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Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman godSaturn, equated to the Greek Cronus (the Titan father of Zeus), the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol (?) represents the Roman god's sickle.HP 586006-321 Battery

Saturn, along with Jupiter, Uranus and Neptune, is classified as a gas giant. Together, these four planets are sometimes referred to as the Jovian, meaning "Jupiter-like", planets. Saturn has an average radius about 9 times larger than the Earth's. While only 1/8 the average density of Earth, due to its larger volume, Saturn's mass is just over 95 times greater than Earth's.HP 586006-361 Battery

Because of Saturn's large mass and resulting gravitation, the conditions produced on Saturn are extreme if compared to Earth. The interior of Saturn is probably composed of a core of iron, nickel, silicon and oxygen compounds, surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium and finally, an outer gaseous layer.HP 586028-341 Battery

Electrical current within the metallic-hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is slightly weaker than Earth's magnetic field and approximately one-twentieth the strength of the field around Jupiter. The outer atmosphere is generally bland in appearance, although long-lived features can appear.HP h588178-141 Battery

Wind speeds on Saturn can reach 1,800 km/h, significantly faster than those on Jupiter.

Saturn has nine rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two known moons orbit the planet; fifty-three are officially named. HP 593553-001 Battery

This is not counting hundreds of "moonlets" within the rings. Titan, Saturn's largest and the Solar System's second largest moon (after Jupiter's Ganymede), is larger than the planet Mercury and is the only moon in the Solar System to possess a significant atmosphere.HP 593554-001 Battery

Physical characteristics

Due to a combination of its lower density, rapid rotation and fluid state, Saturn is an oblate spheroid; that is, it is flattened at the poles and bulges at the equator. Its equatorial and polar radii differ by almost 10%—60,268 km versus 54,364 km.HP HSTNN-CB0W Battery

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.HP HSTNN-CB0X Battery

Saturn is only 95 Earth masses, compared to Jupiter, which is 318 times the mass of the Earth but only about 20% larger than Saturn. 

Internal structure

Though there is no direct information about Saturn's internal structure, it is thought that its interior is similar to that of Jupiter, having a small rocky core surrounded mostly by hydrogen and helium. HP HSTNN-I79C Battery

The rocky core is similar in composition to the Earth, but more dense. This is surrounded by a thicker liquidmetallic hydrogen layer, followed by a liquid hydrogen/helium layer and a gaseous atmosphere in the outermost 1000 km. Traces of various volatiles are also present. The core region is estimated to be about 9–22 times the mass of the Earth.HP HSTNN-I81C Battery

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 this 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. HP HSTNN-IB0N Battery

It is proposed that an additional mechanism might be at play whereby Saturn generates some of its heat through the "raining out" of droplets of helium deep in its interior, thus releasing heat by friction as they fall down through the lighter hydrogen.

Atmosphere

The outer atmosphere of Saturn consists of 96.3% molecular hydrogen and 3.25% helium.HP HSTNN-IB0X Battery

Trace amounts of ammonia, acetylene, ethane, phosphine and methane have also been detected. 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.HP HSTNN-LB0W Battery

The atmosphere of Saturn is significantly deficient in helium relative to the abundance of the elements in the Sun.

The quantity of elements heavier than helium are not known precisely, but the proportions are assumed to match the primordial abundances from the formation of the Solar System. HP HSTNN-OB0X Battery

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.

Cloud layers

Saturn's 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. HP HSTNN-OB0Y Battery

At depth, extending for 10 km and with a temperature of ?23 °C, is a layer made up of water ice. Above this layer is probably a layer of ammonium hydrosulfide ice, which extends for another 50 km and is approximately ?93 °C. Eighty kilometers above that layer are ammonia ice clouds, where the temperatures are roughly ?153 °C. HP HSTNN-Q61C Battery

Near the top of the atmosphere, extending for some 200 km to 270 km above the visible ammonia clouds, are gaseous hydrogen and helium. Saturn's winds are among the Solar System's fastest. Voyager data indicate peak easterly winds of 500 m/s (1800 km/h).HP HSTNN-Q62C Battery

Saturn's finer cloud patterns were not observed until the Voyager flybys. Since then, Earth-based telescopy has improved to the point where regular observations can be made.

Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter.HP HSTNN-YB0X Battery

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, HP NBP6A174B1 Battery

roughly every 30 Earth years, around the time of the northern hemisphere's summer solstice.[30] 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.HP HSTNN-YB0X Battery

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 byRayleigh scattering.HP NBP6A174 Battery

Infrared imaging has shown that Saturn's south pole has a warm polar vortex, the only example of such a phenomenon known to date in the Solar System.[33]Whereas temperatures on Saturn are normally ?185 °C, temperatures on the vortex often reach as high as ?122 °C, believed to be the warmest spot on Saturn.HP NBP6A174B1 Battery

North pole hexagonal cloud pattern

A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.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.HP NBP6A175 Battery

NASAreported in November 2006 that the Cassini spacecraft observed a 'hurricane-like' storm locked to the south pole that had a clearly defined eyewall. This observation is particularly notable because eyewall clouds had not previously been seen on any planet other than Earth. HP NBP6A175B1 Battery

For example, images from the Galileospacecraft did not show an eyewall in the Great Red Spot of Jupiter.

