Nasa rover finds signs of water on Mars

The finding comes three days after Nasa officials announced that Spirit's twin, Opportunity, had uncovered geologic evidence that its landing site on the other side of the Red Planet, the Meridiani Planum, once was covered with water.

Scientists working with Spirit deduced that water formed small holes, or vugs, and left mineral deposits in a rock nicknamed Humphrey. The rover drilled a 2-mm (0.85 inch) deep hole into Humphrey and examined its interior with instruments to determine its mineral composition.

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"If we found this rock on Earth we would say this is a volcanic rock that has had a little bit of fluid move through it either when it formed or shortly thereafter," Ray Arvidson, deputy lead scientist at Nasa's Jet Propulsion Laboratory in Pasadena, said on Friday.

"The best bet is that water was in the magma. I don't think it was a groundwater percolation but water that came up with the magma," he added.

The amount of water found at Gusev Crater -- a canyon the size of Connecticut that scientists believe is an ancient lake bed -- "is by no means the gobs of water at Meridiani, but it again demonstrates that when rocks are made on Mars, fluids are involved."

Spirit, now in the 61st Martian day, or sol, of its mission, is making its way through a rock-strewn plain toward the Bonneville Crater, about 150 meters (500 ft) in diameter.