Saturn

Saturn ♄
Saturn during Equinox.jpg
Pictured in natural color approaching equinox, photographed by Cassini in July 2008; the dot in the bottom left corner is Titan
Designations
Pronunciation/ˈsætərn/ (About this soundlisten)[1]
Named after
Saturn
AdjectivesSaturnian /səˈtɜːrniən/,[2] Cronian[3] / Kronian[4] /ˈkrniən/[5]
Orbital characteristics[10]
Epoch J2000.0
Aphelion1,514.50 million km (10.1238 AU)
Perihelion1,352.55 million km (9.0412 AU)
1,433.53 million km (9.5826 AU)
Eccentricity0.0565
  • 29.4571 yr
  • 10,759.22 d
  • 24,491.07 Saturnian solar days[6]
378.09 days
9.68 km/s (6.01 mi/s)
317.020°[7]
Inclination
113.665°
2032-Nov-29[9]
339.392°[7]
Known satellites83 with formal designations; innumerable additional moonlets.[10]
Physical characteristics[10]
Mean radius
58,232 km (36,184 mi)[a]
9.1402 Earths
Equatorial radius
  • 60,268 km (37,449 mi)[a]
  • 9.449 Earths
Polar radius
  • 54,364 km (33,780 mi)[a]
  • 8.552 Earths
Flattening0.09796
Circumference
  • 4.27×1010 km2 (1.65×1010 sq mi)[12][a]
  • 83.703 Earths
Volume
  • 8.2713×1014 km3 (1.9844×1014 cu mi)[a]
  • 763.59 Earths
Mass
  • 5.6834×1026 kg
  • 95.159 Earths
Mean density
0.687 g/cm3 (0.0248 lb/cu in)[b] (less than water)
0.1246 Earths
  • 10.44 m/s2 (34.3 ft/s2)[a]
  • 1.065 g
Moment of inertia factor
0.22[13]
35.5 km/s (22.1 mi/s)[a]
Synodic rotation period
10 h 32 m 36 s;
10.5433 hours[6]
Sidereal rotation period
10h 33m 38s + 1m 52s
1m 19s
[14][15]
Equatorial rotation velocity
9.87 km/s (6.13 mi/s; 35,500 km/h)[a]
26.73° (to orbit)
North pole right ascension
40.589°; 2h 42m 21s
North pole declination
83.537°
Albedo
Surface temp.minmeanmax
1 bar134 K
0.1 bar88 K[19]97 K[20]151 K[19]
−0.55[18] to +1.17[18]
14.5″ to 20.1″ (excludes rings)
Atmosphere[10]
Surface pressure
140 kPa[21]
Scale height
59.5 km (37.0 mi)
Composition by volume
96.3%±2.4%hydrogen (H2)
3.25%±2.4%helium (He)
0.45%±0.2%methane (CH4)
0.0125%±0.0075%ammonia (NH3)
0.0110%±0.0058%hydrogen deuteride (HD)
0.0007%±0.00015%ethane (C2H6)
Ices:

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth.[22][23] It only has one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive.[24][25][26] Saturn is named after the Roman god of wealth and agriculture. Its astronomical symbol (♄) has been traced back to the Greek Oxyrhynchus Papyri, where it can be seen to be a Greek kappa-rho with a cross-bar, as an abbreviation for Κρονος (Cronos), the Greek name for the planet.[27] It later came to look like a lower-case Greek eta, with the cross added at the top in the 16th century.

The Romans named the seventh day of the week Saturday, Sāturni diēs ("Saturn's Day"), for the planet Saturn.[28]

Saturn's interior is most likely composed of a core of iron–nickel and rock (silicon and oxygen compounds). Its core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally, a gaseous outer layer. Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. An electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's, but which has a magnetic moment 580 times that of Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth of Jupiter's.[29] The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h (1,100 mph; 500 m/s), higher than on Jupiter but not as high as on Neptune.[30]

The planet's most notable feature is its prominent ring system, which is composed mainly of ice particles, with a smaller amount of rocky debris and dust. At least 83 moons[31] are known to orbit Saturn, of which 53 are officially named; this does not include the hundreds of moonlets in its rings. Titan, Saturn's largest moon and the second largest in the Solar System, is larger than the planet Mercury, although less massive, and is the only moon in the Solar System to have a substantial atmosphere.[32]

Physical characteristics

Composite image comparing the sizes of Saturn and Earth

Saturn is a gas giant composed predominantly of hydrogen and helium. It lacks a definite surface, though it may have a solid core.[33] Saturn's rotation causes it to have the shape of an oblate spheroid; that is, it is flattened at the poles and bulges at its equator. Its equatorial and polar radii differ by almost 10%: 60,268 km versus 54,364 km.[10] Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. The combination of the bulge and rotation rate means that the effective surface gravity along the equator, 8.96 m/s2, is 74% of what it is at the poles and is lower than the surface gravity of Earth. However, the equatorial escape velocity of nearly 36 km/s is much higher than that of Earth.[34]

Saturn is the only planet of the Solar System that is less dense than water—about 30% less.[35] Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times Earth's mass,[36] and Saturn is 95 times Earth's mass.[10] Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System.[37]

Internal structure

Diagram of Saturn, to scale

Despite consisting mostly of hydrogen and helium, most of Saturn's mass is not in the gas phase, because hydrogen becomes a non-ideal liquid when the density is above 0.01 g/cm3, which is reached at a radius containing 99.9% of Saturn's mass. The temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to be a metal in the deeper layers.[37]

Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium, with trace amounts of various volatiles.[38] This core is similar in composition to Earth, but is more dense. The examination of Saturn's gravitational moment, in combination with physical models of the interior, has allowed constraints to be placed on the mass of Saturn's core. In 2004, scientists estimated that the core must be 9–22 times the mass of Earth,[39][40] which corresponds to a diameter of about 25,000 km.[41] However, measurements of Saturn's rings suggest a much more diffuse core with a mass equal to about 17 Earths and a radius equal to around 60% of Saturn's entire radius.[42] This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude. The outermost layer spans 1,000 km and consists of gas.[43][44][45]

Saturn has a hot interior, reaching 11,700 °C at its core, and radiates 2.5 times more energy into space than it receives from the Sun. Jupiter's thermal energy is generated by the Kelvin–Helmholtz mechanism of slow gravitational compression, but such a process alone may not be sufficient to explain heat production for Saturn, because it is less massive. An alternative or additional mechanism may be generation of heat through the "raining out" of droplets of helium deep in Saturn's interior. As the droplets descend through the lower-density hydrogen, the process releases heat by friction and leaves Saturn's outer layers depleted of helium.[46][47] These descending droplets may have accumulated into a helium shell surrounding the core.[38] Rainfalls of diamonds have been suggested to occur within Saturn, as well as in Jupiter[48] and ice giants Uranus and Neptune.[49]

Atmosphere

Methane bands circle Saturn. The moon Dione hangs below the rings to the right.

