When NASA's Opportunity rover got trapped in a sand dune on Mars in 2005, it took six weeks of careful maneuvering to escape. The incident highlighted a persistent weakness of wheeled planetary explorers: loose, granular terrain can bring any rover to a halt. A team at the University of Würzburg, working under the German Aerospace Centre's VaMEx (Valles Marineris Explorer) initiative, has taken a radically different approach — instead of trying to avoid sand, they designed a rover that treats it like water.
The secret lies in the wheels. Conventional Mars rover wheels are rigid circles with treads designed for rolling over firm ground. The Würzburg team's wheels are curved and flexible, inspired by the sandfish lizard (Scincus scincus), a reptile native to the Sahara that burrows into sand and propels itself through it using undulating body motions. The wheels mimic this movement by generating both longitudinal and lateral forces simultaneously, effectively letting the rover swim rather than roll. In tests, the rover left sinusoidal S-shaped tracks in the sand — a clear signature that the swimming mechanism was working as intended.
Prototype testing revealed an important lesson: the first-generation wheels were too heavy and narrow, causing the rover to sink. Widening the wheels and reducing their mass lowered ground pressure and eliminated the sinking problem. The team is now working on intelligent control strategies that account for wheel-terrain interaction in real time. The VaMEx project envisions a whole swarm of such rovers, along with walking and flying robots, exploring the vast Valles Marineris canyon system on Mars — a region four times deeper than the Grand Canyon — where steep slopes and deep sand dunes make conventional exploration nearly impossible.
Knowledge takeaway: the sandfish lizard's swimming motion inspired a new class of Mars rover wheels that generate both forward and lateral forces, leaving sinusoidal tracks in sand; wider, lighter wheels solved an early sinking problem; and the technology is part of a broader DLR initiative to send hybrid robot swarms into Valles Marineris, the largest canyon in the Solar System.