Saturn  

Saturn, as seen by Cassini
Orbital characteristics[1][2]
Epoch J2000
Aphelion	1,513,325,783 km 10.11595804 AU
Perihelion:	1,353,572,956 km 9.04807635 AU
Semi-major axis:	1,433,449,370 km 9.58201720 AU
Eccentricity:	0.055723219
Orbital period:	10,832.327 days 29.657 296 yr
Synodic period:	378.09 days[3]
Avg. orbital speed:	9.69 km/s[3]
Mean anomaly:	320.347750°
Inclination:	2.485240° 5.51° to Sun's equator
Longitude of ascending node:	113.642811°
Argument of perihelion:	336.013862°
Satellites:	60 confirmed (up to 63 seen)
Physical characteristics
Equatorial radius:	60,268 ± 4 km[4][5] 9.4492 Earths
Polar radius:	54,364 ± 10 km[4][5] 8.5521 Earths
Flattening:	0.09796 ± 0.00018
Surface area:	4.27×1010 km²[6][5] 83.703 Earths
Volume:	8.2713×1014 km³[3][5] 763.59 Earths
Mass:	5.6846×1026 kg[3] 95.152 Earths
Mean density:	0.687 g/cm³[3][5] (less than water)
Equatorial surface gravity:	8.96 m/s²[3][5] 0.914 g
Escape velocity:	35.5 km/s[3][5]
Sidereal rotation period:	0.439 – 0.449 day[7] (10 h 32 – 47 min)
Rotation velocity at equator:	9.87 km/s[5] 35,500 km/h
Axial tilt:	26.73°[3]
Right ascension of North pole:	2 h 42 min 21 s 40.589°[4]
Declination of North pole:	83.537°[4]
Albedo:	0.342 (bond) 0.47 (geom.)[3]
Surface temp.:    1 bar level    0.1 bar	min mean max 134 K[3] 84 K[3]
Apparent magnitude:	+1.2 to -0.24 [8]
Angular diameter:	14.5" — 20.1" [3] (excludes rings)
Adjectives:	Saturnian
Atmosphere [3]
Scale height:	59.5 km
Composition:	~96% Hydrogen (H2) ~3% Helium ~0.4% Methane ~0.01% Ammonia ~0.01% Hydrogen deuteride (HD) 0.0007% Ethane Ices: Ammonia water ammonium hydrosulfide(NH4SH)

Note: This article contains special characters.

