The rings of Saturn are the most extensive planetary ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometres to metres, that orbit about Saturn. The ring particles are made almost entirely of water ice, with a trace component of rocky material. In February 2016, studies suggest that more opaque areas of the rings may not contain more material. There is still no consensus as to their mechanism of formation; some features of the rings suggest a relatively recent origin, but theoretical models indicate they are likely to have formed early in the Solar System's history.