Wakboth (& others) wrote:

[tide-locked worlds] would be a poor place to hope to
find a viable biosphere.

I'd have to agree with others that tide-locked worlds don't
represent a critical problem for a biosphere (at the very least, not
over here on rasfs grin). Atmospheric circulation is more than
enough, even with thin atmospheres, to prevent the "freeze out"
problem. The hydrologic cycle might be... interesting.

However what if instead this world was in fact a
moon in orbit of a giant planet within the stars lifezone?

This, too, would seem a likely solution. A possibility is that the
bulk of habitable planets orbit M-class stars - simply due to those
stars being by far the most numerous.

The big problem with life around a red dwarf, however, is that the
habitable zone is very narrow.

True, but aren't the changes in the brightness of red dwarves both
small and very, very slow (even in geological timeframes)?

Yes & no. The migration of the habitable zone outward as the star
slowly brightens is unlikely to be much of a problem, for the very
reasons you mention (the biosphere of these planets would fail due to a
lack of internal heat killing plate tectonics long before the habitable
zone migrates too far outward). A more serious issue is flares - low
mass stars are often rather active in terms of flares and sunspots, so
variability is rather greater than would be convenient.
--
Brian Davis