sentences:  Due to the minimal gravity of the asteroid, all four rovers were designed to move around by short hops instead of the normal wheels.They were deployed at different dates from about 60 m altitude and fell freely to the surface under the asteroid's weak gravity.The first two rovers, called HIBOU (previously Rover-1A) and OWL (previously Rover-1B), landed on asteroid Ryugu on 21 September 2018.