Saturn (pronounced /ˈsætɚn/) 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 Saturnus, equated to the Greek Kronos (the Titan father of Zeus) and the Babylonian Ninurta. Saturn's symbol represents the god's sickle (Unicode: ♄). The day in the week Saturday gets its name from the planet. Saturn may refer to: Saturn, the sixth planet from the Sun in the Solar System Saturn (mythology), the Roman god after whom the planet is named Saturn as a symoblic planet and element in astrology and alchemy Saturn, the Bringer of Old Age, a movement in Gustav Holsts The... Image File history File links Saturn_symbol. ... Image File history File links Size of this preview: 800 × 409 pixel Image in higher resolution (8888 × 4544 pixel, file size: 5. ... Cassini–Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... A diagram of Keplerian orbital elements. ... The astronomical unit (AU or au or a. ... A diagram of Keplerian orbital elements. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... (This page refers to eccitricity in astrodynamics. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... Look up day in Wiktionary, the free dictionary. ... In astronomy, a Julian year is a unit of time defined as exactly 365. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ... In the study of orbital dynamics the mean anomaly is a measure of time, specific to the orbiting body p, which is a multiple of 2π radians at and only at periapsis. ... For the science fiction novella by William Shunn, see Inclination (novella). ... The Longitude of the ascending node (☊, also noted Ω) is one of the orbital elements used to specify the orbit of an object in space. ... The argument of periapsis (ω) is the orbital element describing the angle between an orbiting bodys ascending node (the point where the body crosses the plane of reference from South to North) and its periapsis (the point of closest approach to the central body), measured in the orbital plane and... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... The Saturnian system (photographic montage) Saturn has 60 confirmed natural satellites, plus three hypothetical moons. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... A geographical pole is either of two fixed points on the surface of a spinning body or planet, at 90 degrees from the equator, based on the axis around which a body spins. ... The flattening, ellipticity, or oblateness of an oblate spheroid is the relative difference between its equatorial radius a and its polar radius b: The flattening of the Earth is 1:298. ... In mathematics, a spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ... For other uses, see Volume (disambiguation). ... For other uses, see Mass (disambiguation). ... For other uses, see Density (disambiguation). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ... Space Shuttle Atlantis launches on mission STS-71. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ... For other uses, see Albedo (disambiguation). ... The Bond albedo is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space. ... The geometric albedo of an astronomical body is the ratio of its total brightness at zero phase angle to that of an idealised fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. ... For other uses, see Temperature (disambiguation). ... For other uses, see Kelvin (disambiguation). ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... The angular diameter of an object as seen from a given position is the diameter measured as an angle. ... A scale height is a term often used in scientific contexts for a distance over which a quantity decreases by a factor of e. ... This article is about the chemistry of hydrogen. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Methane is a chemical compound with the molecular formula . ... For other uses, see Ammonia (disambiguation). ... Hydrogen deuteride is a bi-atomic compund of the two isotopes of hydrogen: the majority isotope 1H protium and 2H deuterium. ... This article is about a chemical compound. ... For other uses, see Ammonia (disambiguation). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Ammonium sulfide, (NH4)2S, is obtained, in the form of micaceous crystals, by passing hydrogen sulfide mixed with a slight excess of ammonia through a well-cooled vessel; the hydrosulfide NH4·HS is formed at the same time. ... This article is about the astronomical term. ... Sol redirects here. ... This article is about the Solar System. ... For other uses, see Jupiter (disambiguation). ... For other uses, see Jupiter (disambiguation). ... For other uses, see Uranus (disambiguation). ... For other uses, see Neptune (disambiguation). ... This article does not cite any references or sources. ... Saturnus, Caravaggio, 16th c. ... Cronus is not to be confused with Chronos, the personification of time. ... For other uses, see Zeus (disambiguation). ... Ninurta Lord Plough in Sumerian and Akkadian mythology was the god of Nippur, identified with Ningirsu with whom he may always have been identical. ... Using a sickle A sickle is a curved, hand-held agricultural tool typically used for harvesting grain crops before the advent of modern harvesting machinery. ... The Unicode Standard, Version 5. ... This article or section does not cite its references or sources. ...

The planet Saturn is primarily composed of hydrogen, with small proportions of helium and trace elements.^[9] The interior consists of a small 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 speeds 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. This article is about the chemistry of hydrogen. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Metallic hydrogen results when hydrogen is sufficiently compressed and undergoes a phase change; it is an example of degenerate matter. ... For other uses, see Atmosphere (disambiguation). ... This article or section does not adequately cite its references or sources. ... Magnetic field lines shown by iron filings Magnetostatics Electrodynamics Electrical Network Tensors in Relativity This box:      In physics, the magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles. ...

Saturn has a prominent system of rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Sixty known moons orbit the planet. Titan, Saturn's largest and the Solar System's second largest moon (after Ganymede), is larger than the planet Mercury and is the only moon in the Solar System to possess a significant atmosphere.^[10] The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... This article is about water ice. ... Debris (French, pronounced (IPA) dibri) is a word used to describe the remains of something that has been otherwise destroyed. ... “Space dust” redirects here. ... Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ... This article is about the natural satellite of Jupiter. ... [[Link titleBold text // ]] This article is about the planet. ...

Physical characteristics

The Earth is one of Saturn's major satellites.

