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This article is about the planet. Saturn_sentence_0

For the deity, see Saturn (mythology). Saturn_sentence_1

For other uses, see Saturn (disambiguation). Saturn_sentence_2

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. Saturn_sentence_3

It is a gas giant with an average radius of about nine times that of Earth. Saturn_sentence_4

It only has one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive. Saturn_sentence_5

Saturn is named after the Roman god of wealth and agriculture; its astronomical symbol (♄) represents the god's sickle. Saturn_sentence_6

The Romans named the seventh day of the week Saturday, Sāturni diēs ("Saturn's Day") no later than the 2nd century for the planet Saturn. Saturn_sentence_7

Saturn's interior is most likely composed of a core of iron–nickel and rock (silicon and oxygen compounds). Saturn_sentence_8

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_sentence_9

Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. Saturn_sentence_10

An electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than the Earth's, but has a magnetic moment 580 times that of Earth due to Saturn's larger size. Saturn_sentence_11

Saturn's magnetic field strength is around one-twentieth of Jupiter's. Saturn_sentence_12

The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Saturn_sentence_13

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 those on Neptune. Saturn_sentence_14

In January 2019, astronomers reported that a day on the planet Saturn has been determined to be 10 33 38 − 1 19 , based on studies of the planet's C Ring. Saturn_sentence_15

The planet's most famous feature is its prominent ring system, which is composed mostly of ice particles, with a smaller amount of rocky debris and dust. Saturn_sentence_16

At least 82 moons are known to orbit Saturn, of which 53 are officially named; this does not include the hundreds of moonlets in its rings. Saturn_sentence_17

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. Saturn_sentence_18

Physical characteristics Saturn_section_0

Saturn is a gas giant because it is predominantly composed of hydrogen and helium. Saturn_sentence_19

It lacks a definite surface, though it may have a solid core. Saturn_sentence_20

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. Saturn_sentence_21

Its equatorial and polar radii differ by almost 10%: 60,268 km versus 54,364 km. Saturn_sentence_22

Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. Saturn_sentence_23

The combination of the bulge and rotation rate means that the effective surface gravity along the equator, 8.96 m/s, is 74% that at the poles and is lower than the surface gravity of Earth. Saturn_sentence_24

However, the equatorial escape velocity of nearly 36 km/s is much higher than that for Earth. Saturn_sentence_25

Saturn is the only planet of the Solar System that is less dense than water—about 30% less. Saturn_sentence_26

Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm due to the atmosphere. Saturn_sentence_27

Jupiter has 318 times Earth's mass, and Saturn is 95 times Earth's mass. Saturn_sentence_28

Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System. Saturn_sentence_29

Internal structure Saturn_section_1

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/cm, which is reached at a radius containing 99.9% of Saturn's mass. Saturn_sentence_30

The temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to be a metal in the deeper layers. Saturn_sentence_31

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. Saturn_sentence_32

This core is similar in composition to Earth, but is more dense. Saturn_sentence_33

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. Saturn_sentence_34

In 2004, scientists estimated that the core must be 9–22 times the mass of Earth, which corresponds to a diameter of about 25,000 km. Saturn_sentence_35

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. Saturn_sentence_36

The outermost layer spans 1,000 km and consists of gas. Saturn_sentence_37

Saturn has a hot interior, reaching 11,700 °C at its core, and it radiates 2.5 times more energy into space than it receives from the Sun. Saturn_sentence_38

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. Saturn_sentence_39

An alternative or additional mechanism may be generation of heat through the "raining out" of droplets of helium deep in Saturn's interior. Saturn_sentence_40

As the droplets descend through the lower-density hydrogen, the process releases heat by friction and leaves Saturn's outer layers depleted of helium. Saturn_sentence_41

These descending droplets may have accumulated into a helium shell surrounding the core. Saturn_sentence_42

Rainfalls of diamonds have been suggested to occur within Saturn, as well as in Jupiter and ice giants Uranus and Neptune. Saturn_sentence_43

Atmosphere Saturn_section_2

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. Saturn_sentence_44

The proportion of helium is significantly deficient compared to the abundance of this element in the Sun. Saturn_sentence_45

