Saturn

Template:Short description Template:About Template:Redirect Template:Featured article Template:Pp-semi-indef Template:Pp-move Template:Use American English Template:Use dmy dates {{#invoke:infobox|infoboxTemplate | class = vcard | titleclass = fn org | title = Saturn | image = {{#invoke:InfoboxImage|InfoboxImage|image=File:Saturn during Equinox.jpg|upright={{#if:||1.1}}|alt=}} | caption = Saturn and its prominent rings, as captured by the Cassini orbiter<ref group=lower-alpha name=titan>The dot in the bottom left is Titan</ref> | headerstyle = {{#if:Wheat|background-color:Wheat|background-color:#E0CCFF}} | labelstyle = max-width:{{#if:||11em}}; | autoheaders = y

| header1 = Discovery

| label2 = Discovered by | data2 = | label3 = Discovery site | data3 = | label4 = Discovery date | data4 = | label5 = Template:Longitem | data5 =

| header10 = {{#if:|Designations|Designations}}

| label11 = Template:Longitem | data11 = | label12 = Pronunciation | data12 = Template:IPAc-en<ref name="walter2003"/> | label13 = Template:Longitem | data13 = Saturn | label14 = Template:Longitem | data14 = | label15 = Template:Longitem | data15 = | label16 = Adjectives | data16 = Saturnian Template:IPAc-en,<ref>Template:OED</ref> Cronian<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> / Kronian<ref>Template:Cite journal</ref> Template:IPAc-en<ref>Template:OED</ref> | label17 = Symbol | data17 = ♄

| header20 = Orbital characteristics{{#ifeq:|yes| (barycentric)}}<ref name="fact" />

| data21 = | data22 = {{#if:J2000.0 |Epoch J2000.0}} | data23 = {{#if: | Uncertainty parameter {{{uncertainty}}}}} | label24 = Observation arc | data24 = | label25 = Earliest precovery date | data25 = | label26 = {{#switch:{{{apsis}}} |apsis|gee|barion|center|centre|(apsis)=Apo{{{apsis}}} |Ap{{#if:|{{{apsis}}}|helion}}}} | data26 = Template:Convert | label27 = Peri{{#if:|{{{apsis}}}|helion}} | data27 = Template:Convert | label28 = Peri{{#if:|{{{apsis}}}|apsis}} | data28 = | label29 = {{#switch:{{{apsis}}} |helion|astron=Ap{{{apsis}}} |Apo{{#if:|{{{apsis}}}|apsis}}}} | data29 = | label30 = Periastron | data30 = | label31 = Apoastron | data31 = | label32 = Template:Longitem | data32 = Template:Convert | label33 = Template:Longitem | data33 = | label34 = Eccentricity | data34 = Template:Val | label35 = Template:Longitem | data35 = Template:Plainlist | label36 = Template:Longitem | data36 = 378.09 days | label37 = Template:Longitem | data37 = Template:Val | label38 = Template:Longitem | data38 = Template:Val<ref name="VSOP87" /> | label39 = Template:Longitem | data39 = | label40 = Inclination | data40 = Template:Plainlist | label41 = Template:Longitem | data41 = | label42 = Template:Longitem | data42 = Template:Val | label43 = Template:Longitem | data43 = | label44 = Template:Longitem | data44 = 2032-Nov-29<ref name=horizons-perihelion>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> | label45 = Template:Longitem | data45 = Template:Val<ref name="VSOP87" /> | label46 = Template:Nowrap | data46 = | label47 = Satellite of | data47 = | label48 = Group | data48 = | label49 = {{#switch: |yes|true=Satellites |Known satellites}} | data49 = 274 with formal designations; innumerable additional moonlets.<ref name="JPLmoons"/><ref name="UBC-20230511"/> | label50 = Star | data50 = | label51 = Earth MOID | data51 = | label52 = Mercury MOID | data52 = | label53 = Venus MOID | data53 = | label54 = Mars MOID | data54 = | label55 = Jupiter MOID | data55 = | label56 = Saturn MOID | data56 = | label57 = Uranus MOID | data57 = | label58 = Neptune MOID | data58 = | label59 = T_Jupiter | data59 =

| header60 = Proper orbital elements

| label61 = Template:Longitem | data61 = {{#if: |{{{p_semimajor}}} AU}} | label62 = Template:Longitem | data62 = | label63 = Template:Longitem | data63 = | label64 = Template:Longitem | data64 = {{#if: |{{{p_mean_motion}}} degTemplate:\yr}} | label65 = Template:Longitem | data65 = {{#if:|{{#expr:360/1 round 5}} yr
({{#expr:365.25*360/1 round 3}} d) }} | label66 = Template:Longitem | data66 = {{#if:|{{{perihelion_rate}}} arcsecTemplate:\yr }} | label67 = Template:Longitem | data67 = {{#if:|{{{node_rate}}} arcsecTemplate:\yr}}

| header70 = Template:Anchor{{#if:| Physical characteristics|Physical characteristics}}<ref name="fact" />

