The Spirit rover has found evidence of water on Mars, just days after Opportunity found similar traces on the other side of the red planet. Spirit made the discovery at the Gusev Crater site which it is currently examining.
The indications suggest water was in smaller quantities than Opportunities Meridiani Planum find, but is seen as no less significant. Minerals unearthed as the rover probed with its rock abrasion tool are similar to those found on Earth.
"I think the best bet is that water was in the magma and as the magma crystallized, kind of last stages of the fluids led to formation of these white deposits ... and perhaps produced some minerals that filled in the cracks" an investigator reported. Source