Saturn
44474
224402005
2008-07-08T18:15:40Z
J
55594
Restoring after discussion with Saber; also adding Saturnus into otheruses4. That should cover the three most common uses, no?
{{otheruses4|the planet|the car company|Saturn Corporation|the Roman God|Saturn (mythology)|other uses|Saturn (disambiguation)}}
{{sprotect|small=yes}}
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{{Infobox Planet
| bgcolour = #FFCC66
| name = Saturn
| symbol = [[Image:Saturn symbol.svg|25px|Astronomical symbol for Saturn]]
| image = [[Image:Saturn from Cassini Orbiter (2004-10-06).jpg|240px|The planet Saturn]]
| caption = Saturn, as seen by [[Cassini–Huygens|Cassini]]
| orbit_ref =
<ref name=horizons>{{cite web
| last = Yeomans | first = Donald K. | date = 2006-07-13
| url = http://ssd.jpl.nasa.gov/?horizons
| title = HORIZONS System | publisher = NASA JPL
| accessdate = 2007-08-08 }} — At the site, go to the "web interface" then select "Ephemeris Type: ELEMENTS", "Target Body: Saturn Barycenter" and "Center: Sun".</ref><ref name=barycenter>Orbital elements refer to the barycenter of the Saturn system, and are the instantaneous [[osculating orbit|osculating]] values at the precise [[J2000]] epoch. Barycenter quantities are given because, in contrast to the planetary centre, they do not experience appreciable changes on a day-to-day basis from to the motion of the moons.</ref>
| epoch = [[Epoch (astronomy)#J2000.0|J2000]]
| aphelion = 1,513,325,783 km<br />10.11595804 [[Astronomical unit|AU]]
| perihelion = 1,353,572,956 km<br />9.04807635 AU
| semimajor = 1,433,449,370 km<br />9.58201720 AU
| eccentricity = 0.055723219
| period = 10,832.327 [[day]]s<br />29.657296 [[Julian year (astronomy)|yr]]
| synodic_period = 378.09 days<ref name="fact"/>
| avg_speed = 9.69 km/s<ref name="fact"/>
| inclination = 2.485240°<br />5.51° to Sun's equator
| asc_node = 113.642811°
| arg_peri = 336.013862°
| mean_anomaly = 320.346750°
| satellites = [[Saturn's natural satellites|60 confirmed]]<br/>(up to 63 seen)<!--- see http://en.wikipedia.org/wiki/Talk:Saturn/Archive_1#Moon_contradiction --->
|maximum distance from sun = 1.5 billion km (938 million miles)
|minimum distance from sun = 1.35 billion km (840 million miles)
| physical_characteristics = yes
| flattening = 0.09796 ± 0.00018 <!-- calculated using data from ref name=Seidelmann2007 -->
| equatorial_radius = 60,268 ± 4 km<ref name=Seidelmann2007>{{cite journal|last= Seidelmann|first= P. Kenneth|coauthors= Archinal, B. A.; A’hearn, M. F.; et.al.|title= Report of the IAU/IAGWorking Group on cartographic coordinates and rotational elements: 2006|journal= Celestial Mech. Dyn. Astr. |volume=90|pages=155–180|year=2007|doi=10.1007/s10569-007-9072-y|url=http://adsabs.harvard.edu/doi/10.1007/s10569-007-9072-y}}</ref><ref name=1bar>Refers to the level of 1 bar atmospheric pressure</ref><br />9.4492 Earths
| polar_radius = 54,364 ± 10 km<ref name=Seidelmann2007/><ref name=1bar/><br />8.5521 Earths
| surface_area = 4.27×10<sup>10</sup> km²<ref name="nasafact">[http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Facts NASA: Solar System Exploration: Planets: Saturn: Facts & Figures]</ref><ref name=1bar/><br />83.703 Earths
| volume = 8.2713×10<sup>14</sup> km³<ref name="fact">{{cite web
|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html
|title = Saturn Fact Sheet
|publisher = NASA
|last = Williams
|first = Dr. David R.
|accessdate = 2007-07-31
|date = September 7, 2006}}</ref><ref name=1bar/><br />763.59 Earths
| mass = 5.6846×10<sup>26</sup> kg<ref name="fact"/><br />95.152 Earths
| density = 0.687 g/cm³<ref name="fact"/><ref name=1bar/><br /> (less than [[water]])
| surface_grav = 8.96 [[Acceleration|m/s²]]<ref name="fact"/><ref name=1bar/><br />0.914 [[g-force|''g'']]
| escape_velocity = 35.5 km/s<ref name="fact"/><ref name=1bar/>
| sidereal_day = 0.439 – 0.449 day<ref name="saturnDay">{{cite web
|url = http://www.space.com/scienceastronomy/070906_saturn_day.html
|title = Length of Saturn's Day Revised
|publisher = Space.com
|last = Than
|first = Ker
|accessdate = 2007-09-06
|date = September 6, 2007}}</ref><br /> (10 h 32 – 47 min)
| rot_velocity = 9.87 km/s<ref name=1bar/><br />35,500 km/h
| axial_tilt = 26.73°<ref name="fact"/>
| right_asc_north_pole = 2 h 42 min 21 s<br />40.589°<ref name=Seidelmann2007/>
| declination = 83.537°<ref name=Seidelmann2007/>
| albedo = 0.342 ([[Bond albedo|bond]])<br/>
0.47 ([[Geometric albedo|geom.]])<ref name="fact"/>
| magnitude = +1.2 to -0.24<ref name="magnitude">{{cite web
|url = http://findarticles.com/p/articles/mi_qa4015/is_200101/ai_n8933308
|title = Wideband photoelectric magnitude measurements of Saturn in 2000
|accessdate = 2007-10-14
|last = Schmude
|first = Richard W Junior
|date = 2001
|publisher = Georgia Journal of Science}}</ref>
| angular_size = 14.5" — 20.1"<ref name="fact"/><br>(excludes rings)
| temperatures = yes
| temp_name1 = 1 bar level
| min_temp_1 =
| mean_temp_1 = 134 [[Kelvin|K]]<ref name="fact"/>
| max_temp_1 =
| temp_name2 = 0.1 bar
| min_temp_2 =
| mean_temp_2 = 84 K<ref name="fact"/>
| max_temp =
| adjectives = Saturnian
| atmosphere = yes
| atmosphere_ref =
<ref name="fact"/>
| scale_height = 59.5 km
| atmosphere_composition =
<table>
<tr><td>
~96%</td><td>[[Hydrogen]] (H<sub>2</sub>)
</td></tr><tr><td>
~3%</td><td>[[Helium]]
</td></tr><tr><td>
~0.4%</td><td>[[Methane]]
</td></tr><tr><td>
~0.01%</td><td>[[Ammonia]]
</td></tr><tr><td>
~0.01%</td><td>[[Hydrogen deuteride]] (HD)
</td></tr><tr><td>
0.0007%</td><td>[[Ethane]]
</td></tr><tr><td>
'''Ices''':</td><td>
</td></tr><tr><td>
</td><td>[[Ammonia]]
</td></tr><tr><td>
</td><td>[[water]]
</td></tr><tr><td>
</td><td>[[ammonium hydrosulfide]](NH<sub>4</sub>SH)
</td></tr></table>
}}
'''Saturn''' ({{Audio-IPA|en-us-Saturn.ogg|[ˈsætɚn]}}<ref>{{cite book
| first=Elizabeth | last=Walter | date=April 21, 2003
| title=Cambridge Advanced Learner's Dictionary
| publisher=Cambridge University Press
| edition=Second Edition | id=ISBN 0521531063 }}</ref>) is the sixth [[planet]] from the [[Sun]] and the second largest planet in the [[Solar System]], after [[Jupiter]]. Along with the planets Jupiter, [[Uranus]] and [[Neptune]] it is classified as a [[gas giant]] (also known as a Jovian planet, after the planet Jupiter). It was named after the Roman god [[Saturn (mythology)|Saturnus]], equated to the [[Greek mythology|Greek]] [[Cronus|Kronos]] (the [[Titan (mythology)|Titan]] father of [[Zeus]]) and the Babylonian [[Ninurta]]. Saturn's symbol represents the god's [[sickle]] ([[Unicode]]: {{Unicode|♄}}).