Due to a combination of its low density, rapid rotation, and fluid state, Saturn is an oblate spheroid; that is, it is flattened at the poles and bulges at the equator. Its equatorial and polar radii differ by almost 10%— 60268 km vs. 54364 km.^[3] The other gas planets are also oblate, but to a lesser extent. Saturn is the only planet of the Solar System that is less dense than water. Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm³ due to the gaseous atmosphere. Saturn is only 95 Earth masses,^[3] compared to Jupiter, which is 318 times the mass of the Earth^[11] but only about 20% larger than Saturn.^[12] Image File history File linksMetadata Download high resolution version (1024x888, 266 KB)Rough comparison of sizes of Saturn and Earth. ... Image File history File linksMetadata Download high resolution version (1024x888, 266 KB)Rough comparison of sizes of Saturn and Earth. ... An oblate spheroid is ellipsoid having a shorter axis and two equal longer axes. ... In mathematics, a spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... For other uses, see Density (disambiguation). ... The planetary core consists of the innermost layer(s) of a planet. ... For explanation of specific gravity as it relates to renal function, see Specific gravity (kidney). ...

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.^[13] The upper clouds on Saturn are composed of ammonia crystals, while the lower level clouds appear to be composed of either ammonium hydrosulfide (NH₄SH) or water.^[14] The atmosphere of Saturn is significantly deficient in helium relative to the abundance of the elements in the Sun. For other uses, see Ammonia (disambiguation). ... Acetylene (systematic name: ethyne) is a hydrocarbon belonging to the group of alkynes. ... This article is about a chemical compound. ... This article is about the chemical. ... Methane is a chemical compound with the molecular formula . ... Ammonium sulfide, (NH4)2S, is obtained, in the form of micaceous crystals, by passing hydrogen sulfide mixed with a slight excess of ammonia through a well-cooled vessel; the hydrosulfide NH4·HS is formed at the same time. ...

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.^[15]

Internal structure

Saturn's temperature emissions: the prominent hot spot at the bottom of the image is at Saturn's south pole.

Saturn's interior is similar to that of Jupiter, having a small rocky 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. ^[16] Traces of various ices are also present. The core region is estimated to be about 9–22 times the mass of the Earth.^[17] 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.^[18] Infrared image of saturn showing a warm polar vortex File links The following pages link to this file: Saturn (planet) Categories: NASA images ... Infrared image of saturn showing a warm polar vortex File links The following pages link to this file: Saturn (planet) Categories: NASA images ... Metallic hydrogen results when hydrogen is sufficiently compressed and undergoes a phase change; it is an example of degenerate matter. ... The Kelvin-Helmholtz mechanism is an astronomical event that occurs when the surface of a star or a planet cools. ... For other uses, see Friction (disambiguation). ...

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.^[19] Saturn's winds are among the Solar System's fastest. Voyager data indicate peak easterly winds of 500 m/s (1,800 km/h).^[9] Saturn's finer cloud patterns were not observed until the Voyager flybys. Since then, however, Earth-based telescopy has improved to the point where regular observations can be made. Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ... Voyager Project redirects here. ... This article is about Earth as a planet. ... This article does not cite any references or sources. ...

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.^[20] 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.^[21] The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... The Great White Spot on Saturn, named by analogy from Jupiters Great Red Spot, is a name given to storms that are large enough to be visible by telescope from earth by their characteristic white appearance. ... Illumination of Earth by the sun on the northern hemisphere summer solstice The summer solstice is an astronomical term regarding the position of the sun in relation to the celestial equator. ...

In recent images from the 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. Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... Rayleigh scattering causing the blue hue of the sky and the reddening at sunset Rayleigh scattering (named after Lord Rayleigh) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ...

Saturn's northern hemisphere, as seen by Cassini. Notice the planet's blue appearance through the ring.

