NASA's Curiosity rover has been rolling across the surface of Mars since 2012, and in that time it's covered more than 20 miles of some of the roughest terrain in the solar system. Now, a fresh batch of images has given us a much better idea of just how much that mileage has cost the rover's aluminum wheels. Some of the holes are so large, in fact, that it looks like the rover could easily get stuck on a rock or something else and be unable to move. Of course, none of this means Curiosity or NASA is quite ready to give up the fight. The rover continues to provide important scientific data about the Martian surface as NASA engineers work to find ways to extend the rover's lifespan for as long as they can, gathering more scientific data with every passing day.