Saturn

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Saturn is the sixth planet from the sun. It is a gas giant, the second-largest planet in the solar system after Jupiter.

It is probably best known for its famous planetary rings. They were first observed by Galileo Galilei in 1610 with his telescope, but he clearly did not know what to make of it. He wrote to the Grand Duke of Tuscany that "Saturn is not alone but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the zodiac, and the middle one (Saturn itself) is about three times the size of the lateral ones (actually the edges of the rings)." He also described Saturn has having "ears." In 1612 the plane of the rings was oriented directly at the Earth and the rings appeared to vanish, and then in 1613 they reappeared again, further confusing Galileo. The riddle of the rings was not solved until 1655 by Christian Huygens, using a telescope much more powerful than the ones available to Galileo in his time. In 1675 Giovanni Domenico Cassini determined that Saturn's ring was actually composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the Cassini Division.

The rings can be seen in quite modest modern telescopes or a good pair of binoculars. They are composed of silica rock, iron oxide, and ice particles ranging in size from specks of dust to the size of a small automobile. There are two main theories regarding the origin of Saturn's rings. One theory, originally proposed by Edward Roche in the 19th century, is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by tidal forces. A variation of this theory is that the moon disintegrated after being struck by a large comet or asteroid. The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material that Saturn formed out of. This theory is not widely accepted today, since Saturn's rings are thought to be unstable over periods of millions of years and therefore of relatively recent origin.

  • Mean orbital radius: 1,427,000,000 km
    • Aphelion: 1,507,000,000 km
    • Perihelion: 1,347,000,000 km
  • Mass: 5.684×1026 kg (95 Earth masses)
  • Diameter: 120,000 km
  • Surface Area: 43,800,000,000 km2
  • Rotational period: 10.25 hours
  • Orbital period: 10,759 days (29.46 years)
  • Axial tilt: 26.73°
  • Atmospheric composition: 94% hydrogen, 6% helium


It has a large number of moons, 18 of which have names. The exact number of moons is uncertain, there being large numbers of objects of all sizes in orbit around Saturn. A recent survey starting in late 2000 found another 12 moons in orbits suggesting that they were the fragments of larger bodies captured by Saturn (Nature vol. 412, p.163-166)

Saturn's moons:

Name Orbital
radius (km)
Diameter
(km)
Mass
(kg)
Pan 133,583 20 Unknown
Atlas 137,670 30 (40 x 20) Unknown
Prometheus 139,350 91 (145 x 85 x 62) 2.70×1017
Pandora 141,700 84 (114 x 84 x 62) 2.20×1017
Epimetheus 151,422 115 (144 x 108 x 98) 5.60×1017 Co-orbital
Janus 151,472 178 (196 x 192 x 150) 2.01×1018
Mimas 185,520 392 3.80×1019
Enceladus 238,020 498 7.30×1019
Tethys 294,660 1060 6.22×1020Co-orbital
Telesto 294,660 29 (34 x 28 x 36) Unknown
Calypso 294,660 26 (34 x 22 x 22) Unknown
Dione 377,400 1120 1.05×1021Co-orbital
Helene 377,400 33 (36 x 32 x 30) Unknown
Rhea 527,040 1530 2.49×1021
Titan 1,221,830 5150 1.35×1023
Hyperion 1,481,100 286 (410 x 260 x 220) 1.77×1019
Iapetus 3,561,300 1460 1.88×1021
Phoebe 12,952,000 220 4.00×1018

Solar system:
Sun - Mercury - Venus - Earth - Mars - Asteroids - Jupiter - Saturn - Uranus - Neptune - Pluto - Comets