(urth) Green is Urth Redux

[David Duffy]

On Wed, 12 Jan 2011, Jeff Wilson wrote:

> On 1/12/2011 6:03 PM, David Duffy wrote:
>> The moon can keep an atmosphere, once provided, for 10000-20000 years
>> per top-up IIRC. Those Barsoomian air plants would do the trick nicely.
>> 
>> http://www.terraformers.ca/Terraforming-the-Moon.html
>
> I've heard this before, but I have yet to see how the figure was obtained. I 
> cannot find it on the cited website, if that was your intention.
>

No.  But I presume you can google as well as me ;)  Geoffrey Landis gives

http://www.geoffreylandis.com/moonair.html

Could we manufacture the oxygen? We would need something like two hundred 
trillion tons. The chemical composition of lunar rock is about half 
oxygen; all we have to do is reduce the amount of rock equivalent to a 
cube about fifty kilometers on an edge. That's a lot of rock. On the other 
hand, it's a small volume compared to the size of the moon. Such a chunk 
of rock reduced to oxygen would give the moon an atmosphere that would 
last three thousand years--longer than any civilization on Earth has ever 
lasted, and when it leaks away, we could keep replacing it every few 
thousand years for a long, long time before we even begin to use up the 
moon.

There doesn't seem to be a complete text for

H.W. Renn, "Terraforming the Moon: A Viable Step in the Colonization of 
the Solar System?" IAC-02-IAA.13.2.08, 53rd International Astronautical 
Congress, Houston, TX (2002).

I get the impression the 3000 year number is a little arbitrary (it does 
for example assume the sun to be as hot as it at present ;)).  This writer 
(a professor of astronomy) claims 10-fold differences in retention time 
depending on who did the calculations: 
http://cseligman.com/text/planets/retention.htm

The ratio of escape velocity to thermal velocity for H2O and O2 for the 
moon is 5-6, which gives ~100 My.  This assumes a T of 300K.  However, the 
T at the base of Earth's exosphere is more like 1000K, and that for the 
moon in a thick atmosphere is given at 800K in the Willett et al 
presentation "Above the Moon".

Williams et al Nature 1997; 385:234-236 state further

Loss of O is not necessarily fatal to habitability because O2 can be 
replaced by photosynthesis.

Anyway, I don't know if Wolfe necessarily went through all these 
calculations ;)

Cheers, David Duffy.