Rings of Saturn
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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.[1] In 1655, Christiaan Huygens was the first person to propose that there was a ring surrounding Saturn.[1]
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.
Contents |
[edit] 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.
| Name | Distance from Saturn's center (km) | Width (km) | Named after |
|---|---|---|---|
| D Ring | 66,900 - 74,510 | 7,500 | |
| C Ring | 74,658 - 92,000 | 17,500 | |
| Colombo Gap | 77,800 ? (2) | 100 | Giuseppe "Bepi" Colombo |
| Titan Ringlet | 77,800 ? (2) | ? | Titan moon of Saturn |
| Maxwell Gap | 87,491 (2) | 270 | James Clerk Maxwell |
| B Ring | 92,000 - 117,580 | 25,500 | |
| Cassini Division | 117,580 - 122,170 | 4,700 | Giovanni Cassini |
| Huygens Gap | 117,680 ? (2) | 285-440 | Christiaan Huygens |
| A Ring | 122,170 - 136,775 | 14,600 | |
| Encke Division | 133,589 (2) | 325 | Johann Encke |
| Keeler Gap | 136,530 (2) | 35 | James Keeler |
| R/2004 S 1(1) | 137,630 (2) | ? | |
| R/2004 S 2(1) | 138,900 (2) | ? | |
| F Ring | 140,180 (2) | 30-500 | |
| Janus/Epimetheus Ring(3) | 149,000 - 154,000 | 5,000 | Janus and Epimetheus |
| G Ring | 170,000 - 175,000 | 5,000 | |
| Pallene Ring(3) | 211,000 - 213,500 | 2,500 | Pallene |
| E Ring | 181,000 - 483,000 | 302,000 |
Notes:
(1) temporary designation
(2) distance is to centre of gaps, rings and ringlets that are narrower than 1000 km
(3) unofficial name
[edit] 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.
[edit] 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.[1]
[edit] 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 center.
[edit] 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.[2] 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.
[edit] Maxwell Gap
The Maxwell Gap lies within the C Ring.
[edit] 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, and its optical depth varies from 0.4 to 2.5.[3]
Ring particles at this location orbit twice for every orbit 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.
[edit] Huygens Gap
The Huygens Gap separates the B Ring from the Cassini Division.
[edit] Cassini Division
The Cassini Division is a 4,800 km (2,980 mile) wide 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.
The gaps between rings are produced by the gravitational pull of one or more of Saturn's many moons on the tiny particles in the rings.[4]
[edit] 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 interrupted at a location 22% of the ring width from its outer edge by the Encke Division. A narrower division 2% of the ring width from the outer edge is called the Keeler Gap.
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.[5]
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.
[edit] 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.[6] 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.[7]
[edit] Keeler Gap
The Keeler Gap is a 42-kilometre-wide gap in the A Ring, approximately 250 kilometres from the ring's outer edge. It is named after the astronomer James Edward Keeler. The small moon Daphnis, discovered May 1, 2005, orbits within it, keeping it clear.
[edit] 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.
[edit] 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.
[edit] 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.[2] 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 [8]. They also show that Prometheus's gravitational attraction creates kinks and knots in the F Ring as the moon 'steals' material from it.
 The F Ring is the thin ring on the right; its shepherd moons Prometheus and Pandora can be seen on either side of it. |
 Close up view of Prometheus and the F Ring |
 Prometheus (at left) and Pandora (at right) shepherding the F Ring |
[edit] "Janus/Epimetheus" Ring
A faint dust ring is present around the region occupied by the orbits of Janus and Epimetheus, as revealed by images taken in forward-scattered light by the Cassini spacecraft in 2006. The ring has a radial extent of about 5,000 km [3]. Its source is particles blasted off the moons' surfaces by meteoroid impacts, which then form a diffuse ring around their orbital paths [4].
[edit] G Ring
The G Ring is a very thin, faint ring about halfway between the F Ring and the beginning of the E Ring.
[edit] "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 [3]. The ring has a radial extent of about 2,500 km. Its source is particles blasted off Pallene's surface by meteoroid impacts, which then form a diffuse ring around its orbital path [4].
[edit] E Ring
The E Ring is the outermost ring, and is extremely wide, beginning at the orbit of Mimas and ending somewhere around the orbit of Rhea. It is a diffuse disk of icy or dusty material. Unlike the other rings, it is composed of microscopic rather than macroscopic particles. In 2006, cryovolcanism on the moon Enceladus was determined to be the source of the E Ring's material.
[edit] References
- ^ a b Historical Background of Saturn's Rings. Retrieved on March 8, 2006.
- ^ H. Karttunen, P. Kröger, ed al. (2000). in Springer: Fundamental Astronomy.
- ^ a b NASA Planetary Photojournal PIA08328: Moon-Made Rings
- ^ a b Cassini-Huygens press release NASA Finds Saturn's Moons May Be Creating New Rings, 11 October 2006.
[edit] External links
- The Planetary Society: Images of Saturn's Rings
- Planetary Rings Node: Saturn's Ring System
- NASA Solar System Exploration: Saturn: Rings
[edit] See also
- Édouard Roche - French astronomer who described how the breakup of a satellite could form the rings, when it comes within the Roche limit of a celestial body.
- Galileo Galilei - the first person to observe Saturn's ring, in 1610
- Christian Huygens - the first person to propose that there was a ring surrounding Saturn, in 1655
- Giovanni Cassini - discovered the gap between the A and B rings, in 1675 - (Cassini Division)
| Rings of Jupiter • Rings of Saturn • Rings of Uranus • Rings of Neptune |
| See also: gas torus • R/2003 U 1 |
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|---|---|
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Generally listed in increasing distance from Saturn
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| Ring shepherds | Pan · Daphnis · Atlas · Prometheus · S/2004 S 6? · S/2004 S 4? · S/2004 S 3? · Pandora |
| Co-orbitals | Epimetheus · Janus |
| Inner large and Trojan | Mimas · Methone · Pallene · Enceladus · Tethys (trojans Telesto, Calypso) · Dione (trojans Helene, Polydeuces) |
| Outer large | Rhea · Titan · Hyperion · Iapetus |
| Inuit group | Kiviuq · Ijiraq · Paaliaq · Siarnaq |
| Norse group | Phoebe · Skathi · Skoll · S/2004 S 13 · S/2006 S 4 · Hyrokkin · Mundilfari · S/2006 S 6 · S/2006 S 1 · S/2004 S 17 · Narvi · Bergelmir · Aegir · Suttungr · S/2004 S 12 · Bestla · Farbauti · Hati · S/2004 S 7 · Thrymr · S/2006 S 3 · Surtur · Kari · Fenrir · Ymir · Loge · Fornjot |
| Gallic group | Albiorix · Bebhionn · Erriapo · Tarvos |