The straight sides of the northern polar hexagon are each approximately 13,800 km (8,600 mi) long, making them larger than the diameter of the Earth. HP WD548AA Battery

The entire structure rotates with a period of 10h 39m 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.HP WD549AA Battery

The pattern's origin is a matter of much speculation. Most astronomers seem to think it was caused by some standing-wave pattern in the atmosphere; but the hexagon might be a novel aurora. Polygonal shapes have been replicated in spinning buckets of fluid in a laboratory.HP Envy 17 Notebook PC Battery

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.HP Envy 17T Battery

As a result Saturn's magnetosphere is much smaller than Jupiter's and extends slightly beyond the orbit of Titan. 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.HP HSTNN-Q61C Battery

Similarly to those of other planets, this magnetosphere is efficient at deflecting the solar wind particles from the Sun. The moon Titan orbits within the outer part of Saturn's magnetosphere and contributes plasma from theionized particles in Titan's outer atmosphere.HP GSTNN-Q62C Battery

Orbit and rotation

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, it takes Saturn 10,759 Earth days (or about 29½ years), to finish one revolution around the Sun.HP HSTNN-IB1E Battery

The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth.[5] Because of an eccentricity of 0.056, the distance between Saturn and the Sun varies by approximately 155,000,000 km between perihelion andaphelion,[5] which are the nearest and most distant points of the planet along its orbital path, respectively.HP HSTNN-IB0X Battery

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.HP HSTNN-OB0X Battery

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.HP HSTNN-YB0X Battery

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). The cause of the change is unknown—HP 586006-361 Battery

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, HP NBP6A174 Battery

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. HP NBP6A174B1 Battery

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. At the time it was stated that there is no currently known method of determining the rotation rate of Saturn's core. HP 588178-141 Battery

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.

Planetary rings

Saturn is probably best known for its system of planetary rings, which makes it the most visually remarkable object in the solar system.HP Pavilion dv5 Adapter

The rings extend from 6,630 km to 120,700 km above Saturn's equator, average approximately 20 meters in thickness and are composed of 93% water ice with a smattering oftholin impurities and 7% amorphous carbon.[46] The particles that make up the rings range in size from specks of dust to the size of a small automobile.Sony NP-F330 Battery

There are two main theories regarding the origin of the rings. One theory is that the rings are remnants of a destroyed moon of Saturn. The second theory is that the rings are left over from the original nebular material from which Saturn formed. Some ice in the central rings comes from the moon Enceladus' ice volcanoes.Asus Eee PC 904HA Adapter

Beyond the main rings at a distance of 12 million km from the planet is the sparse Phoebe ring, which is tilted at an angle of 27° to the other rings and, likePhoebe, orbits in retrograde fashion.

Natural satellites

Saturn has at least 62 moons. Titan, the largest, comprises more than 90% of the mass in orbit around Saturn, including the rings.Nikon D80  Battery

Saturn's second largest moon, Rhea, may have a tenuous ring system of its own.[51] Many of the other moons are very small: 34 are less than 10 km in diameter and another 14 less than 50 km.[52] Traditionally, most of Saturn's moons have been named after Titans of Greek mythology.Sony PCGA-AC19V9 Adapter

History of exploration

There are three main phases of observation and exploration of Saturn. The first era was ancient observations (such as with the naked eye), before the invention of the modern telescopes. Starting in the 17th century progressively more advanced telescopic observations from earth have been made. Dell T555C Battery

The other type is visitation by spacecraft, either by orbiting or flyby. In the 21st century observations continue from the earth (or earth orbiting observatories) and from the Cassini orbiter at Saturn.

Ancient observations

Saturn has been known since prehistoric times. In ancient times, it was the most distant of the five known planets in the solar system (excluding Earth) and thus a major character in various mythologies.HP Pavilion DV6-3013SL Battery

Babylonian astronomers systematically observed and recorded the movements of Saturn. In ancient Roman mythology, the god Saturnus, from which the planet takes its name, was the god of the agricultural and harvest sector.[55] The Romans considered Saturnus the equivalent of the Greek god Cronus.HP Pavilion DV7-2085EL Battery

The Greeks had made the outermost planet sacred to Cronus,[56] and the Romans followed suit.