| label71 = Dimensions | data71 = | label72 = Template:Longitem | data72 = | label73 = Template:Longitem | data73 = Template:Val<ref group=lower-alpha name=1bar />
Template:Val | label74 = Template:Longitem | data74 = Template:Plainlist | label75 = Template:Longitem | data75 = Template:Plainlist | label76 = Flattening | data76 = Template:Val | label77 = Circumference | data77 = Template:Val (equatorial)<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> | label78 = Template:Longitem | data78 = Template:Plainlist | label79 = Volume | data79 = Template:Plainlist | label80 = Mass | data80 = Template:Plainlist | label81 = Template:Longitem | data81 = Template:Val<ref group=lower-alpha name=1bar_b>Based on the volume within the level of 1 bar atmospheric pressure</ref>
Template:Val Earths | label82 = Template:Longitem | data82 = Template:Cvt<ref group=lower-alpha name=1bar /> | label83 = Template:Longitem | data83 = Template:Val<ref name="Fortney2018">Template:Cite book</ref> | label84 = Template:Longitem | data84 = Template:Val<ref group=lower-alpha name=1bar /> | label85 = Template:Longitem | data85 = 10 h 32 m 36 s;
10.5433 hours,<ref name="CSeligman"/> 10 h 39 m;
10.7 hours<ref name=JPL/> | label86 = Template:Longitem | data86 = Template:RA Template:+- <ref name="NASA-20190118">Template:Cite news</ref><ref name="APJ-20190117">Template:Cite journal</ref> | label87 = Template:Longitem | data87 = Template:Val<ref group=lower-alpha name=1bar /> | label88 = Template:Longitem | data88 = 26.73° Template:Small | label89 = Template:Longitem | data89 = 40.589°; Template:RA<ref name="iau2015">Template:Cite journal</ref> | label90 = Template:Longitem | data90 = 83.537°<ref name="iau2015"/> | label91 = Template:Longitem | data91 = | label92 = Template:Longitem | data92 = | label93 = {{#if: |Template:Longitem |Albedo}} | data93 = Template:Plainlist | label94 = Temperature | data94 =

| data100 = {{#if:1 bar0.1 bar|

{{#if:1 bar|}}{{#if:0.1 bar|}}{{#if:|}}{{#if:|}}

Surface temp.	min	mean	max
1 bar		134 K
0.1 bar	88 K<ref name="min_max">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>	97 K<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>	151 K<ref name="min_max"/>
{{{temp_name3}}}
{{{temp_name4}}}

}}

| label101 = Surface absorbed dose rate | data101 = | label102 = Surface equivalent dose rate | data102 = | label103 = Template:Longitem | data103 = | label104 = Template:Longitem | data104 = | label105 = Template:Longitem | data105 = −0.55<ref name="Mallama_and_Hilton" /> to +1.17<ref name="Mallama_and_Hilton"/> | label106 = Template:Longitem | data106 = −9.7<ref name="IMCCE">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> | label107 = Template:Longitem | data107 = 14.5″ to 20.1″ (excludes rings)

| header110 = Atmosphere<ref name="fact" />

| label111 = Template:Longitem | data111 = >>1000 bars<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> | label112 = Template:Longitem | data112 = Template:Val | label113 = Composition by volume | data113 = Template:Plainlist

| below = {{#if:||Template:Reflist }}

}}{{#invoke:Check for unknown parameters|check|unknown=Template:Main other|preview=Page using Template:Infobox planet with unknown parameter "_VALUE_"|ignoreblank=y| abs_magnitude | adjective | adjectives | albedo | allsatellites | alt_names | angular_dist | angular_size | aphelion | apoapsis | apsis | apoastron | arg_peri | asc_node | atmosphere | atmosphere_composition | atmosphere_ref | avg_speed | axial_tilt | background | barycentric | bgcolour | caption | circumference | declination | density | dimensions | discovered | discoverer | discovery_method | discovery_ref | discovery_site | earliest_precovery_date | eccentricity | epoch | equatorial_radius | escape_velocity | exosolar planets | extrasolarplanet | family | flattening | group | image | image_alt | image_scale | inclination | jupiter_moid | label_width | long_periastron | magnitude | mars_moid | mass | max_temp_1 | max_temp_2 | max_temp_3 | max_temp_4 | mean_anomaly | mean_diameter | mean_motion | mean_orbit_radius | mean_radius | mean_temp_1 | mean_temp_2 | mean_temp_3 | mean_temp_4 | mercury_moid | min_temp_1 | min_temp_2 | min_temp_3 | min_temp_4 | minorplanet | moid | moment_of_inertia_factor | mp_category | mp_name | mpc_name | name | named_after | neptune_moid | node_rate | note | observation_arc | orbit_diagram | orbit_ref | p_eccentricity | p_inclination | p_mean_motion | p_orbit_ref | p_semimajor | periapsis | periastron | perihelion | perihelion_rate | period | physical_ref | polar_radius | pole_ecliptic_lat | pole_ecliptic_lon | pronounce | pronounced | right_asc_north_pole | rot_velocity | rotation | satellite_of | satellites | saturn_moid | scale_height | semi-amplitude | semimajor | sidereal_day | single_temperature | spectral_type | star | surface_area | surface_grav | surface_pressure | surface_absorbed_dose_rate | surface_equivalent_dose_rate | symbol | synodic_period | temp_name1 | temp_name2 | temp_name3 | temp_name4 | time_periastron | tisserand | uncertainty | uranus_moid | venus_moid | volume }} Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 times more massive. Even though Saturn is almost as big as Jupiter, Saturn has less than a third its mass. Saturn orbits the Sun at a distance of Template:Convert, with an orbital period of 29.45 years.

