Re: Pluto's Last Gasp! Was: Re: Orbital dominance


James Nicoll wrote:

The _reporter_ is misinformed or at least probably is, because
any astronomer who cared enough to have an opinion on this would know
that Pluto and Neptune are only related in the negative sense.

Not exactly; there's an orbital resonance.

The third draft defintion is:

A planet is a celestial body that (a) has sufficient mass for
its self-gravity to overcome rigid-body forces so that it assumes a
hydrostatic-equilibrium (nearly round) shape, (b) is the dominant object
in its local population zone, and (c) is in orbit around the Sun.

That is a stupid definition, with a vague term like "dominant
object" and needless heliocentrism, given how many extra-solar worlds
there are but since Pluto and Neptune are never near each other, ever,
they cannot be said to be in each other's "local population zone"
and therefore cannot have any bearing on whether Neptune or Pluto
is a planet. Pluto's problem is the increasingly large population
of big Trans-Neptunian Objects like 2003 EL61 and 2003 UB313.

Why are TNOs a problem for Pluto, but not Neptune? They are a long way
away from both, after all. Santa is around 45 AU out on average, and
Xena usually farther. If they are in Pluto's zone because of how close
they get to the Sun at perihelion, why not also in Neptune's, as
Neptune is 30 AU out. What the hell does this stuff mean?

Apparently they are still trying to figure out what the hell "dominant
object" means:

http://www.chron.com/disp/story.mpl/ap/world/4136088.html

"Though the precise wording of the definition remained a work in
progress Wednesday, if astronomers agree that a planet must have
'orbital dominance' in its own neighborhood, the new guidelines would
eliminate Pluto and the trio of tentative candidates as proper
planets."

This sounds suspiciously like nonsense to me. Planets, after all, are
not even guaranteed not to collide. I understand you can't expect
mathematical definitions, but it's got to be better than this. And what
do they do if they find a relatively large body out there, by the way?

.

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