From a JPL press release: “Careful inspection of the tracks reveals a unique, repeating pattern, which the rover can use as a visual reference to drive more accurately in barren terrain. The pattern is Morse code for JPL, the abbreviation for NASA’s Jet Propulsion Laboratory in Pasadena, Calif., where the rover was designed and built, and the mission is managed.”
This trackable terrain augmentation is a clever form of so-called visual odometry: “The purpose of the pattern is to create features in the terrain that can be used to visually measure the precise distance between drives,” such that the visual appearance of the inscribed code will reveal signs of slippage and, thus, a need to re-chart or correct the rover’s navigation. This will be especially useful on “featureless terrain.”
The example NASA uses is a picket fence:
“Imagine standing in front of a picket fence, and then closing your eyes and shifting to the side. When you open your eyes, you wouldn’t be able to tell how many pickets you passed. If you had one picket that was a different shape though, you could always use that picket as your reference,” said [Matt Heverly, lead rover driver at JPL]. “With Curiosity, it’s a similar problem in featureless terrain like sand dunes. The hole pattern in the wheels gives us one ‘big picket’ to look at.”
In other words, somewhere on the surface of Mars, codes from Earth—a new Linear A—will slowly drift apart over the years, becoming an unreadable road in the sand.
(Thanks to Nicola Twilley for the tip).