The planet Saturn is composed of [[hydrogen]], with small proportions of [[helium]] and trace elements.<ref name="Voyager Summary 1"/> The interior consists of a small [[planetary core|core]] of rock and ice, surrounded by a thick layer of [[metallic hydrogen]] and a gaseous outer layer. The outer [[atmosphere]] is generally bland in appearance, although long-lived features can appear. [[Wind speed]]s on Saturn can reach 1,800 km/h, significantly faster than those on Jupiter. Saturn has a planetary [[magnetic field]] intermediate in strength between that of Earth and the more powerful field around Jupiter.
Saturn has a prominent system of [[Rings of Saturn|rings]], consisting mostly of [[ice]] particles with a smaller amount of rocky [[debris]] and [[cosmic dust|dust]]. Sixty [[Moons of Saturn|known moons]] orbit the planet. [[Titan (moon)|Titan]], Saturn's largest and the Solar System's second largest moon (after [[Jupiter]]'s [[Ganymede (moon)|Ganymede]]), is larger than the planet [[Mercury (planet)|Mercury]] and is the only moon in the Solar System to possess a significant atmosphere.<ref name="Titan ref">{{cite web
|url = http://saturn.jpl.nasa.gov/news/features/saturn-story/moons.cfm
|title = The Story of Saturn
|accessdate = 2007-07-07
|last = Munsell
|first = Kirk
|date = April 6, 2005
|publisher = NASA Jet Propulsion Laboratory; California Institute of Technology}}</ref>
==Physical characteristics==
[[Image:Saturn, Earth size comparison.jpg|thumb|left|180px|A rough comparison of the sizes of Saturn and Earth.]]
Due to a combination of its lower density, rapid rotation, and fluid state, Saturn is an [[oblate]] [[spheroid]]; that is, it is flattened at the [[geographical pole|poles]] and bulges at the [[equator]]. Its equatorial and polar radii differ by almost 10% – 60268 km vs. 54364 km.<ref name="fact"/> The other gas planets are also oblate, but to a lesser extent. Saturn is the only planet of the Solar System that is less [[density|dense]] than water. Although Saturn's [[planetary core|core]] is considerably denser than water, the average [[relative density|specific density]] of the planet is 0.69 g/cm³ due to the gaseous atmosphere. Saturn is only 95 Earth masses,<ref name="fact"/> compared to Jupiter, which is 318 times the mass of the Earth<ref name="Jupiter fact">{{cite web
|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html
|title = Jupiter Fact Sheet
|publisher = NASA
|last = Williams
|first = Dr. David R.
|date = November 16, 2004
|accessdate = 2007-08-02}}</ref> but only about 20% larger than Saturn.<ref>{{cite web
|url = http://ase.arc.nasa.gov/projects/bayes-group/Atlas/size/Jupiter/Saturn.html
|title = Jupiter compared to Saturn
|publisher = NASA
|accessdate = 2007-07-15}}</ref>
===Composition===
The outer atmosphere of Saturn consists of about 93.2% molecular hydrogen and 6.7% helium. Trace amounts of [[ammonia]], [[acetylene]], [[ethane]], [[phosphine]], and [[methane]] have also been detected.<ref>{{cite journal
| author=Courtin, R.; Gautier, D.; Marten, A.; Bezard, B.
| title=The Composition of Saturn's Atmosphere at Temperate Northern Latitudes from Voyager IRIS spectra
| journal=Bulletin of the American Astronomical Society
| year=1967
| volume=15
| pages=831
| url=http://adsabs.harvard.edu/abs/1983BAAS...15..831C
| accessdate=2007-02-04 }}</ref> The upper clouds on Saturn are composed of ammonia crystals, while the lower level clouds appear to be composed of either [[ammonium hydrosulfide]] (NH<sub>4</sub>SH) or water.<ref>{{cite web
| last = Martinez
| first = Carolina
| date =September 5, 2005
| url = http://www.nasa.gov/mission_pages/cassini/whycassini/cassini-090505-clouds.html
| title =Cassini Discovers Saturn's Dynamic Clouds Run Deep
| publisher =NASA
| accessdate = 2007-04-29
}}</ref> The atmosphere of Saturn is significantly deficient in helium relative to the abundance of the elements in the Sun.
The quantity of elements heavier than helium are not known precisely, but the proportions are assumed to match the primordial abundances from the formation of the Solar System. The total mass of these elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.<ref name="science286">{{cite journal
| last = Guillot
| first = Tristan
| title=Interiors of Giant Planets Inside and Outside the Solar System
| journal=Science
| year=1999
| volume=286
| issue=5437
| pages=72–77
| url=http://www.sciencemag.org/cgi/content/full/286/5437/72
| accessdate=2007-04-27
| doi=10.1126/science.286.5437.72
| pmid=10506563 }}</ref>
===Internal structure===
[[Image:Saturn polar vortex.jpg|180px|left|thumb|Saturn's temperature emissions: the prominent hot spot at the bottom of the image is at Saturn's south pole.]]
Though there is little direct information about Saturn's internal structure, it is thought that its interior is similar to that of [[Jupiter]], having a small rocky [[planetary core|core]] surrounded mostly by [[hydrogen]] and [[helium]]. The rocky core is similar in composition to the [[Earth]], but denser. Above this, there is a thicker liquid [[metallic hydrogen]] layer, followed by a layer of liquid hydrogen and helium, and in the outermost 1,000 km a gaseous atmosphere.<ref name="NMM Saturn"/> Traces of various ices are also present. The core region is estimated to be about 9–22 times the mass of the Earth.<ref>{{cite journal
| last = Fortney
| first = Jonathan J.
