NASA has yet to find liquid water on Mars, but analysis of the soil where the Spirit Rover became stuck last year suggests liquid water flowed through the soil — and fairly recently.
For the past year and a half, Spirit has been stuck at a Martian site called Troy, where the rover's wheel broke through a crust and churned into soft sand. But it hasn't sat completely idle. NASA researchers have used Spirit's downtime to investigate the soil at Troy, and have found the site may see liquid water during certain climate cycles.
Near the soil's surface sit relatively insoluble minerals, which the researchers believe to be hematite, silica and gypsum. Further down in the soil are ferric sulfates, more soluble minerals that the researchers speculate were carried down in the soil by liquid water. None of the minerals are exposed at the surface despite the wind constantly stripping and altering the landscape, which indicates that the minerals were carried down relatively recently and continuously, with the ferric sulfates being carried down further than the less soluble minerals.
Currently, Spirit is in hibernation, but if it awakens and its robotic arm is still usable, researchers would like to examine other samples at the site. But these findings suggest that liquid water may not be entirely in Mars' past.