My castaways on Saturn live on fibrous organisms that extract electricity from the turbulence of the atmosphere. They have chosen to adapt to the planet by implanting electrolysis equipment that converts water to hydrogen and oxygen from an internal battery that they can recharge from those organisms. This permits them to "breathe" in Saturn's atmosphere.

  • The electrodes end in a mesh similar to an inferior vena cava filter, on which are mounted many microvilli on which a water splitting enzyme (a highly simplified and very stable version of photosystem II is exposed. The electrical current entering the filter powers these enzymes. Blood is not directly exposed to the electric current -- the enzyme ensures only water is reacted. For convenience I will call this the 'internal gill'.

  • The internal gill is in the portal vein, which passes blood from digestive organs to the liver. This gives an extra layer of protection against potential clotting at the gill, and delivers oxygen in the same manner is it is received during fetal development.

  • The castaways inhale mostly H2 at 15 atm of pressure with a few impurities (dealing with alkaline pH and H2S is a separate issue). They exhale H2 with a small (40 torr - see table) partial pressure of carbon dioxide. A trace of oxygen also gets out, but on Saturn this is not nearly enough> to support combustion.

This system allows people to breathe the right partial pressure of oxygen and exhale the normal amount of CO2 and all is great, I hope, except ... I can't expect castaways on Saturn to invent this from scratch! With this sort of progress you always have to have a certain learning curve, and there aren't enough of them to survive the curve.

While the system might be used elsewhere in space (I made an answer about this regarding Mars), here we're still quite early in the Conquest of Space and we need an Earthly antecedent for the invention of electronic respiration. For now I'm going to say that this invention was by remnants of the Navy Seals, who organized New Atlantis off the California coast after the disintegration of the U.S. What began as a shallow-water network of submerged safe houses for exfiltration of refugees and smuggling ended up moving much deeper. To enjoy the freedom of the seas, the divers perfected the internal gill, and with it, pioneered a new society.

  • On Earth, producing 66% hydrogen and 33% oxygen, most but not all of which is used up and exhaled as carbon dioxide, has some problems. It might be flammable if enough oxygen gets through, though I think it would have to be 25% or more so that may not be a huge issue. The bigger problem is that it is hard to carry out the CO2. If the lungs are 1/3 filled with CO2, partial pressure something like 250 torr instead of 40, and increasing with depth to colossal levels, the person will be in a lethal state of acidosis. Diluting it with nitrogen isn't an option due to nitrogen narcosis. Hydrogen is sort of an option, but splitting that much water would waste most of the battery power, and flammability becomes an issue for sure.

  • One option is to give up entirely on having lungs exhaling gas. Filling them with sea water doesn't sound good, but if they are modified with a few genes to produce alpha-fetoprotein (an albumin-like substance) and sodium and chloride channels, they could maintain themselves with an amniotic fluid like substance unless and until the transgenes are deactivated.

  • I'm also going to allow myself one Fact Not In Evidence and say that when there is fluid in the lungs and oxygen in the portal vein, the medulla instinctively "realizes" there is a fetal circulation pattern, even in an elderly adult. The person loses the impulse to breathe and feels perfectly comfortable never doing so. There is no evidence to support that, but the notion of the Seals giving themselves Ondine's Curse to survive in their habitat is too extreme. (They could do it, with focused ultrasound to the medulla ... let's not go there)

But now -- what to do with the CO2??? [Response: The carbon originates from food. Food energy could be provided by hydrogen given the right modifications, but this starts with humans requiring a wide range of essential nutrients.]

  • It can be converted to bicarbonate and excreted in the urine - with just the right level of bicarbonate vs. urea or even carbonic acid the pH can be controlled, and the kidney tubules can already do that (if in far lesser quantity). The problem is, this works out to secreting kilograms of bicarbonate daily - it's just not going to be feasible to drink water and produce so much filtrate.
  • Or we can picture CO2 being bubbled away from the skin. Maybe a protein actively excretes it, at a considerable cost in energy. But we're talking about as much CO2 bubbling away as in 1/19 of a breathe, in the span of time it takes to breathe. It seems hard to do.
  • Or, we can go metabolic. Convert the CO2 into some kind of food, and then the electrical energy is not being wasted in H2 but recycled. The problem is, CO2 goes to formic acid, formaldehyde, methanol, methane ... it's not the most palatable menu. We could convert it to formaldehyde then polymerize that to carbohydrates (glucose or phosphoglycerate derivatives) but that seems quite complicated, especially at such an early point in history.

Help me sand the rough edges off this. How do we make electronic respiration in deep seas of Earth as plausible but simple as possible, especially regarding CO2 clearance? And ... how implausible is that?

  • $\begingroup$ Sorry, how can they inhale hydrogen and exhale hydrogen and CO2? Where do they take the carbon and the oxygen from? $\endgroup$
    – L.Dutch
    Commented Mar 21, 2021 at 4:27
  • $\begingroup$ A fish tank on a trolley & an oxygen tank? pump blood into tank > bubble oxygen through it with air pump via air stone > pump blood bac > rinse & repeat. $\endgroup$
    – Pelinore
    Commented Mar 21, 2021 at 4:33

3 Answers 3


Carbon Dioxide + Hydrogen (+ <Details>) = Free booze!