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume.[50] The proportion of helium is significantly deficient compared to the abundance of this element in the Sun.[38] The quantity of elements heavier than helium (metallicity) is not known precisely, but the proportions are assumed to match the primordial abundances from the formation of the Solar System. The total mass of these heavier elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.[51]

Trace amounts of ammonia, acetylene, ethane, propane, phosphine, and methane have been detected in Saturn's atmosphere.[52][53][54] The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH4SH) or water.[55] Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion. This photochemical cycle is modulated by Saturn's annual seasonal cycle.[54]

Cloud layers

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

Saturn's atmosphere exhibits a banded pattern similar to Jupiter's, but Saturn's bands are much fainter and are much wider near the equator. The nomenclature used to describe these bands is the same as on Jupiter. Saturn's finer cloud patterns were not observed until the flybys of the Voyager spacecraft during the 1980s. Since then, Earth-based telescopy has improved to the point where regular observations can be made.[56]

The composition of the clouds varies with depth and increasing pressure. In the upper cloud layers, with the temperature in the range 100–160 K and pressures extending between 0.5–2 bar, the clouds consist of ammonia ice. Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185 to 270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 190–235 K. Finally, the lower layers, where pressures are between 10 and 20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in aqueous solution.[57]

Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. In 1990, the Hubble Space Telescope imaged an enormous white cloud near Saturn's equator that was not present during the Voyager encounters, and in 1994 another smaller storm was observed. The 1990 storm was an example of a Great White Spot, a unique but short-lived phenomenon that occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere's summer solstice.[58] 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.[59]

The winds on Saturn are the second fastest among the Solar System's planets, after Neptune's. Voyager data indicate peak easterly winds of 500 m/s (1,800 km/h).[60] In images from the Cassini spacecraft during 2007, Saturn's northern hemisphere displayed a bright blue hue, similar to Uranus. The color was most likely caused by Rayleigh scattering.[61] Thermography has shown that Saturn's south pole has a warm polar vortex, the only known example of such a phenomenon in the Solar System.[62] Whereas temperatures on Saturn are normally −185 °C, temperatures on the vortex often reach as high as −122 °C, suspected to be the warmest spot on Saturn.[62]

North pole hexagonal cloud pattern

Saturn's north pole (IR animation)
Saturn's south pole


A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.[63][64][65] The sides of the hexagon are each about 14,500 km (9,000 mi) long, which is longer than the diameter of the Earth.[66] 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.[67] The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere.[68] The pattern's origin is a matter of much speculation. Most scientists think it is a standing wave pattern in the atmosphere. Polygonal shapes have been replicated in the laboratory through differential rotation of fluids.[69][70]

South pole vortex

HST imaging of the south polar region indicates the presence of a jet stream, but no strong polar vortex nor any hexagonal standing wave.[71] NASA reported in November 2006 that Cassini had observed a "hurricane-like" storm locked to the south pole that had a clearly defined eyewall.[72][73] Eyewall clouds had not previously been seen on any planet other than Earth. For example, images from the Galileo spacecraft did not show an eyewall in the Great Red Spot of Jupiter.[74]

The south pole storm may have been present for billions of years.[75] This vortex is comparable to the size of Earth, and it has winds of 550 km/h.[75]

Other features

Cassini observed a series of cloud features found in northern latitudes, nicknamed the "String of Pearls". These features are cloud clearings that reside in deeper cloud layers.[76]

Magnetosphere

Polar aurorae on Saturn
(c) ESA/Hubble, CC BY 4.0
Auroral lights at Saturn's north pole[77]
Radio emissions detected by Cassini

Saturn has an intrinsic magnetic field that has a simple, symmetric shape – a magnetic dipole. Its strength at the equator – 0.2 gauss (20 µT) – is approximately one twentieth of that of the field around Jupiter and slightly weaker than Earth's magnetic field.[29] As a result, Saturn's magnetosphere is much smaller than Jupiter's.[78] When Voyager 2 entered the magnetosphere, the solar wind pressure was high and the magnetosphere extended only 19 Saturn radii, or 1.1 million km (712,000 mi),[79] although it enlarged within several hours, and remained so for about three days.[80] Most probably, the magnetic field is generated similarly to that of Jupiter – by currents in the liquid metallic-hydrogen layer called a metallic-hydrogen dynamo.[78] 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.[29] Saturn's magnetosphere, like Earth's, produces aurorae.[81]

Orbit and rotation

Saturn and rings as viewed by the Cassini spacecraft (28 October 2016)

The average distance between Saturn and the Sun is over 1.4 billion kilometers (9 AU). With an average orbital speed of 9.68 km/s,[10] it takes Saturn 10,759 Earth days (or about29+12 years)[82] to finish one revolution around the Sun.[10] As a consequence, it forms a near 5:2 mean-motion resonance with Jupiter.[83] The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth.[10] The perihelion and aphelion distances are, respectively, 9.195 and 9.957 AU, on average.[10][84] The visible features on Saturn rotate at different rates depending on latitude, and multiple rotation periods have been assigned to various regions (as in Jupiter's case).

Astronomers use three different systems for specifying the rotation rate of Saturn. System I has a period of 10h 14m 00s (844.3°/d) and encompasses the Equatorial Zone, the South Equatorial Belt, and the North Equatorial Belt. The polar regions are considered to have rotation rates similar to System I. All other Saturnian latitudes, excluding the north and south polar regions, are indicated as System II and have been assigned a rotation period of 10h 38m 25.4s (810.76°/d). System III refers to Saturn's internal rotation rate. Based on radio emissions from the planet detected by Voyager 1 and Voyager 2,[85] System III has a rotation period of 10h 39m 22.4s (810.8°/d). System III has largely superseded System II.[86]

A precise value for the rotation period of the interior remains elusive. While approaching Saturn in 2004, Cassini found that the radio rotation period of Saturn had increased appreciably, to approximately 10h 45m 45s ± 36s.[87][88] An estimate of Saturn's rotation (as an indicated rotation rate for Saturn as a whole) based on a compilation of various measurements from the Cassini, Voyager and Pioneer probes is 10h 32m 35s.[89] Studies of the planet's C Ring yield a rotation period of 10h 33m 38s + 1m 52s
1m 19s
.[14][15]

In March 2007, it was found that the variation of radio emissions from the planet did not match Saturn's rotation rate. This variance may be caused by geyser activity on Saturn's moon Enceladus. The water vapor emitted into Saturn's orbit by this activity becomes charged and creates a drag upon Saturn's magnetic field, slowing its rotation slightly relative to the rotation of the planet.[90][91][92]

An apparent oddity for Saturn is that it does not have any known trojan asteroids. These are minor planets that orbit the Sun at the stable Lagrangian points, designated L4 and L5, located at 60° angles to the planet along its orbit. Trojan asteroids have been discovered for Mars, Jupiter, Uranus, and Neptune. Orbital resonance mechanisms, including secular resonance, are believed to be the cause of the missing Saturnian trojans.[93]

Natural satellites

A montage of Saturn and its principal moons (Dione, Tethys, Mimas, Enceladus, Rhea and Titan; Iapetus not shown). This image was created from photographs taken in November 1980 by the Voyager 1 spacecraft.

