"Gene Partlow" wrote in message
om...
Andrew Yee's Oct. 9th post on the Eddington Probe (could detect moons
of extrasolar planets) got me wondering...

What would be the chances of a rich earthlike biosphere evolving on an
earth-mass moon of an extrasolar jovian planet in orbit -within- the so-
called "habitable zone" of its star? This is obviously a difficult
question
involving huge numbers of factors, but the first factor occurring to me as
I read that post was...what would the climate or seasons be like, since
that 'earth'-moon would have not only seasonal variations through the
year (depending on orbital eccentricity etc., axial tilt etc.), but some
variations due to its monthly changes in distance from its home star
due to its lunar orbit about the jovian.

Hmm..now that I think about it, such changes might not add up to much
since they would generally only be a tiny fraction of the planet's average
distance from its star.


You are right, the latter would be an insignificant effect for a habitable
jovian moon orbiting a planet in the habitable zone.

The moon would also have to be (a) large enough to retain a significant
atmosphere (i.e., a lot larger than Mars but maybe not requiring to be as
large as Earth), (b) far enough from the primary not to be badly affected by
magnetic fields of the primary (in the case of Jupiter this could be a
problem unless the atmosphere is protective), (c) not affected by internal
tidal heating effects such as those that cause Io to be volcanic. The last
of these could be avoided if the large moon is the only large natural
satellite and has a circular orbit, or is orbiting a long way out, like
Callisto. Maybe one would want just enough internal tidal heating to
generate volcanic activity leading to outgassing of CO2, SO2, S2, NO2, NO,
and H2O, so that a breathable atmosphere could eventually evolve.

--
Mike Dworetsky

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