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. Saturn_sentence_46

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. Saturn_sentence_47

Trace amounts of ammonia, acetylene, ethane, propane, phosphine, and methane have been detected in Saturn's atmosphere. Saturn_sentence_48

The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH 4SH) or water. Saturn_sentence_49

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. Saturn_sentence_50

This photochemical cycle is modulated by Saturn's annual seasonal cycle. Saturn_sentence_51

Cloud layers Saturn_section_3

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. Saturn_sentence_52

The nomenclature used to describe these bands is the same as on Jupiter. Saturn_sentence_53

Saturn's finer cloud patterns were not observed until the flybys of the Voyager spacecraft during the 1980s. Saturn_sentence_54

Since then, Earth-based telescopy has improved to the point where regular observations can be made. Saturn_sentence_55

The composition of the clouds varies with depth and increasing pressure. Saturn_sentence_56

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. Saturn_sentence_57

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 185–270 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 10–20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in aqueous solution. Saturn_sentence_58

Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. Saturn_sentence_59

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. Saturn_sentence_60

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. Saturn_sentence_61

Previous Great White Spots were observed in 1876, 1903, 1933 and 1960, with the 1933 storm being the most famous. Saturn_sentence_62

If the periodicity is maintained, another storm will occur in about 2020. Saturn_sentence_63

The winds on Saturn are the second fastest among the Solar System's planets, after Neptune's. Saturn_sentence_64

Voyager data indicate peak easterly winds of 500 m/s (1,800 km/h). Saturn_sentence_65

In images from the Cassini spacecraft during 2007, Saturn's northern hemisphere displayed a bright blue hue, similar to Uranus. Saturn_sentence_66

The color was most likely caused by Rayleigh scattering. Saturn_sentence_67

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. Saturn_sentence_68

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. Saturn_sentence_69

North pole hexagonal cloud pattern Saturn_section_4

Main article: Saturn's hexagon Saturn_sentence_70

A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images. Saturn_sentence_71

The sides of the hexagon are each about 13,800 km (8,600 mi) long, which is longer than the diameter of the Earth. Saturn_sentence_72

The entire structure rotates with a period of 10 39 24 (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. Saturn_sentence_73

The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere. Saturn_sentence_74

The pattern's origin is a matter of much speculation. Saturn_sentence_75

Most scientists think it is a standing wave pattern in the atmosphere. Saturn_sentence_76

Polygonal shapes have been replicated in the laboratory through differential rotation of fluids. Saturn_sentence_77

South pole vortex Saturn_section_5

HST imaging of the south polar region indicates the presence of a jet stream, but no strong polar vortex nor any hexagonal standing wave. Saturn_sentence_78

NASA reported in November 2006 that Cassini had observed a "hurricane-like" storm locked to the south pole that had a clearly defined eyewall. Saturn_sentence_79

Eyewall clouds had not previously been seen on any planet other than Earth. Saturn_sentence_80

For example, images from the Galileo spacecraft did not show an eyewall in the Great Red Spot of Jupiter. Saturn_sentence_81

The south pole storm may have been present for billions of years. Saturn_sentence_82

This vortex is comparable to the size of Earth, and it has winds of 550 km/h. Saturn_sentence_83

Other features Saturn_section_6

Cassini observed a series of cloud features found in northern latitudes, nicknamed the "String of Pearls". Saturn_sentence_84

These features are cloud clearings that reside in deeper cloud layers. Saturn_sentence_85

Magnetosphere Saturn_section_7

Main article: Magnetosphere of Saturn Saturn_sentence_86

Saturn has an intrinsic magnetic field that has a simple, symmetric shape – a magnetic dipole. Saturn_sentence_87

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. Saturn_sentence_88

As a result, Saturn's magnetosphere is much smaller than Jupiter's. Saturn_sentence_89

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), although it enlarged within several hours, and remained so for about three days. Saturn_sentence_90

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. Saturn_sentence_91

This magnetosphere is efficient at deflecting the solar wind particles from the Sun. Saturn_sentence_92

The moon Titan orbits within the outer part of Saturn's magnetosphere and contributes plasma from the ionized particles in Titan's outer atmosphere. Saturn_sentence_93