Ptolemy, a Greek living in Alexandria,[57] observed an opposition of Saturn, which was the basis for his determination of the elements of its orbit.HP Pavilion DV9700 Battery

In Hindu astrology, there are nine astrological objects, known as Navagrahas. Saturn, one of them, is known as "Shani", judges everyone based on the good and bad deeds performed in life. In the 5th century CE, the Indian astronomical textSurya Siddhantaestimated the diameter of Saturn as 73,882 miles,HP Mini 702EA Battery

an error of less than 1% from the currently accepted value of 74,580 miles, for which there exist several possible explanations.[59]Ancient Chinese and Japanese culture designated the planet Saturn as the earth star (??). This was based on Five Elements which were traditionally used to classify natural elements.HP Pavilion DV7-1120EO Battery

In ancient Hebrew, Saturn is called 'Shabbathai'. Its angel is Cassiel. Its intelligence or beneficial spirit is Agiel (layga) and its spirit (darker aspect) is Zazel (lzaz). In Ottoman Turkish, Urdu and Malay, its name is 'Zuhal', derived from Arabic ???.HP Compaq 491278-001 Battery

European observations (17th–19th centuries)

Saturn's rings require at least a 15 mm diameter telescope to resolve and thus were not known to exist until Galileo first saw them in 1610. He thought of them as two moons on Saturn's sides. It was not until Christian Huygens used greater telescopic magnification that this notion was refuted. HP Pavilion DV6-1030US Battery

Huygens also discovered Saturn's moon Titan. Some time later, Giovanni Domenico Cassini discovered four other moons: Iapetus, Rhea, Tethys and Dione. In 1675, Cassini also discovered the gap now known as the Cassini Division.HP Compaq 490306-001 Battery

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.HP Pavilion DV5-1211EM Battery

In 1899 William Henry Pickering discovered Phoebe, a highly irregular satellite that does not rotate synchronously with Saturn as the larger moons do. Phoebe was the first such satellite found and it takes more than a year to orbit Saturn in a retrograde orbit.HP EliteBook 2530P Battery

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.

Pioneer 11 flyby

Saturn was first visited by Pioneer 11 in September 1979. It flew within 20 000 km of the planet's cloud tops. HP Pavilion DV4385EA Battery

Low resolution images were acquired of the planet and a few of its moons; the resolution of the images was not good enough to discern surface features. The spacecraft also studied the rings; among the discoveries were the thin F-ring and the fact that dark gaps in the rings are bright when viewed towards the Sun, in other words, they are not empty of material. Compaq PP2100 Battery

Pioneer 11 also measured the temperature of Titan.[64] The Pioneer images of Saturn were significantly dimmer as the planet and its moons only receive 14.90 W/m^2 (Solar Irradiance) where Jupiter gets around 400 W/m^2 . Camera technology would be improved in subsequent missions to the planet.HP Compaq KU532AA Battery

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, greatly increasing our knowledge of the atmosphere of the moon.HP Pavilion DV6-1270EQ Battery

It also proved that Titan's atmosphere is impenetrable in visible wavelengths; so, no surface details were seen. The flyby also changed the spacecraft's trajectory out from the plane of the solar system.

Almost a year later, in August 1981, Voyager 2 continued the study of the Saturn system. HP Pavilion DV4385EA Battery

More close-up images of Saturn's moons were acquired, as well as evidence of changes in the atmosphere and the rings. Unfortunately, during the flyby, the probe's turnable camera platform stuck for a couple of days and some planned imaging was lost. Saturn's gravity was used to direct the spacecraft's trajectory towards Uranus.HP Compaq Business  NC4400 Battery

The probes discovered and confirmed several new satellites orbiting near or within the planet's rings. They also discovered the small Maxwell Gap (a gap within the C Ring) and Keeler gap (a 42 km wide gap in the A Ring).HP Pavilion ZD8227 Battery

Cassini-Huygens spacecraft

On July 1, 2004, the Cassini–Huygens space probe performed the SOI (Saturn Orbit Insertion) maneuver and entered into orbit around Saturn. Before the SOI, Cassini had already studied the system extensively. In June 2004, it had conducted a close flyby of Phoebe, sending back high-resolution images and data.Nikon D200 Battery

Cassini's flyby of Saturn's largest moon, Titan, has captured radar images of large lakes and their coastlines with numerous islands and mountains. The orbiter completed two Titan flybys before releasing the Huygens probe on December 25, 2004.Acer PA-1650-02 Adapter

Huygens descended onto the surface of Titan on January 14, 2005, sending a flood of data during the atmospheric descent and after the landing. During 2005, Cassini conducted multiple flybys of Titan and icy satellites. Cassini's last Titan flyby started on March 23, 2008.Sony CYBER-SHOT DSC-T10  Battery

Since early 2005, scientists have been tracking lightning on Saturn. The power of the lightning is approximately 1000 times that of lightning on Earth.

In 2006, NASA reported that the Cassini probe found evidence of liquid water reservoirs that erupt in geysers on Saturn's moon Enceladus. HP Compaq Business 6715b Battery

Images had also shown particles of water in its liquid state emitted by icy jets and towering plumes. According to Dr. Andrew Ingersoll, California Institute of Technology, "Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust. Kodak KLIC-7004 Battery

What's different here is that pockets of liquid water may be no more than tens of meters below the surface."[67] In May 2011, NASA scientists at an Encedalus Focus Group Conference reported that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".Acer Aspire 5920G Adapter

Cassini probe photographs have led to other significant discoveries. They 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 believed to be the crashing of a meteoroid off two of the moons of Saturn.Canon Digital IXUS 90 IS Battery

In July 2006, Cassini images provided evidence of hydrocarbon lakes near Titan's north pole, the presence of which were confirmed in January 2007. In March 2007, additional images near Titan's north pole discovered hydrocarbon "seas", the largest of which is almost the size of the Caspian Sea.HP 2133 Mini-Note PC Adapter

In October 2006, the probe detected a 8,000 km diameter hurricane with an eyewall at Saturn's South Pole.

