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In one of the solar system documentaries it was mentioned there are moons in the solar system with lakes of frozen methane.

Assuming humans or robots or whatever could make it there, would there be a way to extract energy from frozen methane without using oxygen? Otherwise, it would seem that the oxygen would have to be carried there as well.

Is it possible to recycle the oxygen efficiently enough to burn methane again and again?

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    $\begingroup$ I would imagine that any oxidizing agent should work. While oxygen has worked on earth, sulfur should do the trick. $\endgroup$
    – bobthejoe
    Oct 1 '12 at 22:46
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    $\begingroup$ ... or add a bit of chlorine trifluoride $\endgroup$
    – 410 gone
    Oct 3 '12 at 14:15
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The planet will have gaseous oxygen if it does have an atmosphere, and if that is the case then with enough energy(like a spark) atomized hydrocarbons could be lit for energy. What is atomizing you say? Well its just breaking a liquid apart into little particles, making it easier for the oxygen to react with said methane.

As for recycling the oxygen from the combustion reaction, it will not be possible to do in an energy efficient way, CO2 is too stable and the bonds are too strong.

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    $\begingroup$ "The planet will have gaseous oxygen if it does have an atmosphere." - Do you have a source for this? Any atmosphere will have a little oxygen, but I don't think the mostly methane atmospheres have enough to make it a viable source of energy. $\endgroup$
    – Kevin
    Oct 3 '12 at 2:07
  • $\begingroup$ Methane in the atmosphere will be low because it will be in liquid form, boiling pt of methane -164°C boiling point of oxegen -182.95°C. Also oxygen is the 3rd most abundant element in our Galaxy. en.wikipedia.org/wiki/… $\endgroup$
    – Mike
    Oct 3 '12 at 3:14
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    $\begingroup$ Oxygen may be the third most abundant element, but not necessarily in its free form. Silicon is one of the most abundant element in the earth's crust, but not as Si(s). $\endgroup$
    – Ben Norris
    Nov 15 '12 at 11:43
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Is it possible to recycle the oxygen efficiently enough to burn methane again and again?

Don't think so. Sounds a little like perpetual motion. Assuming you're burning the methane into $\mathrm{CO_2}$ and $\mathrm{H_2O}$, you would need a large supply of something that would regenerate the $\mathrm{O_2}$. The water's a much easier target -- you could electrolyze it, for example, but you'd only recover 1/2 the oxygen each cycle.

I can't think of many things to act as chemical $\mathrm{X}$ in: $\mathrm{CO_2}+\mathrm{X}\rightarrow{}\mathrm{CX}+\mathrm{O_2}$. That would be a killer reaction for the "carbon capture and storage" crowd -- we could just process our carbon emissions into oblivion! Goodbye greenhouse effect! Would sure help terraform Mars!

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  • $\begingroup$ Nor perpetual motion ideology, think more like trees or algea or what ever process that take sunlight or a planets core thermal energy for recycling $\endgroup$
    – jimjim
    May 24 '20 at 13:15
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No, unless you bring an oxidizer with you

Considering just the chemistry, any oxidiser would work. Unfortunately there isn't any free oxidiser on such worlds.

There is in fact only one solar system body with known hydrocarbon lakes, that is Saturns moon Titan. And while it does have a lot of oxygen, that is all bound up in water ice. There is no free oxygen (or other oxidiser) in Titans atmosphere.

In general you shouldn't expect any free chemical fuel lying around on a celestial body. Chemical systems tend to move to an equilibrium at their lowest energy state, unless there is some mechanism that pushes them out of that equilibrium, like photosyntesising plants on earth. If there were any free oxygen in Titans atmosphere that would have reacted with the hydrocarbons billions of years ago (mediated by e.g. photodissociation in the atmosphere).

You also can't re-use oxygen or anything else without some other form of energy input. In the theoretical best case the energy that you gain from burning methane is exactly the same energy that you need to put in to extract the oxygen from the combustion result (CO₂ and water) and re-form the oxygen and methane. In practice you need to put in a lot more as such reactions are far from 100% efficient.

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