I'm not convinced that the new definition excludes Pluto...

Overall, I really like the new definition of Planet, but I'm not at
all convinced that they are properly applying it. Please follow this
logic and tell me where my thinking is messed up.

First, the inner planets are where they are because two Big Bullies
(Jupiter and the Sun) forced them into position between them. They
are where they are because that is where they could survive. They are
TINY compared to the Gas Giants and if Jupiter's orbit changes, so
will the orbits of the innter planets (well, ALL other planets).
Jupter cleared it's orbit, the others simply moved to where they were
told.

Pluto is in a similar position except that it isn't sandwiched between
two big bullies. It is locked in a stable resonance with Neptune with
neither getting in each other's way. From everything I've read,
Pluto's orbit is stable AND there are no other objects that exist in
it's orbital area of influence other than Neptune. For all practical
purposes, it HAS cleared it's orbit and the only reason that orbit
isn't more circular is that there is no planet beyond it to force it
into a circular orbit. There is no reason why Pluto couldn't have
been Earth Sized and existed in this orbit.

Finally, look at the KBO's discovered so far. We haven't found many
of them, but we are assuming that the Kupier Belt will look similar to
the Asteroid Belt. There is no proof of that to date. If we were to
take a snapshot using the current definition and apply it fairly, we'd
have to say that the KBO's meet the definition. We are ASSUMING that
we'll find more objects out there that will make them more similar to
Ceres, but we have no proof. So far as we know, these bodies orbit
in a path an AU wide.

Another problem is what consititues clearing your orbit? Pretend
Saturn is a Star and we are trying to decide of it's moons are planets
by the current defintion. What do we do about the shepherd moons?
Have they cleared their orbits? They have certainly cleared out areas
in the rings. Is that good enough or would they have had to dissipate
the rings?

So the bottom line is that the definition seems to exclude Ceres, but
I'm not convinced that it excludes Pluto and the other KBO's.

And what to do about Charon? The idea of the location of the
Barycenter is intriguing. Do we need a mass differential limit as
well? What if Nix were big enough to meet the other definitions
(round, etc) but were very light. It would still orbit around a
barycenter that was outside of another body, but that would only be
because Pluto and Charon were so closely matched. Its own
contribution to the Barycenter would be negligible.

These are just musings on the definition and I'd like to seem some
considered discussion on the topic.
.

Relevant Pages

  • Re: Observing & Predicting Planetary Orbits (Easy Step-By-Step Instructions)
    ... the naked-eye visible planets in sidereal ... that ancients didn't have other means to see the stars. ... Mercury whose orbit you can see is eccentric. ... I think this is what makes modern astronomers angry at ...
    (sci.astro)
  • New Horizons Update - September 2005
    ... spaceship to Pluto. ... we were taught that our solar system ... contains four rocky planets on the inside, ... Neptune on a retrograde orbit that is the hallmark of gravitational ...
    (sci.space.news)
  • Re: "Pluto Now Called a Plutoid"
    ... If you include moons in consideration the first definition eliminates Earth, Jupiter, Saturn, Uranus, Neptune, Pluto, and Eris. ... The second eliminates every candidate _except_ Eris, and even then Eris may sometimes temporarily lose planethood when other large Kuiper belt objects pass near it. ... In the second definition Pluto and Eris are sometimes planets and sometimes non-planets depending on how the other large Kuiper belt objects are arranged on any given day. ... Ceres itself is also sometimes a planet and sometimes not depending on where it is in its orbit relative to Mercury, Venus, Earth and Mars. ...
    (rec.arts.sf.science)
  • Re: Evolution and Observation Gap
    ... hundred years and changes the orbit of Pluto or steels it away. ... We also know that planets orbit their parent stars. ... of showing that ID is science by talking about SETI. ...
    (talk.origins)
  • Re: planet help
    ... >>> orbit. ... > that if the twin planets are really really close the ... > apart a satellite that is held together only by its self-gravity. ... Phobos and Deimos are small satellites of Mars. ...
    (rec.arts.sf.science)