Difference between revisions of "Saturn"

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	:''For other uses, please see [[Saturn (disambiguation)]].''		:''For other uses, please see [[Saturn (disambiguation)]].''
−	{{Planet|image=Saturnrings.jpg	+	{{Planet|image=SaturnCassiniOverview.jpg
−	|caption=Image of Saturn captured by the Hubble Space Telescope in October 1996	+	|caption=Composite true-color image of Saturn by spacecraft [[Cassini-Huygens mission|Cassini]] in October of 2004.
−	|symbol=Saturn symbol.svg	+
−	|discname=Known to ancients	+
	|origname=Roman god of harvest		|origname=Roman god of harvest
		+	|symbol=♄
	|order=7		|order=7
	|primary=Sun		|primary=Sun
−	|periapsis=9.02 AU	+	|periapsis=1,352,550,000 km<ref name=saturnfact>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html Saturn Fact Sheet]." National Space Science Data Center, [[National Aeronautics and Space Administration|NASA]], November 23, 2007. Accessed May 19, 2008.</ref>
−	|apoapsis=10.05 AU	+	|apoapsis=1,514,500,000 km<ref name=saturnfact/>
−	|semimajor=9.537 AU	+	|semimajor=1,433,530,000 km<ref name=saturnfact/><ref name=planetsoc>"[http://www.planetary.org/explore/topics/saturn/ Space Topics: Saturn]." ''The Planetary Society''. Accessed May 19, 2008.</ref>
	|bode=10.0 AU		|bode=10.0 AU
	|circumference=59.879 AU		|circumference=59.879 AU
−	|eccentricity=0.054	+	|eccentricity=0.0565<ref name=saturnfact/>
−	|sidereal=29.458 a	+	|sidereal=10,759.22 da (29.4 a)<ref name=saturnfact/>
−	|synodic=378.10 da (1.035 a)	+	|synodic=378.09 da<ref name=saturnfact/>
	|orbitspeed=10.183 km/s		|orbitspeed=10.183 km/s
−	|inclination=2.484°	+	|inclination=2.485°<ref name=saturnfact/>
	|reference=the ecliptic		|reference=the ecliptic
−	|siderealday=10.783 h (0.449 da)	+	|siderealday=10.656 h<ref name=saturnfact/>
−	|axialtilt=26.73°	+	|solarday=10,656 h<ref name=saturnfact/>
−	|mass=5.6846 * 10<sup>26</sup> kg (95.124 * earth)	+	|rotatespeed=9.8663 m/s<ref name=calc>Calculated</ref>
−	|density=687.3 kg/m³	+	|axialtilt=26.73°<ref name=saturnfact/>
−	|surfacegrav=9.05 m/s² (0.923 ''g'')	+	|mass=5.6846 * 10<sup>26</sup> kg<ref name=saturnfact/>
−	|escapespeed=35.49 km/s	+	|density=687.3 kg/m³<ref name=saturnfact/>
−	|equatorradius =60,268 km	+	|surfacegrav=8.96 m/s²<ref name=saturnfact/>
−	|surfacearea=42,700,000,000 km² (83.714 * earth)	+	|escapespeed=35.49 km/s<ref name=saturnfact/>
		+	|meanradius=58,232 km<ref name=saturnfact/>
		+	|equatorradius =60,268 km<ref name=saturnfact/>
		+	|polarradius=54,364 km<ref name=saturnfact/>
		+	|surfacearea=42,612,000,000 km²<ref name=calc/>
	|meantemp=134 K		|meantemp=134 K
−	|moons=60 (approx)	+	|moons=60
−	|composition=75% [[hydrogen]] and 25% [[helium]] gas	+	|composition=hydrogen 96.3%, helium 3.25%, methane 4500 ppm, ammonia 125 pm, hydrogen deuteride 110 ppm, ethane 1.5 ppm, plus aerosols of ammonia ice, water ice, and ammonia hydrosulfide<ref name=saturnfact/>
−	|color=Yellow	+	|color=light yellow
−	|albedo=0.47	+	|albedo=0.47<ref name=saturnfact/>
−	}}	+	|mfd=0.210 G<ref name=saturnfact/>
		+	|pmdm=4.6 * 10<sup>25</sup> N-m/T<ref name=Russell>Russell, C. T., and Luhmann, J. G. "[http://www-ssc.igpp.ucla.edu/personnel/russell/papers/sat_mag.html Saturn: Magnetic Field and Magnetosphere]." ''Encyclopedia of Planetary Sciences'', J. H. Shirley and R. W. Fainbridge, eds. New York: Chapman and Hall, 1997, pp. 718-719. Accessed May 19, 2008.</ref><ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''[[Creation Research Society Quarterly]]'' 21(3), December 1984. Accessed April 29, 2008.</ref>