Saturn has 83 known moons,[31] 53 of which have formal names.[94][95] In addition, there is evidence of dozens to hundreds of moonlets with diameters of 40–500 meters in Saturn's rings,[96] which are not considered to be true moons. Titan, the largest moon, comprises more than 90% of the mass in orbit around Saturn, including the rings.[97] Saturn's second-largest moon, Rhea, may have a tenuous ring system of its own,[98] along with a tenuous atmosphere.[99][100][101]

Possible beginning of a new moon (white dot) of Saturn (image taken by Cassini on 15 April 2013)

Many of the other moons are small: 34 are less than 10 km in diameter and another 14 between 10 and 50 km in diameter.[102] Traditionally, most of Saturn's moons have been named after Titans of Greek mythology. Titan is the only satellite in the Solar System with a major atmosphere,[103][104] in which a complex organic chemistry occurs. It is the only satellite with hydrocarbon lakes.[105][106]

On 6 June 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan, a possible precursor for life.[107] On 23 June 2014, NASA claimed to have strong evidence that nitrogen in the atmosphere of Titan came from materials in the Oort cloud, associated with comets, and not from the materials that formed Saturn in earlier times.[108]

Saturn's moon Enceladus, which seems similar in chemical makeup to comets,[109] has often been regarded as a potential habitat for microbial life.[110][111][112][113] Evidence of this possibility includes the satellite's salt-rich particles having an "ocean-like" composition that indicates most of Enceladus's expelled ice comes from the evaporation of liquid salt water.[114][115][116] A 2015 flyby by Cassini through a plume on Enceladus found most of the ingredients to sustain life forms that live by methanogenesis.[117]

In April 2014, NASA scientists reported the possible beginning of a new moon within the A Ring, which was imaged by Cassini on 15 April 2013.[118]

Planetary rings

The rings of Saturn (imaged here by Cassini in 2007) are the most massive and conspicuous in the Solar System.[44]
False-color UV image of Saturn's outer B and A rings; dirtier ringlets in the Cassini Division and Encke Gap show up red.

Saturn is probably best known for the system of planetary rings that makes it visually unique.[44] The rings extend from 6,630 to 120,700 kilometers (4,120 to 75,000 mi) outward from Saturn's equator and average approximately 20 meters (66 ft) in thickness. They are composed predominantly of water ice, with trace amounts of tholin impurities and a peppered coating of approximately 7% amorphous carbon.[119] The particles that make up the rings range in size from specks of dust up to 10 m.[120] While the other gas giants also have ring systems, Saturn's is the largest and most visible.

There are two main hypotheses regarding the origin of the rings. One hypothesis is that the rings are remnants of a destroyed moon of Saturn. The second hypothesis is that the rings are left over from the original nebular material from which Saturn was formed. Some ice in the E ring comes from the moon Enceladus's geysers.[121][122][123][124] The water abundance of the rings varies radially, with the outermost ring A being the most pure in ice water. This abundance variance may be explained by meteor bombardment.[125]

Beyond the main rings, at a distance of 12 million km from the planet is the sparse Phoebe ring. It is tilted at an angle of 27° to the other rings and, like Phoebe, orbits in retrograde fashion.[126]

Some of the moons of Saturn, including Pandora and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out.[127] Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses.[128]

History of observation and exploration

Galileo Galilei first observed the rings of Saturn in 1610

The observation and exploration of Saturn can be divided into three phases. The first phase is ancient observations (such as with the naked eye), before the invention of modern telescopes. The second phase began in the 17th century, with telescopic observations from Earth, which improved over time. The third phase is visitation by space probes, in orbit or on flyby. In the 21st century, telescopic observations continue from Earth (including Earth-orbiting observatories like the Hubble Space Telescope) and, until its 2017 retirement, from the Cassini orbiter around Saturn.

Ancient observations

Saturn has been known since prehistoric times,[129] and in early recorded history it was a major character in various mythologies. Babylonian astronomers systematically observed and recorded the movements of Saturn.[130] In ancient Greek, the planet was known as Φαίνων Phainon,[131] and in Roman times it was known as the "star of Saturn".[132] In ancient Roman mythology, the planet Phainon was sacred to this agricultural god, from which the planet takes its modern name.[133] The Romans considered the god Saturnus the equivalent of the Greek god Cronus; in modern Greek, the planet retains the name CronusΚρόνος: Kronos.[134]

The Greek scientist Ptolemy based his calculations of Saturn's orbit on observations he made while it was in opposition.[135] In Hindu astrology, there are nine astrological objects, known as Navagrahas. Saturn is known as "Shani" and judges everyone based on the good and bad deeds performed in life.[133][135] Ancient Chinese and Japanese culture designated the planet Saturn as the "earth star" (土星). This was based on Five Elements which were traditionally used to classify natural elements.[136][137][138]

In ancient Hebrew, Saturn is called 'Shabbathai'.[139] Its angel is Cassiel. Its intelligence or beneficial spirit is 'Agȋȇl (Hebrew: אגיאל, romanizedʿAgyal),[140] and its darker spirit (demon) is Zȃzȇl (Hebrew: זאזל, romanizedZazl).[140][141][142] Zazel has been described as a great angel, invoked in Solomonic magic, who is "effective in love conjurations".[143][144] In Ottoman Turkish, Urdu and Malay, the name of Zazel is 'Zuhal', derived from the Arabic language (Arabic: زحل, romanizedZuhal).[141]

European observations (17th–19th centuries)

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

Saturn's rings require at least a 15-mm-diameter telescope[145] to resolve and thus were not known to exist until Christiaan Huygens saw them in 1655 and published about this in 1659. Galileo, with his primitive telescope in 1610,[146][147] incorrectly thought of Saturn's appearing not quite round as two moons on Saturn's sides.[148][149] It was not until Huygens used greater telescopic magnification that this notion was refuted, and the rings were truly seen for the first time. Huygens also discovered Saturn's moon Titan; Giovanni Domenico Cassini later discovered four other moons: Iapetus, Rhea, Tethys and Dione. In 1675, Cassini discovered the gap now known as the Cassini Division.[150]

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.[151]

In 1899 William Henry Pickering discovered Phoebe, a highly irregular satellite that does not rotate synchronously with Saturn as the larger moons do.[151] Phoebe was the first such satellite found and it takes more than a year to orbit Saturn in a retrograde orbit. During the early 20th century, research on Titan led to the confirmation in 1944 that it had a thick atmosphere – a feature unique among the Solar System's moons.[152]

