NASA's Curiosity Rover has been roaming around Mars for more than five years. In that time, it's sent back a ton of data about the red planet. Thanks to the robot, we know that the veins dotted around its craters were likely created by evaporating lakes. It also spotted more water evidence in possible mud cracks. And, its findings led scientists to theorize that ancient Mars had a lot more oxygen that they initially thought. But, all that riding around hasn't been easy on the car-sized machine. In the past, it's suffered a software scare here and there. This time round, its wheels are the problem.