		+	|cmdm=1.34 * 10<sup>26</sup> N-m/T<ref name=Humphreys/>
		+	|mdt=5300 a<ref name=Humphreys/>
		+	|mhl=3700 a<ref name=calc/>
		+	}}'''Saturn''' is the sixth [[planet]] from the [[sun]] and the second largest planet in the [[solar system]]. Saturn is a [[gas giant]] with an atmosphere predominantly of [[hydrogen]], with a small fraction of [[helium]] and trace amounts of several other compounds.<ref name=saturnfact/> The most prominent feature of Saturn is its ring system, which has been known to [[astronomy]] since less than half a century after the invention of the telescope and was for more than three centuries the only ring system known to man.
−	'''Saturn''' is the sixth planet in the [[Solar System]].  Its orbit lies between the orbits of [[Jupiter]] and [[Uranus]].  Saturn is the second largest planet in the Solar System after Jupiter.  Saturn is a gas giant, and is famous for its large, complex system of rings. The rings are composed of thousands of rocks made of ices of various chemical compounds, including methane, hexane, and ammonia.	+	== Ancient knowledge and naming ==
		+	Saturn has been known to post-diluvian man since the beginnings of recorded history.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/saturn.html Entry for Saturn]." ''The <s>Nine</s> 8 Planets'', May 11, 2005. Accessed May 19, 2008.</ref> The Hindus called Saturn Sani, one of nine objects called the ''Navagraha'' that constituted a celestial council. (The other eight members of this council were the [[Sun]], the [[Moon]], the modern planets [[Mars]], [[Venus]], [[Mercury]], and [[Jupiter]], and the ascending and descending nodes of the Moon's orbit, which the Hindus named Rahu and Ketu.) The Hindus feared Sani above all other objects, believing that he could burn any object instantly by merely glancing at it.<ref name=windows>"[http://www.windows.ucar.edu/tour/link=/mythology/sani.html&edu=high Entry for Sani]." ''Windows to the Universe'', University Corporation for Atmospheric Research, University of Michigan, July 19, 2001. Accessed May 19, 2008.</ref>
−	Like the other planets in our solar system, the name Saturn comes from Roman mythology.  Saturn is named for the father of [[Jupiter (god)|Jupiter]], the king of the gods in the Roman pantheon. The ancient Greeks called Saturn [[Cronus]].	+	The ancient [[Greece|Greeks]] regarded this object, the furthest moving object that they knew, as the father of all the classical gods. They named him Kronos,<ref name=Arnett/> a word closely akin to ''chronos'', which means time. That [[Jupiter]] is far more prominent in the sky was a sign to the Greeks that Zeus, the most prominent son of Kronos, had deposed him, even as Kronos had deposed his own father, Ouranos (Uranus).
−	Saturn has approximately 60 moons, including [[Titan (moon)|Titan]], which was long believed to be the largest moon in the Solar System. Some of its other moons include Tethys, Mimas, Dione, Baleet, Phoebe, Phah, and Iapetus.	+	The [[Rome|Romans]] named this deity Saturnus and regarded him not merely as the father of the gods but also as the patron of [[agriculture]] and the harvest. His symbol, a stylized rendering of a sickle, reflects that association. The name Saturn also appears in the name of Saturday, the English name for the seventh day of the week.<ref name=Arnett/>
−	Saturn was known to ancient astronomers, as it was visible to the naked eye.  In [[Mesopotamia]], Saturn was known as Mulanna, or "The Goat."  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.<ref>http://www.nineplanets.org/saturn.html</ref>	+	== Orbital characteristics ==
