process alone, the rings will be gone in ~ million years. While traversing the gap between the rings and planet in September 2017, the Cassini spacecraft detected an equatorial flow of charge-neutral material from the rings to the planet of 4,800–44,000 kg/s. Assuming this influx rate is stable, adding it to the continuous 'ring rain' process implies the rings may be gone in under 100 million years. Subdivisions and structures within the rings The densest parts of the Saturnian ring system are the A and B Rings, which are separated by the Cassini Division (discovered in 1675 by Giovanni Domenico Cassini). Along with the C Ring, which was discovered in 1850 and is similar in character to the Cassini Division, these regions constitute the main rings. The main rings are denser and contain larger particles than the tenuous dusty rings. The latter include the D Ring, extending inward to Saturn's cloud tops, the G and E Rings and others beyond the main ring system. These diffuse rings are characterised as "dusty" because of the small size of their particles (often about a μm); their chemical composition is, like the main rings, almost entirely water ice. The narrow F Ring, just off the outer edge of the A Ring, is more difficult to categorize; parts of it are very dense, but it also contains a great deal of dust-size particles. Physical parameters of the rings Notes: (1) Names as designated by the International Astronomical Union, unless otherwise noted. Broader separations between named rings are termed divisions, while narrower separations within named rings are called gaps. (2) Data mostly from the Gazetteer of Planetary Nomenclature, a NASA factsheet and several papers. (3) distance is to centre of gaps, rings and ringlets that are narrower than 1,000 km (600 miles) (4) unofficial name Major subdivisions C Ring structures Cassini Division structures Source: A Ring structures D Ring The D Ring is the innermost ring, and is very faint. In 1980, Voyager 1 detected within this ring three ringlets designated D73, D72 and D68, with D68 being the discrete ringlet nearest to Saturn. Some 25 years later, Cassini images showed that D72 had become significantly broader and more diffuse, and had moved planetward by 200 km (100 miles). Present in the D Ring is a finescale structure with waves 30 km (20 miles) apart. First seen in the gap between the C Ring and