with a friendly competition about trying to understand Homeplate before we actually see and analyse it.
It seems that I was a bit close to what we see: (predicting a three-layered system)
The latest scenario I suggest, after closest view of sol 742:
Sometimes between the formation of Gussev and the final filling by mudflow, there was a lake (temporary, or permanent). The surface of this lake was about the level of Homeplate, or a little above, so that Husband hills were not covered. Its open surface lasted only some days, and after the surface frozen, and eventually all the water froze to the core in some months or years.
This water was charged with a variety of salts, and these salts were deposited, but very unevenly, from the presence of ice, after one or several of the following processes:
-waves projected water on mounds, where it evaporated very quickly, lefting the salts on priviledged patches. (This is sometimes visible on earth)
-there were faults in the ice cover, allowing strong evaporation of water in some very restricted places.
-There was a continuous ice cover, see the lake froze into its whole depth. But salts were contentred in tiny patches of very salty brines, which can exist at very low temperatures (-50°C for calcium chloride). When ice sublimated, it left the solid salt patches to end drying. Homeplate could be one of these patches. Other were observed all around.
So if this model is true, it predicts that Homeplate and similar smaller patches are just salts. Eventually we may find, from top to bottom:
-basaltic blocks and sands, projected here by more recent impacts
-most soluble salts, such as sodium and calcium chlorides
-less soluble salts, such as jarosite and sulphates
-eventually an iron oxyd layer somewhere in between
-at bottom a sandstone of basaltic sand cemented with sulphates or carbonates (eventually limestone). This layer would be the dark rocky outcrop which seems to encircle Homeplate.
-a "discordance" and under ordinary soil (same as elsewhere around).
and that Homeplate would be the same thing than a much larger similar structure, that of