		+	Saturn's orbit is about 3.4 times as eccentric as Earth's orbit. Saturn keeps an average orbital distance of 1,433,530,000 km from the sun, a distance close to that predicted by the [[Titius-Bode Law]].<ref name=saturnfact/> Saturn's orbit is slightly inclined to the ecliptic, with the result that the [[Earth]] passes from one side to the other of Saturn's ring plane every so often.<ref name=Arnett/> Saturn's sidereal period is about 29.4 [[Earth]] years. Its ''synodic'' period is 378.09 days.
−	== References ==	+	== Physical characteristics ==
−	<references/>	+	Saturn's volumetric mean radius is 58,232 km. Remarkably, Saturn is less dense than [[water]]. Its chief constituent is molecular [[hydrogen]], followed by [[helium]], [[methane]], [[ammonia]], [[hydrogen deuteride]],  and [[ethane]], Aerosols of ammonia ice, water ice, and [[ammonia hydrosulfide]] complete Saturn's composition.
−	{{Solarsystem}}	+
		+	Saturn has high winds, which blow easterly at 500 m/s at the equator.<ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/saturn.htm Entry for Saturn]." ''Views of the Solar System'', 1997-2005. Accessed May 19, 2008.</ref>
		+
		+	== Magnetosphere ==
		+	Saturn has a magnetic dipole moment of 4.6 * 10<sup>25</sup> N-m/T, less than one-thirtieth of that of [[Jupiter]]. Remarkably, the magnetic axis deviates only slightly from the rotational axis. The magnetophere extends slightly beyond the orbit of Titan, and Titan's upper atmosphere contributes plasma particles to the Saturnine magnetosphere.<ref name=Russell/>
		+
		+	== Ring system ==
		+	Saturn’s ring system is the brightest in all the solar system, with an albedo varying from 0.2 to 0.6, often brighter than the planet itself.<ref name=Arnett/>
		+
		+	The rings have radii varying from 60,268 km to 483,000 km. Saturn's rings divide into seven portions, designated D, C, B, A, F, G, and E from inner to outer. A wide gap called the Cassini Division separates the B and A rings, and the A rings themselves have two gaps, called the Encke and Keeler gaps.<ref name=saturnringfact>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/factsheet/satringfact.html Saturnian Rings Fact Sheet]." [[National Aeronautics and Space Administration|NASA]], September 18, 2006. Accessed May 19, 2008.</ref>
		+
		+	The two Voyager spacecraft sent back cinematic images that showed that the rings were spoked, and that the spokes persist, especially in the B ring system.<ref name=Arnett/><ref name=Hamilton/> Current theories suggest that the spokes result from magnetic interaction, because the rings all lie well within Saturn's magnetosphere. Furthermore, the F ring appears to be braided, a phenomenon that remains unexplained today.<ref name=Arnett/>
		+
		+	Many of the innermost moons of Saturn orbit close to the rings, especially the F and E rings, and serve to regularize their structure, a phenomenon called "shepherding."<ref name=Hamilton/>
		+
		+	== Problems for uniformitarian theories ==
		+	The origin of Saturn's rings remains a mystery<ref name=Arnett/><ref name=Hamilton/>, and a troublesome one. The rings are not stable and hence could not have persisted for the whole of the assumed [[deep time]] age of the solar system.<ref name=Arnett/> [[Uniformitarianism|uniformitarians]] admit that Saturn's rings could not be older than about 100 million years.<ref name=Arnett/> They therefore propose that Saturn's rings formed from the disintegration of one or more moons, perhaps following a collision with a [[comet]].<ref name=Arnett/><ref name=Hamilton/> However, Wing-Huan Ip at the Max Planck Institute calculated that a comet-moon collision would not be sufficiently likely to occur in less time than 30 billion years. This is more than twice the age of the universe calculated from the [[Hubble constant]].<ref name=Harris>Harris, David M. "[http://www.answersingenesis.org/creation/v12/i4/saturn.asp How Old are Saturn's Rings]?" ''Creation'', 12(4):40–41. September 1990. Accessed May 18, 2008.</ref>