| title=Looking into the Giant Planets
| journal=Science
| year=2004
| volume=305
| issue=5689
| pages=1414–1415
| url=http://www.sciencemag.org/cgi/content/full/305/5689/1414
| accessdate=2007-04-30
| doi=10.1126/science.1101352
| pmid=15353790 }}</ref> Saturn has a very hot interior, reaching 11,700 °C at the core, and it radiates 2.5 times more energy into space than it receives from the Sun. Most of the extra energy is generated by the [[Kelvin-Helmholtz mechanism]] (slow gravitational compression), but this alone may not be sufficient to explain Saturn's heat production. An additional proposed mechanism by which Saturn may generate some of its heat is the "raining out" of droplets of helium deep in Saturn's interior, the droplets of helium releasing heat by [[friction]] as they fall down through the lighter hydrogen.<ref>{{cite web
|url = http://www.nasa.gov/worldbook/saturn_worldbook.html
|title = NASA - Saturn
|publisher = NASA
|accessdate = 2007-07-27
|date = 2004}}</ref>
===Cloud layers===
Saturn's [[celestial body atmosphere]] exhibits a banded pattern similar to Jupiter's (the nomenclature is the same), but Saturn's bands are much fainter and are also much wider near the equator. At the bottom, extending for 10 km and with a temperature of -23 °C, is a layer made up of water ice. After that comes a layer of ammonium hydrosulfide ice, which extends for another 50 km and is approximately at -93 °C. Eighty kilometers above that are ammonia ice clouds, where the temperatures are about -153 °C. Near the top, extending for some 200 km to 270 km above the clouds, come layers of visible cloud tops and a hydrogen and helium atmosphere.<ref>{{cite web
|url = http://www.mira.org/fts0/planets/100/text/txt002x.htm
|title = Saturn
|accessdate = 2007-07-27
|publisher = MIRA}}</ref> Saturn's winds are among the Solar System's fastest. [[Voyager program|Voyager]] data indicate peak easterly winds of 500 m/s (1,800 km/h).<ref name="Voyager Summary 1">{{cite web
|title = Voyager Saturn Science Summary
|url = http://www.solarviews.com/eng/vgrsat.htm
|first = Calvin
|middle = J.
|last = Hamilton
|accessdate = 2007-07-05
|date = 1997
|publisher = Solarviews}}</ref> Saturn's finer cloud patterns were not observed until the Voyager flybys. Since then, however, [[Earth]]-based [[telescope|telescopy]] has improved to the point where regular observations can be made.
Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. In 1990, the [[Hubble Space Telescope]] observed an enormous white cloud near Saturn's equator which was not present during the Voyager encounters, and, in 1994, another smaller storm was observed. The 1990 storm was an example of a [[Great White Spot]], a unique but short-lived phenomenon which occurs once every Saturnian year, or roughly every 30 Earth years, around the time of the northern hemisphere's [[summer solstice]].<ref>{{cite web|title=Saturn’s cloud structure and temporal evolution from ten years of Hubble Space Telescope images (1994–2003)|author=S. Pérez-Hoyos, A. Sánchez-Lavega, R.G. Frenchb, J.F. Rojas|url=http://www.ajax.ehu.es/sph/principal/tesis/docs/sph.etal.2005.pdf|format=PDF|year=2005|accessdate=2007-07-24}}</ref> Previous Great White Spots were observed in 1876, 1903, 1933, and 1960, with the 1933 storm being the most famous. If the periodicity is maintained, another storm will occur in about 2020.<ref>[[Patrick Moore]], ed., ''1993 Yearbook of Astronomy'', (London: W.W. Norton & Company, 1992), Mark Kidger, "The 1990 Great White Spot of Saturn", pp. 176-215.</ref>
In recent images from the [[Cassini-Huygens|Cassini spacecraft]], Saturn's northern hemisphere appears a bright blue, similar to Uranus, as can be seen in the image below. This blue color cannot currently be observed from Earth, because Saturn's rings are currently blocking its northern hemisphere. The color is most likely caused by [[Rayleigh scattering]].
[[Image:mimasrings.jpg|thumb|180 px|left|Saturn's northern hemisphere, as seen by Cassini. Note the planet's blue appearance through the ring.]]
[[Image:Saturn hexagonal north pole feature.jpg|thumb|180px|right|North polar hexagonal cloud feature, discovered by [[Voyager 1]] and confirmed in 2006 by [[Cassini-Huygens|Cassini]].<ref>{{cite web
|url = http://www.nasa.gov/mission_pages/cassini/multimedia/pia09188.html
|title = Saturn's Strange Hexagon
|accessdate = 2007-07-06
|date = March 27, 2007
|last = Watanabe
|first = Susan
|publisher = [[NASA]]}}</ref>]]
Astronomers using [[infrared]] imaging have shown that Saturn has a warm [[polar vortex]] and that it is the only such feature known in the solar system. This, they say, is the warmest spot on Saturn. Whereas temperatures on Saturn are normally -185 °C, temperatures on the vortex often reach as high as -122 °C.<ref>{{cite web
|url = http://www.mcpstars.org/node/353
|title = Warm Polar Vortex on Saturn
|date = 2007
|publisher = Merrillville Community Planetarium
|accessdate = 2007-07-25}}</ref>
A persisting [[hexagon]]al wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.<ref>{{cite web
|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1988Icar...76..335G&db_key=AST&data_type=HTML&format=
|title = A hexagonal feature around Saturn's North Pole
|last = Godfrey
|publisher = Icarus
|accessdate = 2007-07-09}}</ref><ref>{{cite web
|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993Sci...260..329S&db_key=AST&data_type=HTML&format=
|title = Ground-based observations of Saturn's north polar SPOT and hexagon
|last = Sanchez-Lavega
|first = A.
|accessdate = 2007-07-30
|publisher = Bulletin of the American Astronomical Society}}</ref> Unlike the north pole, HST imaging of the south polar region indicates the presence of a ''jet stream'', but no strong polar vortex nor any ''hexagonal standing wave''.<ref>{{cite web
|url = http://www.aas.org/publications/baas/v34n3/dps2002/10.htm<!--INSERT TITLE; done by Universe=atom-->
|title = Hubble Space Telescope Observations of the Atmospheric Dynamics in Saturn's South Pole from 1997 to 2002
|accessdate = 2007-07-06
|publisher = The American Astronomical Society
|date = October 8, 2002}}</ref> However, [[NASA]] reported in November 2006 that the Cassini spacecraft observed a '[[hurricane]]-like' storm locked to the south pole that had a clearly defined [[eyewall]].<ref>{{cite web
|url = http://photojournal.jpl.nasa.gov/catalog/PIA09187
|title = NASA catalog page for image PIA09187
|accessdate = 2007-05-23
|publisher = NASA Planetary Photojournal}}</ref> This observation is particularly notable because eyewall clouds had not previously been seen on any planet other than Earth (including a failure to observe an eyewall in the [[Great Red Spot]] of Jupiter by the [[Galileo (spacecraft)|Galileo]] spacecraft).<ref>{{cite web
|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=703
|title = NASA Sees into the Eye of a Monster Storm on Saturn
|publisher = [[NASA]]
|date = November 9, 2006
|accessdate = 2006-11-20}}</ref>
The straight sides of the northern polar hexagon are each about 13,800 km long. The entire structure rotates with a period of 10h 39 m 24s, the same period as that of the planet's radio emissions, which is assumed to be equal to the period of rotation of Saturn's interior. The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere.