Saturn's interior is thought to be composed of a rocky core, surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and an outer layer of gas. Saturn has a pale yellow hue, due to ammonia crystals in its upper atmosphere. An electrical current in the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's, but has a magnetic moment 580 times that of Earth because of Saturn's greater size. Saturn's magnetic field strength is about a twentieth that of Jupiter.<ref name="mag" /> The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach Template:Convert.

The planet has a bright and extensive system of rings, composed mainly of ice particles, with a smaller amount of rocky debris and dust. At least 274 moons orbit the planet, of which 63 are officially named; these do not include the hundreds of moonlets in the rings. Titan, Saturn's largest moon and the second largest in the Solar System, is larger (but less massive) than the planet Mercury and is the only moon in the Solar System that has a substantial atmosphere.<ref name="Titan ref">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Name and symbol

Saturn is named after the Roman god of wealth and agriculture, who was the father of the god Jupiter. Its astronomical symbol Template:Nowrap has been traced back to the Greek Oxyrhynchus Papyri, where it can be seen to be a Greek kappa-rho ligature with a horizontal stroke, as an abbreviation for Κρονος (Cronus), the Greek name for the planet (File:Saturn symbol (late classical and medieval mss).png).<ref name="jones-1999">Template:Cite book</ref> It later came to look like a lower-case Greek eta, with the cross added at the top in the 16th century to Christianize this pagan symbol.

The Romans named the seventh day of the week Saturday, Sāturni diēs, "Saturn's Day", for the planet Saturn.<ref name=days>Template:Citation</ref>

Physical characteristics

File:Saturn compared to Earth and the Moon.png

Size of Saturn compared to Earth and Earth's Moon

Saturn is a gas giant, composed predominantly of hydrogen and helium. It lacks a definite surface, though it is likely to have a solid core.<ref name=melosh2011/> The planet's rotation makes it an oblate spheroid—a ball flattened at the poles and bulging at the equator. Its equatorial radius is more than 10% larger than the polar radius: 60,268 km versus 54,364 km (37,449 mi versus 33,780 mi).<ref name="fact" /> Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are less oblate. The combination of the bulge and the rotation rate means that the effective surface gravity along the equator, Template:Val, is 74% of what it is at the poles and is lower than the surface gravity of Earth. However, the equatorial escape velocity, nearly Template:Val, is much higher than that of Earth.<ref name=Gregersen2010>Template:Cite book</ref>

Saturn is the only planet of the Solar System that is less dense than water—about 30% less.<ref name=preserve/> Although Saturn's core is considerably denser than water, the average specific density of the planet is Template:Val, because of the atmosphere. Jupiter has 318 times Earth's mass,<ref name="Jupiter fact"/> and Saturn is 95 times Earth's mass.<ref name="fact"/><ref name="Mass ref">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Mass ref 2">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Mass ref 3" /><ref name="Radius ref">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Radius ref 2">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System.<ref name=ssr152_1_423/>

Internal structure

File:Saturn diagram.svg

Diagram of Saturn, to scale

Despite consisting mostly of hydrogen and helium, most of Saturn's mass is not in the gas phase, because hydrogen becomes a non-ideal liquid when the density is above Template:Val, which is reached at a radius containing 99.9% of Saturn's mass. The temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to be a metal in the deeper layers.<ref name=ssr152_1_423/>

Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium, with trace amounts of various volatiles.<ref name=guillot_et_al2009/> Analysis of the distortion shows that Saturn is substantially more centrally condensed than Jupiter and therefore contains much more material denser than hydrogen near its center. Saturn's central regions are about 50% hydrogen by mass, and Jupiter's are about 67% hydrogen.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

This core is similar in composition to Earth, but is more dense. The examination of Saturn's gravitational moment, in combination with physical models of the interior, has allowed constraints to be placed on the mass of Saturn's core. In 2004, scientists estimated that the core must be 9–22 times the mass of Earth,<ref name="science305_5689_1414" /><ref name="apj609_2_1170" /> which corresponds to a diameter of about Template:Convert.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, measurements of Saturn's rings suggest a much more diffuse core, with a mass equal to about 17 Earths and a radius equal to about 60% of Saturn's entire radius.<ref>Template:Cite journal</ref> This is surrounded by a thicker, liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen, which gradually transitions to a gas as altitude increases. The outermost layer spans about Template:Convert and consists of gas.<ref name="faure_mensing2007" /><ref name="NMM Saturn" /><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Saturn has a hot interior, reaching Template:Convert at its core, and radiates 2.5 times more energy into space than it receives from the Sun. Jupiter's thermal energy is generated by the Kelvin–Helmholtz mechanism of slow gravitational compression; but such a process alone may not be sufficient to explain heat production for Saturn, because it is less massive. An alternative or additional mechanism may be the generation of heat through the "raining out" of droplets of helium deep in Saturn's interior. As the droplets descend through the lower-density hydrogen, the process releases heat by friction and leaves Saturn's outer layers depleted of helium.<ref name=de_pater_lissauer2010/><ref name=nasa_saturn/> These descending droplets may have accumulated into a helium shell surrounding the core.<ref name=guillot_et_al2009/> Rainfalls of diamonds have been suggested to occur within Saturn, as well as in Jupiter<ref name="SC-20131009">Template:Cite news</ref> and ice giants Uranus and Neptune.<ref name="WP-20170825">Template:Cite news</ref>

