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Saturn

converted PNM file

 

Saturn

 

Diameter: 116,464 km
Distance from Sun: 1,433,000,000 km
Surface area: 42,700,000,000 km²
Length of day: 0d 10h 39m
Gravity: 10.44 m/s²
Circumference: 365,882 km
Mass: 568.3E24 kg (95.16 Earth mass)
Length of year: 29 years
Surface temp: -145 C

Saturn is the sixth planet from the Sun and the second largest. 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”.  Saturn has known since prehistoric times.

Saturn small image

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.

Saturn-2 small image

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).

Saturn red cloud image

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.

Saturn's rings

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 F-ring

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 satellite” (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.

Saturn rings small image

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 53 named satellites (as of spring 2010).

 

 

 

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