The pattern's origin is a matter of much speculation. Most astronomers seem to think some sort of standing-wave pattern in the atmosphere; but the hexagon might be a novel sort of aurora. More extreme speculation has Saturn's radio emissions emanating from the hexagon (something we can see and which has the right rotation period) rather than from the planet's interior (something we cannot see).<ref>{{cite web|url=http://www.science-frontiers.com/sf063/sf063a04.htm|title=A Hex on Saturn|publisher=Science Frontiers|date=May 31, 1989|accessmonthday=March 28 |accessyear=2007}}</ref> Polygon shapes have been replicated in spinning buckets of fluid in a laboratory.<ref>{{cite web
|url = http://www.nature.com/news/2006/060515/full/060515-17.html
|title = Geometric whirlpools revealed
|publisher=[[Nature (journal)|Nature]]
|date = May 19, 2006
|accessmonthday=April 27
|accessyear=2007}} Bizarre geometric shapes that appear at the centre of swirling vortices in planetary atmospheres might be explained by a simple experiment with a bucket of water but correlating this to Saturn's pattern is by no means certain.</ref>
=== Magnetic field and magnetosphere ===
Saturn has an intrinsic magnetic field that has a simple, symmetric shape—a magnetic [[dipole]]. Its strength at the equator—0.2 [[Gauss (unit)|gauss]] (20 [[microtesla|µT]])—is approximately one twentieth than that of the field around Jupiter and slightly weaker than Earth's magnetic field.<ref name="mag"/> As a result the cronian magnetosphere is much smaller than the jovian and extends slightly beyond the orbit of Titan.<ref name="mag 2">{{cite web
|url = http://library.thinkquest.org/C005921/Saturn/satuAtmo.htm
|title = Saturn: Atmosphere and Magnetosphere
|publisher = Thinkquest Internet Challenge
|accessdate = 2007-07-15
|last = McDermott
|first = Matthew
|date = 2000}}</ref> Most probably, the magnetic field is generated similarly to that of Jupiter—by currents in the metallic-hydrogen layer, which is called a metallic-hydrogen dynamo.<ref name="mag 2"/> Similarly to those of other planets, this magnetosphere is efficient at deflecting the [[solar wind]] particles from the [[Sun]]. The moon Titan orbits within the outer part of Saturn's magnetosphere and contributes plasma from the ionized particles in Titan's outer atmosphere.<ref name="mag">{{cite web
| author=Russell, C. T.; Luhmann, J. G.
| year=1997
| url =http://www-ssc.igpp.ucla.edu/personnel/russell/papers/sat_mag.html
| title =Saturn: Magnetic Field and Magnetosphere
| publisher =UCLA - IGPP Space Physics Center
| accessdate = 2007-04-29
}}</ref>
== Orbit and rotation ==
[[Image:Rotatingsaturnhexagon.gif|thumb|left|180px|Animation of hexagonal cloud feature.]]
The average distance between Saturn and the [[Sun]] is over 1,400,000,000 km (9 [[astronomical unit|AU]]). With an average orbital speed of 9.69 km/s,<ref name="fact"/> it takes Saturn 10,759 Earth days (or about 29½ years), to finish one revolution around the Sun.<ref name="fact"/> The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth.<ref name="fact"/> Because of an [[Orbital eccentricity|eccentricity]] of 0.056, the distance between Saturn and the Sun varies by approximately 155,000,000 km between [[perihelion]] and [[aphelion]],<ref name="fact"/> which are the nearest and most distant points of the planet along its orbital path, respectively.
The visible features on Saturn rotate at different rates depending on latitude, and multiple rotation periods have been assigned to various regions (as in Jupiter's case): ''System I'' has a period of 10 h 14 min 00 s (844.3°/d) and encompasses the Equatorial Zone, which extends from the northern edge of the South Equatorial Belt to the southern edge of the North Equatorial Belt. All other Saturnian latitudes have been assigned a rotation period of 10 h 39 min 24 s (810.76°/d), which is ''System II''. ''System III'', based on [[radio astronomy|radio]] emissions from the planet in the period of the Voyager flybys, has a period of 10 h 39 min 22.4 s (810.8°/d); because it is very close to System II, it has largely superseded it.
However, a precise value for the rotation period of the interior remains elusive. While approaching Saturn in 2004, the Cassini spacecraft found that the radio rotation period of Saturn had increased appreciably, to approximately 10 h 45 m 45 s (± 36 s).<ref>{{cite web
|url = http://www.nasa.gov/mission_pages/cassini/media/cassini-062804.html
|title = Scientists Find That Saturn's Rotation Period is a Puzzle
|date = June 28, 2004
|publisher = NASA
|accessdate = 2007-03-22}}</ref> The cause of the change is unknown—it was thought to be due to a movement of the radio source to a different latitude inside Saturn, with a different rotational period, rather than because of a change in Saturn's rotation.
Later, in March 2007, it was found that the rotation of the radio emissions did not trace the rotation of the planet, but rather is produced by convection of the plasma disc, which is dependent also on other factors besides the planet's rotation. It was reported that the variance in measured rotation periods may be caused by geyser activity on Saturn's moon [[Enceladus (moon)|Enceladus]]. The water vapor emitted into Saturn's orbit by this activity becomes charged and "weighs down" Saturn's magnetic field, slowing its rotation slightly relative to the rotation of the planet itself. At the time it was stated that there is no currently known method of determining the rotation rate of Saturn's core.<ref>{{cite press release
|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=733
|title = Enceladus Geysers Mask the Length of Saturn's Day
|date = March 22, 2007
|publisher = NASA Jet Propulsion Laboratory
|accessdate=2007-03-22}}</ref><ref>{{cite web
| url = http://www.sciencemag.org/cgi/content/abstract/316/5823/442
|title = The Variable Rotation Period of the Inner Region of Saturn's Plasma Disk
|date = March 22, 2007
|publisher = ''[[Science (journal)|Science]]''
|accessdate = 2007-04-24}}</ref><ref>{{cite web
| url = http://www.sciencemag.org/cgi/content/abstract/316/5823/442
|title = A New Spin on Saturn's Rotation
|date = April 20, 2007
|publisher=''[[Science (journal)|Science]]''
|accessdate=2007-04-24}}</ref>
The latest estimate of Saturn's rotation based on a compilation of various measurements from the Cassini, Voyager and Pioneer probes was reported in September 2007 is 10 hours, 32 minutes, 35 seconds.<ref name=Anderson2007>{{cite journal|author=J.D. Anderson and G. Schubert|journal=Science|title=Saturn's gravitational field, internal rotation, and interior structure|volume=317|pages=1384–1387|year=2007|doi= 10.1126/science.1144835|pmid=17823351}}</ref>
==Planetary rings==
[[Image:Saturn from Cassini Orbiter (2007-01-19).jpg|thumb|right|200px|The [[rings of Saturn]] (as imaged here by [[Cassini–Huygens|Cassini]] in 2007) are the most conspicuous in the Solar System.<ref name="NMM Saturn"/>]]
{{main|Rings of Saturn}}
Saturn is probably best known for its system of [[planetary ring]]s, which makes it the most visually remarkable object in the solar system.<ref name="NMM Saturn">{{cite web
|title = Saturn
|url = http://www.nmm.ac.uk/server/show/conWebDoc.286
|publisher = National Maritime Museum
|accessdate = 2007-07-06}}</ref>
===History===
The rings were first observed by [[Galileo Galilei]] in 1610 with his [[telescope]], but he was unable to identify them as such. He wrote to the [[Cosimo II de' Medici, Grand Duke of Tuscany|Duke of Tuscany]] that "The planet 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 [the edges of the rings]." He also described Saturn as having "ears." In 1612 the plane of the rings was oriented directly at the Earth and the rings appeared to vanish. Mystified, Galileo wondered, "Has Saturn swallowed his children?", referring to the myth of the god Saturn eating his own children to prevent them from overthrowing him.<ref>{{cite web|title=NightSky Friday: See Saturn closest to Earth in 30 Years|work=space.com|author=Joe Rao|url=http://www.space.com/spacewatch/saturn_guide_031205.html|year=2003|accessdate=2007-07-28}}</ref> Then, in 1613, they reappeared again, further confusing Galileo.<ref name="history_of_the_rings">{{cite web|url=http://www2.jpl.nasa.gov/saturn/back.html|title=Historical Background of Saturn's Rings|accessdate=2007-05-23|work=Saturn Ring Plane Crossings of 1995-1996|first=Ron|last=Baalke|publisher=Jet Propulsion Laboratory}}</ref>
In 1655, [[Christiaan Huygens]] became the first person to suggest that Saturn was surrounded by a ring. Using a telescope that was far superior to those available to Galileo, Huygens observed Saturn and wrote that "It [Saturn] is surrounded by a thin, flat, ring, nowhere touching, inclined to the ecliptic."<ref name="history_of_the_rings"/>
In 1675, [[Giovanni Domenico Cassini]] determined that Saturn's ring was composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the [[Rings of Saturn#Cassini Division|Cassini Division]]. This division in itself is a 4,800 km wide region between the [[Rings of Saturn#A Ring|A Ring]] and [[Rings of Saturn#B Ring|B Ring]].<ref name="Cassini Division">{{cite web
|title = Saturn's Cassini Division
|url = http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/cassini_division.html
|accessdate = 2007-07-06
|publisher = StarChild}}</ref>
In 1859, [[James Clerk Maxwell]] demonstrated that the rings could not be solid or they would become unstable and break apart. He proposed that the rings must be composed of numerous small particles, all independently orbiting Saturn.<ref>{{cite web
|url=http://www-history.mcs.st-andrews.ac.uk/~history/Extras/Maxwell_Saturn.html
|title=James Clerk Maxwell on the nature of Saturn's rings
|accessdate = 2007-07-08
|date = March, 2006
|publisher = JOC/EFR}}</ref> Maxwell's theory was proven correct in 1895 through spectroscopic studies of the rings carried out by [[James Keeler]] of [[Lick Observatory]].