		+
		+	== Observation and Exploration ==
		+	[[Galileo Galilei]] was the first astronomer to observe Saturn with a telescope. But he did not realize that he was looking at a ringed planet. Only in 1659 did [[Christiaan Huygens]] understand that Saturn was ringed. For three centuries more, Saturn's ring system was the only such system known, until in 1977 NASA astronomers inferred the ring system of [[Uranus]] from a stellar occultation experiment.
		+
		+	Telescopic observation of Saturn has been ongoing since the earliest observations by Huygens and [[Giovanni Domenico Cassini]]. The [[Hubble Space Telescope]] and many Earth-based telescopes have taken many images of a quality comparable to that of images sent back from spacecraft.
		+
		+	The first spacecraft to visit Saturn was [[Pioneer 11]] in 1979, followed by [[Voyager 1]] (1980) and [[Voyager 2]] (1981).<ref name=Arnett/> The spacecraft of the joint NASA/[[European Space Agency|ESA]] [[Cassini-Huygens mission]] arrived in the Saturnine system on July 1, 2004.<ref name=Arnett/> The Huygens spacecraft landed on Saturn's largest moon, [[Titan]], and transmitted images and data all during its descent and for three hours after landing. The Cassini spacecraft continues to orbit Saturn and make frequent rendezvous with its most prominent moons to this day (May 19, 2008). Its mission was originally scheduled to run for four years, ending in July 2008, but NASA has announced a two-year extension with multiple rendezvous with [[Titan]] and additional rendezvous with [[Enceladus]], [[Rhea]], [[Dione]], and [[Helene]]. Mission planners also suggest that after two years, Cassini might still have enough fuel for another two-year extension, and speak hopefully of specific future missions to Titan and Enceladus.<ref name=extended>Brown, Dwayne, and Martinez, Carolina. "[http://www.nasa.gov/mission_pages/cassini/media/cassini-20080415.html NASA Extends Cassini's Grand Tour of Saturn]." [[National Aeronautics and Space Administration|NASA]], April 15, 2008. Accessed May 16, 2008.</ref>
		+
		+	== Gallery ==
		+	Image:Saturnrings.jpg|Image of Saturn captured by the Hubble Space Telescope in 1996
		+
		+	== Satellites ==
		+	Saturn has at least sixty confirmed satellites and three unconfirmed satellites. Of the sixty known satellites, five are "ring shepherds."<ref>The three unconfirmed satellites, if confirmed, would also be ring shepherds. In addition, the A ring has a large collection of "moonlets" that shepherd the other smaller particles.</ref> Two of the satellites, [[Epimetheus]] and [[Janus]], actually exchange orbits regularly. Two of the largest moons, [[Tethys]] and [[Dione]], each have two moons that occupy the stable libration or "Trojan" points in their respective orbits. Most of Saturn's moons lie beyond the orbit of [[Iapetus]], the outermost of the large spheroidal moons.
		+
		+	==References==
		+	{{reflist|2}}
		+
		+	== Related Links ==
		+	* [http://solarsystem.jpl.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Overview Saturn] by [[National Aeronautics and Space Administration|NASA]]
		+
		+	{{solarsystem}}