Atmosphere

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. The proportion of helium is significantly deficient compared to the abundance of this element in the Sun.<ref name=guillot_et_al2009/> The quantity of elements heavier than helium (metallicity) is 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 heavier elements is estimated to be 19–31 times the mass of Earth, with a significant fraction located in Saturn's core region.<ref name="science286" />

Trace amounts of ammonia, acetylene, ethane, propane, phosphine, and methane have been detected in Saturn's atmosphere.<ref name="baas15_831" /><ref name="cain2009_24029" /><ref name="pfsaa2008" /> The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (Template:Chem2) or water.<ref name="martinez20050905" /> Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion. This photochemical cycle is modulated by Saturn's annual seasonal cycle.<ref name=pfsaa2008/> Cassini observed a series of cloud features found in northern latitudes, nicknamed the "String of Pearls". These features are cloud clearings that reside in deeper cloud layers.<ref>Template:Cite press release</ref>

Cloud layers

File:Saturn Storm.jpg

A global storm girdles the planet in 2011. The storm passes around the planet, such that the storm's head (bright area) passes its tail.

Saturn's atmosphere exhibits a banded pattern similar to Jupiter's, but Saturn's bands are much fainter and are much wider near the equator. The nomenclature used to describe these bands is the same as on Jupiter. Saturn's finer cloud patterns were not observed until the flybys of the Voyager spacecraft during the 1980s. Since then, Earth-based telescopy has improved to the point where regular observations can be made.<ref name=emp105_2_143/>

The composition of the clouds varies with depth and increasing pressure. In the upper cloud layers, with temperatures in the range of 100–160 K and pressures extending between 0.5–2 bar, the clouds consist of ammonia ice. Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185 to 270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 190–235 K. Finally, the lower layers, where pressures are between 10 and 20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in aqueous solution.<ref name=dougherty_esposito2009/>

Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. In 1990, the Hubble Space Telescope imaged an enormous white cloud near Saturn's equator that 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 short-lived phenomenon that occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere's summer solstice.<ref name=icarus176_1_155/> Previous Great White Spots were observed in 1876, 1903, 1933, and 1960, with the 1933 storm being the best observed.<ref>Template:Cite book</ref> The latest giant storm was observed in 2010. In 2015, researchers used Very Large Array telescope to study Saturnian atmosphere, and reported that they found "long-lasting signatures of all mid-latitude giant storms, a mixture of equatorial storms up to hundreds of years old, and potentially an unreported older storm at 70°N".<ref>Template:Cite journal</ref>

The winds on Saturn are the second fastest among the Solar System's planets, after Neptune's. Voyager data indicate peak easterly winds of Template:Convert.<ref name="Voyager Summary 1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In images from the Cassini spacecraft during 2007, Saturn's northern hemisphere displayed a bright blue hue, similar to Uranus. The color was most likely caused by Rayleigh scattering.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Thermography has shown that Saturn's south pole has a warm polar vortex, the only known example of such a phenomenon in the Solar System.<ref name=MCP>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Whereas temperatures on Saturn are normally −185 °C, temperatures on the vortex often reach as high as −122 °C, suspected to be the warmest spot on Saturn.<ref name=MCP/>

Hexagonal cloud patterns

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Template:AnchorA persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref name="NYT-20140806">Template:Cite news</ref> The sides of the hexagon are each about Template:Convert long, which is longer than the diameter of the Earth.<ref name="Hexagon ref">Template:Cite news</ref> The entire structure rotates with a period of Template:RA (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.<ref name=science247_4947_1206/> The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere.<ref name=pss57_14_1671/> The pattern's origin is a matter of much speculation. Most scientists think it is a standing wave pattern in the atmosphere. Polygonal shapes have been replicated in the laboratory through differential rotation of fluids.<ref>Template:Cite journal Bizarre geometric shapes that appear at the center 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><ref name=labmodel>Template:Cite journal Laboratory experiment of spinning disks in a liquid solution forms vortices around a stable hexagonal pattern similar to that of Saturn's.</ref>

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>Template:Cite journal</ref> NASA reported in November 2006 that Cassini had observed a "hurricane-like" storm locked to the south pole that had a clearly defined eyewall.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite news</ref> Eyewall clouds had not previously been seen on any planet other than Earth. For example, images from the Galileo spacecraft did not show an eyewall in the Great Red Spot of Jupiter.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The south pole storm may have been present for billions of years.<ref name="spole"/> This vortex is comparable to the size of Earth, and it has winds of 550 km/h.<ref name="spole">Template:Cite APOD</ref>

