The first nanobots to reach Mars could arrive as a cloud of "smart dust"—sand-grain-size robots that travel like a sand storm, using the Martian wind for propulsion. An orbiting spacecraft would drop a capsule of the dust motes onto the planet. From there, they would take advantage of Mars's low gravity (38 percent of Earth's) to ride the thin Martian winds. John Barker, a physicist at the University of Glasgow, says that according to his computer simulations, one release of 30,000 robots could cover thousands of square miles. Each robot would contain a nanoprocessor, an antenna for communicating with neighboring motes, a sensor for collecting data and an electrode-controlled shape-shifting polymer shell. Once on the ground, the motes would decide which would change from a smooth exterior to a dimpled silhouette that creates drag to help them catch the wind and travel. The motes would use their sensors to collect data about Mars's air currents and chemical composition and then communicate this information to the orbiter, which would relay that data back to Earth. The project might sound impossibly complex, but shape-shifting polymers already exist in the lab, and Barker has started testing the most challenging part of the concept—the communications array—with centimeter-size prototypes.