NASA has determined the origins of the mysterious 'Pinnacle Island' rock which seemed to suddenly appear in a photo taken by the Mars Opportunity Rover this past January. After reviewing observations of the general area, the space agency discovered a larger rock with the same unique composition as well as tire tracks from the rover. This investigation led them to conclude that 'Pinnacle Island' was merely a fragment of the larger rock which had become dislodged. More on the story at the LA Times.