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It would be nice if there were an atmosphere on the Moon with oxygen; in fact it could be just oxygen at 1/5 the Earth's pressure. People could live there. Now of course given the Moon's lower gravity the atmosphere would escape into space, but it'd take hundreds of thousands of years for that (roughly 1 million years if I recollect well). Enough time for 50 human civilizations to develop one after another.

Now there is oxygen on the Moon, but it is fixed in rocks and probably in some water. What would be the best, easiest way to make an atmosphere out of it?

My guess is that can be done with a powerful enough energy source. Rocks or water can be decomposed by heating.

Using the Sun's light for that could do, if it is concentrated. Nuclear reactors and nuclear bombs could be used too, but that doesn't seem that easy because it costs to send them; making an automated nuclear plant / bomb factory on the Moon may be cheaper, but other problems appear (ores, plant defects etc.)

So my first guess to a solution would be using solar energy, with mirrors that can be built in place or brought from Earth (as thin sheets of plastic). But how much of the Moon's surface would have to be used? I wouldn't cover too much of it with oxygen factories; that would cost a lot too. Let's say we want an atmosphere there in a reasonable time (hundreds of years). What approach to use?

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  • $\begingroup$ If it helps you can think of another planet, say Mars. What would work easily on the Moon should work on Mars too. $\endgroup$ – Ferred Jan 2 at 14:25
  • $\begingroup$ "how much of the Moon's surface would have to be used" - this depends only on the timeframe you need. If it is possible to really hold an oxygen by Moon, then you need ten times more mirrors to do it in a decade than you need for a century. $\endgroup$ – Mołot Jan 2 at 14:31
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    $\begingroup$ @Molot: I'm still not sure about the time the atmosphere would escape in space. I'll look for some more exact results about that. $\endgroup$ – Ferred Jan 2 at 16:05
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    $\begingroup$ Does the moon have enough gravity to even hold an atmosphere? Is it within the Earth's magnetosphere deeply enough that the atmosphere wouldn't be stripped by the solar wind? This might be like trying to fill a bucket that's full of holes. You can keep it full briefly... until your source of water runs dry. $\endgroup$ – JBH Jan 2 at 17:16
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    $\begingroup$ Don't forget solar winds. Gravity has less to do with atmosphere retention than a good magnetic field. Your calculations may be grossly overestimating the stability of a moon atmosphere if you don't consider how much is just blown away. A far more realistic model for planets without a molten core is to construct a series of large bio-dombs, or underground bunkers then you just produce the Oxygen and usable real-estate as you need it instead of trying to waste centuries on an unsustainable terraforming project. $\endgroup$ – Nosajimiki Jan 2 at 22:38
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To make a lasting atmosphere on the Moon, we'd need to produce around 10,000 metric tons of gas per day just to keep it stable. Source: http://www.geoffreylandis.com/moonair.html

That is a lot. To give you an idea, in normal conditions, 1m3 of air has a mass of 1.024 kg. 10,000 tons would have a volume of approximatelly 10,000,000m3. That is nearly 50x the discharge per second of the Amazon river.

We can only imagine an industrial setup able to have that output in the realms of sci-fi. By the time we have the technology to set that up on the Moon for real, our solar cells should be more efficient than they are now, and we will have a better understanding of the ice deposits on the Moon. Otherwise, calculating your energy requirements seems pointless to me.

Last but not least, I don't think you want to burn rocks to make an atmosphere. That is wasteful, and the waste by-products may make the air unbreathable. You will also need to rewrite the maps for the lunar surface every few days to make up for all the surface you've been digging and moving around.

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    $\begingroup$ Ferred, I'd like to cite a quote from the article Renan linked: The moon, however, keeps very little of the atmosphere it receives. Any gas it momentarily captures escapes from the surface very rapidly. This answer supports my hole-in-the-bucket comment. $\endgroup$ – JBH Jan 2 at 20:57
  • $\begingroup$ "We can only imagine an industrial setup able to have that output in the realms of sci-fi." I can't stand not having some fun with this. It is sci-fi, after all. Dr. Who could do it with his screwdriver. :-p $\endgroup$ – JBH Jan 2 at 20:59
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    $\begingroup$ @JBH I have a lot of fun with this. I just mentioned that due to the tags in the question. $\endgroup$ – Renan Jan 2 at 21:06
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    $\begingroup$ @JBH: your quote is true for a very rarefied atmosphere, where the mean free path of molecules (length between 2 collisions) is very long, maybe as much as the height of the atmosphere, so molecules escape easily if they have velocities above the escape velocity. But a dense atmosphere would have a self-containing property: the mean free path is so small that it would retain most molecules that move faster than the escape velocity. It would lose only those molecules that lie in the upper layer and are fast enough. $\endgroup$ – Ferred Jan 2 at 22:09
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    $\begingroup$ Btw, 10 000 tons of gas/day (about 100 kg/s) can be achieved with an automated generator powered by solar energy. Compared to that, burning 100 kg/s of petroleum would generate a power of about 4-5 GW, which is not that high. But I'd have to do more research to figure out some realistic model for atmospheric escape on the Moon. $\endgroup$ – Ferred Jan 2 at 22:18
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Using heat to decompose molecules is a bad idea in a low gravity environment like the Moon.

