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The majority of the Moon's mass is oxygen. With energy it could chemically be liberated from its silicon et cetera compounds and be turned into oxygen gas. Given its low gravity, lack of magnetosphere and vicinity to the Solar wind, could enough oxygen gas be produced on the Moon to keep up with the loss to space, so that a pure oxygen atmosphere breathable to humans could be maintained for some time (thousands or millions of years)? Inert gasses would be a problem, I suppose, because of the lack of nitrogen, carbon and nobel gasses, but oxygen is all that we need. Something like a pure oxygen atmosphere at a fifth, maybe a tenth, of Earth's atmospheric pressure is survivable. Aside from technological, economical and mental sanity reasons, is it also somehow physically impossible? Could an object like the Moon have a thick atmosphere even temporarily? Titan does.

How would one estimate the kind of energy required to produce enough oxygen gas, as a fraction or multiple of the Solar irradiance on the Moon?

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    $\begingroup$ looks like worldbuilding question. Here is aluminium production energy 54 MJ/kg - it is half Al half O2 by mass. For each square meter of surface you need 60t of oxigen, minimum for 1bar.(lets skip pyre oxigen atmosphere dangers) that means roughly you have rip about 60m deep of moon crust(probably more), all around of moon. Energy $3.24 TJ/m^2$ for surface of moon. $\endgroup$
    – MolbOrg
    Jul 3 '16 at 13:23
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    $\begingroup$ Relevant (but not a duplicate): Could the Moon keep an atmosphere? $\endgroup$
    – DarkDust
    Jul 3 '16 at 13:45
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The Moon is capable of having an Earth-like atmosphere. Although the escape velocity of the Moon is much smaller than Earth's, it is still around Mach 6.(*)

If the Moon had an atmosphere, it would lose it in some tens of millions of years(*). This is why any atmosphere it once had is long gone, but this would be enough for us and our shorter time scale, which is only some thousands of years in the most optimistic sense.

Nitrogen is rare on the Moon, but it is not really needed. We don't use it for anything. What matters is the partial pressure of the $O_2$ in the atmosphere. In a 100% $O_2$ atmosphere with around 0.2 bar pressure (20% of the air is $O_2$) we could breathe without any major problem.

But the Moon has a much weaker gravity, it is only around 1/6 or the Earth. Therefore, approximately 6 times more per-area mass of the atmosphere would be required to get the same pressure. This means that around of 1.2 kg of $O_2$ would be needed over every $cm^2$ to get the required $O_2$ pressure (on the Earth, it is around 1 kg).

The Moon's radius is also around 1/6 of Earth's, so its surface area is 1/36 of Earth's. The surface area of the Earth is $5.1*10^8 km^2$, so the Moon's surface area is $14*10^6 km^2$, which is $1.4*10^7*10^{10}=1.4*10^{17} cm^2$. So around $1.6*10^{17}$ kg of $O_2$ would be required.

The lunar soil is mainly composed of regolith, which is essentially a mix of different metal oxides. It melts around at $1200K$, which is essentially lava. On the Earth, a similar substance is produced from volcanoes.

Well, most of its components have a much higher melting point (for example, $Al_2 O_3$'s is over $2000K$), but not all of them. The molten salt mixes have a normally much lower melting point, this is why this around $1200K$ would be enough.

These molten salt mixes are poor electrical conductors, but are conductive conductive to be electrolysable, and a temperature of around $1000K$ is not unfeasible. Although most of the electric energy would simply heat the lava, a significant part would produce $O_2$. The electric effectivity of different electrolysis processes are in the order of 10-60%, so we can now calculate with their geometric mean, which is around 25%.

The burning heat of the Al is around 22 $\frac{MJ}{kg}$, its molar mass is 27. Thus, burning of 1kg of Al gives 22 MJ of energy, it is 37 mol, which consumes 37*1.5 (Al2O3!), so 55 mol of $O$. This 55 mol of oxygen is 888 g.

Thus, to produce an Earth-like O2 atmosphere on the Moon, we would need to produce around $1.8*10^{17} kg$ of Al. This would require around $4*10^{18} MJ$ of energy, or $4*10^{24} J$. Considering an effectivity of 20%, it is around $2*10^{25} J$.

The yearly Al production on the Earth is around 40 million tons. To produce this mass of Al we would need 4.5 million years - on the Earth.

According to this article, on Earth there was around 184 TWh of solar energy produced in 2015. This is $6.62*10^{17} J$. Thus, to produce the required $2*10^{25} J$ of energy, we would need around 30 million years.

But on the other hand, although this project doesn't seem feasible in our lifetime, perhaps in a better world it would be possible to make automated factories staffed by robots, to build the required number of PV cells and electrolysis chemical factories on the Moon. Actually, if we had enough robots we could do anything, and robots could be also produced by robots.

(*) I am very happy to google some references if anyone asks.

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  • $\begingroup$ about 11 years worth of solar power collected over the whole surface of the Moon. Solar irradiation of 53.1 petawatt. Create lenses (solar sail like mirrors?) big enough... $\endgroup$
    – SF.
    Jul 5 '16 at 21:11
  • $\begingroup$ @SF. True... I wish I would once work on such a project. :-( Btw, in our current world, we can't even terraform the Sahara. $\endgroup$
    – peterh
    Jul 5 '16 at 21:46
  • $\begingroup$ and with current state of hibernation technology we'd overshoot by a couple centuries. ;) $\endgroup$
    – SF.
    Jul 5 '16 at 22:07
  • $\begingroup$ @SF. Consider a network of tremendous photovoltaic plants, a network of water desalination plants and a network of palm farms. It could give work to a billion of people and also solve the oil problem of the world, on a zero-CO2 way. The only reason why it doesn't happen that nobody cares on it. $\endgroup$
    – peterh
    Jul 5 '16 at 22:07
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    $\begingroup$ @DNA We doesn't get it from the athmosphere, we get it from the proteins we eat. And the plants get it from the nitrate salts in the earth (or, a few of them, by microbes who are really capable to get it from the air). $\endgroup$
    – peterh
    Aug 12 '16 at 4:02

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