Methane Breathing Aliens

[Brian-M]

Watching an old episode of Babylon 5 recently, I began wondering about the plausibility of methane breathing aliens (specifically, methane breathing motile intelligent aliens). Science fiction is full of methane breathing aliens, but how realistic are they?

To make use of methane, it'd need to react with something, probably oxygen. You can't have significant amounts of oxygen in a methane based atmosphere, because the combination would be potentially explosive, so the oxygen would have to come from another source.

Is there any plausible way that enough oxygen could be released by chemical reactions within an organism to make methane breathing aliens a realistic possibility?

Or is there anything else the methane could plausibly react with for the same results?

(Yes, I know that some bacteria can feed off methane by combining it with oxygen from the atmosphere, produced internally from photosynthesis or derived from nitrous oxide. But I don't think these processes would scale up effectively enough to be useful to large organisms.)

[casebro]

If we consider their metabolism being opposite of ours- we breathe oxygen and eat 'fuel', they would breath methane, so need to eat oxygen. Our oxygen is replenished by plants, they would need a replenishable source, an 'oxygen fixing' plant. I assume an organic source, since if it was mineral it would all have been used up during billions of years it took to evolve intelligent life.

Now you all can go ahead and invent the rest of the ecological system- plants, digestion, enzymes,... and make room for a source of building blocks for the alien bodies.

[casebro]

"Big Bang and Abiogenesis Origination theory" - the planet used to have a methane atmosphere, until the geology released enough O2 to explode. Which left CO2 and water. Geology went on contributing more oxygen. The rest is history.

[eirik]

I read 'Methane Breaking Aliens'..

Carry on

[Squeegee Beckenheim]

Imagine their version of oxygen bars...

[anglolawyer]

Originally Posted by casebro

"Big Bang and Abiogenesis Origination theory" - the planet used to have a methane atmosphere, until the geology released enough O2 to explode. Which left CO2 and water. Geology went on contributing more oxygen. The rest is history.

No it isn't. It's almost all pre-history

[Lukraak_Sisser]

You could have a reaction between methane and sulfur, where sulfur would be a solid fuel which one could eat while breathing methane.
Its also reasonably possible to get a temperature range where CH4 is a gas and the reaction products are either a gas/liquid or even solid to allow cycles.
But wether these reactions would be truly able to become sustainable I don't know.

[Dinwar]

Originally Posted by casebro

the planet used to have a methane atmosphere, until the geology released enough O2 to explode. Which left CO2 and water. Geology went on contributing more oxygen. The rest is history.

The more commonaly accepted theory is that photosynthetic organisms (either cyanobacteria or something very similar to them) pumped enough O2 into the atmosphere to react with the carbon mollecules in it. A planet with little O2, or in which chemosynthetic organisms became dominant, wouldn't have those issues.

Organic mollecules can form stable pools of liquid. Considering the fact that photosynthesis (as we know it on Earth, anyway) uses water as part of the process, it's not unlikely that any life on these planets wouldn't have evolved Earth-like photosynthesis. Which means, they would be less likely to pump oxygen into the atmosphere. And without an Oxygen Revolution you'd be able to form a stable atmosphere composed of combustable materials (remove any one of the four apexes in the Fire Tetrahedron and you don't get fire).

This is the really tricky part of exobiolog (xenobiology? anyone ever come up with a term for this?): it is incredibly easy to forget that Earth-like life only represents a subset of potential pathways evolution can take. And even on Earth there are three ecologies: photosynthetic, chemosynthetic, and lithophile. We may simply not know enough to be able to answer these questions yet.

[Sunstealer]

If you have a methane atmosphere then how little oxygen is required to make that flammable?

[Dinwar]

I did a quick Google search for a methane MSDS. The lower limit of flamability is 5%, while the upper limit is 15%. What that means is that above a concentration of 15% in the atmosphere, methane won't actually burn. So if you replaced nitrogen with methane in our own atmosphere, it wouldn't burn for quite some time. What would happen is that the methane would degrade in the presence of oxygen (fire is an uncontroled exothermic chemical reaction; individual mollecules reacting isn't technically fire). Once it got down to 15% then yeah, the atmosphere would catch fire.

This is kind of a backwards way to answer your question, but I think it does: The real issue isn't going to be combustion (at least, not for a while), but rather having enough methane to breath.

[dlorde]

I'm told there are methylotrophic bacteria that oxidise methane and methanol, but what are the energetics of such a metabolism? Would it be able to support multi-cellular life? could one envision mitochondria-like organelles that could generate sufficient energy?

[Hellbound]

Originally Posted by Dinwar

I did a quick Google search for a methane MSDS. The lower limit of flamability is 5%, while the upper limit is 15%. What that means is that above a concentration of 15% in the atmosphere, methane won't actually burn. So if you replaced nitrogen with methane in our own atmosphere, it wouldn't burn for quite some time. What would happen is that the methane would degrade in the presence of oxygen (fire is an uncontroled exothermic chemical reaction; individual mollecules reacting isn't technically fire). Once it got down to 15% then yeah, the atmosphere would catch fire.

