Saturn
 
Saturn information
Average distance from Sun:1426725400 km (9.5369 AU)
Perihelion (closest):1349467000 km
Perihelion (farthest):1503983000 km
Equatorial radius:60268 km (Diameter: 120536 km)
Equatorial circumference:378675 km
Volume:827130000000000 km²
Mass:568510000000000000000000000 kg
Density:0.70 g/cm³
Surface area:43466000000 km²
Equatorial surface gravity:7.207 m/s²
Escape velocity:127760 m/s
Siderial rotation period (length of day):10.656 earth hours
Siderial orbit period (length of year):10755.7 earth days
Mean orbit velocity:9672.4 m/s
Orbital eccentricity:0.0541506
Orbital inclination to ecliptic:2.484 degrees
Equatorial inclination to orbit:26.73 degrees
Orbital circumference:8725000000 km
Surface temperature (min/max):95 K
Atmospheric constituents:H2, He
 Saturn, Sun VI
 
Saturn

In Roman mythology, Saturn is the god of agriculture. The associated Greek god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter). Saturn is the root of the English word 'Saturday' (see Appendix 5).

Saturn has been known since prehistoric times. Galileo was the first to observe it with a telescope in 1610; he noted its odd appearance but was confused by it. Early observations of Saturn were complicated by the fact that the Earth passes through the plane of Saturn's rings every few years as Saturn moves in its orbit. A low resolution image of Saturn therefore changes drastically. It was not until 1659 that Christiaan Huygens correctly inferred the geometry of the rings. Saturn's rings remained unique in the known solar system until 1977 when very faint rings were discovered around Uranus (and shortly thereafter around Jupiter and Neptune).

Saturn was first visited by NASA's Pioneer 11 in 1979 and later by Voyager 1 and Voyager 2. Cassini (a joint NASA / ESA project) arrived on July 1, 2004 and will orbit Saturn for at least four years.

Saturn is visibly flattened (oblate) when viewed through a small telescope; its equatorial and polar diameters vary by almost 10% (120,536 km vs. 108,728 km). This is the result of its rapid rotation and fluid state. The other gas planets are also oblate, but not so much so.

Saturn is the least dense of the planets; its specific gravity (0.7) is less than that of water.

Like Jupiter, Saturn is about 75% hydrogen and 25% helium with traces of water, methane, ammonia and 'rock', similar to the composition of the primordial Solar Nebula from which the solar system was formed.

Saturn's interior is similar to Jupiter's consisting of a rocky core, a liquid metallic hydrogen layer and a molecular hydrogen layer. Traces of various ices are also present.

Saturn's interior is hot (12000 K at the core) and Saturn radiates more energy into space than it receives from the Sun. Most of the extra energy is generated by the Kelvin-Helmholtz mechanism as in Jupiter. But this may not be sufficient to explain Saturn's luminosity; some additional mechanism may be at work, perhaps the 'raining out' of helium deep in Saturn's interior.

The bands so prominent on Jupiter are much fainter on Saturn. They are also much wider near the equator. Details in the cloud tops are invisible from Earth so it was not until the Voyager encounters that any detail of Saturn's atmospheric circulation could be studied. Saturn also exhibits long-lived ovals (red spot at center of image at right) and other features common on Jupiter. In 1990, HST observed an enormous white cloud near Saturn's equator which was not present during the Voyager encounters; in 1994 another, smaller storm was observed (left).

Two prominent rings (A and B) and one faint ring (C) can be seen from the Earth. The gap between the A and B rings is known as the Cassini division. The much fainter gap in the outer part of the A ring is known as the Encke Division (but this is somewhat of a misnomer since it was very likely never seen by Encke). The Voyager pictures show four additional faint rings. Saturn's rings, unlike the rings of the other planets, are very bright (albedo 0.2 - 0.6).

Though they look continuous from the Earth, the rings are actually composed of innumerable small particles each in an independent orbit. They range in size from a centimeter or so to several meters. A few kilometer-sized objects are also likely.

Saturn's rings are extraordinarily thin: though they're 250,000 km or more in diameter they're less than one kilometer thick. Despite their impressive appearance, there's really very little material in the rings -- if the rings were compressed into a single body it would be no more than 100 km across.

The ring particles seem to be composed primarily of water ice, but they may also include rocky particles with icy coatings.

Voyager confirmed the existence of puzzling radial inhomogeneities in the rings called 'spokes' which were first reported by amateur astronomers (left). Their nature remains a mystery, but may have something to do with Saturn's magnetic field.

Saturn's outermost ring, the F-ring, is a complex structure made up of several smaller rings along which 'knots' are visible. Scientists speculate that the knots may be clumps of ring material, or mini moons. The strange braided appearance visible in the Voyager 1 images (right) is not seen in the Voyager 2 images perhaps because Voyager 2 imaged regions where the component rings are roughly parallel. They are prominent in the Cassini images which also show some as yet unexplained wispy spiral structures.

There are complex tidal resonances between some of Saturn's moons and the ring system: some of the moons, the so-called 'shepherding satellites' (i.e. Atlas, Prometheus and Pandora) are clearly important in keeping the rings in place; Mimas seems to be responsible for the paucity of material in the Cassini division, which seems to be similar to the Kirkwood gaps in the asteroid belt; Pan is located inside the Encke Division and S/2005 S1 is in the center of the Keeler Gap. The whole system is very complex and as yet poorly understood.

The origin of the rings of Saturn (and the other jovian planets) is unknown. Though they may have had rings since their formation, the ring systems are not stable and must be regenerated by ongoing processes, perhaps the breakup of larger satellites. The current set of rings may be only a few hundred million years old.