Modern NASA and ESA probes

Pioneer 11 flyby

Pioneer 11 image of Saturn

Pioneer 11 made the first flyby of Saturn in September 1979, when it passed within 20,000 km of the planet's cloud tops. Images were taken of the planet and a few of its moons, although their resolution was too low to discern surface detail. The spacecraft also studied Saturn's rings, revealing the thin F-ring and the fact that dark gaps in the rings are bright when viewed at high phase angle (towards the Sun), meaning that they contain fine light-scattering material. In addition, Pioneer 11 measured the temperature of Titan.[153]

Voyager flybys

In November 1980, the Voyager 1 probe visited the Saturn system. It sent back the first high-resolution images of the planet, its rings and satellites. Surface features of various moons were seen for the first time. Voyager 1 performed a close flyby of Titan, increasing knowledge of the atmosphere of the moon. It proved that Titan's atmosphere is impenetrable in visible wavelengths; therefore no surface details were seen. The flyby changed the spacecraft's trajectory out from the plane of the Solar System.[154]

Almost a year later, in August 1981, Voyager 2 continued the study of the Saturn system. More close-up images of Saturn's moons were acquired, as well as evidence of changes in the atmosphere and the rings. Unfortunately, during the flyby, the probe's turnable camera platform stuck for a couple of days and some planned imaging was lost. Saturn's gravity was used to direct the spacecraft's trajectory towards Uranus.[154]

The probes discovered and confirmed several new satellites orbiting near or within the planet's rings, as well as the small Maxwell Gap (a gap within the C Ring) and Keeler gap (a 42 km-wide gap in the A Ring).

Cassini–Huygens spacecraft

The Cassini–Huygens space probe entered orbit around Saturn on 1 July 2004. In June 2004, it conducted a close flyby of Phoebe, sending back high-resolution images and data. Cassini's flyby of Saturn's largest moon, Titan, captured radar images of large lakes and their coastlines with numerous islands and mountains. The orbiter completed two Titan flybys before releasing the Huygens on 25 December 2004. Huygens descended onto the surface of Titan on 14 January 2005.[155]

Starting in early 2005, scientists used Cassini to track lightning on Saturn. The power of the lightning is approximately 1,000 times that of lightning on Earth.[156]

At Enceladus's south pole geysers spray water from many locations along the tiger stripes.[157]

In 2006, NASA reported that Cassini had found evidence of liquid water reservoirs no more than tens of meters below the surface that erupt in geysers on Saturn's moon Enceladus. These jets of icy particles are emitted into orbit around Saturn from vents in the moon's south polar region.[158] Over 100 geysers have been identified on Enceladus.[157] In May 2011, NASA scientists reported that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".[159][160]

Cassini photographs have revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. The source of this ring is hypothesized to be the crashing of a meteoroid off Janus and Epimetheus.[161] In July 2006, images were returned of hydrocarbon lakes near Titan's north pole, the presence of which were confirmed in January 2007. In March 2007, hydrocarbon seas were found near the North pole, the largest of which is almost the size of the Caspian Sea.[162] In October 2006, the probe detected an 8,000 km diameter cyclone-like storm with an eyewall at Saturn's south pole.[163]

From 2004 to 2 November 2009, the probe discovered and confirmed eight new satellites.[164] In April 2013 Cassini sent back images of a hurricane at the planet's north pole 20 times larger than those found on Earth, with winds faster than 530 km/h (330 mph).[165] On 15 September 2017, the Cassini-Huygens spacecraft performed the "Grand Finale" of its mission: a number of passes through gaps between Saturn and Saturn's inner rings.[166][167] The atmospheric entry of Cassini ended the mission.

Possible future missions

The continued exploration of Saturn is still considered to be a viable option for NASA as part of their ongoing New Frontiers program of missions. NASA previously requested for plans to be put forward for a mission to Saturn that included the Saturn Atmospheric Entry Probe, and possible investigations into the habitability and possible discovery of life on Saturn's moons Titan and Enceladus by Dragonfly.[168][169]

Observation

Amateur telescopic view of Saturn

Saturn is the most distant of the five planets easily visible to the naked eye from Earth, the other four being Mercury, Venus, Mars and Jupiter. (Uranus, and occasionally 4 Vesta, are visible to the naked eye in dark skies.) Saturn appears to the naked eye in the night sky as a bright, yellowish point of light. The mean apparent magnitude of Saturn is 0.46 with a standard deviation of 0.34.[18] Most of the magnitude variation is due to the inclination of the ring system relative to the Sun and Earth. The brightest magnitude, −0.55, occurs near in time to when the plane of the rings is inclined most highly, and the faintest magnitude, 1.17, occurs around the time when they are least inclined.[18] It takes approximately 29.5 years for the planet to complete an entire circuit of the ecliptic against the background constellations of the zodiac. Most people will require an optical aid (very large binoculars or a small telescope) that magnifies at least 30 times to achieve an image of Saturn's rings in which clear resolution is present.[44][145] When Earth passes through the ring plane, which occurs twice every Saturnian year (roughly every 15 Earth years), the rings briefly disappear from view because they are so thin. Such a "disappearance" will next occur in 2025, but Saturn will be too close to the Sun for observations.[170]

Simulated appearance of Saturn as seen from Earth (at opposition) during an orbit of Saturn, 2001–2029
Saturn eclipses the Sun, as seen from Cassini. The rings are visible, including the F Ring.

Saturn and its rings are best seen when the planet is at, or near, opposition, the configuration of a planet when it is at an elongation of 180°, and thus appears opposite the Sun in the sky. A Saturnian opposition occurs every year—approximately every 378 days—and results in the planet appearing at its brightest. Both the Earth and Saturn orbit the Sun on eccentric orbits, which means their distances from the Sun vary over time, and therefore so do their distances from each other, hence varying the brightness of Saturn from one opposition to the next. Saturn also appears brighter when the rings are angled such that they are more visible. For example, during the opposition of 17 December 2002, Saturn appeared at its brightest due to a favorable orientation of its rings relative to the Earth,[171] even though Saturn was closer to the Earth and Sun in late 2003.[171]

HST Saturn portrait from 20 June 2019

From time to time, Saturn is occulted by the Moon (that is, the Moon covers up Saturn in the sky). As with all the planets in the Solar System, occultations of Saturn occur in "seasons". Saturnian occultations will take place monthly for about a 12-month period, followed by about a five-year period in which no such activity is registered. The Moon's orbit is inclined by several degrees relative to Saturn's, so occultations will only occur when Saturn is near one of the points in the sky where the two planes intersect (both the length of Saturn's year and the 18.6-Earth year nodal precession period of the Moon's orbit influence the periodicity).[172]

Farewell to Saturn and moons (Enceladus, Epimetheus, Janus, Mimas, Pandora and Prometheus), by Cassini (21 November 2017).

