The mystery of the jelly doughnut-shaped rock that seemed to materialize on Mars is a mystery no more.
After taking a close look at the small white rock with a deep red center dubbed "Pinnacle Island," a research team has determined it is not a fungus-like organism, or a piece of Martian ejecta that was shot into the air by a nearby unseen impact.
Instead, it is just a small piece that was broken off a larger rock when one of the wheels of NASA's Opportunity rover drove over it, according to a release from the Jet Propulsion Laboratory.
"Once we moved Opportunity a short distance, after inspecting Pinnacle Island, we could see directly uphill an overturned rock that has the same unusual appearance," said Opportunity Deputy Principal Investigator Ray Arvidson in a statement. "We drove over it. We can see the track. That's where Pinnacle Island came from."
The small rock became a subject of worldwide interest soon after it was spotted Jan. 8 by Opportunity's cameras. It was puzzling because it did not show up in images the rover took of the same location taken 12 days earlier.
"One of the things I like to say is Mars keeps throwing things at us," Steven Squyres, principal investigator for the Mars Exploration Rover Mission, said during a presentation describing the appearance of the mysterious rock in January.
"We're completely confused. We're having a wonderful time. Everyone on the team is arguing and fighting," he said at the time.
The story took a strange turn at the end of January when Rhawn Joseph, who describes himself as a neuroscientist and astrobiologist, filed court papers demanding that NASA do more to investigate the mysterious rock.
Joseph asked the judge to order the space agency to closely photograph the rock from several angles, thoroughly examine it, and share that information with the public.
In the court papers Joseph suggests that the rock may not be a rock at all, but rather a fungus-like organism. If so, that would mean Opportunity had discovered life on Mars. (You can read the details of his theory here.)
A NASA spokesman responded with this: "As we do with all our scientific research missions, NASA will continue to discuss any new data regarding the rock and other images and information as new data becomes available."
Even if the rock is not a sign of extraterrestrial life, it is still interesting. Opportunity's instruments have revealed that it has high levels of sulfur and manganese, water soluble ingredients that may have been concentrated in the rock thanks to the action of water.
"This may have happened just beneath the surface relatively recently, or it may have happened deeper below the ground long ago," Arvidson said in a statement. "And then by serendipity, erosion stripped away material above it and made it accessible to our wheels."
A mystery? Not anymore. But it appears it was still a stroke of luck.
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