From 2004 to November 2, 2009, the probe discovered and confirmed 8 new satellites. Its primary mission ended in 2008 when the spacecraft had completed 74 orbits around the planet. Toshiba PA3536U-1BRS Battery

The probe's mission was extended to September 2010 and then extended again to 2017, to study a full period of Saturn's seasons.

Observation

Saturn is the most distant of the five planets easily visible to the naked eye, the other four being Mercury, Venus, Mars and Jupiter (Uranus and occasionally 4 Vesta are visible to the naked eye in very dark skies).HP Compaq Business NX6110 Battery

It was the last planet known to early astronomers until Uranus was discovered in 1781. Saturn appears to the naked eye in the night sky as a bright, yellowish point of light whose magnitude is usually between +1 and 0 and takes approximately 29½ years to make a complete circuit of the ecliptic against the background constellations of the zodiac. HP Pavilion DV9000 Adapter

Most people will require optical aid (large binoculars or a telescope) magnifying at least 20× to clearly resolve Saturn's rings.

While it is a rewarding target for observation for most of the time it is visible in the sky, Saturn and its rings are best seen when the planet is at or near opposition (the configuration of a planet when it is at an elongation of 180° and thus appears opposite the Sun in the sky). Dell Studio 1537 Battery

During the opposition of December 17, 2002, Saturn appeared at its brightest due to a favorable orientation of its rings relative to the Earth,[74] even though Saturn was closer to the Earth and Sun in late 2003.

In culture

Saturn in astrology (Saturn symbol.svg) is the ruling planet of Capricorn and, traditionally, Aquarius.HP PPP009H Adapter

Saturn, the Bringer of Old Age is a movement in Gustav Holst's The Planets.

The Saturn family of rockets were developed by a team of mostly German rocket scientists led by Wernher von Braun to launch heavy payloads to Earth orbit and beyond. Originally proposed as a military satellite launcher, they were adopted as the launch vehicles for the Apollo program.Sony VGP-BPS8 Battery

Sega's video game console, the Sega Saturn, is named after the planet and features a ringed planet as its logo.

The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometre across, to the enormous Titan, which is larger than the planet Mercury. Dell PA-12 Adapter

Saturn has 62 moons with confirmed orbits, fifty-three of which have names, and only thirteen of which have diameters larger than 50 kilometres. Saturn has seven moons that are large enough to become spherical, and dense rings with complex orbital motions of their own. Sony Cyber-shot DSC-T7/B  Battery

Particularly notable among Saturn's moons are Titan, the second largest moon in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape including hydrocarbon lakes and dry river networks, and Enceladus, which emits jets of gas and dust and may harbor liquid water under its south pole region.Dell LATITUDE M65 Battery

Twenty-four of Saturn's moons are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane. They include the seven major satellites, four small moons which exist in a Trojan orbit with larger moons, two mutually co-orbital moons and two moons which act as shepherds of Saturn's F Ring. HP Compaq 6720s Adapter

Two other known regular satellites orbit within gaps in Saturn's rings. The relatively large Hyperion is locked in a resonance with Titan. The remaining regular moons orbit near the outer edge of the A Ring, within G Ring and between the major moonsMimas and Enceladus. Acer AS07B41 Battery

The regular satellites are traditionally named after Titans and Titanesses or other figures associated with the mythological Saturn.

The remaining thirty-eight, all small except one, are irregular satellites, whose orbits are much farther from Saturn, have high inclinations, and are mixed between prograde and retrograde.Dell Vostro 1310 Battery

These moons are probably captured minor planets, or debris from the breakup of such bodies after they were captured, creating collisional families. The irregular satellites have been classified by their orbital characteristics into the Inuit, Norse, and Gallic groups, and their names are chosen from the corresponding mythologies. Sony VGP-BPL13 Battery

The largest of the irregular moons is Phoebe, the ninth moon of Saturn, discovered at the end of the 19th century.

The rings of Saturn are made up of objects ranging in size from microscopic to hundreds of meters, each of which is on its own orbit about the planet.Sony VGP-BPS13 Battery

Thus a precise number of Saturnian moons cannot be given, as there is no objective boundary between the countless small anonymous objects that form Saturn's ring system and the larger objects that have been named as moons.Sony VGP-BPS13/B Battery

At least 150 moonlets embedded in the rings have been detected by the disturbance they create in the surrounding ring material, though this is thought to be only a small sample of the total population of such objects.

