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Re: CONCULTURE: dual planets

From:Andreas Johansson <andjo@...>
Date:Thursday, November 18, 2004, 18:50
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