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I was wondering if it would be possible for humans to be genetically modified enough to the point where they could breathe Martian atmosphere? Could you alter lungs to process CO2 into O2? Would a process akin to photosynthesis be needed? Any ideas would be appreciated. Thanks!

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    $\begingroup$ Processing CO2 into O2 is a well known process called photosynthesis... $\endgroup$ – L.Dutch Mar 22 '17 at 19:51
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    $\begingroup$ A lung is going to produce 0₂ from C0₂? That would be modification I don't think a human body could support. $\endgroup$ – paparazzo Mar 22 '17 at 19:55
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    $\begingroup$ The answer is no, obviously. Not unless you first modify the Martian air to have at least 0.1 atm partial pressure of oxygen... $\endgroup$ – AlexP Mar 22 '17 at 19:58
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    $\begingroup$ You could modify the skin to be photosynthetic, but then you'd have to run around naked, and that would cause a whole nother host of issues. $\endgroup$ – DCShannon Mar 22 '17 at 23:51
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    $\begingroup$ I think you might be able to come up with something, though it may be not what you wanted. Oxygen is a must, as your body literally burns fuel. To turn CO2 into oxygen you need photosynthesis, from genetically modified human skin, maybe with large sprouting crests, or from a symbiotic relationship with GM algae. Then the really awkward/cool part. Because of the paucity of both atmosphere and energy from sunlight your humans need to be modified to have drastically slower metabolisms. They would barely move, spend long periods in torpor - but they may live for millenia! $\endgroup$ – Grimm The Opiner Mar 23 '17 at 12:15
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No.

As has been pointed out in the comments above, there is a distinct lack of oxygen.

There also happens to be a distinct lack of air itself. Assuming you created skin that could survive the low (from our standpoint, near vacuum) pressure, you would also have to create lungs that are thin enough for air transport but will keep all of the rest of the bodily fluids in the body.

Then you have the issue that the low pressure outside would make it very difficult to transport oxygen or anything else into the body.

I'm afraid that without a higher pressure, some oxygen, and a lot of insulation, no one is going to walk the surface of Mars without a space suit. I am using the term space suit on purpose because there's not much in a vacuum suit that you wouldn't need in a Mars suit.

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  • $\begingroup$ Don't forget the low Martian temperatures. $\endgroup$ – sphennings Mar 22 '17 at 21:04
  • $\begingroup$ Aw, but I remember reading books about people living on Mars. All they needed was some sort of oxygen concentrator gizmo in a backpack! $\endgroup$ – Hot Licks Mar 22 '17 at 21:44
  • $\begingroup$ @HotLicks Robinson Crusoe on Mars is one my favorite movies with that premise. $\endgroup$ – Schwern Mar 23 '17 at 0:17
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    $\begingroup$ @HotLicks Was the planet partially terraformed already? (I.E more atmosphere?) $\endgroup$ – Catprog Mar 23 '17 at 6:05
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    $\begingroup$ @Schwern is that an early draft of The Martian? $\endgroup$ – John Dvorak Mar 23 '17 at 6:13
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Strictly speaking, purely in terms of the question of processing the gases involved, no changes are needed to human lung physiology to process carbon dioxide. They already do process it; it's just that it's a waste product to be expelled, rather than a 'raw material' to be taken in.

The challenge is really to come up with a physiological modification that allows the $\require{mhchem}\ce{CO2}$ to be substituted metabolically for $\ce{O2}$. At a high level, oxygen is the final electron acceptor at the end of the electron transport chain (link modified from the original):

The final acceptor of electrons in the electron transport chain during aerobic respiration is molecular oxygen although a variety of acceptors other than oxygen such as sulfate exist in anaerobic respiration.

Interestingly, carbon dioxide is known to be an alternative electron acceptor in certain methanogenic bacteria (emphasis added):

Methanogenesis in microbes is a form of anaerobic respiration. Methanogens do not use oxygen to respire; in fact, oxygen inhibits the growth of methanogens. The terminal electron acceptor in methanogenesis is not oxygen, but carbon. The carbon can occur in a small number of organic compounds, all with low molecular weights. The two best described pathways involve the use of acetic acid and inorganic carbon dioxide as terminal electron acceptors:

$\ce{CO2 + 4 H2 → CH4 + 2H2O}$

So, somehow you have to genetically engineer your Martian explorers to "eat" (inhale?) hydrogen, which their bodies then "burn" with atmospheric $\ce{CO2}$ to form methane and water, while releasing energy. You could catch their exhaled methane to use as, e.g., vehicle fuel, but you'd have the same no-oxygen-around conundrum as what causes breathing problems for us unmodified humans.


