Saturn is the sixth planet from the Sun and the second largest.Saturn appears in the sky as a yellow.

Saturn, the second most massive planet, and the most distant planet known to the ancients, is one of the most beautiful sites in the Solar System, as witnessed by the image (above). The most striking feature of Saturn is the spectacular ring system.

Although this feature is no longer unique, since we now know that all the Gas Giant planets have rings, the rings of Saturn are much more elaborate than those of any of the other planets. Saturn shares many features with its even larger Gas Giant neighbor Jupiter, but has various unique features in its own.

Facts:-

Sign:
Orbit:1,429,400,000 km (9.54 AU) from Sun
Diameter:120,536 km (equatorial)
Mass:5.68e26 kg
Density:687 kg/m^3
Minimum Distance from Sun:1.35 billion km (840 million miles)
Maximum Distance from Sun:1.5 billion km (938 million miles)
Minimum Distance from Earth: 1.2 billion km (746 million miles)
Rotation Period about Axis:10.67 hrs
Revolution Period about the Sun: 29.5 years
Tilt of Axis:26 Degrees 42"
Surface Gravity:8.96 m/s^2 (0.92 x Earth's)
Temperature at Cloud Tops: -170o C (-274o F)
Average Cloud Top Temperature (K): 103K
Name in Roman/Greek Mythology: Saturn/Cronus
Satellites/Rings: 28 known moons, many rings

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 Pioneer 11 in 1979 and later by Voyager 1 and Voyager 2. Cassini, now on its way, will arrive in 2004.

The Rings Of Saturn:-
The ring system of Saturn is divided into 5 major components: the G, F, A, B, and C rings, listed from outside to inside (but in reality, these major divisions are subdivided into thousands of individual ringlets). The F and G rings are thin and difficult to see, while the A, B, and C rings are broad and easily visible. The large gap between the A ring and and the B ring is called the Cassini division (discovered by the Italian-French astronomer),The much fainter gap in the outer part of the A ring is known as the Encke Division (is named after the German astronomer Johann Franz Encke, who discovered it in 1837)

The adjacent image is a rare view of Saturn's rings seen just after the Sun has set below the ring plane, taken with the Hubble Space Telescope on Nov. 21, 1995. This perspective is unusual because the Earth is slightly above and the Sun slightly below the rings. Normally we see the rings fully illuminated by the Sun.

Three bright ring features are seen: the F Ring, the Cassini Division, and the C Ring (moving from the outer rings to the inner). The low concentration of material in these rings allows light from the Sun to shine through them. The A and B rings are much denser, which limits the amount of light that penetrates through them. Instead, they are faintly visible because they reflect light from Saturn's disk.


Ring Structure and Composition
High resolution photographs from the Voyager missions indicate that the rings of Saturn are composed of hundreds of thousands of "ringlets", and that regions like the largest "gap" called the Cassini division, also contain fainter rings.

The rings cannot be solid, because they lie inside the Roche limit. They presumably represent either a satellite torn apart by tidal forces, or (more likely) material that was never allowed to condense into moons because of the tidal forces.

The evidence indicates that the rings are composed of particles that are mostly ice crystals, with sizes as large as centimeters or meters,They range in size from a centimeter or so to several meters. A few kilometer-sized objects are also likely.

The total mass in the rings is about the size of a medium mass moon, and the rings are only about 10 km thick.
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.

The whole system is very complex and as yet poorly understood.

Spokes and other Structure
It was expected that collisions between ring particles would tend to make the rings uniform, but Voyager I found changing structures in the radial direction that are termed "spokes".

It is thought that gravitational forces alone cannot account for the spoke structure, and it has been proposed that electrostatic repulsion between ring particles may play a role.

The Voyagers found that the rings were not necessarily circular, and even found rings that appeared to be braided.They found further that the outer ring was kept in place by the gravitational interaction of two small "shepherd moons" lying just inside and outside it, and that at least some of the other rings are kept narrow by similar small shepherding satellites. Generally, although we have increased immensely our knowledge of the rings of Saturn over the last 2 decades, we still do not fully understand their structure, dynamics, or origin.

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

The Satellite System
Saturn has 18 confirmed Satellite.More than a dozen others have been reported and given provisional status; nine of these were derived from the analysis of data from the 1981 flyby of the Voyager 2 space probe, and seven were identified from Hubble Space Telescope photographs taken during the 1995 ring plane crossings.

