[meteorite-list] Astronomers Lean Toward Eight Planets

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 22 16:29:48 2006
Message-ID: <200608222027.NAA23140_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn9818-astronomers-lean-towards-eight-planets.html

Astronomers lean toward eight planets
Stephen Battersby, Prague
New Scientist
22 August 2006

Finally, astronomers could be homing in on a definition of the word
planet. After a day of public bickering in Prague, followed by
negotiation behind closed doors, the latest draft resolution was greeted
with a broadly friendly reception.

If accepted on Thursday, it would be bad news for Pluto, which would no
longer be a full-fledged planet.

The crucial change in "draft c" is that a planet must be the dominant
body in its orbital zone, clearing out any little neighbours. Pluto does
not qualify because its orbit crosses that of the vastly larger Neptune.

The planet definition committee is also stepping back from trying to
define all planets in the universe, and sticking to our solar system - a
slightly easier task.

It is still a work in progress, however, and the wording will change by
Thursday in part to simplify it and make the final result more palatable
to the public.

Least unpopular

Terminology is still controversial. Objects that do not quite qualify as
planets - because they are big enough to be round but not big enough to
dominate their neighbourhoods - might become "dwarf-planets" or planetoids.

These would include Pluto and Ceres, the largest asteroid. And the small
fry of the solar system, such as asteroids, might be called small solar
system bodies, or retain their current designation as minor planets.

But a supplementary resolution would at least make Pluto the prototype
of a class of icy outer worlds beyond Neptune. "The purpose of this is
to give a nod to those people who are great Pluto fans," said Owen
Gingerich of Harvard University in Massachusetts, US, who is chairman of
the committee.

It is not clear what they would be called, however - most early
suggestions were rejected by an informal show of hands. Pluton, plutoid,
plutonoid and plutid seem to be out of the running, as are "Tombaugh
object" and "Tombaugh planet", which had been proposed in honour of
Pluto's discoverer, Clyde Tombaugh. "Plutonian object" was the least
unpopular choice.

Multiple drafts

The planet definition committee's first draft definition, released last
Wednesday, had admitted Pluto, Ceres and probably dozens more objects to
planethood by virtue of being round objects orbiting the Sun (see Planet
debate: Proposed new definitions
<http://www.newscientistspace.com/article/dn9762>).

Then another group of astronomers, many of whom study the dynamics of
the solar system, responded on Friday by insisting that a planet must
dominate its neighbourhood, which would admit only the eight fully
formed planets (see Pluto may yet lose planet status
<http://www.newscientistspace.com/article/dn9797-pluto-may-yet-lose-planet-status.html>).

At a fractious lunchtime meeting on Tuesday, the committee's first
attempt at a compromise met a hostile response. "They have presented
practically the same resolution as before," said Julio Fernandez of the
University of the Republic in Montevideo, Uruguay, lead author of
Friday's proposal.

Secret negotiations

He was cut off when he tried to read his proposal aloud. When more
questions were prevented, there was a cry of: "If there is democracy,
listen to the questions. Let the people speak!"

Now, although all is not quite sweetness and light, the main sticking
point may have been removed, and there is now hope for a positive result
at Thursday's vote.

Andrea Milani of the University of Pisa in Italy had fiercely opposed
the planet definition committee at the first meeting on Tuesday. But
after participating in the secret negotiations that afternoon, he told
New Scientist: "I'm very satisfied."
Received on Tue 22 Aug 2006 04:27:03 PM PDT