[extropy-chat] SPACE: How many planets?

[Mike Lorrey]

--- Harvey Newstrom <mail at harveynewstrom.com> wrote:
> 
> On Monday, March 22, 2004, at 02:23 pm, Mike Lorrey wrote:
> 
> >
> > --- Brent Neal <brentn at freeshell.org> wrote:
> >>  (3/22/04 5:12) Robert J. Bradbury <bradbury at aeiveos.com> wrote:
> >>
> >>> Space Daily has an interesting article this morning on how
> >>> to settle the is it or isn't it a planet debate (I'll spoil
> >>> the article to some extent by providing a summary -- if it
> >>> has enough gravity to round itself but not enough to start
> >>> nuclear fusion its a planet).
> >>>
> >>
> >> This is new take on the debate I read. I think he leaves out some
> >> interesting physical criteria that could be used in combination
> with
> >> others, but the "roundness" one that he mentions is one I'd not
> seen
> >> before. Of course, when it comes down to it, the final solution
> will
> >> be 'political' in some sense, since the IAU will pick the rules to
> >> create the outcome they find desirable. :)
> >
> > Actually, roundness was the primary criteria I had stated here not
> so
> > long ago...
> 
> I think the orbit plays a bigger role, not only in defining planets
> and 
> planetoids, but also moons which are not usually considered planets.
> 
> Here is my scheme:
> 
> 1.  Planets are in unique orbits as the primary object for that
> orbit.
> 
> 2.  Planetoids or asteroids are in belts with a lot of objects in 
> similar or close orbits.

In my original post, the other criteria I had listed was that the
object was the gravitationally dominant object in its orbital region.

I don't think that point 2, though, is very accurate, though. There are
LOTS of asteroids of significant sizes in orbits resonant with Earth or
that cross Earth's orbit. This doesn't make Earth "not a planet".

I wouldn't say that Sedna and Pluto are in similar or close orbits,
either. Sedna is as far away from Pluto as Pluto is far away from Earth
(and there are a lot of planets between us and Pluto, obviously), and
Sedna is currently near its closest approach to the Sun, its orbit
lasts 10,500 years.

I would suggest holding off making any final decisions about objects in
the Kuiper Belt until we have identified a LOT more of them.

Another issue is orbitally resonant objects. Negating Pluto as a planet
because it is orbitally resonant with Neptune, a much larger object, I
can understand, just as many asteroids and comets are orbitally
resonant with Earth, but Pluto does not, in fact, orbit Neptune as a
moon. The fact that they share an orbit (and even Pluto has its own
moon) does not make Neptune "not a planet".

Sedna does not fall into this category though, and it is the most
significant object we've seen in that region to date. It does, in fact,
fit the bill as the most significant object in its own orbital region,
and it is round.

=====
Mike Lorrey
Chairman, Free Town Land Development
"Live Free or Die, Death is not the Worst of Evils."
                                       - Gen. John Stark
Sado-Mikeyism: http://mikeysoft.zblogger.com

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