NASA's famous robot rover Opportunity, still prowling the haematite steppes of the Meridiani Planum on Mars seven years after setting down, appears to have discovered concrete evidence that liquid water once
flowed across the surface of the red planet.
A bright vein of what scientists believe to be gypsum has been found by the rover, which could only realistically have been formed by flowing water.
According to NASA:
The vein examined most closely by Opportunity is about the width of a human thumb (0.4 to 0.8 inch), 16 to 20 inches long, and protrudes slightly higher than the bedrock on either side of it. Observations by the rover
reveal this vein and others like it within an apron surrounding a segment of the rim of Endeavour Crater. None like it were seen in the 20 miles (33 kilometers) of crater-pocked plains that Opportunity explored for 90 months before it reached Endeavour, nor in the higher ground of the rim.