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For the 2005 television series, see E-Ring. The rings of Saturn are a series of planetary rings that orbit the planet Saturn. They consist largely of ice and dust. Galileo Galilei was the first person known to have reported observations of Saturn's rings, in 1610. With the telescope technology available, he could barely resolve them, and hypothesized that they were two moons on either side of the planet.• There are several gaps between the rings, all of which are caused by orbital resonances between the tiny particles that comprise the rings, and one or more of Saturn's moons. Table The International Astronomical Union has designated the following names for the rings of Saturn and the gaps between them. This NASA factsheet provided most of the distances and widths. Notes: (1) temporary designation (2) distance is to centre of gaps, rings and ringlets that are narrower than 1000 km (3) unofficial name D Ring The D Ring is the innermost ring. It is located inward of the C 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 fainter and moved planetward by 200 kilometres. Present in the gap between the C ring and D73 is finescale structure with waves 30 kilometres apart. C Ring The C Ring is a wide but faint ring located inward of the B Ring, and was discovered in 1850 by William and George Bond when it was termed the 'Crepe Ring' because it seemed to be composed of darker material than the brighter A and B Rings. Its thickness is estimated as 5 metres, its mass as 1.1e18 kilogram, and its optical depth varies from 0.05 to 0.12.* Colombo Gap The Colombo Gap lies in the middle of the C Ring, and contains the bright and narrow Titan Ringlet (also called the Colombo Ringlet) centred at 77,883 kilometres from Saturn's centre. Titan Ringlet The Titan Ringlet (also called the Colombo Ringlet) is centred at 77,883 kilometres from Saturn's centre and is within the Colombo Gap. This ringlet is eccentric; that is, it is slightly elliptical rather than circular. The Titan Ringlet is so named because it is in a resonance with Titan.* In this case, the time period of a ring particle's apsidal precession is equal to the time period of Titan's orbital motion, so that the outer end of this eccentric ringlet always points towards Titan. Maxwell Gap The Maxwell Gap lies within the C Ring. B Ring The B Ring is the innermost of the two largest, brightest rings. Unlike the A Ring, it is made of innumerable ringlets, some of which have eccentric orbits. There are also spoke-like features running across it, which are made of suspended dust particles. Its thickness is estimated as 5 to 10 metres, its mass as 2.8e19 kilogram (about three-quarters of Mimas), and its optical depth varies from 0.4 to 2.5.* The outer edge of the B Ring is maintained by a 2:1 resonance with the moon Mimas. Ring particles at this location orbit twice for every one orbits of Mimas. The resonance causes Mimas' pulls on these ring particles to accumulate, destabilizing their orbits and leading to a sharp cutoff in ring density. Huygens Gap The Huygens Gap separates the B Ring from the Cassini Division. Cassini Division The Cassini Division is a 4,800 km (2,980 mile) region between the A Ring and B Ring. It was discovered in 1675 by Giovanni Cassini. From Earth it appears as a thin black gap in the rings. However, during the Voyager flybys, it was discovered that the gap is full of tiny rings. A Ring The A Ring is the outermost of the two largest, brightest rings. Its inner boundary is the Cassini Division and its sharp outer boundary is the orbit of the small moon Atlas. The A Ring is divided in two near its outer edge by the Encke Division. A smaller, fainter division is called the Keeler Gap, and is kept clear by the moonlet Daphnis. Its thickness is estimated as 10 to 30 metres, its mass as 6.2e18 kilogram (about the mass of Hyperion), and its optical depth varies from 0.4 to 1.0.* Similarly to the B Ring, the A Ring's outer edge is maintained by a resonance, in this case the 7:6 resonance with Janus. Encke Division The Encke Division, also historically called the Encke Gap, is a perceived gap within the A Ring. Johann Encke himself did not observe this division; it was named in honour of his ring observations. The division is centered at a distance 133,580 kilometers from Saturn's center, and has a width of 325 kilometers.* It is caused by the presence of the small moon Pan, which orbits within it. Images from the Cassini probe have shown that there are at least two thin, knotted ringlets within the gap.* Keeler Gap
R/2004 S 1 R/2004 S 1, also known as S/2004 1R, is the temporary designation of a newly discovered ring that lies between the A Ring and the F Ring, in the orbit of the moon Atlas. The faint, thin ring was discovered by the Cassini probe imaging team and announced on September 9, 2004. R/2004 S 2 R/2004 S 2 is a temporary designation for a faint ring recently discovered by the Cassini probe imaging team and announced in 2005. The ring is located at 138,900 km from Saturn's center, between the orbits of Atlas and Prometheus. F Ring The F Ring is one of the outer rings of Saturn. It is located outside the larger rings, just beyond about 3000 Km, the A Ring.• It was discovered in 1979. It is very thin, just few hundred of kilometers wide, and is held together by two shepherd moons, Prometheus and Pandora, which orbit inside and outside it. Recent closeup images from the Cassini probe show that the F Ring consists of one core ring and a spiral strand around it *. They also show that Prometheus's gravitational attraction creates kinks and knots in the F Ring as the moon 'steals' material from it. Image:F Ring.jpg|The F Ring is the thin ring on the right; its shepherd moons Prometheus and Pandora can be seen on either side of it. Image:Prometheus's effect on the F Ring.jpg|Close up view of Prometheus and the F Ring Image:Shepherd moons PIA07653.jpg|Prometheus (at left) and Pandora (at right) shepherding the F Ring "Janus/Epimetheus" Ring
G Ring
"Pallene" Ring A faint dust ring shares Pallene's orbit, as revealed by images taken in forward-scattered light by the Cassini spacecraft in 2006 . The ring has a radial extent of about 2,500 km. Its source are particles blasted off Pallene's surface by meteoroid impacts, which then form a diffuse ring around its orbital path . E Ring
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