That’s why researchers at Massachusetts Institute of Engineering have devised a tether system that is intended to wrap completely around an asteroid. It would let astronauts explore the surface of the asteroid without risk of getting hurled into space. The researchers envision a rocket deploying a spool of rope as it flew around the asteroid. When the craft reaches the starting point, a space explorer would form a loop in the rope and tighten it on. The inventors admit that the asteroid’s surface might not let a rope pass around it and slide easily, thus preventing walking. But, they argue, it would at least give astronauts something to hold on to as they explore the asteroid.