North polar hexagonal cloud feature, discovered by Voyager 1 and confirmed in 2006 by Cassini.^[22]

Astronomers using infrared imaging have shown that Saturn has a warm polar vortex and that it is the only such planet 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.^[23] Image File history File links Size of this preview: 674 × 600 pixelsFull resolution (1010 × 899 pixel, file size: 44 KB, MIME type: image/jpeg)source Mimas and Saturns rings, taken by Cassini. ... Image File history File links Size of this preview: 674 × 600 pixelsFull resolution (1010 × 899 pixel, file size: 44 KB, MIME type: image/jpeg)source Mimas and Saturns rings, taken by Cassini. ... Image File history File links Size of this preview: 688 × 599 pixel Image in higher resolution (15750 × 13717 pixel, file size: 5. ... Image File history File links Size of this preview: 688 × 599 pixel Image in higher resolution (15750 × 13717 pixel, file size: 5. ... For the album by The Verve, see Voyager 1 (album). ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... For other uses, see Infrared (disambiguation). ... The polar vortex is a persistent, large-scale cyclone located near the Earths poles, in the middle and upper troposphere and the stratosphere. ...

A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.^[24][25] 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.^[26] 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.^[27] 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).^[28] For other uses, see Hexagon (disambiguation). ... The National Aeronautics and Space Administration (NASA) (IPA [ˈnæsÉ™]) is an agency of the United States government, responsible for the nations public space program. ... This article is about weather phenomena. ... Eye of Typhoon Odessa, Pacific Ocean, August 1985 The eyewall is the region of a tropical cyclone with the strongest winds, the tallest clouds, and the heaviest rain. ... A false-color image of the Great Red Spot of Jupiter from Voyager 1. ... Galileo is prepared for mating with the IUS booster Galileo and Inertial Upper Stage being deployed after being launched by the Space Shuttle Atlantis on the STS-34 mission Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. ...

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).^[29] Polygon shapes have been replicated in spinning buckets of fluid in a laboratory.^[30]

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 (20 µT)—is approximately one twentieth than that of the field around Jupiter and slightly weaker than Earth's magnetic field.^[31] As a result the cronian magnetosphere is much smaller than jovian and extends slightly beyond the orbit of Titan.^[32] 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.^[32] Similarly to the 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.^[31] The Earths magnetic field, which is approximately a dipole. ... The gauss, abbreviated as G, is the cgs unit of magnetic flux density (B), named after the German mathematician and physicist Carl Friedrich Gauss. ... The tesla (symbol T) is the SI derived unit of magnetic flux density (or magnetic induction). ... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ... Sol redirects here. ...

Orbit and rotation

Animation of hexagonal cloud feature.

The average distance between Saturn and the Sun is over 1,400,000,000 km (9 AU). With an average orbital speed of 9.69 km/s,^[3] it takes Saturn 10,759 Earth days (or about 29½ years), to finish one revolution around the Sun.^[3] The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth.^[3] Because of an eccentricity of 0.056, the distance between Saturn and the Sun varies by approximately 155,000,000 km between perihelion and aphelion,^[3] which are the nearest and most distant points of the planet along its orbital path, respectively. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Sol redirects here. ... The astronomical unit (AU or au or a. ... Look up Eccentricity in Wiktionary, the free dictionary. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...

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 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).^[33] 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. 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.^[34][35][36] Atmosphere Surface pressure: trace, significant spatial variability[8][9] Composition: 91% Water vapour 4% Nitrogen 3. ...

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. ^[37]

Planetary rings

The rings of Saturn (here: as imaged by Cassini in 2007) are the most spectacular in the Solar System.^[16]

Main article: Rings of Saturn

Saturn is probably best known for its system of planetary rings, which makes it the most visually remarkable object in the solar system.^[16] Image File history File links Size of this preview: 800 × 569 pixel Image in higher resolution (4088 × 2908 pixel, file size: 655 KB, MIME type: image/jpeg) Blinding Saturn Taking in the rings in their entirety was the focus of this particular imaging sequence. ... Image File history File links Size of this preview: 800 × 569 pixel Image in higher resolution (4088 × 2908 pixel, file size: 655 KB, MIME type: image/jpeg) Blinding Saturn Taking in the rings in their entirety was the focus of this particular imaging sequence. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... A planetary ring is a ring of dust and other small particles orbiting around a planet in a flat disc-shaped region. ...