Saturn's magnetosphere, like Earth's, produces aurorae. Saturn_sentence_94

Orbit and rotation Saturn_section_8

The average distance between Saturn and the Sun is over 1.4 billion kilometers (9 AU). Saturn_sentence_95

With an average orbital speed of 9.68 km/s, it takes Saturn 10,759 Earth days (or about ​29 ⁄2 years) to finish one revolution around the Sun. Saturn_sentence_96

As a consequence, it forms a near 5:2 mean-motion resonance with Jupiter. Saturn_sentence_97

The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth. Saturn_sentence_98

The perihelion and aphelion distances are, respectively, 9.195 and 9.957 AU, on average. Saturn_sentence_99

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). Saturn_sentence_100

Astronomers use three different systems for specifying the rotation rate of Saturn. Saturn_sentence_101

System I has a period of 10 14 00 (844.3°/d) and encompasses the Equatorial Zone, the South Equatorial Belt, and the North Equatorial Belt. Saturn_sentence_102

The polar regions are considered to have rotation rates similar to System I. Saturn_sentence_103

All other Saturnian latitudes, excluding the north and south polar regions, are indicated as System II and have been assigned a rotation period of 10 38 25.4 (810.76°/d). Saturn_sentence_104

System III refers to Saturn's internal rotation rate. Saturn_sentence_105

Based on radio emissions from the planet detected by Voyager 1 and Voyager 2, System III has a rotation period of 10 39 22.4 (810.8°/d). Saturn_sentence_106

System III has largely superseded System II. Saturn_sentence_107

A precise value for the rotation period of the interior remains elusive. Saturn_sentence_108

While approaching Saturn in 2004, Cassini found that the radio rotation period of Saturn had increased appreciably, to approximately 10 45 45 ± 36. Saturn_sentence_109

The latest 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 was reported in September 2007 is 10 32 35. Saturn_sentence_110

In March 2007, it was found that the variation of radio emissions from the planet did not match Saturn's rotation rate. Saturn_sentence_111

This variance may be caused by geyser activity on Saturn's moon Enceladus. Saturn_sentence_112

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. Saturn_sentence_113

An apparent oddity for Saturn is that it does not have any known trojan asteroids. Saturn_sentence_114

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. Saturn_sentence_115

Trojan asteroids have been discovered for Mars, Jupiter, Uranus, and Neptune. Saturn_sentence_116

Orbital resonance mechanisms, including secular resonance, are believed to be the cause of the missing Saturnian trojans. Saturn_sentence_117

Natural satellites Saturn_section_9

Main article: Moons of Saturn Saturn_sentence_118

Saturn has 82 known moons, 53 of which have formal names. Saturn_sentence_119

In addition, there is evidence of dozens to hundreds of moonlets with diameters of 40–500 meters in Saturn's rings, which are not considered to be true moons. Saturn_sentence_120

Titan, the largest moon, comprises more than 90% of the mass in orbit around Saturn, including the rings. Saturn_sentence_121

Saturn's second-largest moon, Rhea, may have a tenuous ring system of its own, along with a tenuous atmosphere. Saturn_sentence_122

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. Saturn_sentence_123

Traditionally, most of Saturn's moons have been named after Titans of Greek mythology. Saturn_sentence_124

Titan is the only satellite in the Solar System with a major atmosphere, in which a complex organic chemistry occurs. Saturn_sentence_125

It is the only satellite with hydrocarbon lakes. Saturn_sentence_126

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. Saturn_sentence_127

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. Saturn_sentence_128

Saturn's moon Enceladus, which seems similar in chemical makeup to comets, has often been regarded as a potential habitat for microbial life. Saturn_sentence_129

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. Saturn_sentence_130

A 2015 flyby by Cassini through a plume on Enceladus found most of the ingredients to sustain life forms that live by methanogenesis. Saturn_sentence_131

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. Saturn_sentence_132

Planetary rings Saturn_section_10

Main article: Rings of Saturn Saturn_sentence_133

Saturn is probably best known for the system of planetary rings that makes it visually unique. Saturn_sentence_134

