Answer: (JPL) Jet Propulsion Lab

When NASA’s Curiosity rover rolls quietly across the Martian plains, it leaves behind a very subtle calling card that points back to its birthplace tens of millions of miles away. Across the 14.27 miles (22.97 kilometers) of terrain it has slowly rolled over so far, taking samples and photographs along the way, it’s left tracks in the soil tracing its path back to the start of its journey at the Bradbury Landing site inside the Gale crater.

Most of the tread on the rover’s wheels is a simple but effective zig-zag (chevron) pattern designed to provide a long lasting tread with good purchasing power on the dry and loose Martian soil. The whole wheel doesn’t have the same tread, however, a small segment of each wheel tread is devoted to a series of cutouts. The pattern of the cutouts ” .— / .–. / .-.. ” spells out the initials of NASA’s Jet Propulsion Laboratory via Morse code—JPL. As the rover explores Mars, it imprints the letters in the soil, leaving a subtle nod to its birthplace wherever it goes.

While the markings might be part vanity project, they also serve a useful function. When the onboard cameras examine the tread pattern left by the wheels, the different pattern introduced by the Morse code offers a sense of scale researchers can use as a reference to show distance, even if the terrain in the photograph is featureless.