Although researchers figured out where the rock came from, there are other weird aspects of the Pinnacle Island tale. Using Opportunity's tools, mission scientists have discovered that the rock has very high levels of sulfur and manganese. Both of those elements are water-soluble, suggesting that they were concentrated in the rock due to the "action of water," NASA officials said.
"This may have happened just beneath the surface relatively recently, 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," Arvidson said.
The rock is located in a spot on "Murray Ridge" along the wall of Endeavour Crater, where Opportunity is spending the Martian winter. Now that the rover is done examining Pinnacle Island, the Opportunity team is planning to drive the rover uphill to check out exposed rock layers on a different part of the Martian surface.
"We are now past the minimum solar-energy point of this Martian winter," Opportunity project manager John Callas, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. "We now can expect to have more energy available each week. What's more, recent winds removed some dust from the rover's solar array. So we have higher performance from the array than the previous two winters."