At high temperature the molecules have an higher average velocity, meaning that an higher fraction of the molecules will have enough velocity to escape the gravity well. This in turn will mean that your estimated life span for the atmosphere will be considerably shorter.

Moreover from a hot mass you would develop both the Oxygen and the material it was bounded to. You will need to separate them quickly, else they will recombine (that's why you don't use water to extinguish extremely hot fires, because by doing so you just put Oxygen and Hydrogen next to a hot body) And you will also have the additional problem of dissipating the amount of heat, unless you want to have a boiling planet totally unsuited for life.

Once you have an abundant source of energy, go for the electrolytic path: dissolve the material in a suitable solvent, apply current and harvest the developed substances.

On one hand you will get Oxygen for your atmosphere, on the other hand you will get metals which you can use for other purposes on your lunar colony.

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    $\begingroup$ As we can see here even at ambient Moon temperature it won't hold Oxygen for significant time. And on the other hand, using temperature to break water is OK - as long as you cool resulting gases before you let them out, of course. But cooling shouldn't be a problem, mirrors cause things to get hot in one place and cooler in another, so there will be abundant cool rock to work as a heat dump. $\endgroup$ – Mołot Jan 2 at 15:29
  • $\begingroup$ Water is practically a universal solvent. Do you think smothering the moon in water can have any desired effect? Also, water can be irradiated to release diatomic oxygen and hydrogen, perhaps the Sun will work for us in this way? $\endgroup$ – B.fox Jan 2 at 15:31
  • $\begingroup$ I don't intend for the atmosphere to appear all of a sudden, so no huge boiling of the Moon surface. Instead oxygen is to be produced at a small rate and freed into space with high enough pressure that it would cool before molecules escape completely the Moon's gravity. Essentially it is to be released as gas plumes that would expand and cool. $\endgroup$ – Ferred Jan 2 at 15:42
  • $\begingroup$ @B.fox: I'd say water has more important uses on the Moon than obtaining oxygen from it. Besides there may not be enough water for that. Water decomposes at some 3000 degrees Celsius, which is quite a high temperature. It can be decomposed with UV radiation too, but the Sun produces quite a little, so I think it would take a long time that way. Heating water with light may be better. $\endgroup$ – Ferred Jan 2 at 15:46
  • $\begingroup$ @Ferred You're right, however, I'm just pulling from my old notes on terraforming the Moon. The water problem could be mended by bombarding the Moon with cometary fragments hauled from the outer solar system. $\endgroup$ – B.fox Jan 2 at 15:50
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Simple. All you have to do is transfer the oxygen in the atmosphere of Mars to the Moon. Here's how.

  • Mars atmosphere is around 96% CO2. Stations at the poles compress free air into carbon-fiber tanks where the air becomes liquefied. The tanks are shot vertically into space via electromagnetic railgun.

  • Stations in polar orbit catch the tanks and reshoot them via railgun into near equatorial orbits.

  • Ion drive bombers catch as many of the tanks as they can in a single orbital swing-by and slingshot to the Moon.

  • On the way the bombers freeze the liquid contents of the tanks into large blocks which are then dropped to awaiting stations along the lunar equator in another single orbital swing-by, slingshotting off to Mars again with their loads of empty tanks (a circuit). The tanks are dropped in equatorial orbit where they are recollected by the polar orbit stations and dropped back down the the polar stations.

  • The lunar stations regasify the Martian air blocks in solar collectors. The CO2 gas is then combined with hydrogen -- partially obtained by cracking lunar regolith in solar furnaces, the other byproduct being glass -- over locally-mined nickel catalysts, forming a mixture of water and methane.

  • The major waste gasses would be nitrogen and argon, both extremely rare on the moon. The nitrogen would have many practical uses in industry and biochemistry. The argon could be used to make lasers to wage war.

  • The water is electrolyzed via solar voltaics into hydrogen, which is fed back into the catalyzation process, and oxygen, which is freely released into the atmosphere.

  • The methane is passed through glass rod matrices -- made from the cracked regolith -- in high temperature solar collectors producing hydrogen gas, which is also fed back into the catalyzation process, and solid carbons.

  • The carbon is used to manufacture additional carbon-fiber tanks which are shot into equatorial orbit via railgun to be opportunistically collected by passing bombers.

  • Repeat.

The fundamental process is documented here https://patents.google.com/patent/US4452676.

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  • $\begingroup$ This would work, but I don't think it is going to be easy. I'd rather let some simple installations handle all the work. But still neat idea. $\endgroup$ – Ferred Jan 3 at 10:13
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Once you have a significant atmosphere with a density of a hundredth of a millibar or so, it will stabilise itself as it becomes much colder with height. That is as long as you stick to oxygen and nitrogen (don't emit greenhouse gases, and an ozone layer is also bad)! The day/night temperature differences will create quite a lot of wind, but not in the topmost atmosphere layers, because there is not enough pressure there.

The important point is that once the pressure has dropped so far (with height) that the mean free path lenght get's into the kilometer range, the temperature must be so low that practically no particle has escape velocity any more.

The problem will be to get beyond the first step, when the gas molecules can still fly directly off the hot sunlit moon surface into space, without hitting other molecules.

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  • $\begingroup$ @cmaster :-) Happy new year, btw! $\endgroup$ – Karl Jan 4 at 21:11
  • $\begingroup$ Thanks. I appreciate that :-) You too! $\endgroup$ – cmaster Jan 4 at 21:51

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