Early observations

Before the advent of telescopic photography, eight moons of Saturn were discovered by direct observation using optical telescopes.Sony VGP-BPS13/S Battery

Saturn's largest moon,Titan, was discovered in 1655 by Christiaan Huygens using a 57-millimeter (2.2 in) objective lens[6] on a refracting telescope of his own design.Tethys,Dione, Rhea and Iapetus (the "Sidera Lodoicea") were discovered in 1671–1672 by Giovanni Domenico Cassini.Sony VGP-BPS13A/B Battery

Mimas and Enceladus were discovered in 1789 by William Herschel.[8] Hyperion was discovered in 1848 by W.C. Bond, G.P. Bond[9]and William Lassell.

The use of long-exposure photographic plates made possible the discovery of additional moons. Sony VGP-BPS13A/S Battery

The first to be discovered in this manner, Phoebe, was found in 1899 by W.H. Pickering. In 1966 the tenth satellite of Saturn was discovered by Audouin Dollfus, when the rings were observed edge-on near anequinox. It was later named Janus. Sony VGP-BPS13AS Battery

A few years later it was realized that all observations of 1966 could only be explained if another satellite had been present and that it had an orbit similar to that of Janus. This object is now known as Epimetheus, the eleventh moon of Saturn. It shares the same orbit with Janus—the only known example of co-orbitals in the Solar System.Sony VGP-BPS13B/B Battery

In 1980 three additional Saturnian moons were discovered from the ground and later confirmed by the Voyager probes. They are trojan moons of Dione (Helene) and Tethys (Telesto and Calypso).

Observations by spacecraft

The study of the outer planets has since been revolutionized by the use of unmanned space probes. Sony VGP-BPS13B/Q Battery

The arrival of the Voyager spacecraft at Saturn in 1980–1981 resulted in the discovery of three additional moons—Atlas, Prometheus and Pandora, bringing the total to 17. In addition, Epimetheus was confirmed as distinct from Janus. In 1990, Pan was discovered in archival Voyager images.Sony VGP-BPS13B/S Battery

The Cassini mission, which arrived at Saturn in the summer of 2004, initially discovered three small inner moons including Methone and Pallene between Mimas and Enceladus as well as the second Lagrangian moon of Dione—Polydeuces. It also observed three suspected but unconfirmed moons in the F Ring.Sony VGP-BPS13Q Battery

In November 2004 Cassini scientists announced that the structure of Saturn's rings indicates the presence of several more moons orbiting within the rings, although only one, Daphnis, has been visually confirmed so far (in 2005). In 2007 Anthe was announced.Sony VGP-BPS13S Battery

In 2008 it was reported that Cassiniobservations of a depletion of energetic electrons in Saturn's magnetosphere near Rhea might be the signature of a tenuous ring system around Saturn's second largest moon.[17] In March 2009, Aegaeon, a moonlet within the G Ring, was announced.Sony VGP-BPL21 Battery

In July of the same year, S/2009 S 1, the first moonlet within the B Ring, was observed.

Outer moons

Study of Saturn's moons has also been aided by advances in telescope instrumentation, primarily the introduction of digital charge-coupled devices which replaced photographic plates. Sony VGP-BPS21 Battery

For the entire 20th century, Phoebe stood alone among Saturn's known moons with its highly irregular orbit. Beginning in 2000, however, three dozen additional irregular moons have been discovered using ground-based telescopes. Sony VGP-BPS21/S Battery

A survey starting in late 2000 and conducted using three medium-size telescopes found thirteen new moons orbiting Saturn at a great distance, in eccentric orbits, which are highly inclined to both the equator of Saturn and the ecliptic.They are probably fragments of larger bodies captured by Saturn's gravitational pull.Sony VGP-BPS21A Battery

In 2005, astronomers using theMauna Kea Observatory announced the discovery of twelve more small outer moons. In 2006, astronomers using the Subaru 8.2 m telescope reported the discovery of further nine irregular moons. In April 2007, Tarqeq (S/2007 S 1) was announced. In May of the same year S/2007 S 2 and S/2007 S 3 were reported.Sony VGP-BPS21A/B Battery

Naming

The modern names for Saturnian moons were suggested by John Herschel in 1847. He proposed to name them after mythological figures associated with the Roman god of agriculture and harvest, Saturn (equated to the Greek Kronos). In particular, the then known seven satellites were named after Titans and Titanesses—brothers and sisters of Saturn.Sony VGP-BPS21B Battery

In 1848 Lassell proposed that the eighth satellite of Saturn was named Hyperion after another Titan. When in the 20th century the names of Titans were exhausted, the moons were named after different characters of the Greco-Roman mythology or giants from other mythologies.Sony VGP-BPL8 Battery

All the irregular moons (except Phoebe) are named after Inuit and Gallic gods and after Norse ice giants.

