NASA's Mars rover Opportunity has found a Martian rockcovered in weird material as its odometer hit a major milestone this week, withthe long-lived robot completing equivalent to a half?marathon on the red planet.
Opportunity, now in its seventhyear on Mars, found the odd Mars rock during the past six weeks studying investigatinga crater called "Concepci?n." The crater is about 33 feet (10 meters)in diameter, with dark rays extending from it, as seen from orbit, which madeit a target of interest for rover inspection because they suggest the crater isyoung.
What Opportunity has seen are chunks of the same type of bedrockit has seen at hundreds of locations since landing in January 2004: soft,sulfate-rich sandstone holding harder peppercorn-size dark spheres like berriesin a muffin. The little spheres, rich in iron, gained the nickname"blueberries." But these rocks have some unusual twists as well.
"It was clear from the images that Opportunity took onthe approach to Concepci?n that there was strange stuff on lots of the rocksnear the crater," said Steve Squyres of Cornell University in Ithaca,N.Y., principal investigator for Opportunity and its twin rover, Spirit."There's dark, grayish material coating faces of the rocks and fillingfractures in them. At least part of it is composed of blueberries jammedtogether as close as you could pack them. We've never seen anything like thisbefore."
Opportunity used tools on its robotic arm to examine thisunusual material on a rock called "Chocolate Hills." In some places,the layer of closely packed spheres lies between thinner, smoother layers.
"It looks like a blueberry sandwich," said MattGolombek, a rover science-team member at NASA's Jet Propulsion Laboratory,Pasadena, Calif.
Initial analysis of the coating's composition does not showany obvious component from whatever space rock hit Mars to dig the crater, butthat is not a surprise, Golombek said. "The impact is so fast, most of theimpactor vaporizes," he said. "Thin films of melt get thrown out, buttypically the composition of the melt is the stuff that the impactor hit,rather than the impactor material."
"It's possible that when you melt this rock, thesandstone melts before the blueberries do, leaving intact blueberries as partof a melt layer," Squyres said. "As an alternative, we know that thistype of rock has fractures and that the sandstone can dissolve. Long ago, waterflowing through fractures could have dissolved the sandstone and liberatedblueberries that fell down into the fracture and packed together. In thishypothesis, the impact that excavated the crater did not play a role in formingthis material, but split rocks along fractures so the material is exposed onthe exterior like a coating."
Golombek said, "One consideration that jumps out isthat we've been driving around this part of Mars for six years and never seenthis stuff before, then we get to this young crater and it's coating rocks allaround the crater. Sure looks like there's a connection, but it could just be acoincidence."
"We're not ready to attach a number to it, but this isreally young. It is the youngest crater we've ever seen with Opportunity andprobably the youngest either rover has seen," Squyres said.
- Images? Opportunity Rover on Mars
- MarsRovers Most Amazing Discoveries
- Video? Opportunity's Mars Marathon
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