Saturn's halo system is the closest thing we have to the dust and gravel disks that gave birth to Earth and other planets 4.55 billion years ago. This protoplanetary disk is formed by a nebula composed of ultra-low temperature gas and dust acting on its own gravity. As the rotating nebula gradually shrinks, it becomes a disk around the nascent sun. Once the gas has been blown away by the sun, the orbital debris in the disk is very similar to Saturn's halo system. This text mainly introduces the Saturn ring:. ['Shape.', 'Run.', 'Composition.', 'Formation.']