I'm playing around with a story idea that includes vacuum dwelling intelligent life, but I'm not sure I understand the constraints of biochemistry I need to deal with.

There's lots of potential sources of energy and nutrients in space. Radiant energy from stars, the magnetospheres of planets, and so forth, but if if you want to GROW, you need sources of raw materials. Elemental Hydrogen is abundant in the solar wind, but I'm imagining something large (kilometer scale) and solid, which suggests it's going to have to eat something a bit more substantial. I was thinking comets, asteroids, perhaps filter-feeding on clouds of gaseous leftovers from novae and supernovae.

So, the question is, what kind of elements would be needed, and in what kind of quantities? I'm looking for detail in terms of the biochemical lifecycle processes involved. E.g. :extremophile bacteria rely very heavily on elemental sulfur for their metabolic processes (see link below). https://aem.asm.org/content/79/7/2172.full

EDIT: Really what I'm looking for is some help figuring out, based on what a creature like this has available to eat, what their biology would look like. what are they made out of, molecularly? Lots of Carbon? Something else? I'm not really sure what makes sense if you really try to Do The Math in terms of metabolic equations, and I don't have the masters degree in Biochemistry that would let me figure it out for myself.

EDIT the second: People are talking about Silicon, are there gaseous sources of elemental silicon or would this require Asteroid Munching?

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    $\begingroup$ Sorry to rain on your first WB parade Morris, but the answers to "space whales" are good. What else have you got? $\endgroup$
    – Willk
    Aug 18, 2018 at 21:08
  • $\begingroup$ Hey, that's cool. I was apparently too technical in the original google search that landed me on this site. I searched for 'vacuum dwelling life forms' when CLEARLY I should have searched for 'space whales'. Lemme read through the answers to that post and see if I've got more detailed questions. $\endgroup$ Aug 18, 2018 at 21:11
  • $\begingroup$ Ok, so the other post is good, but i'm looking for way, way more detail in terms of the biochemical lifecycle processes involved. E.g. :extremophile bacteria rely very heavily on elemental sulfur for their matabolic processes (see link below). This is the level of detail I'm looking for, but I'm not sure how to phrase the question properly, I guess?aem.asm.org/content/79/7/2172.full $\endgroup$ Aug 18, 2018 at 21:24
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    $\begingroup$ I grok and it will be cool. I love stuff like this. I edited it with the hard science tag and pasted your comments text requesting metabolic biochemistry. No hand wavy reverse fusion for this! $\endgroup$
    – Willk
    Aug 18, 2018 at 22:32
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    $\begingroup$ @StephenG a few years ago I saw a masters-level paper published on the internet that outlined how you could completely replace water with ammonia in EVERY biochemical process in terrestrial life without altering the output of those processes, so I'm not sure I buy that it's not out there. I'm posting here because I'm laying at least 1 in 6 odds that someone with a masters or PhD HAS thought about this, and someone on this board might have read the results. It's not that unreasonable, I don't think. $\endgroup$ Aug 18, 2018 at 23:32

4 Answers 4


Not an answer, but some hints:

One big decision to make is what temperature your critter lives at. One of the advantages of controlled temperature is that you don't need a raft of different enzyme systems for each band of temps you live at. Mammal metabolism is much simpler than amphibian metabolism due to our controlled body temp.

Temp will be logarithmic: Think in terms of percentages of temperature kelvin. If your critter uses liquid helium as it's circulation fluid, it lives between about 2 and 4 K. If it uses parafin, it lives at around 200K.

Temperature will determine what can be a liquid. Life without a liquid to act as a carrier of stuff gets so far beyond our experience that it's just guess work. Each solvent will have a range of temperature it will work at. Water is a poor choice here. Without pressure it sublimes from ice to gas without a liquid state. So you need a liquid that has a lower vapour pressure compared to it's freezing point than water. At cold temps propane might work, at higher temps, gasoline or diesel fuel may work.

The Chemical Rubber Handbook (sometimes referred to as the 'book of random numbers' has freezing and boiling points of lots of liquids, as well as vapour pressure curves for a smaller set.

Water is very polar and is close to the 'universal solvent' All the above are non-polar and have a limited and very different set of things they dissolve. If you can find another polar solvent that is liquid in vacuum, the chemistry will be easier.

With all liquids freezing point can be lowered and boiling point raised by dissolved stuff. So a mix may work better than either liquid alone.

You may want to pressurize the critter. If it has a tough skin, it may be able to maintain an internal pressure sufficient to keep something liquid that would otherwise evaporate.

