It was a complete unknown -- it was a rolling stone. 
 
 A mystery rock that appeared before NASA's Opportunity rover in late January -- and bore a strange resemblance to a jelly donut -- is no more than a common piece of stone that bounced in front of the cameras, NASA said Friday. 
 
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 The strange rock was first spied on Jan. 8, in a spot where nothing had sat a mere two weeks earlier. Dubbed "Pinnacle Island" by NASA scientists, it was only about 1.5 inches wide. But the rock's odd appearance -- white-rimmed and red-centered, not unlike a jelly donut -- made many sit up and take notice. 
 
 'We drove over it. We can see the track. That's where Pinnacle Island came from.' - Opportunity Deputy Principal Investigator Ray Arvidson 
 
 Now researchers with NASA's Jet Propulsion Laboratory at the California Institute of Technology have finally cleared up the mystery. 
 
 Yep. It's a rock. 
 
 "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 of Washington University in St. Louis. "We drove over it. We can see the track. That's where Pinnacle Island came from." 
 
 Examination of Pinnacle Island revealed high levels of elements such as manganese and sulfur, suggesting these water-soluble ingredients were concentrated in the rock by the action of water. 
 
 "This may have happened just beneath the surface relatively recently," Arvidson said, "or it may have happened deeper below ground longer ago and then, by serendipity, erosion stripped away material above it and made it accessible to our wheels." 
 
 Now that the rover is finished inspecting this rock, the team plans to drive Opportunity south and uphill to investigate exposed rock layers on the slope. 
 
 Opportunity has trolled the Martian surface since Jan. 24, 2004, far outlasting its original 90-day mission. 
 
 Steve Squyres, the rover's lead scientist at Cornell University in Ithaca, N.Y said the Red Planet keeps surprising scientists, even 10 years later. 
 
 "Mars keeps throwing new things at us," he said. 

 When a rock suddenly appeared in front of the Opportunity rover on Mars last month, scientists were puzzled. Now, scientists at NASA's Jet Propulsion Lab say they've solved the mystery. 
 
 Back in January when the rock — which scientists helpfully described as "about the size of a jelly doughnut" — was first spotted, a number of different options for how it got there were thrown around including that the rover itself had done it, a meteorite strike, and aliens (except not, because it wasn't). 
 
 So, who was the culprit? Opportunity itself it turns out. The rover rolled over a larger rock, first breaking it, and then kicking a fragment — Pinnacle Island, as the rock eventually became known — over with its wheel to land right in front of the camera at just the right moment. 
 
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 Scientists figured it out by following a time-honored detective's trick — they followed the tracks. "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," Opportunity chief Investigator Ray Arvidson explained in a statement. "We drove over it. We can see the track. That's where Pinnacle Island came from." 
 
 Image: NASA/ JPL
– Remember when the weird "jelly doughnut" object on Mars made news last month? NASA scientists were happily baffled after it suddenly appeared in images taken by the Opportunity rover. They're baffled no more: Scientists today said they're sure that the object is indeed a rock that got kicked into the camera's view by the rover itself, reports Fox News. (That had been a leading theory at the time, though imaginative skeptics weren't convinced.) They figured it out with some old-fashioned sleuthing, notes i09—"they followed the tracks" from the rock (now named Pinnacle Island). "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," says a NASA statement. "We drove over it. We can see the track. That's where Pinnacle Island came from." (Click to see what Earth looks like from Mars.)