Notes

  1. ^ a b c d e f g h Refers to the level of 1 bar atmospheric pressure
  2. ^ Based on the volume within the level of 1 bar atmospheric pressure

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Further reading

See also

  • Stats of planets in the Solar System

External links

Media files used on this page

Solar System Template Final.png
Major Solar System objects. Sizes of planets and Sun are roughly to scale, but distances are not. This is not a diagram of all known moons – small gas giants' moons and Pluto's S/2011 P 1 moon are not shown.
Saturn symbol (fixed width).svg
Author/Creator: Denis Moskowitz, Licence: CC BY-SA 4.0
Planetary symbol for Saturn, ♄ U+2644
Saturn from Cassini Orbiter (2004-10-06).jpg
While cruising around Saturn in early October 2004, Cassini captured a series of images that have been composed into the largest, most detailed, global natural color view of Saturn and its rings ever made.

This grand mosaic consists of 126 images acquired in a tile-like fashion, covering one end of Saturn's rings to the other and the entire planet in between. The images were taken over the course of two hours on Oct. 6, 2004, while Cassini was approximately 6.3 million kilometers (3.9 million miles) from Saturn. Since the view seen by Cassini during this time changed very little, no re-projection or alteration of any of the images was necessary.

Three images (red, green and blue) were taken of each of 42 locations, or "footprints," across the planet. The full color footprints were put together to produce a mosaic that is 8,888 pixels across and 4,544 pixels tall.

The smallest features seen here are 38 kilometers (24 miles) across. Many of Saturn's splendid features noted previously in single frames taken by Cassini are visible in this one detailed, all-encompassing view: subtle color variations across the rings, the thread-like F ring, ring shadows cast against the blue northern hemisphere, the planet's shadow making its way across the rings to the left, and blue-grey storms in Saturn's southern hemisphere to the right. Tiny Mimas and even smaller Janus are both faintly visible at the lower left.

The Sun-Saturn-Cassini, or phase, angle at the time was 72 degrees; hence, the partial illumination of Saturn in this portrait. Later in the mission, when the spacecraft's trajectory takes it far from Saturn and also into the direction of the Sun, Cassini will be able to look back and view Saturn and its rings in a more fully-illuminated geometry.
Solar system.jpg
This is a montage of planetary images taken by spacecraft managed by the Jet Propulsion Laboratory in Pasadena, CA. Included are (from top to bottom) images of Mercury, Venus, Earth (and Moon), Mars, Jupiter, Saturn, Uranus and Neptune. The spacecraft responsible for these images are as follows:
  • the Mercury image was taken by Mariner 10,
  • the Venus image by Magellan,
  • the Earth and Moon images by Galileo,
  • the Mars image by Mars Global Surveyor,
  • the Jupiter image by Cassini, and
  • the Saturn, Uranus and Neptune images by Voyager.
  • Pluto is not shown as it is no longer a planet. The inner planets (Mercury, Venus, Earth, Moon, and Mars) are roughly to scale to each other; the outer planets (Jupiter, Saturn, Uranus, and Neptune) are roughly to scale to each other. PIA 00545 is the same montage with Neptune shown larger in the foreground. Actual diameters are given below:
  • Sun (to photosphere) 1,392,684 km
  • Mercury 4,879.4 km
  • Venus 12,103.7 km
  • Earth 12,756.28 km
  • Moon 3,476.2 km
  • Mars 6,804.9 km
  • Jupiter 142,984 km
  • Saturn 120,536 km
  • Uranus 51,118 km
  • Neptune 49,528 km
Crab Nebula.jpg
This is a mosaic image, one of the largest ever taken by NASA's Hubble Space Telescope, of the Crab Nebula, a six-light-year-wide expanding remnant of a star's supernova explosion. Japanese and Chinese astronomers recorded this violent event in 1054 CE, as did, almost certainly, Native Americans.

The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The rapidly spinning neutron star embedded in the center of the nebula is the dynamo powering the nebula's eerie interior bluish glow. The blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star, like a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star's rotation. A neutron star is the crushed ultra-dense core of the exploded star.

The Crab Nebula derived its name from its appearance in a drawing made by Irish astronomer Lord Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as by large ground-based telescopes such as the European Southern Observatory's Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular demise of a star, 6,500 light-years away.

The newly composed image was assembled from 24 individual Wide Field and Planetary Camera 2 exposures taken in October 1999, January 2000, and December 2000. The colors in the image indicate the different elements that were expelled during the explosion. Blue in the filaments in the outer part of the nebula represents neutral oxygen, green is singly-ionized sulfur, and red indicates doubly-ionized oxygen.
The Earth seen from Apollo 17 with transparent background.png
"The Blue Marble" is a famous photograph of the Earth taken on December 7, 1972 by the crew of the Apollo 17 spacecraft en route to the Moon at a distance of about 29,000 kilometers (18,000 statute miles). It shows Africa, Antarctica, and the Arabian Peninsula.
Top of Atmosphere.jpg
View of the crescent moon through the top of the Earth's atmosphere. Photographed above 21.5°N, 113.3°E by International Space Station crew Expedition 13 over the South China Sea, just south of Macau (NASA image ID: ISS013-E-54329).
He1523a.jpg
Author/Creator: ESO, European Southern Observatory, Licence: CC BY 4.0
Artist's impression of "the oldest star of our Galaxy": HE 1523-0901
  • About 13.2 billion years old
  • Approximately 7500 light years far from Earth
  • Published as part of Hamburg/ESO Survey in the May 10 2007 issue of The Astrophysical Journal
RocketSunIcon.svg
Author/Creator: Me, Licence: Copyrighted free use
SVG replacement for File:Spaceship and the Sun.jpg. A stylized illustration of a spaceship and the sun, based on the description of the emblem of the fictional Galactic Empire in Isaac Asimov's Foundation series ("The golden globe with its conventionalized rays, and the oblique cigar shape that was a space vessel"). This image could be used as a icon for science-fiction related articles.
Earth-moon.jpg
This view of the rising Earth greeted the Apollo 8 astronauts as they came from behind the Moon after the fourth nearside orbit. Earth is about five degrees above the horizon in the photo. The unnamed surface features in the foreground are near the eastern limb of the Moon as viewed from Earth. The lunar horizon is approximately 780 kilometers from the spacecraft. Width of the photographed area at the horizon is about 175 kilometers. On the Earth 240,000 miles away, the sunset terminator bisects Africa.
Saturn Storm.jpg
The huge storm (great white spot) churning through the atmosphere in Saturn's northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI
Saturn-27-03-04.jpeg
Author/Creator: Rochus Hess, Licence: Attribution

Photo of planet Saturn taken in Straßwalchen (Austria) using the following equipement:

  • telescope: 250/1200mm Newton with 2x Barlow
  • camera: Philips Tou Webcam with IR band-elimination filter
  • exposure: 10% best images out of 1200 images added with Giotto (software)
  • seeing: good
Saturn Robert Hooke 1666.jpg
Old drawing of Saturn by Robert Hooke. R indicates Saturn's globe, the two letters a indicate the expected overlap of the globe on the rings. Hooke's shading on the rings to the right of the right-hand a only (i.e. not at the left-hand a), indicates the shadow of the globe on the rings.

