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Columbia Hills is an interesting area because it appears to be made of bedrock. The rock that Spirit traveled across was younger basaltic rock that was scattered when meteorites and comets hit the planet's surface, Crumpler said.

"In the Columbia Hills rock, we can see little cracks with veins of something - maybe some sort of crystal," he said. "That sort of thing is usually caused when fluids move through rock. Unless there's something entirely different going on there than we've ever seen before, I'd say that meant there was significant water flow in the past."

Finding the ages of martian rocks - and that water flow - is difficult. Scientists can guess at the ages of rocks based on the number of impact craters in them.

"I think the water picture is as exciting as we thought it would be," Boston said. "The case is building in just about every direction for more water on Mars and an extensive history of water on Mars beyond just periodic melting from impacts, which we thought in the past."