Where are the salt deposits then?

Those streaks look dark.
Shouldn't salt deposits left behind look
bright?
And, excuse my ignorance, but shouldn't salt deposits (streaks) be detectable to
mass spectrometers or such?

On an indirectly related note:
I'm getting to the point where I'm starting to think that evidence for (physical, carbon-based life) elsewhere in the universe is ASYMTOTIC.
If you recall from your high school math classes, an ASYMTOTE is the mathematical cartesian line which you can get very close to BUT cannot quite connect it with a geometrical figure of an algebraic equation; you can NEVER quite reach it.

Example Y = 1/X.
X can NEVER equal zero, or Y will equal infinity.
So it is with the search for physical life elsewhere in the cosmos.