Gene P. wrote:
The Earth has a large moon to skim it's upper exosphere aggressively.
=A0
The Moon's "exophere" is completely disrupted by the Earth. =A0
Hmm. Seeing as how the exosphere for the Earth is around 500 km, I
suspect the Moon is doing absolutely nothing with respect to
atmospheric escape from the Earth-moon system. After all, if a molecule
or atom leaves the exobasse at escape velocity, it... leaves. The Moon
will not gravitationally confine it to the system, and it's chances of
hitting any molecule leaving the exobase is about 1 in 200,000.
The remarkable thing is that any of the gas giant moons
have an atmosphere at all!
Why? They are shielding from solar wind stripping by large external
magnetic fields, are very cold so thermalJeans escape mechanism are
low, and as you point out, at least for very thin atmospheres, the
presence of a gas torus slows loss.
I firmly believe that Earth is going to turn out to be a fluke...
Fair enough. I'm waiting for evidence. The best argument I've seen
to that effect is the "Earth's obliquity is stabilized by our large
Moon", which is true. But it's only destabilizede in the first place by
Jupiter. If Jupiter had a lower mass, or a different location in the
solar system, then the obliquity of the Earth without the Moon would be
stable. Lasker's paper on this topic is fairly clear (OK, that's not
true; but I think the above is fairly clearly stated).
--=20
Brian Davis
|