NASA’s Mars Curiosity rover may be loaded with a bunch of highly-sophisticated instruments to help it scoop, drill, and snap awesome photographs, but it doesn’t come with a built-in GPS.
The only way to track Curiosity’s whereabouts and how far it has traveled is by following the car-sized Martian explorer’s wheel marks.
For this reason, engineers put holes in Curiosity’s treads so that every time the wheels turn, they leave a unique imprint on Mars. Orbiters photograph the print and scientists can determine how far the rover has moved.