[meteorite-list] Details Emerge on Plan to Demote Pluto

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Aug 21 13:13:44 2006
Message-ID: <200608211710.KAA20999_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/060819_new_proposal.html

Details Emerge on Plan to Demote Pluto
By Robert Roy Britt
space.com
19 August 2006

This was a wild week for astronomers. At a meeting of the International
Astronomical Union (IAU) in Prague, a proposal put forth to
define the term "planet" would boost the tally from nine to 12 by adding
asteroid Ceres, Pluto's moon Charon, and a distant icy object to the list.

Many astronomers criticized the proposal as being vague and setting
arbitrary cutoff points. One researcher pointed out that with the
definition, Earth's Moon might eventually become a planet when it
drifts farther away.

So a second proposal was put forth that would demote Pluto to a
non-planet status, as first reported yesterday by SPACE.com.

The next step is for the IAU Executive Committee to decide whether to
stick with the original proposal, to modify it, or to go with the new
proposal. A vote is slated for Thursday, Aug. 24.

Meanwhile, one of the adherents to the new proposal provided a copy to
SPACE.com. Here it is:

New proposal for Resolution 5: Definition of a Planet

(1) A planet is a celestial body that (a) is by far the largest object
in its local population[1], (b) has sufficient mass for its self-gravity
to overcome rigid body forces so that it assumes a hydrostatic
equilibrium (nearly round) shape [2], (c) does not produce energy by any
nuclear fusion mechanism [3].

(2) According to point (1) the eight classical planets discovered before
1900, which move in nearly circular orbits close to the ecliptic plane
are the only planets of our Solar System. All the other objects in orbit
around the Sun are smaller than Mercury. We recognize that there are
objects that fulfill the criteria (b) and (c) but not criterion (a).
Those objects are defined as "dwarf" planets. Ceres as well as Pluto and
several other large Trans-Neptunian objects belong to this category. In
contrast to the planets, these objects typically have highly inclined
orbits and/or large eccentricities.

(3) All the other natural objects orbiting the Sun that do not fulfill
any of the previous criteria shall be referred to collectively as "Small
Solar System Bodies".[4]

------------------------------------------------------------------------

[1] The local population is the collection of objects that cross or
close approach the orbit of the body in consideration.
Received on Mon 21 Aug 2006 01:10:57 PM PDT