Moon atmosphere

What would be needed for our moon to have an atmosphere that could support human life? Assume getting the atmosphere there isn’t a problem - what would be needed to keep it there? More mass - how much? A magnetic field - does this just require more mass (how much) or also more heat? Would a sufficiently large object impacting the moon give it enough mass and other components such that it would eventually form an earthlike atmosphere? Is there any way such an impact would not also devastate Earth?

Just a total WAG here but perhaps a very dense gas, some inert and non-toxic synthetic compound containing very heavy elements could have enough ‘weight’ to stick to the moon then enriched with oxygen and CO2 to the partial pressures animals and plants need.

Though even if such a gas could be manufactured it would be tough to get into place as the sun would superheat the exposed side of the moon and essentially blow this gas into space, though if it could be placed all at once the gas itself may moderate this effect enough to limit this and produce more moderate temperatures on the moon.

You need gravity. Or a container.

I think the container is more feasible. Basically a roof.

IIRC the Moon has a very tenous atmosphere made up of xenon.

A large spherical ballon covering the planet*. Strong enough to maintain the necessary pressure for life.

*Is so.

If true my very dense gas WAG would seem to at least be a possibility.

Or some way of continually replenishing it as fast as it’s lost.

The Martian atmosphere generator used in Total Recall could manage that for a while.

I believe it has to do with effect on cosmic rays on the rocks and not internal radiation.

But for God’s sake do not store nuclear waste on the Moon.

I suppose it depends on how long you want to live on the Moon. To maintain a respectable atmospheric pessure at the surface, the height of the atmosphere would need to be much greater than on Earth, so the top of the atmosphere would be very loosely bound. However one estimate I’ve read suggested that the Moon could hold on to a breathable atmosphere for ten thousand years or so.

Seeing as it would probably take thousands of years to put it there in the first place, the process of terraforming the Moon would be rather a lot of effort for little return.

Tripolar has mentioned a better idea; ‘A large spherical balloon covering the planet’. Richard L. S. Taylor described this as ‘paraterraforming’ in a 1992 paper.

Obviously a few technical hurdles to overcome before this could become reality…

A paper by Taylor is here

The ability to hold an atmosphere is a function of 3 things. The gravity, the temperature, and the molecular weight of the gas.

Can’t fix the gravity problem. You could help the temperature by increasing the albedo of the moon. IIRC the moon is actually pretty darn “dark”. If you can do the whole atmosphere engineering thing I think you could also do the “lets coat this baby with white paint” sorta thing. That should bring the temps way down.

Then I guess you need to find some gaseous compound that has a very high molecular weight but is still a gas a pretty low temp.

However, if you like you atmospheres hot Uranium Hexaflouride should do in the density department.

So, for the record, how much mass would one have to add to the Moon to get enough gravity to hold the atmosphere permanently?

(Yes, I’m aware that this would probably be harder than encasing the whole thing in an oversized clown balloon. That’s my problem.)

I’ve heard estimates in the 100,000 year range, which would be better.

I’ve also heard proposed the idea of surrounding the Moon with orbiting “atmospheric shrouds”; extremely large, extremely thin membranes that will bounce back most of the escaping gas atoms before they escape. Since the Moon can almost hold an atmosphere you don’t need an actual airtight bubble.

Even the Earth wouldn’t hold onto its atmosphere permanently although the retention time is measured in many tens of billions of years, longer than the Sun remains on the Main sequence. The smallest mass a planet could have and still retain an Earth-like atmosphere at the same distance from the Sun as the Earth/Moon system is somewhere between the mass of the Earth and Mars.

Basically, to retain an Earth-like atmosphere on the Moon during the period the Sun is on the Main Sequence, you would have to add several times the entire mass of Mars, possibly as many as five Mars masses, or half the mass of Earth.

Here’s a cite for the minimum mass of a planet which can hold an Earth-type atmosphere;

Not a very detailed estimate, I’m afraid; it ignores the temperature of the planet, the age of the star and many other factors. But it seems to be roughly in the right ballpark.

and the Moon is 1/80 or 0.0125 the mass of the Moon so by the estimate you quoted you would need about 40 Moons smashed together to hold oxygen.

??? 1/80 mass of the earth maybe?

I think the point is that yes, you could add gas to create an atmosphere on the moon. The logical approach (by what logic???) is to keep diverting comets and ice bodies to crash into the moon. Release enough water and methane, hope these bodies hit before the sun vapourizes them…

Methane not a good idea, except that the upper limit of tHE atmosphere all this breaks down, the hydrogen eventually “boils off”; You get free oxygen and free carbon - so CO2. An atmosphere might remain for 10,000 or 100,000 year - peanuts in geological time scales (heck, barely one ice age cycle, 650 time further back to just dinosaurs…) but enough to encompass more than written human history.

The probable limit of atmosphere would be the equivalent of about 10,000 or 12,000 feet ASL. Of course, earth atmosphere is 21% O2, so if the oxygn partial pressure is ke[t the same, but oxygen is a larger percentage of the atmosphere, we might get by with 50% or 40% of earth sea level pressure. But then, you get secondary effects - the lower boiling point of water, the lower humidity capacity (less rainfall, hard to get beyond desert ecology?). Plus, CO2 in significant quantities can be fatal - we’re not equipped to handle that.

So ideally, you want a source of nitrogen or some inert (noble) gas that we can handle; but that’s a bit harder to find in quantity and deliver, as opposed to ice which we should find all over the outer solar system. At the very least, we get the Avatar/Pandora effect - you can wander in just a breathing mask.