"Slam dunk" evidence that Mars once had water

From NASA:

NASA's Mars Exploration Rover Opportunity has found bright veins of a mineral, apparently gypsum, deposited by water. Analysis of the vein will help improve understanding of the history of wet environments on Mars.

"This tells a slam-dunk story that water flowed through underground fractures in the rock," said Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for Opportunity. "This stuff is a fairly pure chemical deposit that formed in place right where we see it. That can't be said for other gypsum seen on Mars or for other water-related minerals Opportunity has found. It's not uncommon on Earth, but on Mars, it's the kind of thing that makes geologists jump out of their chairs."

The latest findings by Opportunity were presented Wednesday at the American Geophysical Union's conference in San Francisco.