Squyres said he used to think that no matter how long the rovers lasted , at some point there would be a point in the mission where the team could say `` We 're finished '' -- that they had learned everything could about Mars with those particular vehicles . A mysterious rock , shaped and sized like a doughnut , has appeared on Mars . The rover team is studying the rock . Rock appeared in 2004 , 12 years after previous images showed no rock . Opportunity has been exploring Mars since January 2004 .
A mysterious rock , shaped and sized like a doughnut , has appeared on Mars . The rover team is studying the rock . Rock appeared in 2004 , 12 years after previous images showed no rock . Opportunity has been exploring Mars since January 2004 .