===Physical characteristics===
[[Image:PIA08235.jpg|thumb|left|Saturn's rings cut across an eerie scene that is ruled by Titan's luminous crescent and globe-encircling haze, broken by the small moon [[Enceladus (moon)|Enceladus]], whose [[cryovolcano]]s are dimly visible at its south pole. North is up. Imaged by Cassini in 2006.]]
The rings can be viewed using a quite modest modern telescope or with good [[binoculars]]. They extend from 6,630 km to 120,700 km above Saturn's equator, average approximately 20 meters in thickness, and are composed of 93 percent water [[ice]] with a smattering of [[tholin]] impurities, and 7 percent amorphous [[carbon]].<ref>{{cite web|title= The Composition of Saturn's Rings|author=Poulet F.; Cuzzi J.N.|work=NASA Ames Research Center|url=http://www.ingentaconnect.com/content/ap/is/2002/00000160/00000002/art06967|year=2002|accessdate=2007-07-28}}</ref> They range in size from specks of dust to the size of a small automobile.<ref>{{cite web
|url = http://www.ee.kth.se/php/modules/publications/reports/2005/TRITA-ALP-2005-03.pdf
|title = Dusty Plasma Response to a Moving Test Change
|first = Muhammad
|last = Shafiq
|date = 2005
|accessdate = 2007-07-25
|format = PDF}}</ref> There are two main theories regarding the origin of Saturn's rings. One theory, originally proposed by [[Édouard 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 force]]s (see [[Roche limit]]). 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 [[nebula]]r material from which Saturn formed.
While the largest gaps in the rings, such as the Cassini Division and [[Rings of Saturn#Encke Gap|Encke Gap]], can be seen from Earth, both Voyager spacecraft discovered that the rings have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise, in several different ways, from the gravitational pull of Saturn's many moons. Some gaps are cleared out by the passage of tiny moonlets such as [[Pan (moon)|Pan]], many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small [[shepherd satellite]]s such as [[Prometheus (moon)|Prometheus]] and [[Pandora (moon)|Pandora]]. Other gaps arise from [[orbital resonance|resonances]] between the orbital period of particles in the gap and that of a more massive moon further out; [[Mimas (moon)|Mimas]] maintains the Cassini division in this manner. Still more structure in the rings consists of spiral waves raised by the moons' periodic gravitational perturbations.
Data from the Cassini space probe indicate that the rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular [[oxygen]] gas (O<sub>2</sub>) produced when ultraviolet light from the Sun interacts with water ice in the rings. Chemical reactions between water molecule fragments and further [[ultraviolet]] stimulation create and eject, among other things O<sub>2</sub>. According to models of this atmosphere, H<sub>2</sub> is also present. The O<sub>2</sub> and H<sub>2</sub> atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be on the order of one atom thick.<ref>{{cite web
|url = http://news.bbc.co.uk/1/hi/sci/tech/4640641.stm
|title = Saturn rings have own atmosphere
|date = July 1, 2005
|accessdate = 2007-07-06
|last = Rincon
|first = Paul
|publisher = [[BBC|British Broadcasting Corporation]]}}</ref>
The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O<sub>2</sub>, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic [[ion]]s that bombard water molecules ejected by Saturn's moon [[Enceladus (moon)|Enceladus]]. This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope.<ref>{{cite web
|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006ApJ...644L.137J&db_key=AST&data_type=HTML&format=&high=42bf06f4d906731
|title = The Enceladus and OH Tori at Saturn
|last = Johnson
|first = R. E.
|accessdate = 2007-07-07
|date = 2006
|publisher = The [[American Astronomical Society]]}}</ref>
Saturn shows complex patterns in its brightness.<ref name="magnitude"/> Most of the variability is due to the changing aspect of the rings,<ref name="brightness">{{cite web
|url = http://goliath.ecnext.com/coms2/summary_0199-5991060_ITM
|title = Wideband photometric magnitude measurements of Saturn made during the 2005-06 Apparition
|accessdate = 2007-10-14
|last = Schmude
|first = Richard, Jr.
|date = September 22, 2006
|publisher = Georgia Journal of Science}}</ref><ref name="opp2002"/> and this goes through two cycles every orbit. However, superimposed on this is variability due to the eccentricity of the planet's orbit that causes the planet to display brighter oppositions in the northern hemisphere than it does in the southern.<ref>{{cite web
|url = http://www.britastro.org/jbaa/113-1.htm
|title = The Journal of the British Astronomical Association<!--INSERT TITLE; done by Universe=atom-->
|publisher = [[British Astronomical Association]]
|accessdate=2007-07-07
|year = 2003
|month = February}}</ref>
In 1980, Voyager I made a fly-by of Saturn that showed the F-ring to be composed of three narrow rings that appeared to be braided in a complex structure; it is now known that the outer two rings consist of knobs, kinks and lumps that give the illusion of braiding, with the less bright third ring lying inside them.
===Spokes of the rings===
[[Image:Voyager ring spokes.jpg|thumb|right|Spokes in the B ring, imaged by [[Voyager 2]] in 1981]]
Until 1980, the structure of the rings of Saturn was explained exclusively as the action of [[gravitation]]al forces. The Voyager spacecraft found radial features in the [[Rings of Saturn#B ring|B ring]], called ''spokes'', which could not be explained in this manner, as their persistence and rotation around the rings were not consistent with [[orbital mechanics]].<ref name="Spokes 2">{{cite web
|url = http://www.planetary.org/explore/topics/saturn/rings.html
|title = The Alphabet Soup of Saturn's Rings
|publisher = The Planetary Society
|date = 2007
|accessdate = 2007-07-24}}</ref> The spokes appear dark in [[backscatter]]ed light, and bright in [[Forward scatter|forward-scattered]] light. It is assumed that they are microscopic dust particles that have levitated away from the ring plane and that they are connected to [[electromagnetism|electromagnetic]] interactions, as they rotate almost synchronously with the [[magnetosphere]] of Saturn. However, the precise mechanism generating the spokes is still unknown.<ref>{{cite web
|url = http://www.solarviews.com/eng/saturnrings.htm
|title = Saturn's Magnificent Rings
|first = Calvin
|last = Hamilton
|date = 2004
|accessdate = 2007-07-25}}</ref>
[[Image:H cassini spokes 02.jpg|thumb|left|These are three images of the spokes imaged by [[Cassini-Huygens|Cassini]] in 2005.]]