Some asteroids share the same names as moons of Saturn: 55 Pandora, 106 Dione, 577 Rhea, 1809 Prometheus, 1810 Epimetheus, and 4450 Pan. Sony VGP-BPL8A Battery

In addition, two more asteroids previously shared the names of Saturnian moons until spelling differences were made permanent by the International Astronomical Union (IAU): Calypso and asteroid 53 Kalypso; and Helene and asteroid 101 Helena.Sony VGP-BPL8B Battery

Orbital groups

Although the borders may be somewhat nebulous, Saturn's moons can be divided into ten groups according to their orbital characteristics. Many of them, such as Pan and Daphnis, orbit within Saturn's ring system and have orbital periods only slightly longer than the planet's rotation period.Sony VGP-BPS8 Battery

The innermost moons and most regular satellites all have mean orbital inclinations ranging from less than a degree to about 1.5 degrees (except Iapetus, which has an inclination of 7.57 degrees) and small orbital eccentricities.Sony VGP-BPS8A Battery

On the other hand, irregular satellites in the outermost regions of Saturn's moon system, in particular the Norse group, have orbital radii of millions of kilometers and orbital periods lasting several years. The moons of the Norse group also orbit in the opposite direction to Saturn's rotation.Sony VGP-BPS8B Battery

Ring moonlets

During late July 2009, a moonlet was discovered in the B Ring,[3] 480 km from the outer edge of the ring, by the shadow it cast. It is estimated to be 300 m in diameter. Unlike the A Ring moonlets (see below), it does not induce a 'propeller' feature, probably due to the density of the B Ring.Apple MB772LL/A Battery

In 2006, four tiny moonlets were found in Cassini images of the A Ring.[33] Before this discovery only two larger moons had been known within gaps in the A Ring: Pan and Daphnis. These are large enough to clear continuous gaps in the ring.[33] In contrast, a moonlet is only massive enough to clear two small—Dell LATITUDE D800 Battery

about 10 km across—partial gaps in the immediate vicinity of the moonlet itself creating a structure shaped like an airplanepropeller.[34] The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly.Dell Inspiron 6400 AC Adapter

In 2007, the discovery of 150 more moonlets revealed that they (with the exception of two that have been seen outside the Encke gap) are confined to three narrow bands in the A Ring between 126,750 and 132,000 km from Saturn's center. Each band is about a thousand kilometers wide, which is less than 1% the width of Saturn's rings.Sony Vaio VGN-CR190E/L Battery

This region is relatively free from the disturbances related to resonances with larger satellites,[5] although other areas of the A Ring without disturbances are apparently free of moonlets. The moonlets were probably formed from the breakup of a larger satellite.HP 448007-001 Battery

It is estimated that the A Ring contains 7,000–8,000 propellers larger than 0.8 km in size and millions larger than 0.25 km.[5]

Similar moonlets may reside in the F Ring. There, "jets" of material may be due to collisions, initiated by perturbations from the nearby small moon Prometheus, Sony VGP-BPS11 Battery

of these moonlets with the core of the F Ring. One of the largest F-Ring moonlets may be the as-yet unconfirmed object S/2004 S 6. The F Ring also contains transient "fans" which are thought to result from even smaller moonlets, about 1 km in diameter, orbiting near the F Ring core.HP Pavilion DV6-1223EO Battery

One of the recently discovered moons, Aegaeon, resides within the bright arc of G Ring and is trapped in the 7:6 mean motion resonance with Mimas.[18] This means that it makes exactly seven revolutions around Saturn while Mimas makes exactly six. The moon is the largest among the population of bodies that are sources of dust in this ring.Compaq CQ35-100 Battery

Ring shepherds

Shepherd satellites are small moons that orbit within, or just beyond, a planet's ring system. They have the effect of sculpting the rings: giving them sharp edges, and creating gaps between them. Saturn's shepherd moons are Pan (Encke gap), Daphnis (Keeler gap), Atlas (A Ring), Prometheus (F Ring) and Pandora (F Ring).HP DV9700 Battery

These moons together with co-orbitals (see below) probably formed as a result of accretion of the friable ring material on preexisting denser cores. The cores with sizes from one-third to one-half the present day moons may be themselves collisional shards formed when a parental satellite of the rings disintegrated.Sony VGP-BPS13 Battery

Co-orbitals

Janus and Epimetheus are called co-orbital moons. They are of roughly equal size, with Janus being slightly larger than Epimetheus.anus and Epimetheus have orbits with only a few kilometers difference in semi-major axis, close enough that they would collide if they attempted to pass each other. HP Pavilion DV8 Battery

Instead of colliding, however, their gravitational interaction causes them to swap orbits every four years.

Inner large moons

The innermost large moons of Saturn orbit within its tenuous E Ring, along with three smaller moons of the Alkyoniods group.Compaq CQ50 Battery

