"Gene Partlow" wrote in message
om...
"Mike Dworetsky" wrote in message
news:
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),
Yes...the Van Allen Belt problem. I was ignoring this just to focus on
the
possible monthly climate changes. While I know about as much about
chaos theory as Curly, I yet wonder if something like the much abused
butterfly effect might still apply due to the 'cumulative' effects of
countless
small lunar-cycle related weather perturbations...generating something
out of proportion to the tiny individual excursions away from 'perfect'
ellipticity. ?? Very hard to say.

(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.

Yes, these are good points and would seem to be necessary. A further
qualm is the Jovian itself. Jovians seem to act as system-clearers acting

on the inevitable comets and occasional asteroids. This role, due to
their
huge g-fields, might put the kibosh on stable biosphere evolution since
our earth-size-moon might experience many more catastrophic collisions
than did the earth itself as these objects are deflected briefly toward
the
Jovian primary.


The existence of asteroid belts, Kuiper Belts and Oort clouds is not
inevitable in all systems, though probably likely. The craters on Callisto
are mostly very ancient, so maybe a biosphere can exist after a few billion
years. Every once in a while there may be an "evolution's helper" event.

--
Mike Dworetsky
(remove "pants" spamblock to send email)