Magnetosphere

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}

File:Hubble sees a flickering light display on Saturn.jpg

Auroral lights at Saturn's north pole

Saturn has an intrinsic magnetic field that has a simple, symmetric shape—a magnetic dipole. Its strength at the equator—0.2 gauss (20 μT)—is approximately one twentieth of that of the field around Jupiter and slightly weaker than Earth's magnetic field.<ref name="mag" /> As a result, Saturn's magnetosphere is much smaller than Jupiter's.<ref name="mag 2">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

When Voyager 2 entered the magnetosphere, the solar wind pressure was high and the magnetosphere extended only 19 Saturn radii, or 1.1 million km (684,000 mi),<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> although it enlarged within several hours, and remained so for about three days.<ref name="atkinson2010" /> Most probably, the magnetic field is generated similarly to that of Jupiter—by currents in the liquid metallic-hydrogen layer called a metallic-hydrogen dynamo.<ref name="mag 2" /> 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">Template:Cite journal</ref> Saturn's magnetosphere, like Earth's, produces aurorae.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Orbit and rotation

File:Solar system orrery outer planets.gif

Animation of Saturn and the Solar System's outer planets orbiting around the Sun

File:Saturnoppositions-animated.gif

Simulated appearance of Saturn as seen from Earth (at opposition) during an orbit of Saturn, 2001–2029

The average distance between Saturn and the Sun is over 1.4 billion kilometers (9 AU). With an average orbital speed of 9.68 km/s,<ref name="fact" /> it takes Saturn 10,759 Earth days (or about Template:Frac years)<ref name="cain2009" /> to finish one revolution around the Sun.<ref name="fact" /> As a consequence, it forms a near 5:2 mean-motion resonance with Jupiter.<ref>Template:Cite journal</ref> The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth.<ref name="fact" /> The perihelion and aphelion distances are, respectively, 9.195 and 9.957 AU, on average.<ref name="fact" /><ref>Jean Meeus, Astronomical Algorithms (Richmond, VA: Willmann-Bell, 1998). Average of the nine extremes on p 273. All are within 0.02 AU of the averages.</ref> 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).

Astronomers use three different systems for specifying the rotation rate of Saturn. System I has a period of Template:RA (844.3°/d) and encompasses the Equatorial Zone, the South Equatorial Belt, and the North Equatorial Belt. The polar regions are considered to have rotation rates similar to System I. All other Saturnian latitudes, excluding the north and south polar regions, are indicated as System II and have been assigned a rotation period of Template:RA (810.76°/d). System III refers to Saturn's internal rotation rate. Based on radio emissions from the planet detected by Voyager 1 and Voyager 2,<ref>Template:Cite journal</ref> System III has a rotation period of Template:RA (810.8°/d). System III has largely superseded System II.<ref name=benton2006/>

A precise value for the rotation period of the interior remains elusive. While approaching Saturn in 2004, Cassini found that the radio rotation period of Saturn had increased appreciably, to approximately Template:RA Template:+-.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=cain2008_15298/> An estimate of Saturn's rotation (as an indicated rotation rate for Saturn as a whole) based on a compilation of various measurements from the Cassini, Voyager, and Pioneer probes is Template:RA.<ref name=Anderson2007/> Studies of the planet's C Ring yield a rotation period of Template:RA Template:+- .<ref name="NASA-20190118" /><ref name="APJ-20190117" />

In March 2007, it was found that the variation in radio emissions from the planet did not match Saturn's rotation rate. This variance may be caused by geyser activity on Saturn's moon Enceladus. The water vapor emitted into Saturn's orbit by this activity becomes charged and creates a drag upon Saturn's magnetic field, slowing its rotation slightly relative to the rotation of the planet.<ref>Template:Cite press release</ref><ref name=science316_5823_442/><ref name=science316_5823_380/>

An apparent oddity for Saturn is that it does not have any known trojan asteroids. These are minor planets that orbit the Sun at the stable Lagrangian points, designated L₄ and L₅, located at 60° angles to the planet along its orbit. Trojan asteroids have been discovered for Mars, Jupiter, Uranus, and Neptune. Orbital resonance mechanisms, including secular resonance, are believed to be the cause of the missing Saturnian trojans.<ref>Template:Cite journal</ref>

Natural satellites

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File:Saturn's Rings PIA03550.jpg

Artist conception of Saturn, its rings and major icy moons—from Mimas to Rhea

Saturn has 274 known moons,<ref name="NYT 2025-03-13">Template:Cite news</ref><ref name="MPEC-2023-J49">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 63 of which have formal names.<ref name="UBC-20230511">Template:Cite news</ref><ref name="JPLmoons">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In addition, there is evidence of dozens to hundreds of moonlets with diameters of 40–500 meters in Saturn's rings,<ref>Template:Cite journal</ref> which are not considered to be true moons. Titan, the largest moon, comprises more than 90% of the mass in orbit around Saturn, including the rings.<ref name="brunier2005" /> Saturn's second-largest moon, Rhea, may have a tenuous ring system of its own,<ref name="Jones2008" /> along with a tenuous atmosphere.<ref name=atkinson20101126/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=ryan20101126/>

