Proof for Water, Hints of Life?

Since 25 January of this year, NASA9s Opportunity rover has been exploring Mars9 Meridiani Planum, a smooth, flat plain that is unlike any feature studied by earlier martian landers. In his Perspective, Kargel discusses the insights into martian geochemistry and geology gained from the rover that are reported in 11 reports and research articles in this issue of Science . Together with observations from spacecraft that are currently orbiting the planet, the data provide an unprecedented glimpse into how water shaped the martian surface. The author cautions that Mars may never have been very Earth-like and that we must, until we learn otherwise, assume that life exists on Mars, in order to protect Earth and any species that might be present on Mars.