<P> Saturn's rings may be very old, dating to the formation of Saturn itself . There are two main theories regarding the origin of Saturn's inner rings . One theory, originally proposed by Édouard Roche in the 19th century, is that the rings were once a moon of Saturn (named Veritas, a Roman goddess who hid in a well) whose orbit decayed until it came close enough to be ripped apart by tidal forces (see Roche limit). A variation on this theory is that this moon disintegrated after being struck by a large comet or asteroid . The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material from which Saturn formed . </P> <P> A more traditional version of the disrupted - moon theory is that the rings are composed of debris from a moon 400 to 600 km in diameter, slightly larger than Mimas . The last time there were collisions large enough to be likely to disrupt a moon that large was during the Late Heavy Bombardment some four billion years ago . </P> <P> A more recent variant of this type of theory by R.M. Canup is that the rings could represent part of the remains of the icy mantle of a much larger, Titan - sized, differentiated moon that was stripped of its outer layer as it spiraled into the planet during the formative period when Saturn was still surrounded by a gaseous nebula . This would explain the scarcity of rocky material within the rings . The rings would initially have been much more massive (~ 1,000 times) and broader than at present; material in the outer portions of the rings would have coalesced into the moons of Saturn out to Tethys, also explaining the lack of rocky material in the composition of most of these moons . Subsequent collisional or cryovolcanic evolution of Enceladus might then have caused selective loss of ice from this moon, raising its density to its current value of 1.61 g / cm, compared to values of 1.15 for Mimas and 0.97 for Tethys . </P> <P> The idea of massive early rings was subsequently extended to explain the formation of Saturn's moons out to Rhea . If the initial massive rings contained chunks of rocky material (> 100 km across) as well as ice, these silicate bodies would have accreted more ice and been expelled from the rings, due to gravitational interactions with the rings and tidal interaction with Saturn, into progressively wider orbits . Within the Roche limit, bodies of rocky material are dense enough to accrete additional material, whereas less - dense bodies of ice are not . Once outside the rings, the newly formed moons could have continued to evolve through random mergers . This process may explain the variation in silicate content of Saturn's moons out to Rhea, as well as the trend towards less silicate content closer to Saturn . Rhea would then be the oldest of the moons formed from the primordial rings, with moons closer to Saturn being progressively younger . </P>

Particles of saturn's rings are large enough to reflect this type of light