Twenty-five years later, the spokes were observed again, this time by Cassini. They appear to be a seasonal phenomenon, disappearing in the Saturnian midwinter/midsummer and reappearing as Saturn comes closer to [[equinox]]. The spokes were not visible when Cassini arrived at Saturn in early 2004. Some scientists speculated that the spokes would not be visible again until 2007, based on models attempting to describe spoke formation. Nevertheless, the Cassini imaging team kept looking for spokes in images of the rings, and the spokes reappeared in images taken on [[September 5]], [[2005]].<ref name="Spokes">{{cite web
|url = http://www.space.com/scienceastronomy/050915_cassini_spokes.html
|title = Cassini Probe Spies Spokes in Saturn's Rings
|accessdate = 2007-07-06
|date = 2005-09-15
|publisher = Imaginova Corp.
|first = Tarig
|last = Malik}}</ref>
== Natural satellites ==
{{main|Moons of Saturn}}
[[Image:Four Saturnian moons PIA07644.jpg|thumb|right|300px|Four of Saturn's moons: [[Dione (moon)|Dione]], [[Titan (moon)|Titan]], [[Prometheus (moon)|Prometheus]] (edge of rings), [[Telesto (moon)|Telesto]] (top center)]]
Saturn has a large number of [[natural satellite|moons]]. The precise figure is indeterminate, as the orbiting chunks of ice in Saturn's rings are all technically moons, and it is difficult to draw a distinction between a large ring particle and a tiny moon. As of 2007, 60 moons had been identified, plus 3 unconfirmed moons that could be large dust clumps in the rings. Of those, 52 had been given proper names. Many of the moons are very small: 34 are less than 10 km in diameter, and another 13 less than 50 km.<ref name="Saturn moons">{{cite web
|url = http://www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html|title=www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html
|title = Saturn's Known Satellites
|accessdate=2007-05-23}}</ref> Only seven are massive enough to have collapsed into [[hydrostatic equilibrium]] under their own gravitation. These are compared with Earth's moon in the table below.
Titan, Saturn's largest moon, is the only moon in the Solar System to have a dense atmosphere. While most of the moons in the Saturnian system are small in size, Titan is, relatively speaking, gigantic. After the Sun, the eight planets and Jupiter's moon Ganymede, Titan is the most massive object in the Solar System.<ref name="Titan ref"/> Titan comprises more than 90 percent of the mass in orbit around Saturn, including the rings, and the other moons range from one hundredth to one hundred millionth its mass.<ref>{{cite book|title=Solar System Voyage|author=Serge Brunier|pages=164|publisher=Cambridge University Press|year=2005}}</ref>
Saturn's second largest moon [[Rhea (moon)|Rhea]] may have a tenuous [[Rings of Rhea|ring system of its own]].<ref name="Jones2008">{{cite journal
| last = Jones
| first = Geraint H.
| coauthors = ''et al.''
| title = The Dust Halo of Saturn's Largest Icy Moon, Rhea
| url = http://www.sciencemag.org/cgi/content/short/319/5868/1380
| journal = Science
| volume = 319
| issue = 5868
| pages = 1380–1384
| publisher = [[American Association for the Advancement of Science|AAAS]]
| date = 2008 March 07
| doi = 10.1126/science.1151524
| pmid = 18323452
}}</ref>
Traditionally, most of Saturn's moons have been named after [[Titan (mythology)|Titans]] of Greek mythology. This started because [[John Herschel]]—son of [[William Herschel]], discoverer of Mimas and Enceladus—suggested doing so in his 1847 publication ''Results of Astronomical Observations made at the Cape of Good Hope'',<ref>Herschel, J.; ''Results of Astronomical Observations made at the Cape of Good Hope'', 1847 —as reported by Lassell, W.; [http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000042.000.html Monthly Notices of the Royal Astronomical Society], Vol. 8, No. 3 ([[January 14]], [[1848]]), pp. 42–43</ref> because they were the sisters and brothers of [[Cronus|Cronos]] (the Greek Saturn).
{{Saturn's main moons}}
:''For a timeline of discovery dates, see [[Timeline of discovery of Solar System planets and their natural satellites]]''.
== History and exploration ==
{{main|Exploration of Saturn}}
[[Image:Saturn's rings.jpg|250px|thumb|left|A Hubble Space Telescope image, captured in October 1996, shows Saturn's rings from just past edge-on. Credit: [[NASA]]/[[European Space Agency|ESA]].]]
<!-- more about experiments other than imaging should be here -->
===Ancient times and observation===
{{seealso|Planet#Etymology}}
Saturn has been known since prehistoric times.<ref name="NMM Saturn 2">{{cite web
|title = Saturn > Observing Saturn
|url = http://www.nmm.ac.uk/server/show/conWebDoc.13852/viewPage/5
|publisher = [[National Maritime Museum]]
|accessdate = 2007-07-06}}</ref> In ancient times, it was the most distant of the five known planets in the solar system (excluding Earth) and thus a major character in various mythologies. In [[Roman mythology|ancient Roman mythology]], the god [[Saturn (mythology)|Saturnus]], from which the planet takes its name, was the god of the agricultural and harvest sector.<ref name="Saturn in ancient mythologies"/> The Romans considered Saturnus the equivalent of the [[Greek mythology|Greek god]] [[Kronos]].<ref name="Saturn in ancient mythologies"/> The Greeks had made the outermost planet sacred to Kronos,<ref>{{cite book|title=The History and Practice of Ancient Astronomy|author=James Evans|publisher=Oxford University Press|year=1998|pages=296-7}}</ref> and the Romans followed suit.
In [[Jyotisha|Hindu astrology]], there are nine astrological objects, known as [[Navagraha]]s. Saturn, one of them, is known as "Sani" or "[[Shani]]," the Judge among all the planets, and by everyone accordingly to their own performed deeds bad or good.<ref name="Saturn in ancient mythologies">{{cite web
|title = Starry Night Times
|url = http://www.starrynight.com/sntimes/2006/2006-01-full.html
|accessdate = 2007-07-05
|date = 2006
|publisher = Imaginova Corp.
}}</ref> Ancient [[Chinese astrology|Chinese]] and Japanese culture designated the planet Saturn as the ''earth star'' (土星). This was based on [[Five elements (Chinese philosophy)|Five Elements]] which were traditionally used to classify natural elements. In ancient [[Hebrew language|Hebrew]], Saturn is called 'Shabbathai'. Its angel is [[Cassiel]]. Its intelligence, or beneficial spirit, is [[Agiel]] (layga), and its spirit (darker aspect) is Zazel (lzaz). In [[Ottoman Turkish]], [[Urdu]] and [[Malay language|Malay]], its name is 'Zuhal', derived from [[Arabic language|Arabic]] زحل.
