Lunar Atmosphere

Studies indicate that the Moon once had an atmosphere denser than Mars'.

https://www.liebertpub.com/doi/10.1089/ast.2018.1844

With the low gravity, though, any atmosphere beyond a trace amount today is going to get blown away by the solar wind.

The lower the gravity the more rapidly the atmosphere will bleed away --- the lighter gases first.

Resha Caner said:

IOW, what keeps an atmosphere in place? Is it gravity, production from the planet itself, or both?

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Gravity is big, and a good magnetic field helps.

Resha Caner said:

If the gases were available (oxygen, etc.) could the moon sustain an atmosphere?

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It already does.

But for living there? No.

Resha Caner said:

OK. So building a dome would do at least the part of gravity & the magnetosphere. yes? You could even design the dome to vent if that would help - the question being: Is it helpful in some way that part of the atmosphere bleeds away over time?

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Well, Yahuweh the Sovereign Almighty Creator Created the moon just as it is (allowing for the effects of time that He also Designed) (but without man's stuff on it (if it is there actually) ) , man almost always if not always just messes up His Creation.

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Resha Caner said:

Well, yes, I knew it had something, but not much to speak of.
I see. Does that mean earth's atmosphere would dissipate over time if the planet were "dead"? IOW, what keeps an atmosphere in place? Is it gravity, production from the planet itself, or both?

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I think that what holds the universe together counts more than anything.

Resha Caner said:

I see. Does that mean earth's atmosphere would dissipate over time if the planet were "dead"? IOW, what keeps an atmosphere in place? Is it gravity, production from the planet itself, or both?

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The lightest gases, like helium, are lost more rapidly than heavier gases.

Since the atmosphere is at some temperature (a statistical measure of kinetic energy), the lighter gases have higher average velocities (since they have smaller masses). And some atoms and molecules literally achieve escape velocity and fly away.

Atmospheric escape of hydrogen on Earth is due to Jeans escape [the mechanism I mentioned above] (~10 - 40%), charge exchange escape (~ 60 - 90%), and polar wind escape (~ 10 - 15%), currently losing about 3 kg/s of hydrogen.[1] The Earth additionally loses approximately 50 g/s of helium primarily through polar wind escape. Escape of other atmospheric constituents is much smaller.[1] A Japanese research team in 2017 found evidence of a small number of oxygen ions on the moon that came from the Earth.[10]

In 1 billion years, the Sun will be 10% brighter than it is now, making it hot enough for Earth to lose enough hydrogen to space to cause it to lose all of its water (See Future of Earth#Loss of oceans).