(urth) Dome, Dome on the Range

[Gerry Quinn]

From: "Jerry Friedman" <jerry_friedman at yahoo.com>
>> From: Gerry Quinn <gerryq at indigo.ie>
> >> From: "Jeff Wilson" <jwilson at io.com>
>>
>> > It occured  to me at lunch today that a problem with the open air 
>> > atmosphere
>>schemes, even  ones that last thousands of years between refills, is that 
>>they
>>take half to 3/4  the mass of earth's atmosphere to work. When this does 
>>escape
>>from the moon,  only small amount of that will also escape from the earth, 
>>and
>>the reset  will eventually come to fall on the earth, raising its surface 
>>air
>>pressure  accordingly; this is a serious problem
> ...
>> Seriously, will this actually happen, anyway?  I couldn't find  detailed
>>references to a proper calculation, but here are my thoughts:
>>
>> If  an atom leaves the top of Lune's atmosphere at lunar escape velocity, 
>> the
>>question of whether it is likely to end up in Urth's atmosphere on Urth 
>>depends
>>on whether it exceeds Urth escape velocity at this point (unless it's 
>>headed
>>directly for Urth, which is unlikely.
>
> [snip calculation]
>
> I like it, but you need to add in the orbital velocity of Lune, which 
> makes
> molecules substantially more likely to escape.  (This could actually be a 
> bigger
> problem than air ending up back on Urth, where as you note it's not lost.)

It doesn't affect their likelihood to escape.  All motion is relative.


> Also, molecules that escape from Lune but not the Lune-Urth system will be 
> in
> orbits that intersect Lune's orbit where they left it. Except for the 
> relatively
> small portion aimed at Urth, they're not going to come to rest on Urth 
> until
> their orbits are modified by collisions with other molecules or brushes 
> with
> Lune.  I suspect they're a good deal more likely to come to rest back on 
> Lune
> than on Urth.

Those are molecules that don't escape.  The ones we care about are ones 
which achieve escape velocity near the top of the lunar atmosphere, where 
the atmosphere is very thin (mostly these will be hydrogen molecules or 
atoms)..  In this case they are unlikely to collide with anything and will 
escape Lune.  If the top of the atmosphere is less than 3000 miles above the 
lunar surface, they will be fast enough to escape Urth as well.

I'd expect them to become widely dispersed in a sphere around the region of 
Urth's orbit, and eventually to be blown away by the solar wind.

- Gerry Quinn