Saturn's rings require at least a 75 mm diameter [[telescope]] to resolve and thus were not known to exist until [[Galileo]] first saw them in 1610.<ref>{{cite web
|url = http://library.thinkquest.org/C005921/Saturn/satuHist.htm
|title = Saturn: History Timeline
|accessdate = 2007-07-16
|date = 2000
|last = Chan
|first = Gary}}</ref> He, though, thought of them as two moons on Saturn's sides. It was not until [[Christian Huygens]] used greater telescopic magnification that the rings were assumed to be rings. Huygens also discovered Saturn's moon Titan. Some time later, [[Jean-Dominique Cassini]] discovered four other moons: [[Iapetus (moon)|Iapetus]], [[Rhea (moon)|Rhea]], [[Tethys (moon)|Tethys]], and [[Dione (moon)|Dione]]. In 1675, Cassini also discovered the gap now known as the Cassini Division.<ref>{{cite web
|url = http://huygensgcms.gsfc.nasa.gov/Shistory.htm
|title = Saturn: History of Discoveries
|accessdate = 2007-07-15
|last = Micek
|last = Catherine}}</ref>
No further discoveries of significance were made until 1789 when [[William Herschel]] discovered two further moons, [[Mimas (moon)|Mimas]] and [[Enceladus (moon)|Enceladus]]. The irregularly shaped satellite [[Hyperion (moon)|Hyperion]], which has a [[orbital resonance|resonance]] with Titan, was discovered in 1848 by a British team.
In 1899 [[William Henry Pickering]] discovered [[Phoebe (moon)|Phoebe]], a highly [[irregular satellite]] that does not rotate synchronously with Saturn as the larger moons do. Phoebe was the first such satellite found, and it takes more than a year to orbit Saturn in a [[retrograde orbit]]. During the early twentieth century, research on Titan led to the confirmation in 1944 that it had a thick atmosphere - a feature unique among the solar system's moons.
===Pioneer 11 flyby===
Saturn was first visited by [[Pioneer 11]] in September 1979. It flew within 20,000 km of the planet's cloud tops. Low resolution images were acquired of the planet and a few of its moons; the resolution of the images was not good enough to discern surface features. The spacecraft also studied the rings; among the discoveries were the thin F-ring and the fact that dark gaps in the rings are bright when viewed towards the Sun, or in other words, they are not empty of material. Pioneer 11 also measured the temperature of Titan.<ref>{{cite web
|url = http://web.archive.org/web/20060130100401/http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PN10&11.html
|title = The Pioneer 10 & 11 Spacecraft<!--INSERT TITLE; done by Universe=atom-->
|accessdate=2007-07-05
|publisher = Mission Descriptions}}</ref>
===Voyager flybys===
In November 1980, the [[Voyager 1]] probe visited the Saturn system. It sent back the first high-resolution images of the planet, rings, and satellites. Surface features of various moons were seen for the first time. Voyager 1 performed a close flyby of Titan, greatly increasing our knowledge of the atmosphere of the moon. However, it also proved that Titan's atmosphere is impenetrable in visible wavelengths; so, no surface details were seen. The flyby also changed the spacecraft's trajectory out from the plane of the solar system.<ref name="Voyager">{{cite web
|url = http://www.planetary.org/explore/topics/saturn/missions.html
|title = Missions to Saturn
|publisher = The Planetary Society
|date = 2007
|accessdate = 2007-07-24}}</ref>
Almost a year later, in August 1981, [[Voyager 2]] continued the study of the Saturn system. More close-up images of Saturn's moons were acquired, as well as evidence of changes in the atmosphere and the rings. Unfortunately, during the flyby, the probe's turnable camera platform stuck for a couple of days, and some planned imaging was lost. Saturn's gravity was used to direct the spacecraft's trajectory towards Uranus.<ref name="Voyager"/>
The probes discovered and confirmed several new satellites orbiting near or within the planet's rings. They also discovered the small [[Rings of Saturn#Maxwell Gap|Maxwell]] gap (a gap within the [[Rings of Saturn#C Ring|C Ring]]) and [[Rings of Saturn#Keeler Gap|Keeler]] gap (a 42 km wide gap in the [[Rings of Saturn#A Ring|A Ring]]).
===Cassini orbiter===
[[Image:Saturn eclipse.jpg|thumb|250px|Saturn eclipses the Sun, as seen from Cassini.]]
On [[July 1]] [[2004]], the [[Cassini–Huygens]] spacecraft performed the SOI (Saturn Orbit Insertion) maneuver and entered into orbit around Saturn. Before the SOI, Cassini had already studied the system extensively. In June 2004, it had conducted a close flyby of [[Phoebe (moon)|Phoebe]], sending back high-resolution images and data.
Cassini's flyby of Saturn's largest moon, Titan, has captured radar images of large lakes and their coastlines with numerous islands and mountains. The orbiter completed two Titan flybys before releasing the [[Huygens probe]] on [[December 25]], [[2004]]. Huygens descended onto the surface of Titan on [[January 14]], [[2005]], sending a flood of data during the atmospheric descent and after the landing. During 2005, Cassini conducted multiple flybys of Titan and icy satellites. Cassini's last Titan flyby commenced on [[March 23]], [[2008]].
Since early 2005, scientists have been tracking lightning on Saturn, primarily found by Cassini. The power of the lightning is said to be approximately 1000 times than that of the lightning on Earth. In addition, scientists believe that this storm is the strongest of its kind ever seen.<ref>{{cite web
|url = http://www.sciencedaily.com/releases/2006/02/060215090726.htm
|title = Astronomers Find Giant Lightning Storm At Saturn
|date = 2007
|accessdate = 2007-07-27
|publisher = ScienceDaily LLC}}</ref>
On [[March 10]], [[2006]], NASA reported that, through images, the Cassini probe found evidence of liquid water reservoirs that erupt in [[geyser]]s on Saturn's moon [[Enceladus (moon)|Enceladus]]. Images had also shown particles of water in its liquid state being emitted by icy jets and towering plumes. According to Dr. Andrew Ingersoll, California Institute of Technology, "Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust. What's different here is that pockets of liquid water may be no more than tens of meters below the surface."<ref>{{cite web
|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=639
|title = NASA's Cassini Discovers Potential Liquid Water on Enceladus<!--INSERT TITLE; done by Universe=atom-->
|accessdate = 2007-07-08
|date = March 9, 2006
|publisher = NASA Jet Propulsion Laboratory
|first = Michael
|last = Pence}}</ref>
On [[September 20]], [[2006]], a Cassini probe photograph revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. Apparently, the source of this ring is the result of the crashing of a meteoroid off two of the moons of Saturn.<ref>{{cite web
|url = http://space.newscientist.com/channel/solar-system/cassini-huygens/dn10124-faint-new-ring-discovered-around-saturn.html
|title = Faint new ring discovered around Saturn
|accessdate = 2007-07-08
|date = September 20, 2007
|last = Shiga
|first = David
|publisher = NewScientist.com}}</ref>
In July 2006, Cassini saw the first proof of hydrocarbon lakes near Titan's north pole, which was confirmed in January 2007. In March 2007, additional images near Titan's north pole discovered hydrocarbon "seas", the largest of which is almost the size of the [[Caspian Sea]].<ref>{{cite web
|url = http://news.bbc.co.uk/2/hi/science/nature/6449081.stm
|title = Probe reveals seas on Saturn moon
|publisher = BBC
|last =
|first =
|accessdate = 2007-09-26
|date = March 14, 2007}}</ref>
In October 2006, the probe detected a 5,000 km diameter hurricane with an eyewall at Saturn's South Pole.<ref>{{cite web
|url = http://news.bbc.co.uk/2/hi/science/nature/6135450.stm
|title = Huge 'hurricane' rages on Saturn
|publisher = BBC
|last = Rincon
|first = Paul
|accessdate = 2007-07-12
|date = November 10, 2006}}</ref>
As of 2006, the probe has discovered and confirmed 4 new satellites. Its primary mission will end in 2008 when the spacecraft will be expected to have completed 74 orbits around the planet. The probe, however, is expected to have at least one mission extension.
