I've discussed this only with some of my close freinds, but to no avail, so I come to you, my fellow Bad Astronomers, for a solution to this interesting problem. When speaking of terraformation, most people assume that we're talking about Mars. This is not at all an unreasonable assumption, since Mars is particularly well suited to terraformation. Evidence suggest that there are probably reasonably sized reserves of water ice below the surface, the planet holds a non-negligible atmosphere composed of carbon-dioxide, as well as ample supplies of additional CO2 at its poles, the axial tilt of the planet is nearly the same as that of Earth, and its day is also approximately the same length as Earth's. However, I speak to my freinds about another world for terraformation, a world which would prove to be far more difficult, and perhaps even impractical to terraform. If Luna is impractical to terraform, then think of all this as an interesting thought experiment.

In this, my first post, I'd like to ask you all about an idea I've had concerning a method for keeping an atmosphere on Luna. The literature tends to suggest, and I am willing to believe, that Luna's gravity is not strong enough to maintain a nontenuous atmosphere. Any atmosphere will tend to effuse into space. Obviously, if Luna were to be terraformed, this problem would have to be remedied. The one solution that I've come up with is hypothetical at best, and I have no idea if it would work at all.

The rings of Saturn are in degenerative orbits. The billions of particles which comprise these rings are slowly spiralling into Saturn, and some day, millions of years hence, they will plummet into the clouds in the upper reaches of Saturn's atmosphere. There will be a period, many millennia long, during which the rings are actually falling into the atmosphere. That is, the rings will still exist, but their inner-most regions will be just over the clouds, and pieces will be burning up daily.

Thus, my idea for Luna; use comets or other sources of oxygen and nitrogen to create a breathable atmosphere on Luna. Immediately, it will begin to dissipate into space. Using other comets, create rings of nitrogen and oxygen ice chunks in severely degenerative orbits about Luna, such that just enough of the innermost rings evaporate in Luna's upper atmosphere to replenish whatever gas is lost due to effusion.

Now, there are some serious issues with this plan that I have already identified:

One, I have no idea how quickly the Lunar atmosphere will dissipate. I'm thinking that it would happen on a timescale in terms of millenia, and not overnight or anything, but I don't actually know. This is vital for calculating how often the rings would have to be replenished. (The rings, of course, would tend to get smaller as time passed, and more comets would have to be crushed up periodically.)

Two, with pieces of the rings constantly vaporizing in the upper atmosphere, quite a lot of heat would be generated. Depending on how quickly we have to replenish the atmosphere, this might make Luna an uncomfortably hot planet. This might range anywhere from making Luna into a planet composed entirely of deserts and tropics, to making Luna into an unbearable furnace.

Three, how do we sift through the contents of a comet to get all the good icy material for our rings and remove all the rock and metal? I've thought of using huge magnets on the cometary debris field after we shatter the thing with nuclear charges, but frankly, that's just going to far. The energy required for such a task would be emmense, and any magnetic field that strong would probably disrupt nearby communications equipment - and by nearby, I mean several thousand kilometers. Otherwise, all I can think of is manually mining out the rock and metal and ejecting it before we even break the comet into ring material.

So this is my proposal, as huge-scale and ridiculous as it is. Like I've said, if nothing else, it's an interesting thought experiment, and I would be interested in any comments, suggestions, or answers to my questions. Also, if anyone has any other ideas for maintaining a Lunar atmosphere, please post them. I'd be glad to comment.

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"Of COURSE fish can live in space. There's no air. Fish don't NEED air."
"I know that, man, but it's cold."
"Duh - so is water, man."
-Actual conversation overheard while walking to class

According to Stephen Baxter's novel Moonseed (science fiction, but heavy on the science), Luna would sustain a breathable, although thin, atmosphere for a couple/few tens of thousands of years.

There are a few problems with your idea.

One: Getting the correct materials into lunar orbit. Probably just be cheaper to live in domes. The idea of using a magnetic field to 'clean' the comets won't work. If you're lucky, you'd clean out the iron, but all the other metals would just sit there. A better solution for this is to just mine the metals out, and use the discards to keep Luna inhabitable.

Two: You're right about the heat thing, but I don't think it would make Luna a hot planet (it's already a desert). The problem is that a hot atmosphere would boil off faster.

I think, in the end, it would just be better to forgo terraforming. Even Martian terraforming is well outside of our technology to do without taking milleniua.

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People who think they know everything are a great annoyance to those of us who do.

The Moon's gravity is too low to hold a significant atmosphere; random thermal motion and the solar wind will strip it away in short order. So any program of lunar terraforming would have to include a way to continually replenish those losses. Your suggestion is interesting, but I don't really have a clue as to whether it's workable.

One thing that might be a problem is the proximity of Earth, which would tend to strip away the Replenisment Rings (tm) by tidal effects. Also, there's the problem of getting the ring particles to be the correct composition to become the future atmosphere. It might be easier to simply land the required gasses on the surface in solid form (frozen or as compounds) and release them where they're needed -- why bother with the complex ring system? Other than for aesthetic reasons, that is.