---

Revision as of 01:21, May 20, 2008

For other uses, please see Saturn (disambiguation).

Saturn
Composite true-color image of Saturn by spacecraft Cassini in October of 2004.
Symbol	40px
Name origin	Roman god of harvest
Orbital characteristics
Primary	Sun
Order from primary	7
Perihelion	1,352,550,000 km[1]
Aphelion	1,514,500,000 km[1]
Semi-major axis	1,433,530,000 km[1][2]
Titius-Bode prediction	10.0 AU
Circumference	59.879 AU
Orbital eccentricity	0.0565[1]
Sidereal year	10,759.22 da (29.4 a)[1]
Synodic year	378.09 da[1]
Avg. orbital speed	10.183 km/s
Inclination	2.485°[1] to the ecliptic
Rotational characteristics
Sidereal day	10.656 h[1]
Solar day	10,656 h[1]
Rotational speed	9.8663 m/s[3]
Axial tilt	26.73°[1]
Physical characteristics
Mass	5.6846 * 1026 kg[1]
Density	687.3 kg/m³[1]
Mean radius	58,232 km[1]
Equatorial radius	60,268 km[1]
Polar radius	54,364 km[1]
Surface gravity	8.96 m/s²[1]
Escape speed	35.49 km/s[1]
Surface area	42,612,000,000 km²[3]
Mean temperature	134 K
Number of moons	60
Composition	hydrogen 96.3%, helium 3.25%, methane 4500 ppm, ammonia 125 pm, hydrogen deuteride 110 ppm, ethane 1.5 ppm, plus aerosols of ammonia ice, water ice, and ammonia hydrosulfide[1]
Color	light yellow
Albedo	0.47[1]
Magnetosphere
Magnetic flux density	0.210 G[1]
Magnetic dipole moment at present	4.6 * 1025 N-m/T[4][5]
Magnetic dipole moment at creation	1.34 * 1026 N-m/T[5]
Decay time	5300 a[5]
Half life	3700 a[3]

Saturn is the sixth planet from the sun and the second largest planet in the solar system. Saturn is a gas giant with an atmosphere predominantly of hydrogen, with a small fraction of helium and trace amounts of several other compounds.^[1] The most prominent feature of Saturn is its ring system, which has been known to astronomy since less than half a century after the invention of the telescope and was for more than three centuries the only ring system known to man.

Ancient knowledge and naming

Saturn has been known to post-diluvian man since the beginnings of recorded history.^[6] The Hindus called Saturn Sani, one of nine objects called the Navagraha that constituted a celestial council. (The other eight members of this council were the Sun, the Moon, the modern planets Mars, Venus, Mercury, and Jupiter, and the ascending and descending nodes of the Moon's orbit, which the Hindus named Rahu and Ketu.) The Hindus feared Sani above all other objects, believing that he could burn any object instantly by merely glancing at it.^[7]

The ancient Greeks regarded this object, the furthest moving object that they knew, as the father of all the classical gods. They named him Kronos,^[6] a word closely akin to chronos, which means time. That Jupiter is far more prominent in the sky was a sign to the Greeks that Zeus, the most prominent son of Kronos, had deposed him, even as Kronos had deposed his own father, Ouranos (Uranus).

The Romans named this deity Saturnus and regarded him not merely as the father of the gods but also as the patron of agriculture and the harvest. His symbol, a stylized rendering of a sickle, reflects that association. The name Saturn also appears in the name of Saturday, the English name for the seventh day of the week.^[6]

Orbital characteristics

Saturn's orbit is about 3.4 times as eccentric as Earth's orbit. Saturn keeps an average orbital distance of 1,433,530,000 km from the sun, a distance close to that predicted by the Titius-Bode Law.^[1] Saturn's orbit is slightly inclined to the ecliptic, with the result that the Earth passes from one side to the other of Saturn's ring plane every so often.^[6] Saturn's sidereal period is about 29.4 Earth years. Its synodic period is 378.09 days.

Physical characteristics

Saturn's volumetric mean radius is 58,232 km. Remarkably, Saturn is less dense than water. Its chief constituent is molecular hydrogen, followed by helium, methane, ammonia, hydrogen deuteride, and ethane, Aerosols of ammonia ice, water ice, and ammonia hydrosulfide complete Saturn's composition.

