Mars Exploration Rover Opportunity has discovered gypsum and its "single most powerful piece of evidence for liquid water on Mars," Steve Squyres, the mission's principal science investigator and Cornell University professor, announced today during the American Geophysical Union (AGU) fall meeting being held in San Francisco.
Opportunity found the gypsum last month in a striking light-toned vein "running" through bedrock. The vein, which the team dubbed Homestake, is small, but the rover easily spotted it in late October as it was as it driving north/northwest along the western edge of Cape York on the rim of Endeavour Crater. By the first week in November it was checking out the vein with its scientific instruments.
"The morphology of this just screams water," Squyres said.
Opportunity found Homestake and other veins like it in an apron or Bench, as the team calls it, that surrounds a segment of the rim of Endeavour Crater, a zone where the sulfate-rich sedimentary bedrock of the plains meets older, volcanic bedrock of the rim.