  • Mimas is the smallest and least massive of the inner round moons,[28] although its mass is sufficient to alter the orbit of Methone.[37] It is noticeably ovoid-shaped, having been made shorter at the poles and longer at the equator (by about 20 km) by the effects of Saturn's gravity.HP DV6-1120SA Battery
  • Mimas has a large impact crater one-third its diameter, Herschel, situated on the moon's leading hemisphere.[38] The moon has no known past or present geologic activity, and its surface is dominated by impact craters. The only tectonic features known are a few arcuate and linear troughs, which probably formed when Mimas was shattered by the Herschel impact.HP Pavilion DV7 Battery
  • Enceladus is one of the smallest of Saturn's m
oons that is spherical in shape—only Mimas is smaller[27]—yet is the only small Saturnian moon that is currently endogenously active, and the smallest known body in the Solar System that is geologically active today.HP Pavilion DV6-1020ED Battery
  • The surface of the moon is morphologically diverse; it includes ancient heavily cratered terrain as well as younger smooth areas with few impact craters. Many plains on Enceladus are fractured and intersected by systems of lineaments.[HP NX8200 Battery
  • The area around the south pole of the moon was found by Cassini to be unusually warm and cut by a system of fractures about 130 km long called "tiger stripes", some of which emit jets of water vapor and dust.[39] These jets form a large plume off the south pole of the moon,HP NX7400 Battery
  • which replenishes Saturn's E ring and serves as the main source of ions in the magnetosphere of Saturn.[40] The gas and dust are released with a rate of more than 100 kg/s. Enceladus may have liquid water underneath the south-polar surface.HP NW8440 Battery
  • The source of the energy for this cryovolcanism is thought to be a 2:1 mean motion resonance with Dione.[39] The pure ice on the surface makes Enceladus one of the brightest known objects in the Solar System—its geometrical albedo is more than 140%.HP NW8200 Battery
  • Tethys is the third largest of Saturn's inner moons. Its most prominent features are a large (400 km diameter) impact crater named Odysseus on its leading hemisphere and a vast canyon system named Ithaca Chasma extending at least 270° around the moon.HP NC6400 Battery
  • The Ithaca Chasma is concentric with Odysseus, and these two features may be related. Tethys appears to have no current geological activity. A heavily cratered hilly terrain occupies the majority of its surface, while a smaller and smoother plains region lies on the hemisphere opposite to that of Odysseus.HP NC6200 Battery
  • The plains contain fewer craters and are apparently younger. A sharp boundary separates them from the cratered terrain. There is also a system of extensional troughs radiating away from Odysseus.[38] The density of Tethys (0.97 g/cm3) is less than that of water, indicating that the moon is made mainly of water ice with only a small fraction of rock.HP NC6100 Battery
  • Dione is the second-largest inner moon of Saturn. It has a higher density than geologically dead Rhea, the largest inner moon, but lower than that of active Enceladus. While the majority of Dione's surface is heavily cratered old terrain, this moon is also covered with an extensive network of troughs and lineaments, indicating that in the past it had global tectonic activity.HP NC6000 Battery
  • The troughs and lineaments are especially prominent on the trailing hemisphere, where several intersecting sets of fractures form what is called "wispy terrain". The cratered plains have a few large impact craters reaching 250 km in diameter.HP NC4400 Battery
  • Smooth plains with low impact crater counts are present as well on a small fraction of the moon's surface. They were probably tectonically resurfaced relatively later in the geological history of Dione. At two locations within smooth plains strange landforms (depressions) resembling oblong impact craters have been identified, HP 6710B Battery
  • both of which lie at the centers of radiating networks of cracks and troughs;[42] these features may be cryovolcanic in origin. Dione may be geologically active even now, although on a scale much smaller than the cryovolcanism of Enceladus. HP 6530B Battery
  • This follows from Cassini magnetic measurements that show Dione is a net source of plasma in the magnetosphere of Saturn, much like Enceladus. HP 6510B Battery
  • Alkyonides

    Three small moons orbit between Mimas and Enceladus: Methone, Anthe, and Pallene. Named after the Alkyonides of Greek mythology, they are some of the smallest moons in the Saturn system. All Alkyonides possess very faint ring arcs along their orbits.HP Pavilion DM4T-1000 Battery

    Trojan moons

    Trojan moons are a unique feature not found outside the Saturnian system. A Trojan body orbits at either the leading L4 or trailing L5 Lagrange point of a much larger object, such as a large moon or planet.HP Pavilion DM4T Battery

    Tethys has two Trojan moons, Telesto (leading) and Calypso (trailing), and Dione also has two, Helene (leading) and Polydeuces (trailing).[14] Helene is by far the largest Trojan moon,[27] while Polydeuces is the smallest and has the most chaotic orbit.HP Pavilion DM4-1090LA Battery

