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Humans have colonized the subsurface oceans of Europa - building large cities embedded in the icy crust, hanging beneath it, and resting on the rocky seafloor. These colonists mine metals for construction from the mantle and harvest local fauna for food - but where do they get their air?

Known resources:

  • Europa has a thin oxygen exosphere.
  • The ocean is mostly water, and it's salty.
  • The seafloor is in contact with a rocky mantle composed of mafic rock.
  • Hydrothermal vents produced by tidal heating are common, and they release Earth-analogous minerals into the water.
  • The ocean is enriched in oxygen due to radiolysis and crustal ice circulation.
  • Fusion technology exists, so fusion-associated helium isotopes are available
  • Resource can be imported or mined off-world but only if no cheaper alternatives exist

What resources would be most efficient to draw on in order to create air breathable for whole lifetimes inside the colonies? Oxygen seems abundant, but assuming many of the submarines on this world will be pressurized, colonists won't want to risk oxygen toxicity. Thus, other gases need to be mixed in.

What resources can be drawn on most efficiently and combined to make breathable air?

One starting point might be looking at breathing gases.

CLARIFYING EDIT: Oxygen is abundant, as evidenced by the list of resources above. I'm looking for an answer that specifies how to achieve a healthy atmosphere beyond just getting oxygen because just oxygen is poisonous. How can other complimentary gases be harvested?

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    $\begingroup$ Humans can breath a pure oxygen atmosphere if the pressure is significantly less than one Earth atmosphere. All the Apollos missions used pure oxygen at 5 pounds per square inch, much thinner than sea level air pressure. Presumably there would be a source of nitrogen for the local lifeforms and for food produced by the colonists. Therefore they could use that source of nitrogen to produce nitrogen gas for the atmosphere of their colonies. $\endgroup$
    – M. A. Golding
    Jan 21, 2020 at 17:36
  • $\begingroup$ @M.A.Golding I didn't know that pure oxygen had been used in space exploration before, that's interesting. I anticipate these colonists will need much greater pressures than 1 atm to combat the pressure of the deep sea, however. $\endgroup$
    – Zxyrra
    Jan 21, 2020 at 17:39
  • $\begingroup$ @Zxyrra Why? The structure holds the pressure of the sea, not some sort of air balance from inside. $\endgroup$
    – Trevor
    Jan 21, 2020 at 17:40
  • $\begingroup$ @Trevor I assumed that a lesser pressure difference would require less expensive structures to maintain. Knowing that the pressure in an ocean as deep as Europa's is likely extremely high and that mining metal underwater is expensive, I figured boosting internal pressure would be the cheapest way to build. $\endgroup$
    – Zxyrra
    Jan 21, 2020 at 17:47
  • $\begingroup$ @Zxyrra only if you don't plan on humans living there $\endgroup$
    – Trevor
    Jan 21, 2020 at 17:47

3 Answers 3

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It seems very likely that Europa has a vast subsurface salt water ocean. Such an ocean would in all likelihood contain some nitrogen as dissolved gas, nitrate or ammonium salts or other more complex amides and amines. Such chemicals could be processed to release the nitrogen for use in a habitat. The exact method would depend on the form that nitrogen takes but unless it occurs at a very low concentration and requires a lot of work to concentrate it, it should be relatively easy to extract via an appropriate molecular sieve or ion exchange method.

Oxygen is also likely to be dissolved in the ocean and might be released just by applying a vacuum. If this did not produce enough electrolysis could be used to split water into hydrogen and oxygen.

I very much doubt that the local fauna would be on the menu. Having a separate biogenesis and evolutionary path in an environment significantly different to the earth (ocean depth, lack of significant atmosphere and gravitation for instance) it is highly unlikely that the same biochemistry found in life on earth would be replicated. There might be some similarity in some molecular reactions but there would in all likelihood be many variants some toxic to human life in the same way that random organic compounds from a lab might be toxic.

For example would life be based on DNA or use pentose sugars? Would it use the same amino acids? Would they be the same handedness? How much of this would evolve in the same way on Europa?

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  • $\begingroup$ Thanks for addressing nitrogen acquisition. I agree that different biochemistry might not be compatible and I agree that much of the life on Europa should be inedible. $\endgroup$
    – Zxyrra
    Jan 21, 2020 at 17:36
  • $\begingroup$ Also seeking out new life just to eat it seems wrong. $\endgroup$
    – Trevor
    Jan 21, 2020 at 17:42
  • $\begingroup$ Is dissolved nitrogen inevitable or is that just a consequence of Earth's atmosphere interacting with the ocean on Earth? Would an ocean world lacking air above necessarily still have substantial nitrogen dissolved in it? Also @Trevor that is fully intentional; hydroponics could support the whole population but having people eat "exotic alien crustaceans" bolsters a man-vs-nature theme. $\endgroup$
    – Zxyrra
    Jan 21, 2020 at 18:13
  • $\begingroup$ Here's some supporting documentation on the Nitrogen question: lpi.usra.edu/meetings/LPSC98/pdf/1418.pdf $\endgroup$
    – Morris The Cat
    Jan 22, 2020 at 14:09
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    $\begingroup$ Right. There's no way to be sure one way or the other till we land probes there, but there's no reason there WOULDN'T be plenty of ammonia around for the colonists to use, which should address OP's problem nicely. $\endgroup$
    – Morris The Cat
    Jan 22, 2020 at 14:41
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Cant you obtain a starting supply of oxygen from water itself via electrolisis? I dont know if its the best way to obtain it, but its a way. And you still have to get the rest of the gases to get the atmosphere. Once there, you can get oxygen and food from hidroponic farms (I guess they are not consuming ONLY local fauna)

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    $\begingroup$ Electrolisis of water seems the way to go. Water is plentyful and electrolisis is a relatively simple technique. The only drawback is the large need of electric power. As they have fusion power, this shouldn't really be an issue. $\endgroup$
    – quarague
    Jan 21, 2020 at 16:00
  • $\begingroup$ "And you still have to get the rest of the gases to get the atmosphere" this is the main point of the question. Oxygen is abundant on Europa and can be filtered from the water, mined from the ice or split from electrolysis. The main point of the question is that you need more than oxygen to build an atmosphere - and that's where the problems arise. Can you specify how to do the rest? $\endgroup$
    – Zxyrra
    Jan 21, 2020 at 16:02
  • $\begingroup$ See clarification edited into the question $\endgroup$
    – Zxyrra
    Jan 21, 2020 at 17:11
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There are various methods out there, some more effective than others.

  1. Extract diluted oxygen. There's always air in water, its a given. You would generally extract the air shaking the water, causing the air to escape. That being said, this is not turning water into air, its just removing air that's already there.

  2. The Electrolysis Approach. Popular as a science fair experiment, this method uses electrodes to add large amounts of energy to the water. This overloads the water molecules, causing the water to separate into hydrogen and oxygen. While this is a very cool and science-y approach, it does have one problem: Water by itself does not conduct energy very well, its the salts in the water. As a result, you have to add salt to the solution in order for this approach to be effective. Unfortunately, this salt breaks down into chlorine gas during the process, poisoning the resulting air. It is possible to filter out the chlorine, but it would be too expensive on a large scale.

  3. Boil the water. You know those bubbles in boiling water? Those are air bubbles made from the breakdown of water molecules. This approach is almost as effective as electrolysis, but without the chlorine. If I were your hypothetical colonists, I would use this approach, as it also solves the problem of heating the colony. All in all, this is the best approach.

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