Courtesy of NASA/JPL

After seven months and 205 sunrises on Mars, the Spirit rover looks back on Gusev Crater. The robot dug a shallow pit and performed a chemical scan, showing that this outcrop of soft rock may have been chemically altered by flowing water. Opportunity, the sister rover, found clearer evidence of an ancient lake halfway across the planet. The robots are now conserving power to try to survive the cold, dim Martian winter.