Many of the other moons are small: 131 are less than 50 km in diameter.<ref name="Saturn moons">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Traditionally, most of Saturn's moons have been named after Titans of Greek mythology. Titan is the only satellite in the Solar System with a major atmosphere,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> in which a complex organic chemistry occurs. It is the only satellite with hydrocarbon lakes.<ref>Template:Cite news</ref><ref>Template:Cite news</ref>

On 6 June 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan, a possible precursor for life.<ref name="IAA-20130606">Template:Cite news</ref> On 23 June 2014, NASA claimed to have strong evidence that nitrogen in the atmosphere of Titan came from materials in the Oort cloud, associated with comets, and not from the materials that formed Saturn in earlier times.<ref name="NASA-201450623">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Saturn's moon Enceladus, which seems similar in chemical makeup to comets,<ref name="NS-20080326">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> has often been regarded as a potential habitat for microbial life.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=madrigal20090624/><ref name=spotts20050928/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Evidence of this possibility includes the satellite's salt-rich particles having an "ocean-like" composition that indicates most of Enceladus's expelled ice comes from the evaporation of liquid salt water.<ref>Template:Cite news</ref><ref>Template:Cite news</ref><ref>Template:Cite news </ref> A 2015 flyby by Cassini through a plume on Enceladus found most of the ingredients to sustain life forms that live by methanogenesis.<ref name="nasa20170413">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In April 2014, NASA scientists reported the possible beginning of a new moon within the A Ring, which was imaged by Cassini on 15 April 2013.<ref name="NASA-20140414a">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Planetary rings

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File:Saturn from Cassini Orbiter (2004-10-06).jpg

The rings of Saturn (imaged here by Cassini in October 2004) are the most massive and conspicuous in the Solar System.<ref name="NMM Saturn" />

Saturn is probably best known for the system of planetary rings that makes it visually unique.<ref name="NMM Saturn">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The rings extend from Template:Convert outward from Saturn's equator and average approximately Template:Convert in thickness. They are composed predominantly of water ice, with trace amounts of tholin impurities and a peppered coating of approximately 7% amorphous carbon.<ref>Template:Cite journal</ref> The particles that make up the rings range in size from specks of dust up to 10 m.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> While the other gas giants also have ring systems, Saturn's is the largest and most visible.

There is a debate on the age of the rings. One side supports that they are ancient, and were created simultaneously with Saturn from the original nebular material (around 4.6 billion years ago),<ref>Template:Cite journal</ref> or shortly after the LHB (around 4.1 to 3.8 billion years ago).<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> The other side supports that they are much younger, created around 100 million years ago.<ref>Template:Cite journal</ref><ref name="NYT-210230928">Template:Cite news</ref><ref name="TAJ-20230927">Template:Cite journal</ref> An MIT research team, supporting the latter theory, proposed that the rings are remnant of a destroyed moon of Saturn, named ″Chrysalis″.<ref name="chrysalis">Template:Cite journal</ref>

Beyond the main rings, at a distance of 12 million km (7.5 million mi) from the planet is the sparse Phoebe ring. It is tilted at an angle of 27° to the other rings and, like Phoebe, orbits in retrograde fashion.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Some of the moons of Saturn, including Pandora and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out.<ref name=russell2004/> Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

History of observation and exploration

The observation and exploration of Saturn can be divided into three phases: (1) pre-modern observations with the naked eye, (2) telescopic observations from Earth beginning in the 17th century, and (3) visitation by space probes, in orbit or on flyby. In the 21st century, telescopic observations continue from Earth (including Earth-orbiting observatories like the Hubble Space Telescope) and, until its 2017 retirement, from the Cassini orbiter around Saturn.

Pre-telescopic observation

Saturn has been known since prehistoric times,<ref name="NMM Saturn 2">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and in early recorded history it was a major character in various mythologies. Babylonian astronomers systematically observed and recorded the movements of Saturn.<ref name=ptrsl276_1257_43/> In ancient Greek, the planet was known as {{#invoke:Lang|lang}} Phainon,<ref>Template:LSJ.</ref> and in Roman times it was known as the "star of Saturn" or the "star of the Sun (i.e. Helios)".<ref>Cicero, De Natura Deorum.</ref><ref>Template:Cite journal</ref> In ancient Roman mythology, the planet Phainon was sacred to this agricultural god, from which the planet takes its modern name.<ref name="Saturn in ancient mythologies" /> The Romans considered the god Saturnus the equivalent of the Greek god Cronus; in modern Greek, the planet retains the name Cronus—Template:Langx: Kronos.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }} See also the Greek article about the planet.</ref>

The Greek scientist Ptolemy based his calculations of Saturn's orbit on observations he made while it was in opposition.<ref name=ps04_1893_862/> In Hindu astrology, there are nine astrological objects, known as Navagrahas. Saturn is known as "Shani" and judges everyone based on the good and bad deeds performed in life.<ref name="Saturn in ancient mythologies">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=ps04_1893_862/> Ancient Chinese and Japanese culture designated the planet Saturn as the "earth star" ({{#invoke:Lang|lang}}). This was based on Five Elements which were traditionally used to classify natural elements.<ref>Template:Cite book</ref><ref>Template:Cite book</ref><ref>Template:Cite book</ref>