Saturn has high winds, which blow easterly at 500 m/s at the equator.^[8]

Magnetosphere

Saturn has a magnetic dipole moment of 4.6 * 10²⁵ N-m/T, less than one-thirtieth of that of Jupiter. Remarkably, the magnetic axis deviates only slightly from the rotational axis. The magnetophere extends slightly beyond the orbit of Titan, and Titan's upper atmosphere contributes plasma particles to the Saturnine magnetosphere.^[4]

Ring system

Saturn’s ring system is the brightest in all the solar system, with an albedo varying from 0.2 to 0.6, often brighter than the planet itself.^[6]

The rings have radii varying from 60,268 km to 483,000 km. Saturn's rings divide into seven portions, designated D, C, B, A, F, G, and E from inner to outer. A wide gap called the Cassini Division separates the B and A rings, and the A rings themselves have two gaps, called the Encke and Keeler gaps.^[9]

The two Voyager spacecraft sent back cinematic images that showed that the rings were spoked, and that the spokes persist, especially in the B ring system.^[6][8] Current theories suggest that the spokes result from magnetic interaction, because the rings all lie well within Saturn's magnetosphere. Furthermore, the F ring appears to be braided, a phenomenon that remains unexplained today.^[6]

Many of the innermost moons of Saturn orbit close to the rings, especially the F and E rings, and serve to regularize their structure, a phenomenon called "shepherding."^[8]

Problems for uniformitarian theories

The origin of Saturn's rings remains a mystery^[6][8], and a troublesome one. The rings are not stable and hence could not have persisted for the whole of the assumed deep time age of the solar system.^[6] uniformitarians admit that Saturn's rings could not be older than about 100 million years.^[6] They therefore propose that Saturn's rings formed from the disintegration of one or more moons, perhaps following a collision with a comet.^[6][8] However, Wing-Huan Ip at the Max Planck Institute calculated that a comet-moon collision would not be sufficiently likely to occur in less time than 30 billion years. This is more than twice the age of the universe calculated from the Hubble constant.^[10]

Observation and Exploration

Galileo Galilei was the first astronomer to observe Saturn with a telescope. But he did not realize that he was looking at a ringed planet. Only in 1659 did Christiaan Huygens understand that Saturn was ringed. For three centuries more, Saturn's ring system was the only such system known, until in 1977 NASA astronomers inferred the ring system of Uranus from a stellar occultation experiment.

Telescopic observation of Saturn has been ongoing since the earliest observations by Huygens and Giovanni Domenico Cassini. The Hubble Space Telescope and many Earth-based telescopes have taken many images of a quality comparable to that of images sent back from spacecraft.

The first spacecraft to visit Saturn was Pioneer 11 in 1979, followed by Voyager 1 (1980) and Voyager 2 (1981).^[6] The spacecraft of the joint NASA/ESA Cassini-Huygens mission arrived in the Saturnine system on July 1, 2004.^[6] The Huygens spacecraft landed on Saturn's largest moon, Titan, and transmitted images and data all during its descent and for three hours after landing. The Cassini spacecraft continues to orbit Saturn and make frequent rendezvous with its most prominent moons to this day (May 19, 2008). Its mission was originally scheduled to run for four years, ending in July 2008, but NASA has announced a two-year extension with multiple rendezvous with Titan and additional rendezvous with Enceladus, Rhea, Dione, and Helene. Mission planners also suggest that after two years, Cassini might still have enough fuel for another two-year extension, and speak hopefully of specific future missions to Titan and Enceladus.^[11]

Gallery

Image:Saturnrings.jpg|Image of Saturn captured by the Hubble Space Telescope in 1996

Satellites

Saturn has at least sixty confirmed satellites and three unconfirmed satellites. Of the sixty known satellites, five are "ring shepherds."^[12] Two of the satellites, Epimetheus and Janus, actually exchange orbits regularly. Two of the largest moons, Tethys and Dione, each have two moons that occupy the stable libration or "Trojan" points in their respective orbits. Most of Saturn's moons lie beyond the orbit of Iapetus, the outermost of the large spheroidal moons.

References

Related Links

• Saturn by NASA

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