Curiosity's Morse Wheel Marks Double as a Mars Navigation Aid
Curiosity stamps the letters JPL in Morse code on Martian terrain with its six aluminum wheels. Those repeating marks serve as a built‑in visual odometry reference, helping NASA's navigation software compare commanded wheel rotations with actual movement across difficult ground to detect wheel slip. The feature is an engineering convenience, not a sensor, designed to provide landmarks and scale while respecting the rover's mass and design limits.