Scientists were stunned on May 30 when a rock that NASA’s Curiosity Mars rover drove over cracked open to reveal something never seen before on the Red Planet: a geode full of yellow crystals.
Since August 2012, Curiosity has been exploring Gale Crater, a large basin in the equatorial region of Mars. Billions of years ago, this impact crater hosted a shallow lake, as shown by fossil ripple marks and the sulfate-bearing unit, a sedimentary rock formation rich in sulfur-based minerals (a mix of sulfur and other elements) deposited as water evaporated.
Using an instrument on the rover’s arm, scientists later determined the yellow crystals are elemental sulfur—and it’s the first time this kind of crystalline sulfur has been found on the Red Planet.
It isn’t clear what relationship, if any, the sulfur geode has to other sulfur-based minerals in the area. On Earth elemental sulfur forms in only a narrow range of conditions. Sulfur crystals can from by the oxidation of hydrogen-sulfide along the borders of a fumarole—a vent from which hot volcanic gases and vapors are emitted. But so far Curiosity didn’t find any evidence of past or recent volcanic activity in this location. It is also found in some vein deposits and as an alteration product of other sulfur-bearing minerals. Pure sulfur in sedimentary rocks can be formed by reduction of sulfates (sulfur-oxygen minerals)—and intriguing enough for the search of life on Mars—by microbial activity.
The scientists also believe that elemental sulfur is more common in Martian rocks than previously believed. Nine days earlier, Curiosity spotted an entire field of bright rocks resembling the one the rover accidentally crushed.
“Finding a field of stones made of pure sulfur is like finding an oasis in the desert,” said Curiosity’s project scientist, Ashwin Vasavada of NASA’s Jet Propulsion Laboratory in Southern California. “It shouldn’t be there, so now we have to explain it. Discovering strange and unexpected things is what makes planetary exploration so exciting.”
Additional material and interviews provided by NASA.
