Opportunity has been gingerly testing the edge of Endurance Crater to make sure it's stable enough for the rover to roll in without slipping down the slope. If that works out, the rover will enter the crater today and begin 2-3 weeks of scientific study, analyzing exposed layers of rock to get a better picture of water that covered the area millions of years ago. Scientists are expecting the crater will return a tremendous amount of scientific data because it's much deeper than Eagle Crater, which Opportunity first landed in when it arrived on Mars.