It's commonly known that sulfuric acid rain doesn't reach Venus' surface. It evaporates instead because the surface it too hot.

But considering how high the pressure at the surface (9.3 MPa), shouldn't sulfuric acid stays liquid there? To compare, Venus surface is 737 K and 9.3 MPa, while sulfuric acid's critical point, according to Wikipedia, is 927 K and 4.6 MPa. (Unfortunately I can't find a more reliable source for this).

What is the cause of this? Is Venus actually much hotter than 737 K? Are sulfuric acid's critical temperature and pressure actually lower and higher? Is there just not enough sulfuric acid?

  • 1
    $\begingroup$ Part of the answer, though it's perhaps not complete, is concentration. There's a low enough concentration of SO3 and water vapor needed to make sulfuric acid that it remains in the vapor state. If it was much more abundant, then, perhaps, lakes would be possible, though at temperature that high - I don't want to say that for certain. Just as, in a hot and dry desert on Earth, there might not be any lakes because all the water evaporates and remains in the air. $\endgroup$
    – userLTK
    Mar 26, 2022 at 13:37
  • 2
    $\begingroup$ A fun, related fact. Sulfuric acid is somewhat unstable (making it's phase diagram somewhat more complicated and harder to look up). It requires some water to be stable, though the concentration in the rain on Venus can be quite high, ranging from 70%-99%. guinnessworldrecords.com/world-records/… $\endgroup$
    – userLTK
    Mar 26, 2022 at 13:40
  • $\begingroup$ There is little to no Sulfuric acid at surface level on Venus $\endgroup$ Mar 27, 2022 at 1:04


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