July 31, 2009--Even as mission managers work to free its twin, Spirit, from its sandy trap, the Mars rover Opportunity has stumbled across what could be a meteorite on the surface of Mars.

Rover drivers first noticed the craggy, 2-foot-wide (0.6-meter-wide) rock--dubbed Block Island--on July 18. Opportunity had been headed away from the object at the time, so the team had the rover backtrack for a closer look.

Both rovers have spotted several meteorite candidates on Mars over the past five years, but only one has been officially confirmed so far.