The two letters b indicate the expected overlap of the rings on the globe. Hooke's shading on the globe between the right-hand and left-hand bs could indicate the shadow of the rings on the globe, or the faint C-ring faintly blocking part of the globe.

The abbreviations marked around Saturn indicate directions: Sep. for Septentrional or northern; Mer. for Meridional; Occ. for Occidental or western; and Ori. for Oriental or eastern.
Saturn during Equinox.jpg
This Natural color view of the planet Saturn was created from images collected shortly after Cassini began its extended Equinox Mission in July 2008. (Saturn actually reached equinox on August 11, 2009.)
En-us-Saturn.ogg
(c) I, EncycloPetey, CC-BY-SA-3.0
Pronunciation of the term in US English
Saturnoppositions-animated.gif
Author/Creator: Tdadamemd, Licence: CC BY-SA 4.0
This is an animation of the 28 images of Saturn shown in Saturnoppositions.jpg (simulated views using a computer program written by Tom Ruen). This animation demonstrates the 29.5-year orbital period of Saturn by opposition date, as well as the dramatic changes in the orientation of the planet's ring disk. The ring system revolves around a fixed axis, so both sides of the ring disk are visible from Earth during each period in which Saturn orbits the Sun.
(See source file for more info and references.)
Saturn diagram.svg
Author/Creator: Kelvinsong, Licence: CC BY-SA 3.0
Diagram of the planet saturn!!


Sourcelistt : 1, 2, 3, 4, 5, 6, & the wikipedia article on Saturn, && w:Rings of Saturn, &&& File:Saturn Rings annotated.jpg, &&&& ring colors were stolen from File:Saturn's rings in visible light and radio.jpg.
Saturn symbol (bold).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
heavier line weight (1.333 px)
Saturn in natural colors (captured by the Hubble Space Telescope).jpg

The NASA/ESA Hubble Space Telescope has provided images of Saturn in many colors, from black-and-white, to orange, to blue, green, and red. But in this picture, image processing specialists have worked to provide a crisp, extremely accurate view of Saturn, which highlights the planet's pastel colors. Bands of subtle color (yellows, browns, grays) distinguish differences in the clouds over Saturn, the second largest planet in the solar system.

Saturn's high-altitude clouds are made of colorless ammonia ice. Above these clouds is a layer of haze or smog, produced when ultraviolet light from the sun shines on methane gas. The smog contributes to the planet's subtle color variations. One of Saturn's moons, Enceladus, is seen casting a shadow on the giant planet as it passes just above the ring system.

The flattened disk swirling around Saturn is the planet's most recognizable feature, and this image displays it in sharp detail. This is the planet's ring system, consisting mostly of chunks of water ice. Although it appears as if the disk is composed of only a few rings, it actually consists of tens of thousands of thin ringlets. This picture also shows the two classic divisions in the ring system. The narrow Encke Gap is nearest to the disk's outer edge; the Cassini division, is the wide gap near the center.
Saturn eclipse.jpg
Saturn eclipsing the sun, seen from behind from the Cassini orbiter. The image is a composite assembled from images taken by the Cassini spacecraft on 15 September, 2006.

Individual rings seen include (in order, starting from most distant)

  • E ring
  • Pallene ring (visible very faintly in an arc just below Saturn)
  • G ring
  • Janus/Epimetheus ring (faint)
  • F ring (narrow brightest feature)
  • Main rings (A,B,C)
  • D ring (bluish, nearest Saturn)
Saturn - HST 2019-06-20 full size.jpg
Uploader's notes: the original ESA / NASA 2505 x 1592 pixel TIFF image has been modified by cropping and conversion to JPEG format.

Original caption released with image:
Anyone who has ever peered at Saturn through a small telescope is immediately enticed by its elegant rings, which make the far-flung planet one of the most exotic-looking, opulent worlds in the solar system.

The latest view of Saturn from NASA's Hubble Space Telescope captures exquisite details of the ring system—which looks like a phonograph record with grooves that represent detailed structure within the rings—and atmospheric details that once could only be captured by spacecraft visiting the distant world.

One such intriguing feature is the long-lasting hexagon-shaped structure circling the planet's north pole. It is a mysterious six-sided pattern caused by a high-speed jet stream. NASA's Voyager 1 spacecraft first discovered the "hexagon" during its flyby in 1981. The hexagon is so large that four Earths could fit inside its boundaries. (There is no similar structure at Saturn's south pole.)

Other features, however, are not as long lasting. A large storm in the north polar region spotted by Hubble last year has disappeared. Smaller, convective storms—called super "thunderheads"—such as the one just above the center of the planet's image, also come and go.

Saturn's appearance changes with its seasons, which occur because Saturn's equator is tilted 27 degrees with respect to the plane of its orbit around the Sun. The Earth, similarly, has seasons because our planet is tilted by about 23.5 degrees, but seasons on Saturn last more than seven years. This new Saturn image was taken during summer in the planet's northern hemisphere.

The amber colors of the planet in this image come from summer smog-like hazes, produced in photochemical reactions driven by solar ultraviolet radiation. Below the haze lie clouds of ammonia ice crystals, as well as deeper, unseen lower-level clouds of ammonium hydrosulfide and water. Saturn's banded structure is caused by alternating winds that result in clouds at different altitudes at each latitude.

Saturn's trademark ring system is now tilted toward Earth, giving viewers a magnificent look at its bright, icy structure. The high resolution of Hubble's Wide Field Camera 3 allows us to see numerous ringlets and the fainter inner rings.

The planet teased and tantalized Galileo Galilei in 1610, who was astonished when he first saw its rings through the newly invented telescope. However, Galileo mistook them for weird appendages stuck to the planet, because his handheld telescope wasn’t very powerful. Dutch astronomer Christiaan Huygens first identified the rings as a separate phenomenon in 1655, but still he thought they were a continuous disk encircling the planet. Today, we know the rings are mostly made of pieces of ice, with sizes ranging from tiny grains to giant boulders. And they are constantly moving around the planet in an intricate cosmic dance.

The age of Saturn's ring system continues to be debated. And, even more perplexing, no one knows what cosmic catastrophe formed the rings. Additional clues came as NASA's Cassini spacecraft plunged into Saturn's atmosphere on Sept. 15, 2017. NASA ended the mission in this way to prevent the spacecraft from accidentally crashing into one of Saturn's moons, but Cassini's dramatic finish also provided valuable scientific insights. During its final orbits, Cassini measured the mass of the ring system as merely 1/1000th the mass of Earth's Moon. Some astronomers have interpreted this low mass to mean that the rings may only be 100 million years old, a fraction of Saturn's age. However, there is still no consensus among planetary astronomers today.

