Evidence for Water on Mars
From JPL comes this interesting picture of a structure on Mars which ..
.. lines a fracture in the local pavement and scientists hypothesize that it is a fracture fill, formed by water that percolated through the fracture. This would mean the feature is younger than surrounding rocks and, therefore, might provide evidence of water that was present some time after the formation of Meridiani Planum sedimentary rocks.
To my untrained eye it looks like a water effect - that sort of pooling, rounding and weathering looks like so many water worn rocks - but I'm not even a geologist and especially not an exo-geologist - so my opinion is necessarily suspect.
It doesn't mean there is water on Mars - but it does give some clue as when there was water on Mars.
Tags: jpl, nasa, mars, mars-rover