Salt on Venus

In my previous posts on the run-away greenhouse (which we know must
have happened to Venus some time in its past), I have assumed that
liquid water would disappear when the surface temperature reached the
critical point (705 degrees F). This is not true, though, because of
the presence of salts which will raise the critical point beyond any
reasonable surface temperature [1] causing the last parts of the ocean
to remain liquid as long as the atmosphere is near saturated with
water vapor, which it will be until almost all the water is lost to
space. When this occurs there should remain large deposits of salts on
the surface. Now though Venus has HCl in its atmosphere, it is only a
small fraction (10^-4) of the amount that must have existed in its
oceans.

So where is all the salt on Venus? Obviously, it is thought that Venus
underwent complete resurfacing ~700 my, which must have been later
than losing its water. Therefore there need be no large salt deposits
today, but it would still be interesting to now where the halogens go
in the absence of water; they are still largely incompatible elements.

[1] There is probably no limiting critical point, and salts and water
have then a continuous critical curve, but that can never be
determined in the laboratory. Not only NaCl, but I don't know any
salts that have a low enough critical point for observation and do not
decompose or react with water below that temperature.

Andrew Usher