Hubble's Wide Field Camera 3 observed Saturn on June 20, 2019, as the planet made its closest approach to Earth, at about 845 million miles away.

This image is the second in a yearly series of snapshots taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL is helping scientists understand the atmospheric dynamics and evolution of our solar system's gas giant planets. In Saturn's case, astronomers will be able to track shifting weather patterns and other changes to identify trends.
Enceladus geysers June 2009.jpg
Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. The tiger stripes are fissures that spray icy particles, water vapor and organic compounds.

More than 30 individual jets of different sizes can be seen in this image and more than 20 of them had not been identified before. At least one jet spouting prominently in previous images now appears less powerful.

This mosaic was created from two high-resolution images that were captured by the narrow-angle camera when NASA's Cassini spacecraft flew past Enceladus and through the jets on Nov. 21, 2009. (For other images captured during the same flyby, see PIA11686 and PIA11687). Imaging the jets over time will allow Cassini scientists to study the consistency of their activity.
Hubble sees a flickering light display on Saturn.jpg
(c) ESA/Hubble, CC BY 4.0
Astronomers using the NASA/ESA Hubble Space Telescope have captured new images of the dancing auroral lights at Saturn’s north pole. Taken from Hubble’s perspective in orbit around the Earth, these images provide a detailed look at Saturn’s stormy aurorae — revealing previously unseen dynamics in the choreography of the auroral glow.

The cause of the changing patterns in Saturn's aurorae is an ongoing mystery in planetary science. These ultraviolet images, taken by Hubble’s super-sensitive Advanced Camera for Surveys, add new insight by capturing moments when Saturn’s magnetic field is affected by bursts of particles streaming out from the Sun.

Saturn has a long, comet-like magnetic tail known as a magnetotail — as do Mercury, Jupiter, Uranus, Neptune and Earth [1]. This magnetotail is present around planets that have a magnetic field, caused by a rotating core of magnetic elements. It appears that when bursts of particles from the Sun hit Saturn, the planet’s magnetotail collapses and later reconfigures itself, an event that is reflected in the dynamics of its aurorae.

Some of the bursts of light seen shooting around Saturn’s polar regions travelled at over three times faster than the speed of the gas giant’s rotation!

The new images also formed part of a joint observing campaign between Hubble and NASA's Cassini spacecraft, which is currently in orbit around Saturn itself. Between them, the two spacecraft managed to capture a 360-degree view of the planet’s aurorae at both the north and south poles. Cassini also used optical imaging to delve into the rainbow of colours seen in Saturn’s light shows. On Earth, we see green curtains of light with flaming scarlet tops. Cassini’s imaging cameras reveal similar auroral veils on Saturn, that are red at the bottom and violet at the top.

Notes

[1]A magnetosphere is the area of space around an astronomical object in which charged particles are controlled by that object’s magnetic field. The magnetosphere is compressed on the side of the sun, and on the other side it extends far beyond the object. It is this extended region of the magnetosphere that is known as the magnetotail.
Saturn.ogg
Author/Creator:

Speaker: Mangst

Authors of the article, Licence: CC BY-SA 3.0

This is a spoken word version of the Wikipedia article: Saturn
Listen to this article (audio help)

Saturn System Montage - GPN-2000-000439.jpg
This montage of images of the Saturnian system was prepared from an assemblage of images taken by the Voyager 1 spacecraft during its Saturn encounter in November 1980.

This artist's view shows Dione in the forefront, Saturn rising behind, Tethys and Mimas fading in the distance to the right, Enceladus and Rhea off Saturn's rings to the left, and Titan in its distant orbit at the top.

The Voyager Project is managed for NASA by the Jet Propulsion Laboratory, Pasadena, California.
Saturn sound2.ogg
Saturn is a source of intense radio emissions, which have been monitored by the Cassini spacecraft. The radio waves are closely related to the auroras near the poles of the planet. These auroras are similar to Earth's northern and southern lights. This is an audio file of radio emissions from Saturn. An animation with a cursor moving through the color spectrogram in sync with the audio file is available at: http://www-pw.physics.uiowa.edu/cassini/.

The Cassini spacecraft began detecting these radio emissions in April 2002, when Cassini was 374 million kilometers (234 million miles) from the planet, using the Cassini radio and plasma wave science instrument.

The radio and plasma wave instrument has now provided the first high resolution observations of these emissions, showing an amazing array of variations in frequency and time. The complex radio spectrum with rising and falling tones, is very similar to Earth's auroral radio emissions. These structures indicate that there are numerous small radio sources moving along magnetic field lines threading the auroral region.

Time on this recording has been compressed, so that 73 seconds corresponds to 27 minutes. Since the frequencies of these emissions are well above the audio frequency range, we have shifted them downward by a factor of 44.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radio and plasma wave science team is based at the University of Iowa, Iowa City.
Looking saturn in the eye.jpg
Cassini stares deep into the swirling hurricane-like vortex at Saturn's south pole, where the vertical structure of the clouds is highlighted by shadows. Such a storm, with a well-developed eye ringed by towering clouds, is a phenomenon never before seen on another planet.

This image shows a swirling cloud mass centered on the south pole, around which winds blow at 550 kilometers (350 miles) per hour. The frames have been aligned to make the planet appear stationary, while the sun appears to revolve about the pole in a counterclockwise direction. The clouds inside the dark, inner circle are lower than the surrounding clouds, which cast a shadow that follows the sun.

The width of the shadow and the height of the sun above the local horizon yield a crude estimate of the height of the surrounding clouds relative to the clouds in the center. The shadow-casting clouds tower 30 to 75 kilometers (20 to 45 miles) above those in the center. This is two to five times greater than the tallest terrestrial thunderstorms and two to five times the height of clouds surrounding the eye of a terrestrial hurricane. Such a height difference arises because Saturn's hydrogen-helium atmosphere is less dense at comparable pressures than Earth's atmosphere, and is therefore more distended in the vertical dimension.

The south polar storm, which displays two spiral arms of clouds extending from the central ring and spans the dark area inside a thick, brighter ring of clouds, is approximately 8,000 kilometers (5,000 miles) across, which is considerably larger than a terrestrial hurricane.

Eye-wall clouds are a distinguishing feature of hurricanes on Earth. They form where moist air flows inward across the ocean's surface, rising vertically and releasing a load of precipitation around an interior circular region of descending air, which is the eye itself.

Though it is uncertain whether moist convection is driving this storm, as is the case with Earthly hurricanes, the dark 'eye' at the pole, the eye-wall clouds and the spiral arms together indicate a hurricane-like system. The distinctive eye-wall clouds especially have not been seen on any planet beyond Earth. Even Jupiter's Great Red Spot, much larger than Saturn's polar storm, has no eye, no eye-wall, and is relatively calm at the center.

This giant Saturnian storm is apparently different from hurricanes on Earth because it is locked to the pole, does not drift around like terrestrial hurricanes and because it does not form over liquid water oceans.

