Derby Trail Forums - Pluto no longer a planet

... in the eyes of International Astronomical Union which voted to demote of its planet status.

By WILLIAM J. KOLE
Associated Press Writer
PRAGUE, Czech Republic (AP) -- 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.
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.
It was unclear how Pluto's demotion might affect the mission of
NASA's New Horizons spacecraft, which earlier this year began a
91/2-year journey to the oddball object to unearth more of its
secrets.
The decision 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.
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.