[extropy-chat] Re: SPACE: new planet?
mlorrey at yahoo.com
Sat Feb 21 05:45:31 UTC 2004
--- Technotranscendence <neptune at superlink.net> wrote:
> On Friday, February 20, 2004 9:21 PM Mike Lorrey mlorrey at yahoo.com
> >> Mike Lorrey wrote:
> >> >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.
> 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.
I would say that Earth is a planet in a unique situation which likely
is the primary reason it is the only planet with significant and easily
detectable ecosystems: it was grazed by a planetesimal that never
either bonded to Earth or escaped its grasp, allowing a significant
amount of its primordial lithosphere to be peeled off, eventually
accreting around that planetesimal, the moon. That moon has also had a
continuing influence in being the root cause of the geomagnetic dynamo
that generates Earth's large magnetic field and shielding radiation
Pluto may exhibit similar but less significant effects, but certainly
not much different than we will likely find on Europa and Ganymede,
which are tidally influenced by Jupiter.
All of this, however, is irresepective of the planetary status of Earth
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
"Live Free or Die, Death is not the Worst of Evils."
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- Mike Lorrey
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