The brave little rover has been stuck in the sand for a year and a half, spinning her wheels and wiggling her robot arm futilely. As she's kicked up sand, though, she has uncovered deeper layers of Martian soil, and analysis of the difference between the surface and what lies beneath shows evidence of water.

Spirit is not exactly parked in a puddle yet, but the pattern of the ferric sulfates in the red soil look like it was caused by seeping of liquid — recently, perhaps seasonally, perhaps continually.

If Spirit survives the coming Martian winter, during which the rover will be placed in a hibernation state, she will continue to do valuable science when she wakes up.

[NASA]