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Was Mars' ocean 3.5 billion years ago salt water or fresh water?

On a related note: would we be able to drink the water that is on Europa?

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The article "Water Activity and the Challenge for Life on Early Mars" finds that the early Martian ocean would have been acidic and almost as salty as the dead sea.

The estimates for salinity of the Europan ocean vary widely, but most place the salinity above 50 g/kg, more than that of sea water (about 45 g/kg).

You couldn't drink it, but there are plenty of life forms that are adapted to this level of salt.

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    $\begingroup$ +1 but it's important to note that this is "educated speculation" rather than scientific fact or a widely held certainty. That there once was surface water now beyond reproach, but guesses about what the water was like exactly may evolve as more information becomes available. And as on Earth, since there was likely to have been rainfall and potentially less tidal mixing (no giant moon, further from the Sun), there could certainly have been a variety of different salinities rather than just one. $\endgroup$
    – uhoh
    Mar 14, 2022 at 0:01
  • $\begingroup$ To that end I've just asked in Earthscience SE How large were Mars' ocean tides and to what extent did they would keep the oceans mixing and tend to keep salinity uniform? Has this been modeled? $\endgroup$
    – uhoh
    Mar 14, 2022 at 0:27
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    $\begingroup$ That said, you could purify the salty water to make it potable - something worth considering since it'd be easier to send desalination equipment than to send a large quantity of fresh water if there's enough usable water already there. $\endgroup$
    – Darrel Hoffman
    Mar 14, 2022 at 16:54
  • $\begingroup$ It's a little better than "speculation". It is a peer-reviewed article published in Science, one of the world's top academic journals. $\endgroup$
    – James K
    Mar 14, 2022 at 17:54
  • $\begingroup$ “Best-effort” scientific speculation or extrapolation from limited data can always be published in reputable journals as long as it’s presented as such, it gets the conversation started and provides methods and frameworks for further analysis. It also sends your citation count skyrocketing when it’s the first in a long series of papers that unfold when more data is available that might in fact support the opposite conclusion. I’ll take a look at the paper and see what’s there, but absolutely nothing wrong with deductive speculation. $\endgroup$
    – uhoh
    Mar 15, 2022 at 2:09

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