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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 travelled 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.

What’s really cool is that the track pattern spells out “JPL” in Morse code through a series of “dots” and “dashes.” JPL is an acronym for NASA’s Jet Propulsion Laboratory, the agency arm in charge of Curiosity.

On 22 August, the six-wheeled, one-ton roving laboratory left its coded track on Mars after completing its first successful test drive, rolling forward 15 feet, rotating 90 degrees and then reversing about 8 feet back to see its original spot.

Mechanical Engineer Armen Toorian explains the purpose of Curiosity’s unique wheel print in the video below:

(via Exploratorium/Youtube)

- Dina Spector