It is possible that some of these are actually the same as some of the known satellites or duplicates of one another. The data probably will not be sorted out until the arrival of the Cassini probe, which is designed to do a detailed study of Saturn, its rings, its magnetosphere, its icy satellites, and Titan.

All but two of Saturn's moons form a regular system of satellites; that is, their orbits are nearly circular and lie in the equatorial plane of the planet. The exceptions are Iapetus, whose orbit is inclined almost 15°, and Phoebe, whose orbit is inclined 175°. Except for Hyperion, which has a chaotic orbit, and Phoebe, all the satellites are believed to have synchronous orbits; that is, their orbital and rotational periods are the same so that they keep the same face turned toward Saturn, just as the moon keeps the same face turned toward the earth.

The largest satellite, Titan, is 3,200 mi (5,150 km) in diameter and has the size and cold temperatures necessary to retain an atmosphere; it is the only natural satellite in the solar system with a substantial atmosphere.

Saturn has six major icy satellites that can be easily seen through earth-based telescopes. The most prominent feature of heavily cratered Mimas, the innermost of the six, is a large impact crater about one third the diameter of the satellite.

Certain broad regions of Enceladus are uncratered, indicating geological activity that has somehow resurfaced the satellite within the last 100 million years.

Tethys also has a very large impact crater, as well as an extensive series of valleys and troughs that stretches three quarters of the way around the satellite.

Both Dione and Rhea have bright, heavily cratered leading hemispheres and darker trailing hemispheres with wispy streaks that are thought to be produced by deposits of ice inside surface troughs or cracks.

Iapetus, the outermost of the large icy satellites, has a dark leading hemisphere and a bright trailing hemisphere.

The remaining eleven satellites, some sharing orbits with others, are smaller. The two largest of these, the dark-surfaced Phoebe and the irregularly shaped Hyperion, orbit far from the planet; the outermost satellite, Phoebe, orbits with retrograde motion, i.e., opposite to that of the planet's rotation. The smallest, ranging from c.12 to 20 mi (20 to 32 km) in diameter, are Pan and Atlas, the satellites closest to the planet, and Telesto, Calypso, and Helene. Prometheus and Pandora, c.55 mi (90 km) in diameter, share an orbit, as do Epimetheus and Janus.

Satellite	Distance (000)Km	Radius Km	Mass Kg	Discover	Date
Pan	134	10	?	Showalter	1990
Atlas	138	14	?	Terrile	1980
Prometheus	139	46	2.70e17	Collins	1980
Pandora	142	46	2.20e17	Collins	1980
Epimetheus	151	57	5.60e17	Walker	1980
Janus	151	89	2.01e18	Dollfus	1966
Mimas	186	196	3.80e19	Herschel	1789
Enceladus	238	260	8.40e19	Herschel	1789
Tethys	295	530	7.55e20	Cassini	1684
Telesto	295	15	?	Reitsema	1980
Calypso	295	13	?	Pascu	1980
Dione	377	560	1.05e21	Cassini	1684
Helene	377	16	?	Laques	1980
Rhea	527	765	2.49e21	Cassini	1672
Titan	1222	2575	1.33e23	Huygens	1655
Hyperion	1481	143	1.77e19	Bond	1848
Hyperion	3561	730	1.88e21	Cassini	1671
Phoebe	12952	110	4.00e18	Pickering	1898

Saturn's Rings:-

Name	Radius Inner	Radius Outer	approx. Width	approx Position	Mass Kg
D-Ring	67.000	74.000	7.500	(ring)
Guerin Division
C-Ring	74.500	92.000	17.500	(ring)	1.1e18
Maxwell Divisions	87.500	88.000	500	(divide)
B-Ring	92.000	117.500	25.500	(ring)	2.8e19
Cassini Division	115.800	120.600	7.800	(divide)
Huygens Gap	117.680	(n/a)	285-400	(subdiv)
A-Ring	122.200	136.800	14.600	(ring)	6.2e18
Encke Minima	126.430	129.940	3.500	29%-35%
Encke Division	133.580		325	78%
F-Ring	140.210		30-500	(ring)
G-Ring	165.800	173.800	8.000	(ring)	1e7?
E-Ring	180.000	480.000	300.000	(ring)

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