    Outer large moons

    These moons all orbit beyond the E Ring. They are:-

    • Rhea is the second-largest of Saturn's moons. In 2005 Cassini detected a depletion of electrons in the plasma wake of Rhea, which forms when the co-rotating plasma of Saturn's magnetosphere is absorbed by the moon.HP Pavilion DM4-1065DX Battery
    • The depletion was hypothesized to be caused by the presence of dust-sized particles concentrated in a few faint equatorial rings.[17] Such a ring system would make Rhea the only moon in the solar System known to have rings. HP Pavilion DM4-1030EZ Battery
    • However, subsequent targeted observations of the putative ring plane from several angles by Cassini's narrow-angle camera turned up no evidence of the expected ring material, leaving the origin of the plasma observations unresolved.HP Pavilion DM4-1019TX Battery
    • Otherwise Rhea has rather a typical heavily cratered surface, with the exceptions of a few large Dione-type fractures (wispy terrain) on the trailing hemisphere[45] and a very faint "line" of material at the equator that may have been deposited by material deorbiting from present or former rings.HP Pavilion DM4-1017TX Battery
    • Rhea also has two very large impact basins on its anti-Saturnian hemisphere, which are about 400 and 500 km across. The first, Tirawa, is roughly comparable to the Odysseus basin on Tethys. There is also a 48 km-diameter impact crater called Inktomi at 112°W that is prominent because of an extended system of bright rays, HP Pavilion DM4-1016TX Battery
    • which may be one of the youngest craters on the inner moons of Saturn. No evidence of any endogenic activity has been discovered on the surface of Rhea.
    • Titan, at 5,150 km diameter, is the second largest moon in the Solar System.[HP Pavilion DM4-1014TX Battery
    • Out of all the large moons, Titan is the only one with a dense (surface pressure of 1.5 atm), cold atmosphere, primarily made of nitrogen with a small fraction of methane.[49] The dense atmosphere frequently produces bright white convective clouds, especially over the south pole region.HP Pavilion DM4-1013TX Battery
    • The surface of Titan, which is difficult to observe due to persistent atmospheric haze, shows only a few impact craters and is probably very young.[ It contains a pattern of light and dark regions, flow channels and possibly cryovolcanoes.HP Pavilion DM4-1012TX Battery
    • Some dark regions are covered by longitudinal dune fields shaped by tidal winds, where sand is made of frozen water or hydrocarbons. Titan is the only moon with large bodies of a liquid on its surface, in the form of methane/ethane lakes in Titan's north and south polar regions.HP Pavilion DM4-1011TX Battery
    • The largest lake, Kraken Mare, is larger than the Caspian Sea.[53] Like Europa and Ganymede, it is believed that Titan has a subsurface ocean made of water mixed with ammonia, which can erupt to the surface of the moon and lead to cryovolcanism.HP Pavilion DM4-1010TX Battery
    • Hyperion is Titan's nearest neighbor in the Saturn system. The two moons are locked in a 4:3 mean motion resonance with each other, meaning that while Titan makes four revolutions around Saturn, Hyperion makes exactly three.[28] With an average diameter of about 270 km, Hyperion is smaller and lighter than Mimas.HP Pavilion DM4-1009TX Battery
    • It has an extremely irregular shape, and a very odd, tan-colored icy surface resembling a sponge, though its interior may be partially porous as well. The average density of about 0.55 g/cm3 indicates that the porosity exceeds 40% even assuming it has a purely icy composition. HP Pavilion DM4-1008TX Battery
    • The surface of Hyperion is covered with numerous impact craters—those with diameters 2–10 km are especially abundant.[54]It is the only moon known to have a chaotic rotation, which means Hyperion has no well-defined poles or equator.HP Pavilion DM4-1006TX Battery
    • While on short timescales the satellite approximately rotates around its long axis at a rate of 72–75° per day, on longer timescales its axis of rotation (spin vector) wanders chaotically across the sky.[54] This makes the rotational behavior of Hyperion essentially unpredictable.HP Pavilion DM4-1004TU Battery
    • Iapetus is the third-largest of Saturn's moons.[27] Orbiting the planet at 3.5 million km, it is by far the most distant of Saturn's large moons, and also possesses the greatest orbital inclination, at 14.72 degrees.[29] Iapetus has long been known for its unusual two-toned surface; HP Pavilion DM4-1002TX Battery
    • its leading hemisphere is pitch-black and its trailing hemisphere is almost as bright as fresh snow.[56] Cassini images showed that the dark material is confined to a large near equatorial area on the leading hemisphere called Cassini Regio, which extends approximately from 40°N to 40°S.HP Pavilion DM4-1001TX Battery
    • The pole regions of Iapetus are as bright as its trailing hemisphere. Cassini also discovered a 20 km tall equatorial ridge, which spans nearly the moon's entire equator. Otherwise both dark and bright surfaces of Iapetus are old and heavily cratered.HP Pavilion DM4-1001TU Battery
    • The images revealed at least four large impact basins with diameters from 380 to 550 km and numerous smaller impact craters.[56] No evidence of any endogenic activity has been discovered.[56] A clue to the origin of the dark material covering part of Iapetus' starkly dichromatic surface may have been found in 2009, HP Pavilion DM4-1000 Battery
    • when NASA's Spitzer Space Telescope discovered a vast, nearly invisible disk around Saturn, just inside the orbit of the moon Phoebe—the Phoebe ring. Scientists believe that the disk originates from dust and ice particles kicked up by impacts on Phoebe. HP Pavilion DM4 Battery
    • Because the disk particles, like Phoebe itself, orbit in the opposite direction to Iapetus, Iapetus collides with them as they drift in the direction of Saturn, darkening its leading hemisphere slightly. Once a difference in albedo, and hence in average temperature, Dell Latitude E6400 Battery Battery
    • was established between different regions of Iapetus, athermal runaway process of water ice sublimation from warmer regions and deposition of water vapor onto colder regions ensued. Iapetus' present two-toned appearance results from the contrast between the bright, primarily ice-coated areas and regions of dark lag, the residue left behind after the loss of surface ice. HP Pavilion DV6-1020ED Battery

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