Rings of Saturn - D Ring

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 kilometres.

Present in the D ring is a finescale structure with waves 30 kilometres apart. First seen in the gap between the C ring and D73, the structure was found during Saturn's 2009 equinox to extend a radial distance of 19000 km from the D ring to the inner edge of the B ring. The waves are interpreted as a spiral pattern of vertical corrugations of 2 to 20 m amplitude; the fact that the period of the waves is decreasing over time (from 60 km in 1995 to 30 km by 2006) allows a deduction that the pattern may have originated in late 1983 with the impact of a cloud of debris (with a mass of ~1012 kg) from a disrupted comet that tilted the rings out of the equatorial plane. A similar spiral pattern in Jupiter's main ring has been attributed to a perturbation caused by impact of material from Comet Shoemaker-Levy 9 in 1994.