Re: Mars vs Titan

gswork_at_mailcity.com
Date: 03/14/05 

Date: 14 Mar 2005 02:23:54 -0800

Eric wrote:
> Is it known why Mars has such a thin atmosphere and yet Titan has a
very
> thick one? I used to think it had to do with size but apparently that
> is not a big factor. Maybe these are still unanswered?

in detail they are unanswered, but some well developed ideas apply.

Generally, whether an atmosphere stays on a body is a function of 1)
what constitutes the atmosphere, 2) the velocity needed to escape the
planet's gravity and 3) the speed at which the gas molecules are
travelling.

the last one is important because it's affected by temperature - the
hotter the faster. the actual mechanics of it can be simulated using
mathematical modelling but in practice we can say that hot light gases
escape quickly.

Mars may require about twice the escape velocity of Titan but it's a
lot warmer, being so much closer to the sun, so much so that most of
it's atmosphere has long 'escaped'. There'll be other significant
reasons too, but i think that's a big reason over time, the other being
that Titan seems to started off with a lot of atmosphere.

Jupiter's big four moons, with compable escape velocities don't have
thick atmospheres though (or at least may have lost them sooner, maybe
by getting just that bit extra warmth, or by Jupiter's influence)

each body in this solar system has it's own history and it's own unique
qualities - then to think there are probably solar systems of some kind
round just about every star, the possibilities seem endless!

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