Mars once had an ocean at least a half-kilometer deep and larger than the combined area of all five Great Lakes on Earth. That's the conclusion of researchers who have analyzed data collected by orbiting spacecraft as well as the Mars rover Opportunity.
Last March, Opportunity found at its Meridiani Planum landing site rocks containing sulfates, which could have been created only in the presence of water (SN: 3/6/04, p. 147: Red Planet Makes a Splash: Rover finds gush of evidence for past water). The sulfates occurred in an outcrop of light-colored rock.
Brian M. Hynek of the University of Colorado in Boulder then compared infrared and visible-light images of those rocks with images of light-toned outcrops extending hundreds of kilometers to the north, east, and west. The colors of the distant rocks, recorded by the orbiters Mars Global Surveyor and Mars Odyssey, match the signature of sulfates examined by the rover. "I see evidence for this [wa