Like the other jovian planets, Saturn has a significant magnetic field.

When it is in the nighttime sky, Saturn is easily visible to the unaided eye. Though it is not nearly as bright as Jupiter, it is easy to identify as a planet because it doesn't 'twinkle' like the stars do. The rings and the larger satellites are visible with a small astronomical telescope. There are several Web sites that show the current position of Saturn (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program.

Saturn's Satellites



Saturn has 34 named satellites:
  • Of those moons for which rotation rates are known, all but Phoebe and Hyperion rotate synchronously.
  • The three pairs Mimas-Tethys, Enceladus-Dione and Titan-Hyperion interact gravitationally in such a way as to maintain stable relationships between their orbits: the period of Mimas' orbit is exactly half that of Tethys, they are thus said to be in a 1:2 resonance; Enceladus-Dione are also 1:2; Titan-Hyperion are in a 3:4 resonance.
  • See http://www.ifa.hawaii.edu/%7Esheppard/satellites/ for the latest about recently discovered moons.
  • See http://spaceflightnow.com/cassini/040816newmoons.html for info about two discovered in 2004 by Cassini.


Saturn's Rings



NameRadius
inner		Radius
outer		Widthapprox.
position		approx.
mass (kg)
D-Ring67,00074,5007,500(ring)
Guerin Division
C-Ring74,50092,00017,500(ring)1.1e18
Maxwell Division87,50088,000500(divide)
B-Ring92,000117,50025,500(ring)2.8e19
Cassini Division115,800120,6004,800(divide)
Huygens Gap117,680(n/a)285-440(subdiv)
A-Ring122,200136,80014,600(ring)6.2e18
Encke Minima126,430129,9403,50029%-53%
Encke Division133,410133,740
Keeler Gap136,510136,550
F-Ring140,210?30-500(ring)
G-Ring165,800173,8008,000(ring)1e7?
E-Ring180,000480,000300,000(ring)


Notes:
  • distance is kilometers from Saturn's center
  • the 'Encke Minima' is a slang term used by amateur astronomers, not an official IAU designation


This categorization is actually somewhat misleading as the density of particles varies in a complex way not indicated by a division into neat regions: there are variations within the rings; the gaps are not entirely empty; the rings are not perfectly circular.
 
Satellites of Saturn
SatelliteDistance
(km)		Radius
(km)		Mass
(kg)		DiscovererYear
Pan13358300010Mark R. Showalter1990
Daphnis1365050003.51.5.2005
Atlas13767000018.5 x 17.2 x 13.5R. Terrile1980
Prometheus13935300074.0 x 50.0 x 34.0800000000000S.A. Collins, D. Carlson1980
S/2004 S6000Cassini team28.10.2004
S/2004 S4140100000Cassini team9.9.2004
S/2004 S31405800002Cassini team21.6.2004
Pandora14170000055.0 x 44.0 x 31.0800000000000S. A. Collins, D. Carlson1980
Epimetheus15142200069 x 55 x 55R. Walker1966/1978
Janus15147200097.0 x 95.0 x 77.01920000000000Audouin Dollfus1966
Mimas186520000209.1 x 196.2 x 191.437500000000000William Herschel1789
Methone1944400001.5S. Charnoz, C. Porco1.6.2004
Pallene2110000002S. Charnoz, C. Porco1.6.2004
Enceladus238020000256.3 x 247.3 x 244.670000000000000William Herschel1789
Telesto29466000015 x 12.5 x 7.5800000000000B. Smith &(amp; H. Reitsema, S. Larson & J. Fountain)1980
Tethys294660000535.6 x 528.2 x 525.8627000000000000G.D. Cassini1684
Calypso29466000015.0 x 8.0 x 8.0800000000000D. Pascu1980
Dione3774000005601100000000000000G.D. Cassini1684
Helene37740000018 x 16 x 15800000000000P. Laques & J. Lecacheux1980
Polydeuces3774000006.5
Rhea527040000764G.D. Cassini1672
Titan12218300002575134550000000000000C. Huygens1655
Hyperion1481100000180 x 140 x 112.5800000000000W. & G.Bond & W. Lassell1848
Iapetus35613000007181600000000000000G.D. Cassini1671
Kiviuq1133300000072000
Ijiraq113720000005John J. Kavelaars2000
Phoebe12952000000110400000000000W. Pickering1898
Paaliaq149240000009.52000
Skathi155760000003.2John J. Kavelaars2000
Albiorix1640200000013Matthew J. Holman2000
S/2004S111689800000032004
Erriapo174090000004.3John J. Kavelaars2000
Siarnaq17906000000162000
Tarvos181600000006.52000
Mundilfari183600000002.8Brett J. Gladman2000
S/2004 S171909900000025.3.2005
Narvi193710000003.3Scott S. Sheppard and David C. Jewitt5.2.2003
S/2004 S15193720000003Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden4.5.2005
S/2004 S10196180000003Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden14.5.2005
Suttungr196670000002.82000
S/2004 S12199060000002.5Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden4.5.2004
S/2004 S18199590000003.5Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden4.5.2004
S/2004 S9202910000002.5Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden4.5.2004
S/2004 S14203030000003Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden4.5.2004
S/2004 S7205770000003Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden4.5.2004
Thrymr208100000002.8Gladman2000
S/2004S16226110000002Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden4.5.2004
Ymir231750000008Brett J. Gladman2000
S/2004 S82360900000032004
S/2004S1390600032004
 
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