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Astronomers say Pluto is not a planet
PRAGUE, Czech Republic - Leading astronomers
declared Thursday that Pluto is no longer a
planet under historic new guidelines that
downsize the solar system from nine planets to
eight. After a tumultuous week of
clashing over the essence of the cosmos, the
International Astronomical Union stripped Pluto
of the planetary status it has held since its
discovery in 1930.
By WILLIAM J. KOLE,
Associated Press
Writer
Thu Aug 24, 12:20 PM
ET
PRAGUE, Czech Republic -
Leading astronomers
declared Thursday that
Pluto is no longer a
planet under historic
new guidelines that
downsize the solar
system from nine planets
to eight.
After a tumultuous week
of clashing over the
essence of the cosmos,
the International
Astronomical Union
stripped Pluto of the
planetary status it has
held since its discovery
in 1930. The new
definition of what is —
and isn't — a planet
fills a centuries-old
black hole for
scientists who have
labored since Copernicus
without one.
Although astronomers
applauded after the
vote, Jocelyn Bell
Burnell — a specialist
in neutron stars from
Northern Ireland who
oversaw the proceedings
— urged those who might
be "quite disappointed"
to look on the bright
side.
"It could be argued that
we are creating an
umbrella called 'planet'
under which the dwarf
planets exist," she
said, drawing laughter
by waving a stuffed
Pluto of Walt Disney
fame beneath a real
umbrella.
"Many more Plutos wait
to be discovered," added
Richard Binzel, a
professor of planetary
science at the
Massachusetts Institute
of Technology.
The decision by the
prestigious
international group
spells out the basic
tests that celestial
objects will have to
meet before they can be
considered for admission
to the elite cosmic
club.
For now, membership will
be restricted to the
eight "classical"
planets in the solar
system: Mercury, Venus,
Earth, Mars, Jupiter,
Saturn, Uranus and
Neptune.
Much-maligned Pluto
doesn't make the grade
under the new rules for
a planet: "a celestial
body that is in orbit
around the sun, has
sufficient mass for its
self-gravity to overcome
rigid body forces so
that it assumes a ...
nearly round shape, and
has cleared the
neighborhood around its
orbit."
Pluto is automatically
disqualified because its
oblong orbit overlaps
with Neptune's.
Instead, it will be
reclassified in a new
category of "dwarf
planets," similar to
what long have been
termed "minor planets."
The definition also lays
out a third class of
lesser objects that
orbit the sun — "small
solar system bodies," a
term that will apply to
numerous asteroids,
comets and other natural
satellites.
Experts said there could
be dozens of dwarf
planets catalogued
across the solar system
in the next few years.
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"Creativity is allowing yourself
to make mistakes. Art is
knowing which ones to
keep."
-- Scott
Adams, creator of the
Dilbert comic strip
NASA
said that
Pluto's demotion would
not affect its US$700
million New Horizons
spacecraft mission,
which earlier this year
began a 9 1/2-year
journey to the oddball
object to unearth more
of its secrets.
"We will continue
pursuing exploration of
the most scientifically
interesting objects in
the solar system,
regardless of how they
are categorized," Paul
Hertz, chief scientist
for the science mission
directorate, said in a
statement.
The decision on Pluto at
a conference of 2,500
astronomers from 75
countries was a dramatic
shift from just a week
ago, when the group's
leaders floated a
proposal that would have
reaffirmed Pluto's
planetary status and
made planets of its
largest moon and two
other objects.
That plan proved highly
unpopular, splitting
astronomers into
factions and triggering
days of sometimes
combative debate that
led to Pluto's undoing.
In the end, only about
300 astronomers cast
ballots.
Now, two of the objects
that at one point were
cruising toward possible
full-fledged planethood
will join Pluto as
dwarfs: the asteroid
Ceres, which was a
planet in the 1800s
before it got demoted,
and 2003 UB313, an icy
object slightly larger
than Pluto whose
discoverer, Michael
Brown of the California
Institute of Technology,
has nicknamed Xena.
Charon, the largest of
Pluto's three moons, is
no longer under
consideration for any
special designation.
Brown, who watched the
proceedings from Cal
Tech, took Thursday's
vote in stride — even
though his discovery
won't be christened a
planet.
"UB313 is the largest
dwarf planet. That's
kind of cool," he said.
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AP
Science Writer Alicia
Chang in Los Angeles
contributed to this
story.
___
On
the Net:
International
Astronomical Union,
http://www.iau.org
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