Galilean terraformation

I will have to do the calculations, but I had calculated the
equilibrium pressure in a gas torus around Europa to be about 2%
of the earth atmospheric pressure, if there was enough material on
Europa, which there wasn't.

Yes technically this is an atmosphere, but for practical purposes
it is a vacuum to us.

I'll dig up the calculations.

Bill

>
> Does anyone realize that the Jovian satellites don't have enough
> gravity to hold an atmospere? There wouldn't be a liquid ocean,
> because it would immediately evaporate and be lost to space, and
> Jupiter orbit. There isn't enough material on all of the planets
> combined to produce a gas torus effect, so by melting the ice
surface,
> you will effectively boil off the water.
>
> Not exactly. Using E=3/2kT, where K is the Boltzmann Constant, one
can
> calculate that the average kinetic energy of a molecule at 15 C
(Earth's
> average temperature) is 5.96x10^-21. Since a water molecule has a
mass of
> about 3.00x10^-26, then the average velocity of a water vapor
molecule at
> that temperature would be (from Ec=mv^2/2) just 630 m/s.
>
> Well, the escape velocity for Ganymede is 2740 m/s; 2450 m/s for
Callisto;
> and 2020 m/s for Europa. (Data from http://www.solarviews.com/ .) As
you can
> see, it is far above than the velocity of our molecule.
>
> Of course that is an *average* velocity: there will be molecules
that will
> be faster, and other ones will be slower. Anyhow, most of them will
be
> trapped in the moon's gravity well. Immediately after you begin your
heating
> process, it is true that, for an observer in the surface of any of
those icy
> moons, the water vapor would seems to be dispersing completely in
space, but
> in fact most of it would be dispersing (and staying) into a sphere
with many
> millions of cubic kilometers around the moon. After some time
(decades?
> centuries? millennia? I don't know, and I'm too lazy at his moment
to do
> another napkin calculation... ;-), however, the cumulative effect of
all
> those molecules would manifest as a thin atmosphere; given more
time, that
> atmosphere could be thick enough to allow liquid water, and then we
would
> have our long-sought oceans.
>
> Of course the atmospheric loss of those moons - the volume of
molecules fast
> enough to leave the atmosphere - would be huge compared to the same
rate for
> Earth. But the volume of vapor and water would be so huge that, for
a human
> civilization, the time necessary for all the water in a Galilean
moon to
> dissipate in space would be an eternity, in practice.
>
> So, I would rephrase what you said - "the Jovian satellites don't
have
> enough gravity to hold an atmosphere" - to "the Galilean satellites
don't
> have enough gravity to hold an atmosphere *during geological time
spans*".
> But human civilizations don't live through a geological lifespan,
anyway...