Robots that explore the surface of Mars might someday resemble cats rather than carts. The Biomorphic Robot with Distributed Power (BiRoD), developed by the University of Arizona’s Kumar Ramohalli and students, uses a series of battery-activated wires and springs to mimic the expansion and contraction of muscles while moving its legs. With no motor-and-gear systems to get jammed or clogged with dust, the BiRoD should be less prone to mechanical failure than robots like the six-wheeled Sojourner rover that rolled across the Martian terrain in 1997. Mechanical muscles can also store energy slowly and release it suddenly-“like a cat,” Ramohalli says-to perform such tasks as crushing a rock, which would be impossible with a conventional rover. And the spring system is extremely compact: 25 BiRoDs could fit in the same space and have the same mass as Sojourner, giving future planetary missions added versatility and redundancy.