[meteorite-list] 'New Planet' Forces Rethink of Planet Definition
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:51 2004
'New planet' forces rethink
By Helen Briggs
March 17, 2004
Astronomers are to rethink the system for classifying planets following the
discovery of what some claim is the 10th in the Solar System.
A working group of the International Astronomy Union (IAU) will consider
whether objects such as Sedna should be classed as planets.
The IAU says the group will consider the definition of a minimum size for a
But in the meantime Sedna will not be considered one.
The outcome could lead to a demotion for Pluto, which some astronomers argue is
too small to be called a planet.
"If we were starting anew, undoubtedly Pluto wouldn't be labelled a planet,"
Professor Iwan Williams, of the IAU, told BBC News Online.
"But we have almost a 100 years of culture that says Pluto's a planet. So the
IAU will set up a working group to try to ponder the imponderable."
Sedna, named unofficially after the Inuit goddess of the sea, is the latest
in a string of icy objects approaching the size of Pluto discovered in the
outer reaches of the Solar System.
Sedna is believed to be about three-quarters of the size of Pluto, based on
measurements of light reflected from its surface detected by telescopes on
Many astronomers, including Mike Brown of the California Institute of
Technology, who led the team that discovered Sedna, admit it is not a true
planet, preferring to describe it as a planetoid - somewhere between a planet
and an asteroid.
But like other objects found in recent months that inhabit the band of
cosmic debris beyond the Inner Solar System, the Kuiper Belt, it is much
bigger than a typical asteroid.
Some believe it is only a matter of time before another such body is found
which dwarfs Pluto.
Reclassifying Pluto is one way to solve the dilemma. When it was discovered
in 1930 it was thought to be much bigger - and thus more planet-like - than
it really is.
However, the astronomical community will not take kindly to the idea of
downgrading Pluto's status. The last time it was suggested, in 1999, it
caused an uproar.
Received on Wed 17 Mar 2004 12:45:49 PM PST