In the quest to explore the Martian surface, engineers are turning to an unexpected source of inspiration: a small desert-dwelling lizard that "swims" through sand with remarkable efficiency. Researchers at Germany's University of Würzburg have developed an innovative rover wheel design based on the locomotion mechanics of the sandfish skink, a reptile that has perfected the art of traversing loose, granular terrain over millions of years of evolution. This breakthrough in biomimetic engineering could revolutionize how future Mars missions navigate the Red Planet's challenging sandy landscapes, potentially addressing one of the most persistent problems faced by wheeled rovers since the days of NASA's Sojourner rover.
The challenge of Martian surface mobility has plagued space agencies for decades. Traditional wheeled designs, while effective on solid ground, frequently struggle with the planet's ubiquitous fine-grained regolith—sand-like material that can cause wheels to slip, sink, or become completely immobilized. The Spirit rover famously became trapped in soft Martian soil in 2009, ultimately ending its mission. By studying how nature has solved similar problems on Earth, the German research team has developed a radical alternative that doesn't simply roll across sand but actively propels itself through it using a swimming motion.
The Sandfish Skink: Nature's Master of Granular Locomotion
The Scincus scincus, commonly known as the sandfish skink, is a remarkable creature native to the deserts of North Africa and the Arabian Peninsula. This small lizard has evolved an extraordinary ability to literally swim through sand, undulating its body in a wave-like motion that allows it to move beneath the surface with minimal resistance. Unlike most desert animals that simply walk across sand, the sandfish skink uses lateral undulation—the same basic movement pattern used by snakes and fish—to generate thrust in a granular medium.
Research conducted at Georgia Institute of Technology in previous studies revealed that the sandfish can achieve speeds of up to 15 centimeters per second while submerged in sand, an impressive feat considering the material's resistance. The lizard's scales are specially adapted with a unique microstructure that reduces friction, and its body shape creates optimal pressure distributions that prevent it from sinking. These biological adaptations have been studied extensively in the field of granular physics, providing valuable insights for robotics engineers.
Engineering Innovation: From Biology to Robotics
Professor Marco Schmidt and his team at the Embedded Systems and Sensors for Earth Observation (ESSEO) group have translated the sandfish's biological mechanisms into practical engineering solutions. Their work is part of the VaMEx (Valles Marineris Explorer) initiative coordinated by the German Aerospace Centre (DLR), which focuses on developing technologies for exploring Mars' most challenging terrains, including the massive Valles Marineris canyon system.
Amenosis Lopez, a key researcher on the project, explained the fundamental problem with conventional designs: "Conventional wheel designs are often optimised for driving at low speeds and tend to slip, sink or get stuck on soft ground." The team's solution involves wheels that don't simply rotate but incorporate a swimming mechanism that generates both forward and lateral forces, mimicking the sandfish's interaction with granular material.
"The wheels mimic the animal's characteristic interaction with the ground, generating both longitudinal and lateral forces. The rover leaves sinusoidal tracks in the sand – this confirms that the intended swimming mechanism has been achieved."
Design Evolution and Performance Testing
The development process involved multiple iterations to optimize the wheel design. Early prototypes faced significant challenges—they were narrower and heavier than traditional wheels, paradoxically suffering from the same slipping and sinking problems they were designed to solve. However, through systematic testing and refinement, the team created a second-generation design that addressed these issues by incorporating lighter materials and wider wheel profiles.
The improved design demonstrated superior performance in controlled sand environments, leaving distinctive sinusoidal track patterns that confirmed the swimming mechanism was functioning as intended. These wave-like tracks are the signature of the lateral force generation that sets this design apart from conventional wheels. In comparative testing, the sandfish wheels showed reduced slip rates and better weight distribution across soft surfaces, maintaining forward momentum where traditional designs would falter.
Technical Challenges and Multi-Terrain Performance
While the sandfish wheels excel on sandy terrain, Mars presents a far more complex environment than Earth's deserts. The Martian surface varies dramatically, featuring not only fine regolith but also rocky outcrops, fields of pebbles, hardened soil, and mixed terrain types. Each of these surfaces presents unique challenges for any mobility system.
The research team acknowledges that achieving optimal performance across all terrain types remains a work in progress. Professor Schmidt noted: "The experiments also provided us with clear pointers for improvements." Current development efforts focus on refining the wheel surface texture and structure to enhance traction on rocky surfaces without compromising the swimming capability that makes them effective on sand. This represents a classic engineering challenge: optimizing for multiple, sometimes contradictory, requirements.
The team is exploring several approaches to improve multi-terrain adaptability:
- Surface texture modifications: Incorporating patterns or materials that provide grip on hard surfaces while maintaining low friction in sand
- Adaptive stiffness: Developing wheels that can adjust their flexibility based on terrain conditions detected by onboard sensors
- Hybrid designs: Combining elements of traditional wheels with swimming mechanisms to create versatile solutions
- Smart control algorithms: Programming the rover to adjust wheel motion patterns based on real-time terrain analysis
Timeline for Mars Implementation
The path from laboratory prototype to Mars surface deployment is lengthy and complex. The European Space Agency's Rosalind Franklin rover, originally scheduled for launch in 2022 and now targeted for 2028, has already finalized its design and will use conventional wheel technology. This rover, part of the ExoMars program, will carry a sophisticated drill capable of reaching two meters below the surface to search for signs of past or present life.
However, the ESA is planning another mission to Mars with a launch window in 2035—a particularly favorable alignment between Earth and Mars that occurs approximately every 26 months, with 2035 offering optimal conditions for the next decade. This future mission is currently in its conceptual phase, with priorities focused on developing precision landing technologies that would enable targeted deployment to specific scientific sites.
The timing could align perfectly with the sandfish wheel development. By 2035, the technology should have undergone extensive testing, refinement, and validation. If the ESA successfully lands a rover on Mars—which would be a historic first for the agency—there's a genuine possibility it could feature this innovative biomimetic mobility system. The technology would be particularly valuable for exploring regions with extensive sand dunes, such as those found in Olympia Undae near Mars' north polar cap.
Broader Implications for Planetary Exploration
The sandfish wheel concept represents more than just an incremental improvement in rover technology—it exemplifies a fundamental shift in how engineers approach planetary exploration challenges. Rather than attempting to impose Earth-based solutions on alien environments, biomimicry allows designers to leverage billions of years of evolutionary problem-solving.
This approach has applications beyond Mars. Saturn's moon Titan, with its vast dune fields of organic sand, could be an ideal testing ground for swimming wheel technology. Similarly, the concept could inform the design of vehicles for exploring the lunar surface, particularly in permanently shadowed craters where fine regolith accumulates. The principles learned from the sandfish might even inspire solutions for terrestrial applications, from desert rescue vehicles to agricultural equipment operating in sandy soils.
The collaboration between biological research and engineering continues to yield unexpected innovations. As space agencies worldwide plan increasingly ambitious missions to explore our solar system, the sandfish skink's ancient adaptations may help write the next chapter in humanity's journey across the cosmos. The humble desert lizard, swimming through sand for millions of years, never knew it would one day inspire machines exploring another world—a testament to the unexpected connections that drive scientific progress.