In Hebrew, Saturn is called Shabbathai.<ref>Template:Cite news</ref> Its angel is Cassiel. Its intelligence or beneficial spirit is 'Agȋȇl (Template:Langx),<ref name="TheMagus" /> and its darker spirit (demon) is Zȃzȇl (Template:Langx).<ref name="TheMagus">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="CrystalLinks">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="TC-20170308">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Zazel has been described as a great angel, invoked in Solomonic magic, who is "effective in love conjurations".<ref name="FE-2014">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="HP-1998">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In Ottoman Turkish, Urdu, and Malay, the name of Zazel is 'Zuhal', derived from the Arabic language (Template:Langx).<ref name="CrystalLinks" />

Telescopic pre-spaceflight observations

File:Galileo.arp.300pix.jpg

Galileo Galilei observed the rings of Saturn in 1610, but was unable to determine what they were.

File:Saturn Robert Hooke 1666.jpg

Robert Hooke noted the shadows (Template:Var and Template:Var) cast by both the globe and the rings on each other in this drawing of Saturn in 1666.

Saturn's rings require at least a 15-mm-diameter telescope<ref name=binoculars/> to resolve and thus were not known to exist until Christiaan Huygens saw them in 1655 and published his observations in 1659. Galileo, with his primitive telescope in 1610,<ref name=chan2000/><ref name=cain2008_15390/> incorrectly thought of Saturn's appearing not quite round as two moons on Saturn's sides.<ref name=cain2008_15418/><ref name=cain2008_46237/> It was not until Huygens used greater telescopic magnification that this notion was refuted, and the rings were truly seen for the first time. Huygens also discovered Saturn's moon Titan; Giovanni Domenico Cassini later discovered four other moons: Iapetus, Rhea, Tethys, and Dione. In 1675, Cassini discovered the gap now known as the Cassini Division.<ref name=micek2007/>

No further discoveries of significance were made until 1789 when William Herschel discovered two further moons, Mimas and Enceladus. The irregularly shaped satellite Hyperion, which has a resonance with Titan, was discovered in 1848 by a British team.<ref name=pa54_122/>

In 1899, William Henry Pickering discovered Phoebe, a highly irregular satellite that does not rotate synchronously with Saturn as the larger moons do.<ref name=pa54_122/> Phoebe was the first such satellite found and it took more than a year to orbit Saturn in a retrograde orbit. During the early 20th 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.<ref name=apj100_378/>

Spaceflight missions

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Pioneer 11 flyby

File:P11saturnb.jpg

Pioneer 11 image of Saturn

Pioneer 11 made the first flyby of Saturn in September 1979, when it passed within Template:Convert of the planet's cloud tops. Images were taken of the planet and a few of its moons, although their resolution was too low to discern surface detail. The spacecraft also studied Saturn's rings, revealing the thin F-ring and the fact that dark gaps in the rings are bright when viewed at a high phase angle (towards the Sun), meaning that they contain fine light-scattering material. In addition, Pioneer 11 measured the temperature of Titan.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</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, its rings and satellites. Surface features of various moons were seen for the first time. Voyager 1 performed a close flyby of Titan, increasing knowledge of the atmosphere of the moon. It proved that Titan's atmosphere is impenetrable at visible wavelengths; therefore no surface details were seen. The flyby changed the spacecraft's trajectory out of the plane of the Solar System.<ref name="Voyager">{{#invoke:citation/CS1|citation |CitationClass=web }}</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. 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, as well as the small Maxwell Gap (a gap within the C Ring) and Keeler gap (a 42 km-wide gap in the A Ring).<ref>Template:Cite book</ref>

Cassini–Huygens spacecraft

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File:Enceladus geysers June 2009.jpg

At Enceladus's south pole geysers spray water from many locations along the tiger stripes.<ref name="NASA-20140728" />

The Cassini–Huygens space probe entered orbit around Saturn on 1 July 2004. In June 2004, it conducted a close flyby of Phoebe, sending back high-resolution images and data. CassiniTemplate:'s flyby of Saturn's largest moon, Titan, 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 25 December 2004. Huygens descended onto the surface of Titan on 14 January 2005.<ref name="nature438_7069_758" />

Starting in early 2005, scientists used Cassini to track lightning on Saturn. The power of the lightning is approximately 1,000 times that of lightning on Earth.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In 2006, NASA reported that Cassini had found evidence of liquid water reservoirs no more than tens of meters below the surface that erupt in geysers on Saturn's moon Enceladus. These jets of icy particles are emitted into orbit around Saturn from vents in the moon's south polar region.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Over 100 geysers have been identified on Enceladus.<ref name="NASA-20140728">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In May 2011, NASA scientists reported that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web

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File:Saturn eclipse.jpg

Saturn eclipses the Sun, as seen from Cassini. The rings are visible, including the F Ring.

