"Mars rover Opportunity has found evidence that the Red Planet was once wet enough for life to exist there, but the robot has not found any direct traces of living organisms, NASA scientists announced Tuesday.
A study of a fine, layered rock by the rover detected evidence of sulfates and other minerals that form in the presence of water. The finding suggests that if there had been life present when the rocks were formed, then the living conditions could have permitted an organism to flourish. The study, however, has found no direct evidence of life."