[extropy-chat] Re: SPACE: new planet?
neptune at superlink.net
Sat Feb 21 14:56:46 UTC 2004
On Saturday, February 21, 2004 12:45 AM Mike Lorrey mlorrey at yahoo.com
>> >> >It is actually rather easy to define a planet:
>> >> >a) it has its own independent orbit around the sun, and,
>> >> >b) its own internal gravity has caused it to be round
>> >> What is "round"?
>> > Spherical
>> No planet seems perfectly spherical/round,
>> but would you then say Ceres is a planet?
>> IIRC, it looks round.
> Minor distortions due to centor of mass/center of angular momentum
> imbalances, as well as tidal influences, are irrelevant.
You misunderstand. I wasn't disagreeing with you. I thought you meant
round within limits. Obviously, the Earth is round when compared to
But what about Ceres? Planet or no? It looks round to me. Let me take
a look again. Yep. Well, it's close enough that you wouldn't notice
from this distance.
> > Also, can it be said that the Earth has an independent orbit since
> > the Moon impacts its orbit so much? Certainly, Luna impacts Earth's
> > orbit much more than any other IAU defined planet's moon(s)
> > save for Pluto.
> > While I'd still call Earth a planet - and Pluto too:) - I see them
> > - Earth-Luna and Pluto-Charon - as special cases.
> The distortion of Earth's orbit does not exceed the boundaries even of
> the earth's core. The center of angular momentum is only a few meters
> from the center of the earth, or so I've heard. The primary influence
> of both Earth's and Pluto's moons are tectonic rather than orbital.
See my other post on this. The barycenters of both planets are far
enough from their centers to be noticed. This is not the case with,
> All of this, however, is irresepective of the planetary status of
> or Pluto. They are the overwhelmingly major bodies in their orbit, in
> size and mass, they are spherical to such a degree that naked eye
> observation could not ascertain and significant deviation. They are
> therefore planets.
Pluto is too far away for naked eye observations to notice a deviation.
However, if you're going to use the naked eye as the arbiter here, then
you're either amending or even disposing of your definition. It all
seems rather arbitrary, but, as I've mentioned before, the lines are
quite fuzzy here. I'm prepared to stick with convention and call Pluto
and Earth planets, Charon and Luna moons, Ceres an asteroid, etc. but
only for convenience and I'm prepared to alter such distinctions when
they become inconvenient.
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