For interest, that above reaction of carbon dioxide and hydrogen is called the Sabatier reaction, which is in active use on the International Space Station as a method for processing exhaled $\ce{CO2}$ and recovering water. The methane generated there is apparently just vented into space, but the same sort of reaction is being investigated (NASA pdf link) for actual Mars missions, as a potential source of fuel, generated from solar power and local carbon dioxide.

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    $\begingroup$ Look at the heat generation in the Sabatier reaction. You'd generate a MJ for every 100g of CO$_2$ you process. If you get symbiotic Sabatier microbes in your lungs, maybe you can now breathe fire? $\endgroup$ – kingledion Mar 23 '17 at 0:11
  • $\begingroup$ @kingledion Could perhaps be consciously controlled. Enzymatic reactions are well known to be able to take one big energetic leap and break it down into multiple small steps (case in point, the actual mitochondrial electron transport chain!) better suited for extracting biologically useful amounts of energy. Posit the same thing with methanogenesis -- normal metabolism, but plus the ability to decouple it and allow massive, rapid heat generation & firebreathing, like you said. Parasite Eve, anyone? :-) $\endgroup$ – hBy2Py Mar 23 '17 at 0:20
  • $\begingroup$ It seems (from the poisonous effect) that carbon monoxide is more active than dioxide. Could we engineer to use it as oxygen replacement? Can we get it on Marses? $\endgroup$ – Džuris Mar 23 '17 at 0:32
  • $\begingroup$ @Džuris It sounds like there is trace $\ce{CO}$ in the Martian atmosphere, but there's probably too little for it to be of practical use. $\endgroup$ – hBy2Py Mar 23 '17 at 3:17
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    $\begingroup$ @Džuris The poisonous effect of carbon monoxide is irrelevant; the toxicity is caused by the inability of hemoglobin to bind both oxygen and carbon monoxide at the same time, combined with its persistence (it can't be "unbound" in the lungs). It's a denial-of-service attack on our red blood cells, basically. Carbon monoxide is used industrially as a reducing agent - it "steals" oxygen (e.g. in iron ore smelting, binding the oxygen in the iron oxides in carbon dioxide). But it's pointless anyway, the air pressure on Mars is simply too low regardless. Venus might be a lot more interesting :) $\endgroup$ – Luaan Mar 23 '17 at 9:13
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You would require more energy to process the C0₂ into oxygen than you would gain by then performing the reverse during aerobic respiration. Plants get this energy from sunlight. Humans only harness energy from aerobic respiration. Additionally the martian atmosphere is only 0.6% the pressure of Earth's. This sounds pretty impossible to me.

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  • $\begingroup$ Even if you want to try to use photosynthesis. Our skin doesn't have enough surface area for that to work on Earth and Mars gets less sunlight than we do. $\endgroup$ – ShadoCat Mar 22 '17 at 20:42
  • $\begingroup$ @ShadoCat Less sunlight and less carbon dioxide. People tend to forget that the latter is just as important as the former :) And of course, you also need the electron donor (water for most photosynthesising organisms on Earth). But it's quite enough to say that photosynthesis couldn't feed our metabolic needs on Earth, and the martian environment is much worse :D $\endgroup$ – Luaan Mar 23 '17 at 9:34
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In reality this likely wouldn't be possible. Consumption of Oxygen is literally ingrained into every cell of our being. Our bodies function the way they do in great part to how oxygen reacts with other elements. Even on earth, those types of organisms are classified as an entirely different kingdom (plantae) and any genetic modification to that degree would essentially make people a completely different species, one that likely can't function at a level we would call sentient...At least to our current understanding of biology.

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  • $\begingroup$ Plants also consume oxygen. Their metabolism is entirely supported by the sugars they produce during photosynthesis and ambient oxygen. If you want photosynthesising organisms that have oxygen as nothing more than a waste product, you need to go all the way to Archaea or at least cyanobacteria (some suggest that the choloroplasts in plants were originally cyanobacteria endosymbiotes), which worked mostly in a reducing atmosphere. $\endgroup$ – Luaan Mar 23 '17 at 9:45
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Let's assume you could get your lungs to turn co2 into oxygen. Why go through the trouble of getting the co2 from the atmosphere? Just design the lungs to convert the co2 you already have in you.

That said, you could design a proteindriven transport through the lungs to overcome the objections about the pressure difference that impedes diffusion, but the atmosphere on Mars does simply not provide enough oxygen and the energy to turn co2 into o2 cannot come from a human only because we get energy by burning o2.

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