Space

NASA's Curiosity rover will launch on Saturday (Nov. 26) toward a frigid and dry Mars, but the robot will likely spend much of its time staring deep into the Red Planet's warmer, wetter past, scientists say.

Curiosity, also known as the Mars Science Laboratory (MSL), aims to assess whether Mars is, or ever was, capable of supporting microbial life. The $2.5-billion rover will work hard to reconstruct and investigate ancient environments, because Martian life likely had a better shot at gaining a foothold long ago, researchers said.

"We've learned that Mars is a dynamic planet," Michael Meyer, lead scientist for NASA's Mars exploration program, told reporters today (Nov. 21). "We've learned that it has a history where it was warm and wet at the same time that life started here on Earth."

A changing Mars

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Most scientists hunting for signs of life beyond Earth have focused on wet environments, because life on our planet is reliant on water. By this measure, modern Mars would seem a poor candidate, because its surface is mostly cold and dry today (although water ice does lurk beneath the red dirt).

But this was not always so. Many ancient riverbeds snake around the Red Planet's surface, and most scientists think they were carved by liquid water in the distant past. [7 Biggest Mysteries of Mars]

Various Mars orbiters and rovers have also spotted lots of clays on Mars, suggesting that water once persisted on the surface for extended periods of time.

"Clay minerals form from long-term chemical interaction of water with rock," said Bethany Ehlmann of NASA's Jet Propulsion Laboratory and Caltech in Pasadena, Calif.

This wet period...