Two more pieces of the water-on-Mars puzzle in the last few days… the Mars rover Spirit has found new evidence of liquid water having trickled down into the soil in the relatively recent past, while the Mars Reconnaissance Orbiter has found an old volcanic cone which would have been warm and wet even after most of Mars had already started to change to the cold, dry place we see today.
When Spirit became stuck in the sand last year, the wheels churned up the soil during extraction attempts, which turned out to be a blessing in disguise. The revealed layers below the surface indicated that small amounts of water, perhaps from frost or snow, trickled down into the soil, likely sometime within the last few hundreds of thousands of years (recently, geologically-speaking) and on an on-going basis. See also the published paper here.
Meanwhile, the deposits of hydrated silica on an old volcanic cone in Nili Patera, photographed by the Mars Reconnaissance Orbiter, are thought to be the best evidence yet for ancient hydrothermal vents (fumaroles or hot springs). On Earth, such places are prime areas of habitability for microbes. They would also have been habitable places on Mars, but were they actually inhabited? The deposits are similar to ones found at hydrothermal vents in Iceland. The Mars rover Spirit had also previously found similar deposits directly in the soil (another tie-in to the other findings discussed above), evidence that fumaroles or hot springs were once present at its landing site.