The last time humanity tried to explore a comet, things didn't go so well -- the ESA comet lander Philae bounced during touchdown and wound up under a cliff, unable to right itself. Eventually its batteries ran down we lost contact. A sad way to end the mission, but we can't say that we didn't learn anything: NASA engineers are now working on a low-gravity unmanned exploration vehicle designed to bounce, tumble and roll around asteroids and comets. It's called the Hedgehog.
Hedgehog is just a concept robot right now, but its current prototype shows a lot of promise. The small cube is outfitted with several internal flywheels that create momentum by spinning up and suddenly stopping -- causing the built up momentum to "throw" the device in a specific direction. It sounds (and looks) a little silly, but this kind of movement is ideal for the extreme-low gravity conditions found on asteroids and comets. It also potentially allows the robot to "jump" out of potholes or craters that would otherwise trap a traditional rover.
Although the device is experimental, NASA's Jet Propulsion Laboratory and researchers at Standford have already tested it in an airplane-simulated low-gravity environment. It seems to work. The team is now working on Phase II of the Hedgehog's development, adding sensors, spikes for gripping loose surfaces and other improvements. If things go well, we'll be bouncing our way across the cosmos in no time.