Wikipedia dicit:
The sky crane system lowers the rover with a 7.6 m (25 ft) tether to a soft landing—wheels down—on the surface of Mars. This system consists of a bridle lowering the rover on three nylon tethers and an electrical cable carrying information and power between the descent stage and rover. As the support and data cables unreel, the rover’s six motorized wheels snap into position. At roughly 7.5 m (25 ft) below the descent stage the sky crane system slows to a halt and the rover touches down. After the rover touches down, it waits two seconds to confirm that it is on solid ground by detecting the weight on the wheels and fires several pyros (small explosive devices) activating cable cutters on the bridle and umbilical cords to free itself from the descent stage. The descent stage then flies away to a crash landing site 650 m (2,100 ft) away.
Video credit: Aerojet Rocketdyne