As scientists investigate whether there are any signs of life on Mars, they're using one guiding principle - follow the water.

NASA experts told Reuters that their entire approach for the latest stage of Mars exploration is based on sending twin robotic rovers, Spirit and Opportunity, to two spots on the red planet where the evidence of water is most compelling. The two rovers are intended to roam the surface of Mars for approximately three months, during which time they will seek to unlock clues to the mystery of water on Mars by examining its rocks and soil.