What do you think made the bright features in the picture below?
Was it a deep layer of rock underneath sand that was swept away by wind? Or maybe it was salt left over from the drying of an ancient lake? Or perhaps even ash left over by an ancient volcano. One of the answers is correct, and not the one I was hoping for.
I wish it was from an ancient lakebed, oh what the salt deposits could teach us. But alas, it is only volcanic ash. So as true scientists, we follow what the data tells us, and learn what we can from it, before moving on to the next interesting feature that has us saying ‘that’s strange.’
Still, it makes for a nice photo of Mars.
Well, maybe that volcano was not so ancient. Assuming that this is a standard THEMIS 32 km wide pushbroom, and using the standard crater counting models, the underlying surface looks like it is Noachian in age or older (3.5 billion years old), with lots of km sized craters (expected value, ~ 5 / 1000 km^2). The ash deposits, however, do not seem to haev any craters down to the resolution limit, which suggests that they are < 100 million years old (and, possibly considerably less). Geologically, that is basically yesterday. If HiRise ever imaged this region, you could count 20 meter craters and maybe get a more definitive age.