As to making a living: Some kind of photosynthesis to turn light into stored energy. Either it has diamond/tungsten carbide teeth to gnaw asteroids, or some very fine mesh to catch tiny quantities of dust on the solar wind.

An ecosystem is complex. Needs certain roles filled -- simplified:

  • primary producer -- plants, something that makes a living from light.
  • primary consumer -- herbivore, something that gets it's energy from eating the producers
  • preditor -- something that eats the consumers.
  • decomposer -- critters that recycle the bits and pieces into things that primary producers can use.

There are also nutrient cycles: Space is vast. Unless you are on a planet without atmosphere, you need to deal with how nutrients can be gotten back into a critter.


Let us start with an autotrophic archon. Bacteriorhodopsin is an energy capturing pigment used by some of these ancients.

Bacteriorhodopsin is a protein used by Archaea, most notably by Halobacteria, a class of the Euryarchaeota. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell. The resulting proton gradient is subsequently converted into chemical energy...The bacteriorhodopsin molecule is purple and is most efficient at absorbing green light (wavelength 500-650 nm, with the absorption maximum at 568 nm).

This is light-capturing tech from before the great oxygenation event. As I understand it there is no oxygen, sulfur or other byproduct. It is light, a molecule, and protons.

I was surprised how little hard metabolic biochemistry I could find on where bacteriorhodopsin-using organisms get organic carbon to build their bodies. This old article provides circumstantial evidence that [Halobacteria can use their light-energy capturing abilities to fix CO2.] but I could not find any biochemistry on how they accomplish this feat. (https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.1983.28.1.0033) Probably some can handle CO which would have been a more common molecule on the ancient earth. Maybe without energy needs finding carbon to use for structural purposes was not a big deal. If there is not a lot of competition in a nutrient poor environment, and you can get your energy directly from light, maybe you can scrounge up enough naturally occurring organic carbon to be used solely for anabolic processes.

These space dwellers will live in comets. Comets have all the elements necessary for archaebacterial life.

comet https://universe-review.ca/F07-planets08.htm


One surprising observation is that comets contain a mixture of materials that form at widely varying temperatures. The finding suggests that the materials were created separately and somehow mixed together while forming a comet.

Lisse remarks that "it's really neat to see that the materials we find are all simple and what one would expect if you vaporized everything in the solar system today, then let it cool slowly, while stirring."

The surface of a comet will not be suitable for life - too much radiation and the vacuum will boil it. These things will live down in the comet, maybe taking refuge behind larger solid components (like the forward rocky crust) that can shield them from hard radiation. The visible light that gets to them will be that which is not absorbed but is scattered by the ice, and so will be shifted to shorter wavelengths; blues and greens. You can see this effect in this glacier cave where longer wavelengths are filtered out.

glacier cave

It is early days for this sort of research but there are indications that organisms adapted to harvesting short wavelength light energy are a major part of deep sea ice ecosystems.

Proteorhodopsin-Bearing Bacteria in Antarctic Sea Ice

Solar radiation, which regulates the production and growth of SIMCO (22), is highly scattered in sea ice, and the more-energetic blue light predominates (16). However, given the abundance of microalgae in the bottom 5 to 10 cm of annual fast ice, the only available light for prokaryotic phototrophs at the bottom of the ice will be in the green waveband (31). The disjunct distribution of green- and blue-absorbing PRs over a distance of more than 300 km uncovered in our study suggests a response to the light environment and further indicates that these organisms may be functional in the ice and not simply trapped there during ice formation. If this is true, they may play an important role in the microbial sea ice ecosystem either as a means of energy harvesting or via a sensory role.

This is not especially creative world building: comet instead of sea ice, archaebacteria doing what they do in a comet instead of in the sea ice. One could get more creative by making the archae part of a colonial organism along the lines of a slime mold - perhaps forward facing energy capturing components are without DNA so they will not mutate. If the organism has the ability to detect light it might steer its comet to some degree by exposing volatile materials from one side or another, thus pushing the comet on its path to optimally harvest nutrients. The creature would power down during the long dark trip at the far edge of the comets orbit. Spores would be shed from the tail, hoping to be intercepted someday by another passing comet.


As far as composition goes, Silicon and Carbon are the most likely building blocks for life. In space, Silicon is more common and can be found in space rocks. Carbon can also be found in space rocks, but it is less common and forms rocks less often. Any other element than these two seem fairly unlikely, since only these two both form bonds easily for life building and can be found in fair amounts in space.

So whatever your creature is, a specialized way to break down silicon based rocks and incorporate the material is probably a must.

