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, 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 “Homestake” deposit, whether gypsum or another form of calcium sulfate, likely formed from water dissolving calcium out of volcanic rocks. The calcium combined with sulfur that was either leached from the rocks or introduced as volcanic gas, and it was deposited as calcium sulfate into an underground fracture that later became exposed at the surface.

“It could have formed in a different type of water environment, one more hospitable for a larger variety of living organisms,” said Opportunity science-team member Benton Clark of the Space Science Institute.

NASA launched the next-generation Mars rover, the car-sized Curiosity, on Nov. 26. It is slated for arrival at the planet’s Gale Crater in August 2012. For more information about the rovers, visit http://www.nasa.gov/rovers and http://marsrovers.jpl.nasa.gov . You can follow the project on Twitter at http://twitter.com/MarsRovers and on Facebook at http://www.facebook.com/marsrovers .