Cassini photographs have revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. The source of this ring is hypothesized to be the crashing of a meteoroid off Janus and Epimetheus.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In July 2006, images were returned of hydrocarbon lakes near Titan's north pole, the presence of which were confirmed in January 2007. In March 2007, hydrocarbon seas were found near the North pole, the largest of which is almost the size of the Caspian Sea.<ref>Template:Cite news</ref> In October 2006, the probe detected an Template:Convert diameter cyclone-like storm with an eyewall at Saturn's south pole.<ref>Template:Cite news</ref>

From 2004 to 2 November 2009, the probe discovered and confirmed eight new satellites.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In April 2013, Cassini sent back images of a hurricane at the planet's north pole 20 times larger than those found on Earth, with winds faster than Template:Convert.<ref>Template:Cite news</ref> On 15 September 2017, the Cassini–Huygens spacecraft performed the "Grand Finale" of its mission: a number of passes through gaps between Saturn and Saturn's inner rings.<ref name="NASA-20170915">Template:Cite news</ref><ref name="NYT-20170914">Template:Cite news</ref> The atmospheric entry of Cassini ended the mission.

Possible future missions

The continued exploration of Saturn is still considered to be a viable option for NASA as part of their ongoing New Frontiers program of missions. NASA previously requested for plans to be put forward for a mission to Saturn that included the Saturn Atmospheric Entry Probe, and possible investigations into the habitability and possible discovery of life on Saturn's moons Titan and Enceladus by Dragonfly.<ref>Template:Cite news</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Observation

File:Saturn-27-03-04.jpeg

Amateur telescopic view of Saturn

Saturn is the most distant of the five planets easily visible to the naked eye from Earth, the other four being Mercury, Venus, Mars, and Jupiter. (Uranus, and occasionally 4 Vesta, are visible to the naked eye in dark skies.) Saturn appears to the naked eye in the night sky as a bright, yellowish point of light. The mean apparent magnitude of Saturn is 0.46 with a standard deviation of 0.34.<ref name="Mallama_and_Hilton" /> Most of the magnitude variation is due to the inclination of the ring system relative to the Sun and Earth. The brightest magnitude, −0.55, occurs near the time when the plane of the rings is inclined most highly, and the faintest magnitude, 1.17, occurs around the time when they are least inclined.<ref name="Mallama_and_Hilton" /> It takes approximately 29.4 years for the planet to complete an entire circuit of the ecliptic against the background constellations of the zodiac. Most people will require an optical aid (very large binoculars or a small telescope) that magnifies at least 30 times to achieve an image of Saturn's rings in which a clear resolution is present.<ref name="NMM Saturn" /><ref name="binoculars" /> When Earth passes through the ring plane, which occurs twice every Saturnian year (roughly every 15 Earth years), the rings briefly disappear from view because they are so thin. Such a "disappearance" will next occur in 2025, but Saturn will be too close to the Sun for observations.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Saturn and its rings are best seen when the planet is at, or near, opposition, the configuration of a planet when it is at an elongation of 180°, and thus appears opposite the Sun in the sky. A Saturnian opposition occurs every year—approximately every 378 days—and results in the planet appearing at its brightest. Both the Earth and Saturn orbit the Sun on eccentric orbits, which means their distances from the Sun vary over time, and therefore so do their distances from each other, hence varying the brightness of Saturn from one opposition to the next. Saturn also appears brighter when the rings are angled such that they are more visible. For example, during the opposition of 17 December 2002, Saturn appeared at its brightest due to the favorable orientation of its rings relative to the Earth,<ref name="opp2002">Template:Cite journal</ref> even though Saturn was closer to the Earth and Sun in late 2003.<ref name="opp2002" />

From time to time, Saturn is occulted by the Moon (that is, the Moon covers up Saturn in the sky). As with all the planets in the Solar System, occultations of Saturn occur in "seasons". Saturnian occultations will take place monthly for about a 12-month period, followed by about a five-year period in which no such activity is registered. The Moon's orbit is inclined by several degrees relative to Saturn's, so occultations will only occur when Saturn is near one of the points in the sky where the two planes intersect (both the length of Saturn's year and the 18.6-Earth-year nodal precession period of the Moon's orbit influence the periodicity).<ref name="Jon">Template:Cite news</ref>

In fiction

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Saturn has frequently appeared in fiction since at least 1752, when Voltaire published his novel Micromégas.<ref name="GreenwoodOuterPlanets">Template:Cite book</ref> Early works generally depicted it as solid,<ref name="WestfahlSaturn">Template:Cite book</ref> whereas Saturn is later correctly described as a gaseous planet. Saturn's moons are also featured in fiction, especially Titan.<ref name="StablefordSaturn">Template:Cite book</ref>

See also

• Statistics of planets in the Solar System
• Outline of Saturn

Further reading

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External links

• Saturn overview by NASA's Science Mission Directorate
• Saturn fact sheet at the NASA Space Science Data Coordinated Archive
• Saturnian System terminology by the IAU Gazetteer of Planetary Nomenclature
• Cassini-Huygens legacy website by the Jet Propulsion Laboratory
• Interactive 3D gravity simulation of the Cronian system Template:Webarchive