Everyone knows that water is necessary for life because it is such a good solvent, but could a lifeform use water vapor as a solvent instead of water, or any other gas that works a solvent instead of a liquid? The environment I'm thinking of for this creature would be a planet without an atmosphere so their isn't enough pressure to have liquids.

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    $\begingroup$ I'm not sure everyone does know that water is necessary for life. Certainly it is for the lifeforms that we do know of here on Earth, but I think it's a little too early to conclude life without water is impossible. $\endgroup$
    – AngelPray
    Feb 10 '18 at 22:16
  • $\begingroup$ @AngelPray I was exaggerating but yeah I see your point $\endgroup$
    – Amoeba
    Feb 10 '18 at 22:21
  • $\begingroup$ I am not sure I get this question: many bacteria live very happily by floating around in the air. --- For a more detailed study, this could be of reference cabdirect.org/cabdirect/abstract/19612704448 Or are you asking whether the inner compartment of cells could be based on water vapor (or some other non-liquid compound) instead of a saline solution? $\endgroup$
    – NofP
    Feb 10 '18 at 23:09
  • $\begingroup$ @NofP whether the inner compartment of cells could be based on a non-liquid compound $\endgroup$
    – Amoeba
    Feb 10 '18 at 23:10
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    $\begingroup$ If you don't have enough pressure to have liquids, it's unlikely you can have gasses... $\endgroup$
    – LSerni
    Feb 10 '18 at 23:37

Supercritical CO2 might fit the bill.

CO2 is a gas, and people are familiar with it as a cold solid: dry ice. But it can be a liquid and under pressure, also a weird state called a supercritical gas.

from linked wikipedia

phases of CO2

It is polar like water. It can dissolve things like water (or better) and for that reason is being used as dry-cleaning fluid and other industrial solvent uses. It can flow like water but also sort of like a gas.

supercritical CO2


When the vessel is heated, the CO2 becomes supercritical -- meaning the liquid and gas phases merge together into a new phase that has properties of a gas, but the density of a liquid.

Venus may have once had lakes and rivers of supercritical CO2.


The atmospheric pressure on the surface of Venus is currently more than 90 times that of Earth, but in the early days of the planet, Venus' surface pressure could have been dozens of times greater. This could have lasted over a relatively long time period of 100 million to 200 million years. Under such conditions, supercritical carbon dioxide with liquidlike behavior might have formed, Bolmatov said.

"This in turn makes it plausible that geological features on Venus like rift valleys, riverlike beds, and plains are the fingerprints of near-surface activity of liquidlike supercritical carbon dioxide," Bolmatov told Space.com.

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    $\begingroup$ Who are you and what did you do with Will? :) $\endgroup$
    – kingledion
    Feb 11 '18 at 0:35
  • $\begingroup$ @kingledion: That pesky k on the tail end! The lotion I am supposed to put on it is not working very fast. $\endgroup$
    – Willk
    Feb 11 '18 at 1:13
  • $\begingroup$ “It is polar like water” actually, it isn’t. Sorry. It has2 dipole moments, but they point in opposite directions so the molecule as a whole is non-polar and thus would make a pretty poor solvent. $\endgroup$
    – Dubukay
    Feb 11 '18 at 1:56
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    $\begingroup$ @Dubukay That is true for sub-critical CO2, but supercritical CO2 has quite different properties, and does indeed dissolve many polar molecules quite well. It is used as an industrial solvent for many organic chemistry processes, most famously decaffeination. $\endgroup$ Feb 11 '18 at 3:06

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