If you could magic an atmosphere into place around the moon...?

[Deimos Anomaly]

If you could snap your fingers like Q from Star Trek and suddenly an atmosphere appeared clothing earth's moon, such that pressure at the moon's mean surface level was roughly equivelant to the pressure at mean sea level on earth...

How long would it take before the moon lost it all again?

Or how long would it be before pressure diminished to the point where it was no longer capable of supporting human life?

Minutes? Hours? Weeks? Centuries?

I don't have a clue how to work this one out but I'm thinking (too hopeful no doubt) there might be someone here who would know a bit more in this regard.

 

[Michael_One]

Back when I was in college this came up when some friends and I were doing physics class homework. The estimate we came up with was the Moon could hold a breathable atmosphere for around 200,000 years.

The core of our thinking was that the root mean square velocity of gas molecules at standard temperature and pressure is about 1,150 ft/ sec and lunar escape velocity is about 7,700 feet/ sec means the Moon should be able to hold an Earth density atmosphere.

Over the long run the Sun's heat excites the air molecules at higher altitudes ( also the Moon's gravity falls off with altitude, and with it, escape velocity ) so the upper lunar atmosphere escapes into space. Over long periods of time the atmosphere thins out.

I'm sure there are other complicating factors at work, but there's no reason to think our estimate is off by more than a factor of ten or so.

Even if the Moon had an atmosphere there is no reason to think it would be habitable; the temperatures would be extreme due to its slow rotation. I can't start to speculate on the convection winds you'd get between the sunlit side and the night side.

Not a bad guess from a group of friends studying together close to thirty years ago... I've long since lost the paper we worked out all the estimates on.

 

[Asbo Zaprudder]

Other loss processes are solar radiation pressure and UV-ionization combined with interaction with the interplanetary magnetic field. I don't know the relative importance of these factors as compared to thermal loss from the tail of the Maxwell-Boltzmann distribution. This estimate from 1974 argued that the Moon could retain a substantial atmosphere for a period that is long by typical human considerations (hundreds of years):

http://www.nature.com/nature/journal/v248/n5450/pdf/248657a0.pdf

(Access to the full article requires a payment.)

This means that the Moon could acquire an atmosphere over time simply by human activity on its surface. See for example:

http://www.islandone.org/Settlements/DegradeLunarVacuum.html

The paper makes the following statement about the escape lifetime for the existing very tenuous lunar atmosphere:

"The atmospheric escape lifetime from the sunlit side of the moon is approximately 10000 seconds (fifteen minutes) for the lightest molecules (hydrogen and helium), and up to 1 E7 seconds, approximately 100 days, for heavier molecules [7]. 1 E7 seconds is roughly the maximum lifetime of atmosphere constituents; this is approximately the time it takes for the molecules to become ionized by the solar ultraviolet, at which time they are swept away by electric fields associated with the solar wind in times which are typically no more than a few hundred seconds [7]. As noted by Vondrak [8], this mechanism becomes ineffective if the atmosphere is thick, however, the gas input rate (on the order of 250,000 tons/month) required to reach such a level is considerably higher than what is likely to be produced in any near-term industrial facility."

 

[Zachary Smith]

Clearly the moon needs to be encased in a glass bubble to prevent the atmosphere from evaporating into space. Somebody's gonna have to ride back and get a shitload of sand.

 

[Alpha_Geek]

I know just the person for the job!