Darren Williams and
Jim Kasting -- remember him? -- at Penn State
have studied the possibility of
habitable moons around extrasolar
giant planets.
They found, not too surprisingly, that
if you had a planet with the habitable
and it had a moon orbiting it, that the
moon would also be within the habitable
zone.
They also found that such moons, in order
to truly be habitable in more than just
the sense of having their temperatures be
appropriate for liquid water would
also need to
be sufficiently massive to
hold in a thick atmosphere and retain any
water
and also
possess a strong magnetic field to keep
harmful radiation off of the surface
of the moon.
How does this compare to what we know about
moons of giant planets in our Solar System?