astroengine writes "After a decade of exploring the Martian surface, the scientists overseeing veteran rover Opportunity thought they'd seen it all. That was until a rock mysteriously 'appeared' a few feet in front of the six wheeled rover a few days ago. News of the errant rock was announced by NASA Mars Exploration Rover lead scientist Steve Squyres of Cornell University at a special NASA Jet Propulsion Laboratory '10 years of roving Mars' event at the California Institute of Technology (Caltech), Pasadena, Calif., on Thursday night. The rock, about 'the size of a jelly doughnut' according to Squyres, is thought to have either come from a freak "flipping" event or a very recent meteorite impact. However, the latter isn't thought to be very likely. Although they are still working on the rock's origin, the rover team believe it was 'tiddlywinked' by Opportunity's broken wheel; as the rover was turning on the spot, the rock was kicked from place under the wheel and flipped a few feet away from the rover. Never missing a science opportunity, Squyres told Discovery News, 'It obligingly turned upside down, so we're seeing a side that hasn't seen the Martian atmosphere in billions of years and there it is for us to investigate. It's just a stroke of luck.'"