Re: Planet Definition revised


Mike Rhino wrote:
"steve" <stephen.colbourne@xxxxxxxxxxxxxxx> wrote in message
news:1156318353.296230.103970@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
See:-

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

The requirement that an orbit not be goofy strikes me as arbitrary. Another
solar system is bound to have an Earth-like object in a goofy orbit. Are we
going to declare that it isn't a planet?

There are planets and moons. The Neptune Pluto pair is called what? If two
large objects cross orbits, the larger one is a planet and the smaller one
is what?

Asteriod, comet, Centuar and now Trans Neptuian Object (TNO), yet to be
named.
The point is the a TNO is new but the notion of smaller bodies crossing
larger bodies' orbits is not new.

The division between moons and planets strikes me as arbitrary.

No, a moon orbits a planet while a planet orbits a star. Other objects
can orbit a star as well, such as comets, asteriods and Centaurs (look
up Chiron).

There
should be word that encompasses both large moons and small planets. We
could look at atmosphere as a dividing characteristic. Objects large enough
to have atmospheres could be called planets. Distance from the sun affects
that (Mercury), so we could pick a size that sometimes has an atmosphere.

Now you're being arbitrary. Just because Titan has an atmosphere and
Mecury doesn't, doesn't make one more of one thing than another. Titan
orbits Saturn and Mercury orbits the sun, therefore the former is a
moon and the latter is a planet.


How close was the vote? Can the status of Pluto be changed every two years?

I doubt it will be as its new classification makes sense in lieu of the
recent discoveries of other objects like it. Sedna and Xena (probably
will be renamed), which is larger than Pluto, have forced the issue of
whether Pluto is in fact a planet. If you leave Pluto a planet then
what of Xena? Sedna? Where does it end with these Trans Neputian
Objects? We went through this with the asteroids. People should read
and understand what happened with that.

No one can ever take back the fact that for 70 years Pluto was in fact
a Planet. Then some of its cousins were found. The rest is history.

Eric

.

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