If you have an unlimited source of CO2 and Hydrogen (hydrogen in water in the sea, hydrogen in the saturn atmosphere) , there are multiple ways you can convert that to ethanol. This can be mixed 2:3 with water to make Vodka, or 1:14 with fruit juice to make Cider, and used to stock the colony bar.

This is probably best used to make rocket fuel, but if its occurring close to the body as part of a respirator system, a little bit of surplus ethanol getting into the blood stream sounds like a benefit - it means you don't need to take your respirator off to take a swig out of your hip flask.

Your body can also break down ethanol to energy. 1 gram of alcohol is 29 kJ. 40 grams of alcohol (50 ml) is the energy content of a cheeseburger. That's 5 standard drinks (Under the AU guides anyway). Spread over a few hours you'll feel the effects but wont be considered intoxicated.

... And plastic:

There are a few different ways of making Ethanol, each with their own waste product. I'd lean towards the ones which make Ethylene, as you can use that to make Polyethylene, the most common plastic on Earth. This would be useful for repairing things, building things, etc. It can also be used in 3d printing processes, so you can stockpile polyethylene filament as you make it, and then 3d print parts as required.

A source of plastic inside the body can be used by some smart tech to repair the respirator, or you can excrete it out of the colon as plastic pellets.


we need an Earthly antecedent for the invention of electronic respiration

Here is my regularly scheduled shilling for Peter Watts' Rifters series. You can read em for free... the first one, Starfish, can be found here.

The Rifters who give their name to the series are maintainance crew for deep ocean geothermal power systems, and as such need to live and work on abyssal plains, and are equipped with breathing implants that extract air from water using fuel-cell driven electrolysis.

The things they maintain provide a substantial amount of power to a large swathe of the US, and in the event of an emergency which can't be fixed by automated or remotely operated things they're on hand to sort it out.

It takes a conscious effort to feel the machines lurking where her left lung used to be. She's so acclimated to the chronic ache in her chest, to that subtle inertia of plastic and metal as she moves, that she's scarcely aware of them any more. She can still feel the memory of what it was to be fully human, and mistake that ghost for honest sensation.

Not gonna lie, it isn't entirely cheerful and upbeat.

the ritual takes her, step by reflexive step, to that horrible moment when she awakens the machines sleeping within her, and changes.

When she catches her breath, and loses it.

When a vacuum opens, somewhere in her chest, that swallows the air she holds. When her remaining lung shrivels in its cage, and her guts collapse; when myoelectric demons flood her sinuses and middle ears with isotonic saline. When every pocket of internal gas disappears in the time it takes to draw a breath.

Filling lungs and airways with fluid isn't necessary... diving mammals such as sealions can collapse their lungs and airways and reinflate them at the surface. Humans are already surprisingly capable of deep diving due to phenomena such as blood shift, interesting. Of course, humans do have some non-collapsible bits... sinus passages and so on, hence why the rifters have a mechanism for pumping them full of neutral saline prior to a dive.

Whilst such technology might have military use, there are plenty of commercial and scientific uses for it too. If you're already looking at colonising the system out as far as Saturn, there's mileage in having the ability to drop humans into the deep oceans of the ice moons.

How do we make electronic respiration in deep seas of Earth as plausible but simple as possible, especially regarding CO2 clearance?

You've already got a system that can drive oxygen into blood cells. The gas exchange mechanism you use to do this could work just as well for extracting CO2 from the blood, too. Shifting carbonate ions this way also seems plausible. The waste products can be flushed out of the water-splitting system with the excess water and hydrogen that will be produced.

  • $\begingroup$ Alexey Molchanov free dived to 130 meters, so lungs are pretty collapsible. I found mention of his sinuses and middle ear... seems hard to fathom. Still, flushing sinuses doesn't usually require demons. $\endgroup$ Commented Mar 21, 2021 at 21:41

Pee out the bicarbonate.

Yeah, you already thought of it. With the lungs out of commission, the second best way to CO2 waste is via the kidneys. Kidneys do a fine job at producing bicarbonate and getting rid of it in the pee and they can already augment ailing lungs in this regard. Their lungs dont do much now so your engineered folks have got super kidneys.

Your argument against your own idea:

/it's just not going to be feasible to drink water and produce so much filtrate./

Your scenario /How do we make electronic respiration in deep seas of Earth as plausible but simple as possible/

Your deep dwellers have all the water they want! They are living deep in the ocean. Guzzle it up and pee it out, yes, yes. Your engineered kidney actually concerns itself a lot with maintaining internal tonicity in the context of lots of seawater and salt ingestion.

Now adapting this to Saturn will be tricky. There is less to drink. Possibly some stigma about peeing freely all the time. Thirsty, soggy folks your Saturn dwellers will be. Good think they are not smelling because they are not breathing because the smell might get kind of ripe.


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