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 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.^[38] Then, in 1613, they reappeared again, further confusing Galileo.^[39] Galileo redirects here. ... This article does not cite any references or sources. ... Cosimo II de Medici, Grand Duke of Tuscany (12 May 1590 – 28 February 1621) ruled as Grand Duke of Tuscany from 1609 to 1621. ... The term zodiac denotes an annual cycle of twelve stations along the ecliptic, the apparent path of the sun across the heavens through the constellations that divide the ecliptic into twelve equal zones of celestial longitude. ...

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."^[39] Christiaan Huygens (pronounced in English (IPA): ; in Dutch: ) (April 14, 1629 – July 8, 1698), was a Dutch mathematician, astronomer and physicist; born in The Hague as the son of Constantijn Huygens. ...

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 Cassini Division. This division in itself is a 4,800 km wide region between the A Ring and B Ring.^[40] Giovanni Domenico (Jean-Dominique) Cassini Portrait Giovanni Domenico Cassini (June 8, 1625–September 14, 1712) was an Italian astronomer, engineer, and astrologer. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ...

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.^[41] Maxwell's theory was proven correct in 1895 through spectroscopic studies of the rings carried out by James Keeler of Lick Observatory. James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and theoretical physicist from Edinburgh, Scotland, UK. His most significant achievement was aggregating a set of equations in electricity, magnetism and inductance — eponymously named Maxwells equations — including an important modification (extension) of the Ampères... James Edward Keeler (September 10, 1857 – August 12, 1900) was an American astronomer. ... The Lick Observatory is an astronomical observatory, owned and operated by the University of California. ...

Physical characteristics

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, whose cryovolcanos 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 one kilometer in thickness, and are composed of 93 percent water ice with a smattering of tholin impurities, and 7 percent amorphous carbon.^[42] They range in size from specks of dust to the size of a small automobile.^[43] 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 forces (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 nebular material from which Saturn formed. This theory is not widely accepted today, since Saturn's rings are thought to be unstable over periods of millions of years and therefore of relatively recent origin. Image File history File links Download high-resolution version (890x524, 13 KB) Other versions http://photojournal. ... Image File history File links Download high-resolution version (890x524, 13 KB) Other versions http://photojournal. ... Atmosphere Surface pressure: trace, significant spatial variability[8][9] Composition: 91% Water vapour 4% Nitrogen 3. ... Ganesa Macula, a dark feature on Saturns moon Titan, might be a cryovolcanic dome. ... Porro-prism binoculars with central focusing Binocular telescopes, or binoculars, (also known as field glasses) are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. ... This article is about water ice. ... Tholin is a heteropolymer formed by solar ultraviolet irradiation of simple organic compounds such as methane or ethane. ... For other uses, see Carbon (disambiguation). ... Édouard Albert Roche (1820-1883) was a French scientist. ... Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... The Roche limit, sometimes referred to as the Roche radius, is the distance within which a celestial body held together only by its own gravity will disintegrate due to a second celestial bodys tidal forces exceeding the first bodys gravitational self-attraction. ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ... For other uses, see Asteroid (disambiguation). ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ...

While the largest gaps in the rings, such as the Cassini Division and Encke Division, can be seen from Earth, the Voyager spacecrafts discovered the rings to have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise from the gravitational pull of Saturn's many moons in several different ways. Some gaps are cleared out by the passage of tiny moonlets such as Pan, many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small shepherd satellites such as Prometheus and Pandora. Other gaps arise from resonances between the orbital period of particles in the gap and that of a more massive moon further out; 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. The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... Atmosphere none Pan (pan, Greek Πάν) is a moon of Saturn, named after the god Pan. ... A planetary ring is a ring of dust and other small particles orbiting around a planet in a flat disc-shaped region. ... Prometheus (proe-mee-thee-us, Greek Προμηθέας) is a moon of Saturn. ... Pandora (pan-dor-a, Greek Πανδώρα) is a moon of Saturn. ... In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other. ... Mimas (mee-məs or mye-məs, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ...