The images were acquired over a period of three hours on Oct. 11, 2006, when Cassini was approximately 340,000 kilometers (210,000 miles) from Saturn. Image scale is about 17 kilometers (11 miles) per pixel. The images were taken with the wide-angle camera using a spectral filter sensitive to wavelengths of infrared light centered at 752 nanometers. All frames have been contrast enhanced using digital image processing techniques. The unprocessed images show an oblique view toward the pole, and have been reprojected to show the planet from a perspective directly over the south pole.
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Image of Saturn and its polar aurorae from vertically above its equator in light of 115 and 125 nanometres of wavelength (ultraviolet light) taken by the Hubble Space Telescope in 2009.

In January and March 2009, astronomers using NASA's Hubble Space Telescope took advantage of a rare opportunity to record Saturn when its rings were edge-on, resulting in a unique movie featuring the nearly symmetrical light show at both of the giant planet's poles. It takes Saturn almost thirty years to orbit the Sun, with the opportunity to image both of its poles occurring only twice during that time.

The light shows, called aurorae, are produced when electrically charged particles race along the planet's magnetic field and into the upper atmosphere where they excite atmospheric gases, causing them to glow. Saturn's aurorae resemble the same phenomena that take place at the Earth's poles.
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Satellite picture of the "hexagon on Saturn" - it is a hexagon twice as wide as Earth around Saturn's north pole. First observed by the Voyager 1 probe in the 1980s, the hexagon has been sighted still by the Cassini probe
PIA17218 – A Farewell to Saturn, Annotated Version.jpg
After more than 13 years at Saturn, and with its fate sealed, NASA's Cassini spacecraft bid farewell to the Saturnian system by firing the shutters of its wide-angle camera and capturing this last, full mosaic of Saturn and its rings two days before the spacecraft's dramatic plunge into the planet's atmosphere. During the observation, a total of 80 wide-angle images were acquired in just over two hours. This view is constructed from 42 of those wide-angle shots, taken using the red, green and blue spectral filters, combined and mosaicked together to create a natural-color view. Six of Saturn's moons -- Enceladus, Epimetheus, Janus, Mimas, Pandora and Prometheus -- make a faint appearance in this image. (Numerous stars are also visible in the background.)

A second version of the mosaic is provided in which the planet and its rings have been brightened, with the fainter regions brightened by a greater amount. (The moons and stars have also been brightened by a factor of 15 in this version.) The ice-covered moon Enceladus -- home to a global subsurface ocean that erupts into space -- can be seen at the 1 o'clock position. Directly below Enceladus, just outside the F ring (the thin, farthest ring from the planet seen in this image) lies the small moon Epimetheus. Following the F ring clock-wise from Epimetheus, the next moon seen is Janus. At about the 4:30 position and outward from the F ring is Mimas. Inward of Mimas and still at about the 4:30 position is the F-ring-disrupting moon, Pandora. Moving around to the 10 o'clock position, just inside of the F ring, is the moon Prometheus.

This view looks toward the sunlit side of the rings from about 15 degrees above the ring plane. Cassini was approximately 698,000 miles (1.1 million kilometers) from Saturn, on its final approach to the planet, when the images in this mosaic were taken. Image scale on Saturn is about 42 miles (67 kilometers) per pixel. The image scale on the moons varies from 37 to 50 miles (59 to 80 kilometers) pixel. The phase angle (the Sun-planet-spacecraft angle) is 138 degrees. The Cassini spacecraft ended its mission on Sept. 15, 2017.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado. For more information about the Cassini-Huygens mission visit https://saturn.jpl.nasa.gov and https://www.nasa.gov/cassini. The Cassini imaging team homepage is at https://ciclops.org.
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כוכב הלכת החיצוני שבתאי.
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Rough comparison of sizes of Saturn and Earth.
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An image of Saturn's A Ring, taken by the Cassini Orbiter using an Ultraviolet Imaging Spectrograph.
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PIA18354: Methane Saturn

September 6, 2015; released February 1, 2016.

http://photojournal.jpl.nasa.gov/catalog/PIA18354

The soft, bright-and-dark bands displayed by Saturn in this view from NASA's Cassini spacecraft are the signature of methane in the planet's atmosphere.

This image was taken in wavelengths of light that are absorbed by methane on Saturn. Dark areas are regions where light travels deeper into the atmosphere (passing through more methane) before reflecting and scattering off of clouds and then heading back out of the atmosphere. In such images, the deeper the light goes, the more of it gets absorbed by methane, and the darker that part of Saturn appears.

The moon Dione (698 miles or 1,123 kilometers across) hangs below the rings at right. Shadows of the rings are also visible here, cast onto the planet's southern hemisphere, in an inverse view compared to early in Cassini's mission at Saturn (see PIA08168).

This view looks toward the unilluminated side of the rings from about 0.3 degrees below the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on Sept. 6, 2015, using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 728 nanometers.

The view was acquired at a distance of approximately 819,000 miles (1.32 million kilometers) from Saturn. Image scale is 49 miles (79 kilometers) per pixel. Dione has been brightened by a factor of two to enhance its visibility.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org.
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Commotion at Ring's Edge May Be Effect of Small Icy Object

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA18078

http://www.jpl.nasa.gov/news/news.php?release=2014-112

The disturbance visible at the outer edge of Saturn's A ring in this image from NASA's Cassini spacecraft could be caused by an object replaying the birth process of icy moons.

The image is adapted from one in a paper in the journal Icarus, reporting the likely presence of an icy body causing gravitational effects on nearby ring particles, producing the bright feature visible at the ring's edge. The object, informally called "Peggy," is estimated to be no more than about half a mile, or one kilometer, in diameter. It may be in the process of migrating out of the ring, a process that one recent theory proposes as a step in the births of Saturn's several icy moons.

This image is a portion of an observation recorded by the narrow-angle camera of Cassini's imaging science subsystem on April 15, 2013. The bright feature at the edge of the A ring is about 750 miles (about 1,200 kilometers) long.

This view looks toward the illuminated side of the rings from about 53 degrees above the plane of the rings. It was obtained from a distance of approximately 775,000 miles (1.2 million kilometers) from Saturn, with a sun-Saturn-spacecraft, or phase, angle of 31 degrees. The scale is about 4 miles (about 7 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org.
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PIA20517: Peeking over Saturn's Shoulder

No Earth-based telescope could ever capture a view quite like this. Earth-based views can only show Saturn's daylit side, from within about 25 degrees of Saturn's equatorial plane. A spacecraft in orbit, like Cassini, can capture stunning scenes that would be impossible from our home planet.

This view looks toward the sunlit side of the rings from about 25 degrees (if Saturn is dominant in image) above the ring plane. The image was taken in violet light with the Cassini spacecraft wide-angle camera on Oct. 28, 2016.

The view was obtained at a distance of approximately 810,000 miles (1.3 million kilometers) from Saturn. Image scale is 50 miles (80 kilometers) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org.