Mars mythology, including speculation about life on the red planet, dates back to ancient times. It reached a high point in the late 19th century when astronomers reported seeing "canals" on the Martian surface. Since then science fiction and B-movies have been full of sentient beings from Mars.
Twenty years ago the Viking landers failed to find conclusive evidence of life. But that doesn't mean that there was never life there; like on Earth bacteria might have developed on Mars billions of years ago. In 1997 a spacecraft called Mars Pathfinder will land a large instrument package on the Martian surface. It will lay the groundwork for future efforts to find fossil remains on Mars.
NASA scientists chose the landing site in part because they think it is likely to contain mineral deposits in which early Martian life might have been entrapped. By studying "Mars analogue" sites on Earth such as the the Grand Prismatic Spring in Yellowstone National Park and Mono Lake in California, the scientists hope to understand how Martian fossil bacteria might have formed. This understanding could be invaluable in answering basic questions for biologists: Does life have to be based on cells regulated by DNA? Does life always develop as early and quickly as terrestrial evidence suggests, or was Earth a fluke?