A comparison of two raw Pancam photographs from sols 3528 and 3540 of Opportunity's mission (a sol is a Martian day). Notice the "jelly doughnut"-sized rock in the center of the photograph to the right. Minor adjustments for brightness and contrast.
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 science star-studded public event was held in celebration of the decade since twin rovers Spirit and Opportunity landed on the red planet in January 2004.
While chronicling the scientific discoveries made by both rovers over the years, Squyres discussed the recent finding of suspected gypsum near the rim of Endeavour Crater — a region of Meridiani Planum that Opportunity has been studying since 2011 — and the discovery of clays that likely formed in a pH-neutral wet environment in Mars past. While these discoveries have been nothing short of groundbreaking, Squyres shared the Mars rover’s team’s excitement for that one strange rock, exclaiming: “Mars keeps throwing new stuff at us!”
For the rest of the story: http://news.discovery.com/space/mystery-rock-appears-in-front-of-mars-rover-140117.htm