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The process of osmosis makes it possible for water to be sucked through a semi-permeable membrane in order to balance the concentrations of two solutions. Thus, a sufficiently salty ocean might drain all the water out of possible organisms; for instance, in the so-called Dead Sea only tiny micro-organisms are able to survive.

Since they've discovered salt on Enceladus, could this prevent this moon from hosting life, or at least certain types of life?

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I actually found this very useful article, which seems to answer the question:

https://phys.org/news/2021-05-salty-enceladus-ocean-ice.html

It suggests that the liquid water in the Enceladus ocean has between 10 and 30 grams of salt per kg of water. This is comparable with, or slightly less than, the Earth's oceans (with an average of 35g/kg)

This is based on modelling of the thermohaline circulation on Enceladus, and while the science seems sound, there must be some question marks about the validity of the models used.

Moreover we don't know anything about life evolving on other worlds. We know that life can evolve to tolerate much higher levels of salt, There are Halobacteria that can tolerate the salinity of the dead sea.

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Limitations to life via osmosis is mostly a modern limitation. Modern in the 'geological era'-sense.

Why osmosis can affect life negatively is, very roughly, when concentration gradients past a bi-lipid cell wall becomes large enough, the transport proteins in the cell wall can't keep up to fight the chemical gradient, and the cell looses its water, thus ceasing functionality.

Older microbes, most prominently certain Archaea (most prominently the Salt-loving Halobacterium) have important differences in their cell wall structure decreasing their permeability to osmotic flow drastically. Considering that Archaea presumably evolved first on this planet, and got later displaced into all the exotic corners where they live now by those hefty-multiplying Prokcaryotes, it would make sense to assume that a high sailinity in lunar oceans does not prohibit the development of life.

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  • $\begingroup$ “Prokaryotes” means both bacteria and archaea, neither of which are demonstrably older than the other. $\endgroup$ Jun 2, 2021 at 23:26
  • $\begingroup$ Still, they did apparently not evolve into all the diverse forms of life that dominate this planet, so perhaps they can't. $\endgroup$ Jun 3, 2021 at 10:46
  • $\begingroup$ @AlgebraicsAnonymous FWIW, archaea did evolve into complex life like you and me. There was a symbiosis between archea that formed the complex Eukaryotic cell, and that went on to form all multi-cellular life. In a couple of telling biochemical ways, you are closer to an archea than either you or the archea is to a bacteria. $\endgroup$
    – James K
    Jul 31, 2021 at 21:47
  • $\begingroup$ @JamesK When I speak of "they", I do not mean those Archaea which did evolve into complex life, but those whose cell wall keeps out the salt. But thanks for the interesting information! $\endgroup$ Jul 31, 2021 at 23:20

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