It's in its early stages, but the idea is to replace modern rovers — which are slow, bulky and very expensive — with swarms of sensor-studded, fast-moving micro-bots that can cover much more ground at a relatively low cost. Literally called Marsbees, the little bots are "flapping wing flyers of a bumblebee size with cicada-sized wings," NASA officials wrote. The planet has just one-third of Earth's gravitational pull, offering the Marsbees an advantage despite the thin atmosphere. Flapping-wing bots are pretty uncommon on Earth, the NASA statement noted, because rotary-wing bots like quadcopters are much more popular. But the flapping-wing design allows the team...