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 (O₂) produced when ultraviolet light from the Sun disintegrates water ice in the rings. Chemical reactions between water molecule fragments and further ultraviolet stimulation create and eject, among other things O₂. According to models of this atmosphere, H₂ is also present. The O₂ and H₂ 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.^[44] The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O₂, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic ions that bombard water molecules ejected by Saturn's moon Enceladus. This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope.^[45] General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... For other uses, see Ultraviolet (disambiguation). ... This article is about the electrically charged particle. ... Atmosphere Surface pressure: trace, significant spatial variability[8][9] Composition: 91% Water vapour 4% Nitrogen 3. ...

Saturn shows complex patterns in its brightness.^[8] Most of the variability is due to the changing aspect of the rings,^{[46] [47]} 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.^[48]

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

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 gravitational forces. The Voyager spacecraft found radial features in the 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.^[49]The spokes appear dark against the lit side of the rings, and light when seen against the unlit side. It is assumed that they are microscopic dust particles that have levitated away from the ring plane and that they are connected to electromagnetic interactions, as they rotate almost synchronously with the magnetosphere of Saturn. However, the precise mechanism generating the spokes is still unknown.^[50] Image:Voyager ring spokes. ... Image:Voyager ring spokes. ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... Gravity redirects here. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... This article or section should be merged with Celestial Mechanics Astrodynamics is the study and creation of orbits, especially those of artificial satellites. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ...

These are three images of the spokes imaged by 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.^[51] Image File history File links Size of this preview: 800 × 205 pixelsFull resolution (1000 × 256 pixel, file size: 54 KB, MIME type: image/jpeg) Saturn Ring Spokes captured by Cassini on Sept. ... Image File history File links Size of this preview: 800 × 205 pixelsFull resolution (1000 × 256 pixel, file size: 54 KB, MIME type: image/jpeg) Saturn Ring Spokes captured by Cassini on Sept. ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... For other uses, see Equinox (disambiguation). ... is the 248th day of the year (249th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ...

Natural satellites

Main article: Saturn's natural satellites

Four of Saturn's moons: Dione, Titan, Prometheus (edge of rings), Telesto (top center)

Saturn has a large number of moons. The precise figure is uncertain, 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, a total of 60 individual moons have been identified, plus 3 unconfirmed moons that could be small dust clumps in the rings. Out of those, 48 have been named. Many of the moons are very small: out of 60, 34 are less than 10 km in diameter, and another 13 less than 50 km.^[52] Only seven of them are massive enough to have collapsed into spheroids under their own gravitation. These are compared with Earth's moon in the table below. The Saturnian system (photographic montage) Saturn has 60 confirmed natural satellites, plus three hypothetical moons. ... Image File history File links Download high resolution version (962x877, 30 KB) Summary Original Caption Released with Image: In a rare moment, the Cassini spacecraft captured this enduring portrait of a near-alignment of four of Saturns restless moons. ... Image File history File links Download high resolution version (962x877, 30 KB) Summary Original Caption Released with Image: In a rare moment, the Cassini spacecraft captured this enduring portrait of a near-alignment of four of Saturns restless moons. ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ... Prometheus (proe-mee-thee-us, Greek Προμηθέας) is a moon of Saturn. ... Atmosphere none Telesto IPA: , Greek Τελεστώ) is a moon of Saturn. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ...

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.^[10] 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.^[53]

Traditionally, most of Saturn's other moons are named after 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,^[54] because they were the sisters and brothers of Cronos (the Greek Saturn). This article is about the race of Titans in Greek mythology. ... John Herschel Sir John Frederick William Herschel (7 March 1792 – 11 May 1871) was an English mathematician and astronomer. ... For other persons named William Herschel, see William Herschel (disambiguation). ... Cronus is not to be confused with Chronos, the personification of time. ...

For a timeline of discovery dates, see