Re: CONCULTURE: dual planets

Quoting Roger Mills <rfmilly@...>:

> Barry Garcia wrote:
>
> > This was never answered with my post about the discovery of a world
> > where the sentient life is extinct. So...
> >
> > How big would a moon orbiting an earth sized (or slightly bigger)
> > planet have to be to have a visible atmosphere? Would a moon that size
> > cause problems?
> >
> Good question. In Le Guin's "The Dispossessed" there is just such a system--
> the secondary moon/companion planet is habitable (though it's a difficult
> environment), and it's where a large group of political dissidents from the
> main planet set up their communal society.  But the novel is far more
> concerned with politics and personalities, so the technical details get
> short shrift.
>
> IIRC some of the moons of Jupiter and/or Saturn apparently have atmospheres,
> so it's not impossible.
Well, only Titan has got a worthwhile one - the others are extremely tenuous.

It's worth noting that Titan's greater distance from the Sun gives it an easier
time retaining an atmosphere than a similar-mass object at the Earth's distance
would have. OTOH, something at the Earth's distance with Titan's radius would
probably have a greater mass, which would to some degree compensate.

                                                    Andreas