It was the lowly (but expensive, I’m sure) shovel that did the job. Phoenix
took three scoops of Martian dirt to analyze, and then a few days later looked back where it had scooped. Some of the dirt was gone. Originally, the team allowed that the white stuff seen in the digging trench might be salt or some other white mineral.
But the best explanation for the disappearing white stuff is.. sublimation, which means water. Well, small creatures that don’t leave tracks could have scurried in, grabbed some chunks and zapped a shrinking ray at still-buried chunks.
But Occam’s Razor is pretty harsh on that kind of thinking. Now, hasn’t ice been found in comets before? Or is this the first, confirmed, off-planet ice?