Hayden Planetarium at New
York's American Museum of Natural History - miscast as a
"Pluto-hater," he contends, merely because Pluto was excluded
from a solar system exhibit - said the new guidelines would clear
up the fuzzier aspects of the Milky Way.

      "For the first time since ancient Greece, we have an
unambiguous definition," he said. "Now, when an object is debated
as a possible planet, the answer can be swift and clear."
      

Gallery

The universe really is expanding -
astronomers are proposing to rewrite the textbooks to say that our
solar system has 12 planets rather than the nine memorized by
generations of schoolchildren.

Solar system may grow to 12 planets

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