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So, i'm just searching around in spaceengine and got the idea of worldbuilding based on one of the planets that exists in the simulation (not quite worldbuilding in a complete sense, but speculating and "building" life on that planet). Now, I've "worldbuilded" many times using spaceengine before, often using hours researching information and finding the scientifically realistic planet for building ecosystems and even civilizations on, but this time is different, I want to build ecosystems based on a planet like Titan, where water-ice is essentially rock and there are life as we don't know it living in the oceans, but so far, I've only found planets with liquid CO2 as oceans, so may I ask, is it scientifically realistic that some lifeforms use liquid CO2 as solvent and what might the chemical composition of that type of lifeform be?

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    $\begingroup$ Hypothetical types of biochemistry, see under Non-water Solvents. Unfortunately, the carbon dioxide molecule is non-polar, which makes it a poor solvent for most things which may be useful for life. $\endgroup$ – AlexP Jul 11 at 15:59
  • $\begingroup$ @AlexP solvents like ethane and methane is also non-polar, but according to the article, it should work very fine for dissolving lipids as a substitute for proteins, and lipids can also substitute for carbohydrates as energy source, while using something lipophobic as a cell membrane (you wouldn't want the whole cell to dissolve into the ocean). as co2 and n2 is also non-polar, wouldn't it logically be great solvents for those substitutes? $\endgroup$ – someone Jul 12 at 14:50
  • $\begingroup$ Maybe. That's why I didn't write an answer. $\endgroup$ – AlexP Jul 12 at 15:21
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To get liquid CO2 you need above 5.1 atmospheres of pressure, and below -69°F. Note that if the pressure ever falls below this you get flashing to vapor above -109.3°F. So an organism that maintains an internal pressure to keep CO2 liquid might have to worry a lot about cuts.

Once you get liquid CO2 at least some things can dissolve to some extent. This article seems to be some kind of measurement of a process to use liquid CO2 to dissolve the active ingredient out of cannabis.

Presumably there are tweaks that can be made to enhance dissolving things that are needed. And adaptations that would make the things that do dissolve more readily useful.

There might be interesting processes of distillation. Perhaps an organism can dissolve something it wants, then slightly decrease the pressure around the solution and thus draw off the CO2 and leave the material it wants.

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    $\begingroup$ Not only that - at 5.1 atm we are at "triple point" for CO2, meaning that the temperature window for liquid CO2 to exist is infinitely small. To get to a more comfortable range in which it wont freeze or boil very quickly, we need more like 20-30 atm pressure. $\endgroup$ – Alexander Jul 11 at 16:26
  • $\begingroup$ @Alexander Something like a 'Megatitan' world perhaps? $\endgroup$ – Arkenstein XII Jul 11 at 20:25
  • $\begingroup$ If the lifeforms are living in an ocean of liquid CO2, wouldn't that mean that their environment would be at 5.1 atm anyway and therefore would your point about them needing to worry about being cut still be valid? $\endgroup$ – Bee Jul 12 at 12:07

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