I don't know this for sure, but it might be problematic to get enough of an atmosphere so that air pressure at the surface is sufficient to sustain life, no matter how much gas you had available. It's the same probem: low gravity. An atmosphere as deep as the Earth's would have much lower pressure at the surface. This may also modify the thermal gradient from top to bottom as well. These problems may be tractable if we could vary the composition, adding some extra high-mass inert gasses and/or greenhouse gasses.

The Moon does not have an appreciable magnetic field, which means that charged particles will be able to penetrate to the surface more readily than on Earth. That may make life more difficult. And there's the low-gravity problem itself -- we have no idea whether humans could thrive long-term under those conditions.

All in all, it seems to me you'd get a lot more bang for the buck by terraforming, say, the Sahara, Gobi, or Sonoran.

Ah, yes, I knew I was forgetting something to post in my little problems list. Earth stripping the rings. One solution I thought of for that would be to place some small, asteroidal "shepard moons" into stable orbits about Luna to create a sort of gravitational barrier. However, I can't guarantee that Earth wouldn't steal those too!

As for the pressure of the atmosphere, I'd thought of that some as well, though I wasn't sure how much of an issue it would be. The way I figure it, to sustain life, we really only need an atmosphere of about 20 kPa - so long as that atmosphere were pure oxygen! We could probably live with less even, maybe as low as 16 or 15 kPa, but it would be like living on a high mountain. Being a Coloradan, I can tell you from experience that it is NOT easy to breath on top of a mountain. And wedgebert seems to suggest that an atmosphere like this might be maintainable without any fancy rings! Huzzah!

Though...the rings WOULD look really, really shweet...

__________________
"Of COURSE fish can live in space. There's no air. Fish don't NEED air."
"I know that, man, but it's cold."
"Duh - so is water, man."
-Actual conversation overheard while walking to class

But would an atmosphere that thin be able to retain the heat necessary for survival during the 14 day long night? If the atmosphere begins to freeze out on one side, there'll be problems.

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"I'm making wheatloaf. It's like meatloaf, only with wheat"
"Isn't that just...bread?"

One problem is that there are no "stable" orbits about the moon--if you're close to the moon, the lumpiness of the mass concentrations will perturb your orbit until it eventually intersects the surface; if you're far from the moon the earth will pick you off.

Aye, the day-night cycle is one thing which has bothered me to no end about this whole Lunar fiasco. To be perfectly honest, I'm not even sure that a 101 kPa atmosphere would have the capability to maintain livable temperatures through 14 days of darkness. Consider that on Earth, during a summer night (about 8 hours) the temperature drops about 10 degrees Celsius. On a winter night (about 16 hours), differences of up to 25 degrees Celsius are not unknown in Colorado. So for 14 days of darkness - oof! Thats about 20 times longer than a Coloradan winter night. I doubt that the temperature drop would also escalate by a factor of 20, but it would not be comfortable.

In the polar regions it goes dark for days at a time during the deep of winter, so we can use these times also as a good indicator of what kind of temperature drop can be expected. In these regions, the temperature can drop to between -35 and -45 degrees Celsius for that time of the year. And with a thinner atmosphere - well I had never even considered that, but I imagine it'd get quite a bit colder than the Earth's polar regions in winter.

That brings to mind the Lunar day. It's 14 days long also. I imagine the sun can get pretty oppressive when its shining on you for three hundred consecutive hours, and EVEN with a very thin atmosphere.

I'd like to think, that somehow, these extremes will balance each other out, but of course that's never right. In fact, thinking on it now, the difference between night and day on Luna would be the difference between the hottest summer and the coldest winter on Earth.

"Uh-oh. The sun's setting. Better get out of this silk shirt and into my parka." Cripes.

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"Of COURSE fish can live in space. There's no air. Fish don't NEED air."
"I know that, man, but it's cold."
"Duh - so is water, man."
-Actual conversation overheard while walking to class

Other than its a cool idea, why would you want to terraform the moon? At the point where we have the technology to move comets around, it would be lots easier to either build big domes or to tunnel underground on the moon. A favorite science fiction idea is to dome over some of the bigger craters.

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At night the stars put on a show for free (Carole King)

I like the dome/tunnel idea. An atmosphere outside the domes could be used as insulation, but it wouldn't have to be breatheable. But, I distinctly get the impression that that's not what's being looked for here.

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"I'm making wheatloaf. It's like meatloaf, only with wheat"
"Isn't that just...bread?"

Also with the domes, instead of the atmosphere, you still have a great place to use as an observatory!

I figure that its impractical to terraform Luna, but keep in mind that this is all just an interesting thought experiment. It would be impractical to do it, but by God - wouldn't it be cool? That's the only reason I really even bother to think about it. If I were going to talk seriously about terraformation, I'd talk about Mars. :wink: Heh.

But anyway, since we seem to have discussed the atmosphere at some length, I'd like to return to Donnie B's assertion that Luna's lack of an appreciable magnetic field will leave any inhabitants open to charged particles from space, particularly the solar wind. Barring the creation of an artificial magnetic field (which even I must admit is far too impractical to even TALK about), I have little notion of how we might overcome this problem. Any thoughts?

__________________
"Of COURSE fish can live in space. There's no air. Fish don't NEED air."
"I know that, man, but it's cold."
"Duh - so is water, man."
-Actual conversation overheard while walking to class