The rocks that revealed the strongest sign yet that water once pooled on Mars are also ideal for preserving evidence that life once existed on the planet – if it ever did, according to the lead scientist of NASA’s current twin-rover mission. Meridiani Planum, the area now being studied by the rover Opportunity, could be the target of future missions equipped to look for organic materials or return samples to Earth, said Steve Squyres, the principal scientist of NASA’s Mars Exploration Rover program.