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If we assume a planet the size of Earth with an equally dense atmosphere of nitrogen and methane, rather than oxygen, and it's in the goldilocks zone. Would a hypothetical alien species be able to use oxygen for lanterns and stoves the same way we use methane (or natural gas, etc)?

If so, what primary differences in ratios and/or densities of gasses would have to exist? If not, why not?

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    $\begingroup$ Hopefully it's in the Goldilocks zone for methane/nitrogen, which is different from the GZ for other mixtures. Anyway, the ultimate answer is yes - if two gases react with each other producing heat and a flame, you can burn either one of them in an atmosphere made of the other. $\endgroup$ – Florin Andrei Jan 4 '18 at 21:11
  • $\begingroup$ Oxygen masses 32. Methane only 16. So oxygen will tend to sink into low areas, while methane will tend to float and disperse. The are places on earth where carbon dioxide (mass 44) can sink and build up to lethal levels. "Hill, P.M., 2000. Possible asphyxiation from carbon dioxide of a cross-country skier in eastern California: a deadly volcanic hazard. Wilderness and Environmental Medicine, 11: 192-195." ivhhn.org/… $\endgroup$ – Wayfaring Stranger Jan 5 '18 at 16:32
  • $\begingroup$ @WayfaringStranger - yes, but that would not lead to a complete separation of gases. E.g. on Earth, CO2, which is much heavier than O2, can be found throughout the whole atmosphere. It's only pooling in low places on the short term. Long term it tends to disperse. Regardless, a mixture of O2 and CH4 is thermodynamically unstable - the atmosphere would blow up very quickly from a random lightning bolt. $\endgroup$ – Florin Andrei Jan 5 '18 at 19:34
  • $\begingroup$ @FlorinAndrei No, not complete separation, but you might easily find low spots where you could get in trouble. On earth people have even died from CO2 buildup in their basements. $\endgroup$ – Wayfaring Stranger Jan 6 '18 at 17:00
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Yes, it would work.

The difference between "fuel" and "oxidizer" is rather made for convenience, but it's not a fundamental distinction at the macroscopic level. The only differences are at the microscopic level, related to what the electrons do during the reaction. All such processes are redox reactions (reduction-oxidation), where one participant is the reducer, and the other is the oxidizer. That simply means the reducing agent loses electrons, while the oxidizing agent gains electrons; once the electron balance is final, the two components are bound together and the reaction is complete.

The oxidizer doesn't even have to be oxygen, it can be many elements or compounds hungry for electrons.

The bottom line is - you can burn either gas in an atmosphere made of the other. The gases don't care, as long as they react with each other. There are videos online where you can see chemists burning oxygen in an atmosphere of hydrogen, or burning hydrogen in an atmosphere of chlorine, etc. All these are redox reactions.

As to what's the minimum percentage of methane in the atmosphere that could sustain an oxygen flame, I am unsure. But it must be similar to the situation on Earth, where a low-enough oxygen contents in the air will eventually extinguish any flame. I would guess that 20% methane would work just fine for burning oxygen, but that's just a guess, so take it for what it's worth.


As others have pointed out, a methane atmosphere would indicate a very different chemistry at the planetary level, which may or may not be able to sustain life in general. It would definitely not sustain life as we know it.

Also, the Goldilocks zone for a methane atmosphere is different from the same zone for an oxygen atmosphere - it's further away from the star, because methane retains infrared better than oxygen (methane is a "greenhouse gas").


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    $\begingroup$ Looks good, thanks! I've added links to some proposed, related videos at the bottom. $\endgroup$ – uhoh Jan 6 '18 at 0:05
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    $\begingroup$ @uhoh Those links are great! I looked for something on that topic myself, but couldn't find anything. Thank you. $\endgroup$ – Florin Andrei Jan 6 '18 at 1:07
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I agree with Cipher's answer, but just to add, from a certain point of view, Oxygen could be stored and used like a fuel in a situation like that.

Now, as far as aliens doing so, I have some doubt that you can have life (intelligent life if they're using fuel) on a planet with a Nitrogen/CH4 atmosphere cause I don't see how that would actually work and how the resperatory cycles would balance out. I looked into that a little bit and it gets pretty complicated, so, I don't want to say it's impossible, but I suspect it's unlikely, but, if we take your scenario and work with the assumption that there's intelligent life on a Goldilocks planet that breathes N2/CH4 (maybe throw some CO2 in there), on a rocky planet with oceans, I see no reason why they couldn't use Oxygen as fuel, at least, running "oxygen lines" inside their alien homes to make fire, perhaps to cook with - sure. It seems like it would be a useful convenience. You don't gain much energy pulling Oxygen from Silicate rock or Iron Oxide or from water and then using it to burn in a methane atmosphere, so I don't think it would be an energy source, unless they use bacteria to produce oxygen and then, maybe. Oxygen wouldn't concentrate underground the way hydrocarbons do, so in that sense, it wouldn't be drill-able, but as a transportable "fuel like" substance, it would work. I see no reason why that couldn't be done.

If we ever set up an astronaut colony on Titan, which, while much farther away from the earth than Mars, it has several advantages, one being, the surface pressure is manageable, so structures wouldn't need to be able to contain a significant fraction of 14.4 PSI. They'd need to be mostly air tight, but compared to the structural integrity needed to not lose atmosphere to a vacuum, that's easy.

Astronauts/colonists on Titan would be able to collect rocky CO2 and H2O from the Moon's surface and use that to grow plants inside and in time, they would probably have an abundance of oxygen and under certain circumstances, that Oxygen could be used in a similar way to fuel. I think the scenario the way you wrote it is very unlikely, but oxygen being used like fuel on a methane or hydrogen abundant atmosphere, more likely some kind of astronaut colony, there's no reason why that couldn't be done that I can think of.

PS - That's on the speculative side for an answer here, but that's my thoughts on the question.

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    $\begingroup$ Cipher's answer is wrong in several fundamental ways. Yours is correct. As long as two gases react with each other, making heat and a flame, you can burn either one of them in an atmosphere made of the other. I've seen an experiment where oxygen was burning at the end of a pipe in an atmosphere of hydrogen. But I agree with you that chemistry on that planet would be weird and may not be able to sustain life as we know it. $\endgroup$ – Florin Andrei Jan 4 '18 at 21:15
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I think in the spirit of the question, the answer is yes. In an atmosphere like hydrogen or methane that can react with oxygen, oxygen is a resource that allows combustion to occur and therefore represents an energy reserve. For example, here's a demonstration of an oxygen flame in a hydrogen atmosphere.

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    $\begingroup$ Oxygen has no special status in this reaction, other than being the oxidizer, while the other gas is the reducer; one donates electrons, the other receives electrons, that's all. It's not a "resource that allows the combustion to occur"; combustion is simply the reaction of those two gases. It's not "an energy reserve" - both gases can be said to store the energy released by the reaction. $\endgroup$ – Florin Andrei Jan 4 '18 at 22:10
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    $\begingroup$ People get hung up too much on differences between "fuel" and "oxidizer", or reducer and oxidizer; other than the electron transfer at the molecular level, these differences are largely artificial, and only occur in our minds because our atmosphere has a lot of oxygen but not a lot of reducing agents, hence the asymmetry in our thinking. $\endgroup$ – Florin Andrei Jan 4 '18 at 22:10

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