Over at the Space.com forum rlb2 has posted one of his processed images from Mars, to wit:

This is one of the wettest looking pictures yet. Of course, as we know, "wet" in a terrestrial sense isn't likely on Mars under presently known conditions at any time. Well, maybe it is possible in isolated pockets under blankets of snow.

But this site is wide open to the atmosphere, that tenuous, cold, near vacuum. So "wet" as we would know it just isn't gonna happen here.

But is there a distinctive Mars "wetness?" It might seem to be dust-dry to us, and yet by Mars own standards -- not our standards -- the surface in question might be drenched. Of course you might claim that "wet" is a universal standard. Or even more appropriately, you might claim that Mars is able to mimic just about anything we might want to find, whether it be life or mud or -- as here -- a surface that appears to be "wet."

How would we know? Measure the water content of this surface? Well, let's do that. Only... we can't. Got to send different landers to conduct different tests.

Another reason I wonder about a distinctive Mars "wetness" is due to the close up appearance of the sulfate deposits. There's a kind of sheen on the material that suggests a fluid, and it's not due to sandblasting. I asked at the time whether the material may be dissolving in part because of the appearance of the material, and in part because there seemed to be very little erosion spoil from it. Where does the light colored eroded material go?

The facile answer is that it blows away with the wind. All well and good -- except there appear to be no areas of deposition. It's just gone. Someone might say it is spread far and wide, as an extremely fine powder that can't be separated out of any other surface dust. Maybe. But what if the material actually is dissolving in the air? Maybe the all-purpose ultra-violet light that bathes the surface acts on the sulfates to destroy them. Or maybe the sulfates are so loaded with water/sulfuric acid that when in contact with the air, the water/acid sublimes. In effect, the surface is dissolving. Do we know how much water the sulfate deposits currently contain? Are these deposits "wet" by Mars standards?