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    $\begingroup$ I've always wondered whats wrong with sulfur? Sulfur is relatively common and can form chains, as well as being able to form 6 bonds. (Thats like 2 more than carbon!). Is sulfur too reactive or something? $\endgroup$
    – tox123
    Aug 18, 2018 at 23:59
  • $\begingroup$ I don't know that anything is wrong with Sulfur. Where you do get it in space though? $\endgroup$ Aug 19, 2018 at 1:47
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    $\begingroup$ @tox123 I think it has to do with what things it bonds with, an also how easily it bonds with them, as opposed to what kind of bonds it can form. On the other hand, maybe sulfur has too many bonds and that's actually the problem. $\endgroup$ Aug 19, 2018 at 1:57
  • $\begingroup$ @Morris The Cat Keep in mind I am talking about the majority element that makes up the body, not what it uses for food. Sulfur consuming microbes are still carbon based. $\endgroup$ Aug 19, 2018 at 2:00
  • $\begingroup$ The only thing wrong with sulfur is it is a heavier element (the Silicon abs carbon) and hence more rare. Remember most of the universe is composed of hydrogen. Remove hydrogen, and Harrod of the universe is composed of helium. This goes on with each element significantly rarer then the next element above it on the list $\endgroup$
    – Pliny
    Aug 20, 2018 at 19:21

Every type of life require a form of solvent to work. Water, Ammonia, Methane, Sulfuric acid etc. But how about using the Vacuum itself as a solvent?

When visualizing the international working of cells, we often sees different molecules, enzymes and machines floating freely through a transparent background, while the presence of water itself is often omitted. This is known as the Implied Water model.

The presence of a liquid solvent mostly accomplishes these two things: it helps to arrange like structures when it comes to polarity, and it helps molecules to diffuse.

However, self assembly, folding, docking and arrangement of molecules can also happen in a gaseous environment, often needing a (very high) vacuum. For example, molecular beam deposition , plasma deposition/cleaning/synthesis and formation of buckyballs, aerogels, and other exotic chemical constructs. In fact, the original nanobots and molecular assemblers REQUIRES a very high vacuum to even work!

There are two possible routes: diamondoid mechanosynthesis, and gaseous self assembly.

For the first kind of life, imagine the crevices and/or other contacts of a suitable rock/mineral in vacuum: rocks grind away on each other from some periodic force, for example thermal expansion or seismic activity.

Small particles adsorbs a certain molecules, guided by a pattern etched on the rocks, the particle adds molecules in sequence, forming the basic components of life. Now, the patterns themselves could be copied by some other process, for example, a molecule that have a form of connector on both ends, which would work like the needle of a record player, etching the pattern from one crystal onto another, and vice versa. If one of the pattern happens to be the one that makes these replicating pins by some process, it will become more dominant, and this would then produce some error, recruiting more molecules, and starting to assemble components of the patterns themselves. Creating a form of Diamondoid life.

For the second kind of life, think of the Implied water model, but change the "Solvent" space with the actual vacuum of space.

Consider somewhere very hot to keep most materials gaseous, and devoid of any gravity to cause molecules to fall on one side of the container, and this space is filled with a low pressure gas. Now, the molecules within such space could produce three kinds of interaction: Electrostatic, London dispersion and Pi-Pi interactions: the first one causes unlike charges to attract each other, the other two causes like surface to attract each other. The low pressure and high temperature helps the molecules to diffuse across each other, just like a solvent would be for the more "normal" life.

In this space, polymers will radiate heat away, collide with small molecules(gases), and consequently assumes a specific shape, or fold. Vibrational transitions would cool the molecules down, and newly formed polymers will fold. Folded polymers would then catalyze a wide variety of reactions, many known to be happening in a gas phase. One of these polymers consists of units that formed a shape that is complementary to one another, adamantanes, PAHs, and other sort of chemicals that would hydrogen bond. (hydrogen bonds does not(technically) require a solvent)

Some of these polymers would catalyze the polymerisation of the polymer itself through the complementary shape of the molecules, forming the first self replicating molecule within this environment. (Keep in mine that most non-protein solvents within the modern cell have concentrations of mmols to umols a litre, corresponds to pressures of a few hundred torrs of pressure) then, other molecules, then, the first polymerization based molecular assembler (not necessarily the ribosome), encapsulate the resulting mix with some form of polymeric barrier, and you get almost exactly the same sort of life as your everyday cells, with everything from dna analogues to protein analogues, except the implied water background of the cell is replaced with a vacuum (actually low pressure high temperature gaseous) background in zero gravity.


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