== Best viewing ==
[[Image:Saturnoppositions.png|thumb|left|Saturn Oppositions: 2001–2029]]
Saturn is the most distant of the five planets easily visible to the naked eye, the other four being [[Mercury (planet)|Mercury]], [[Venus]], [[Mars]], and Jupiter (Uranus and occasionally [[4 Vesta]] are visible to the naked eye in very dark skies), and was the last planet known to early astronomers until Uranus was discovered in 1781. Saturn appears to the naked eye in the night sky as a bright, yellowish point of light whose magnitude is usually between +1 and 0 and takes approximately 29½ years to make a complete circuit of the [[ecliptic]] against the background constellations of the [[zodiac]]. Most people will require optical aid (large binoculars or a telescope) magnifying at least 20X to clearly resolve Saturn's rings.<ref name="NMM Saturn"/>
While it is a rewarding target for observation for most of the time it is visible in the sky, Saturn and its rings are best seen when the planet is at or near [[opposition (astronomy)|opposition]] (the configuration of a planet when it is at an [[Elongation (astronomy)|elongation]] of 180° and thus appears opposite the Sun in the sky). During the opposition of [[December 17]] [[2002]], Saturn appeared at its brightest due to a favorable orientation of its rings relative to the [[Earth]].<ref name="opp2002">{{cite web
|url = http://findarticles.com/p/articles/mi_qa4015/is_200301/ai_n9338203
|title = SATURN IN 2002-03
|accessdate = 2007-10-14
|last = Schmude
|first = Richard W Jr
|date = 2003
|publisher = Georgia Journal of Science}}</ref>
{{-}}
== See also ==
{{portal|Solar System|Solar system.jpg}}
*[[Dragon Storm (astronomy)]]
*[[Planets in astrology#Saturn|Saturn in astrology]]
*[[Saturn in fiction]]
==References==
{{reflist|2}}
* {{ cite book | author = Lovett, L.; Horvath, J.; Cuzzi, J. | year = 2006 | title =Saturn: A New View | location = New York | publisher = Harry N. Abrams, Inc. | id=ISBN 0810930900 }}
* {{ cite book | author = Karttunen, H.; Kröger, P.; ''et al.'' | year = 2007 | title =Fundamental Astronomy | location = New York | publisher = Springer, 5th edition | id=ISBN 3540341439 }}
==External links==
{{SpecialChars}}
{{commonscat|Saturn (planet)|Saturn}}
{{sisterlinks|Saturn}}
*[http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn Introduction to Saturn] by NASA's Solar System Exploration
*[http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html Saturn Fact Sheet], by NASA
*[http://saturn.jpl.nasa.gov/home/index.cfm Cassini-Huygens mission] to Saturn, by NASA
*[http://www.sciencedaily.com/news/space_time/saturn/ Research News] about Saturn
*[http://www.solarviews.com/eng/saturn.htm General information] about Saturn
*[http://www.affs.org/html/studies_on_the_rings_of_saturn.html Studies on the Rings] of Saturn
*[http://www.astronomycast.com/astronomy/episode-59-saturn/ Astronomy Cast: Saturn]
{{Saturn}}
{{Solar System}}
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[[Category:Saturn|*]]
[[Category:Planets of the Solar System]]
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[[zh-min-nan:Thó͘-chheⁿ]]
[[be:Планета Сатурн]]
[[be-x-old:Сатурн (плянэта)]]
[[bs:Saturn]]
[[br:Sadorn (planedenn)]]
[[bg:Сатурн (планета)]]
[[ca:Saturn (planeta)]]
[[cv:Сатурн]]
[[cs:Saturn (planeta)]]
[[co:Saturnu]]
[[cy:Sadwrn (planed)]]
[[da:Saturn (planet)]]
[[de:Saturn (Planet)]]
[[et:Saturn]]
[[el:Κρόνος (πλανήτης)]]
[[eml:Saturn]]
[[es:Saturno (planeta)]]
[[eo:Saturno]]
[[eu:Saturno (planeta)]]
[[fa:کیوان (سیاره)]]
[[fo:Saturn]]
[[fr:Saturne (planète)]]
[[ga:Satarn (pláinéad)]]
[[gan:土星]]
[[gv:Sarn (planaid)]]
[[gd:Satarn]]
[[gl:Saturno (planeta)]]
[[gu:શનિ (ગ્રહ)]]
[[ko:토성]]
[[hy:Սատուրն]]
[[hi:शनि]]
[[hr:Saturn (planet)]]
[[io:Saturno]]
[[ilo:Saturno (planeta)]]
[[id:Saturnus]]
[[ia:Saturno (planeta)]]
[[os:Сатурн (планетæ)]]
[[is:Satúrnus (reikistjarna)]]
[[it:Saturno (astronomia)]]
[[he:שבתאי]]
[[jv:Saturnus]]
[[pam:Saturn]]
[[kn:ಶನಿ]]
[[ka:სატურნი (პლანეტა)]]
[[csb:Saturna]]
[[kw:Sadorn (planet)]]
[[sw:Zohali]]
[[ht:Satin]]
[[ku:Keywan]]
[[la:Saturnus (planeta)]]
[[lv:Saturns (planēta)]]
[[lb:Saturn (Planéit)]]
[[lt:Saturnas]]
[[li:Saturnus (planeet)]]
[[ln:Saturne]]
[[hu:Szaturnusz]]
[[mk:Сатурн]]
[[ml:ശനി (ഗ്രഹം)]]
[[mt:Saturnu (pjaneta)]]
[[mr:शनी ग्रह]]
[[ms:Zuhal]]
[[mdf:Сатурн]]
[[nah:Tzitzimicītlalli]]
[[nl:Saturnus (planeet)]]
[[ne:शनिग्रह]]
[[ja:土星]]
[[no:Saturn]]
[[nn:Planeten Saturn]]
[[nov:Saturne (planete)]]
[[oc:Saturne (planeta)]]
[[uz:Saturn]]
[[pl:Saturn]]
[[pt:Saturno (planeta)]]
[[ksh:Satturrən (Planneet)]]
[[ro:Saturn (planetă)]]
[[qu:Hawcha]]
[[ru:Сатурн (планета)]]
[[se:Saturnus]]
[[sa:शनि]]
[[stq:Saturn]]
[[sq:Saturni]]
[[scn:Saturnu]]
[[simple:Saturn (planet)]]
[[sk:Saturn]]
[[sl:Saturn]]
[[sr:Сатурн (планета)]]
[[sh:Saturn (planeta)]]
[[fi:Saturnus]]
[[sv:Saturnus]]
[[tl:Saturno (planeta)]]
[[ta:சனி (கோள்)]]
[[te:శని]]
[[th:ดาวเสาร์]]
[[vi:Sao Thổ]]
[[tg:Зуҳал]]
[[tr:Satürn (gezegen)]]
[[uk:Сатурн (планета)]]
[[ur:زحل]]
[[zh-yue:土星]]
[[zh:土星]]