The long-lived Mars rover Opportunity has spotted bright veins of a water-deposited mineral, apparently gypsum, on the surface of the planet. The vein is informally named 'Homestake,' and it and other similar-looking deposits are located in a zone where sulfate-rich bedrock meets volcanic bedrock, at the rim of the Endeavour Crater. Homestake is roughly 0.4 to 0.8 inches wide, 16 to 20 inches long, and protrudes slightly above the surrounding bedrock.
Researchers used three of Opportunity's instruments - the Micrcosopic Imager, the Alpha Particle X-Ray Spectrometer and the Panoramic Camera's filters - to identify calcium and sulfur in a ratio that indicates "relatively pure" calcium sulfate, specifically hydrated calcium sulfate, or gypsum.
The Homestake vein likely formed as calcium, dissolved by water out of volcanic rocks, combined with sulfur and was deposited as calcium sulfate in an underground fracture, which was then exposed at the surface of Mars.
Steve Squyres, principal investigator for Opportunity, said in a statement: "This tells a slam-dunk story that water flowed through underground fractures in the rock. 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."
Opportunity has found other evidence of water on Mars in the form of magnesium, iron and calcium sulfate in the bedrock, but that same evidence has also indicated a highly acidic environment. This new deposit indicates more neutral conditions, which could have hosted a greater variety of organisms.
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