This is kind of a backwards way to answer your question, but I think it does: The real issue isn't going to be combustion (at least, not for a while), but rather having enough methane to breath.

Now I am curious, though. Is that 5% to 15% figure for concentrations inside our atmosphere? Where we're 78% nitrogen?

Would the figures differ if it was all either methane or oxygen? No Nitrogen "buffer" in the way?

ETA: Found this interesting article at http://en.wikipedia.org/wiki/Explosive_limit:

Quote:

Oxygen enriched atmospheres lower the LFL and increase the UFL. An atmosphere devoid of an oxidizer is neither flammable or explosive regardless of the fuel gas concentration. Increasing the fraction of inert gases in an air mixture raises the LFL and decreases the UFL.

So that 5% to 15% is going to grow, but no idea how far towards 0% and 99.9% it would be

As an aside, temperature and pressure of the atmosphere also come into play.

[Brian-M]

Originally Posted by Lukraak_Sisser

You could have a reaction between methane and sulfur, where sulfur would be a solid fuel which one could eat while breathing methane.
Its also reasonably possible to get a temperature range where CH4 is a gas and the reaction products are either a gas/liquid or even solid to allow cycles.
But wether these reactions would be truly able to become sustainable I don't know.

Googling it, I see that some microbes actually do feed off methane and sulfur. http://aem.asm.org/content/72/9/6257.abstract

But would I be right in assuming that the amount of energy produced by this reaction would be far less than the energy from a methane-oxygen (or oxygen-carbohydrate) reaction?

[Libra]

Originally Posted by casebro

If we consider their metabolism being opposite of ours- we breathe oxygen and eat 'fuel', they would breath methane, so need to eat oxygen.

I might have this completely wrong, but a slight twist on this view could be : we breathe Oxygen, eat "fuel" and our interflora causes us to produce Methane as a waste gas.

They would thus need to breathe Methane, also eat "fuel" and have interflora and a digestive system that produces Oxygen ?


With the expected Methane-Oxygen reaction, farting for these lifeforms could be fatal.

[Wolrab]

Originally Posted by Libra

I might have this completely wrong, but a slight twist on this view could be : we breathe Oxygen, eat "fuel" and our interflora causes us to produce Methane as a waste gas.

They would thus need to breathe Methane, also eat "fuel" and have interflora and a digestive system that produces Oxygen ?


With the expected Methane-Oxygen reaction, farting for these lifeforms could be fatal.

Or a defense mechanism!

[Dinwar]

Originally Posted by Brian-M

Googling it, I see that some microbes actually do feed off methane and sulfur. http://aem.asm.org/content/72/9/6257.abstract

But would I be right in assuming that the amount of energy produced by this reaction would be far less than the energy from a methane-oxygen (or oxygen-carbohydrate) reaction?

Probably not. It's almost certainly more comlicated than that. Also, remember that Earth-like life only exists at certain temperatures and pressures. Outside of that range you'd have to re-do the calculations (pressure and temperature as so important to this sort of thing that we've developed a standard method of looking at how these parameters change things: P/T Space).

[luchog]

Originally Posted by Lukraak_Sisser

You could have a reaction between methane and sulfur, where sulfur would be a solid fuel which one could eat while breathing methane.
Its also reasonably possible to get a temperature range where CH4 is a gas and the reaction products are either a gas/liquid or even solid to allow cycles.
But wether these reactions would be truly able to become sustainable I don't know.

There is a variety of life that doesn't have the regular oxygen-carbon cycle, but which metabolize hydrogen sulfide, primarily in deep-sea vents.

[Mark6]

Originally Posted by Libra

I might have this completely wrong, but a slight twist on this view could be : we breathe Oxygen, eat "fuel" and our interflora causes us to produce Methane as a waste gas.

They would thus need to breathe Methane, also eat "fuel" and have interflora and a digestive system that produces Oxygen ?


With the expected Methane-Oxygen reaction, farting for these lifeforms could be fatal.

No more fatal than for us. There is no fundamental difference between adding methane to oxygen, and adding oxygen to methane. The two gases do not just ignite on contact. And even if you are foolish enough to apply a match, results are almost never fatal.

[luchog]

Originally Posted by Brian-M

Googling it, I see that some microbes actually do feed off methane and sulfur. http://aem.asm.org/content/72/9/6257.abstract

But would I be right in assuming that the amount of energy produced by this reaction would be far less than the energy from a methane-oxygen (or oxygen-carbohydrate) reaction?

There are entire localized ecosystems that live off of hydrogen sulfide metabolism; some of them quite bizarre. Some of these are clustered around volcanic vents that spew superheated hydrogen sulfide-rich waters; others form around hydrogen sulfide seeps, creating a strange sort of underwater "sea" that mirror terrestrial beaches with transition layers, river-like and tide-like flows, and clusters of hydrogen sulfide metabolizing organisms. Said organisms include various bacteria; polychaete and annelid worms; clams, mussels and snails; crabs, shrimp and other crustaceans.