Saturn |
Saturn is the sixth planet from the Sun and the second largest:
orbit: 1,429,400,000 km (9.54 AU) from Sun diameter: 120,536 km (equatorial) mass: 5.68e26 kg
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.
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.
Distance Radius Mass Satellite (000 km) (km) (kg) Discoverer Date --------- -------- ------ ------- ---------- ----- Pan 134 10 ? Showalter 1990 Atlas 138 14 ? Terrile 1980 Prometheus 139 46 2.70e17 Collins 1980 Pandora 142 46 2.20e17 Collins 1980Epimetheus 151 57 5.60e17 Walker 1980 Janus 151 89 2.01e18 Dollfus 1966 Mimas 186 196 3.80e19 Herschel 1789Enceladus 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 1.35e23 Huygens 1655 Hyperion 1481 143 1.77e19 Bond 1848Iapetus 3561 730 1.88e21 Cassini 1671 Phoebe 12952 110 4.00e18 Pickering 1898
Radius Radius approx. approx. Name inner outer width position mass (kg) ---- ------ ------ ----- -------- -------- D-Ring 67,000 74,500 7,500 (ring) Guerin Division C-Ring 74,500 92,000 17,500 (ring) 1.1e18 Maxwell Division 87,500 88,000 500 (divide) B-Ring 92,000 117,500 25,500 (ring) 2.8e19 Cassini Division 115,800 120,600 4,800 (divide) Huygens Gap 117,680 (n/a) 285-440 (subdiv) A-Ring 122,200 136,800 14,600 (ring) 6.2e18 Encke Minima 126,430 129,940 3,500 29%-53% Encke Division 133,410 133,740 Keeler Gap 136,510 136,550 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)Notes: * distance is kilometers from Saturn's center * the "Encke Minima" is a slang term used by amateur astronomers, not an official