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. Saturn_sentence_135

They are composed predominantly of water ice, with trace amounts of tholin impurities and a peppered coating of approximately 7% amorphous carbon. Saturn_sentence_136

The particles that make up the rings range in size from specks of dust up to 10 m. While the other gas giants also have ring systems, Saturn's is the largest and most visible. Saturn_sentence_137

There are two main hypotheses regarding the origin of the rings. Saturn_sentence_138

One hypothesis is that the rings are remnants of a destroyed moon of Saturn. Saturn_sentence_139

The second hypothesis is that the rings are left over from the original nebular material from which Saturn was formed. Saturn_sentence_140

Some ice in the E ring comes from the moon Enceladus's geysers. Saturn_sentence_141

The water abundance of the rings varies radially, with the outermost ring A being the most pure in ice water. Saturn_sentence_142

This abundance variance may be explained by meteor bombardment. Saturn_sentence_143

Beyond the main rings, at a distance of 12 million km from the planet is the sparse Phoebe ring. Saturn_sentence_144

It is tilted at an angle of 27° to the other rings and, like Phoebe, orbits in retrograde fashion. Saturn_sentence_145

Some of the moons of Saturn, including Pandora and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out. Saturn_sentence_146

Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses. Saturn_sentence_147

History of observation and exploration Saturn_section_11

The observation and exploration of Saturn can be divided into three phases. Saturn_sentence_148

The first phase is ancient observations (such as with the naked eye), before the invention of modern telescopes. Saturn_sentence_149

The second phase began in the 17th century, with telescopic observations from Earth, which improved over time. Saturn_sentence_150

The third phase is visitation by space probes, in orbit or on flyby. Saturn_sentence_151

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. Saturn_sentence_152

Ancient observations Saturn_section_12

See also: Saturn (mythology) Saturn_sentence_153

Saturn has been known since prehistoric times, and in early recorded history it was a major character in various mythologies. Saturn_sentence_154

Babylonian astronomers systematically observed and recorded the movements of Saturn. Saturn_sentence_155

In ancient Greek, the planet was known as Φαίνων Phainon, and in Roman times it was known as the "star of Saturn". Saturn_sentence_156

In ancient Roman mythology, the planet Phainon was sacred to this agricultural god, from which the planet takes its modern name. Saturn_sentence_157

The Romans considered the god Saturnus the equivalent of the Greek god Cronus; in modern Greek, the planet retains the name Cronus—Κρόνος: Kronos. Saturn_sentence_158

The Greek scientist Ptolemy based his calculations of Saturn's orbit on observations he made while it was in opposition. Saturn_sentence_159

In Hindu astrology, there are nine astrological objects, known as Navagrahas. Saturn_sentence_160

Saturn is known as "Shani" and judges everyone based on the good and bad deeds performed in life. Saturn_sentence_161

Ancient Chinese and Japanese culture designated the planet Saturn as the "earth star" (土星). Saturn_sentence_162

This was based on Five Elements which were traditionally used to classify natural elements. Saturn_sentence_163

In ancient Hebrew, Saturn is called 'Shabbathai'. Saturn_sentence_164

Its angel is Cassiel. Saturn_sentence_165

Its intelligence or beneficial spirit is 'Agȋȇl (Hebrew: אגיאל‎‎, romanized: ʿAgyal), and its darker spirit (demon) is Zȃzȇl (Hebrew: זאזל‎, romanized: Zazl). Saturn_sentence_166

Zazel has been described as a great angel, invoked in Solomonic magic, who is "effective in love conjurations". Saturn_sentence_167

In Ottoman Turkish, Urdu and Malay, the name of Zazel is 'Zuhal', derived from the Arabic language (Arabic: زحل‎, romanized: Zuhal). Saturn_sentence_168

European observations (17th–19th centuries) Saturn_section_13

Saturn's rings require at least a 15-mm-diameter telescope to resolve and thus were not known to exist until Christiaan Huygens saw them in 1659. Saturn_sentence_169

Galileo, with his primitive telescope in 1610, incorrectly thought of Saturn's appearing not quite round as two moons on Saturn's sides. Saturn_sentence_170

It was not until Huygens used greater telescopic magnification that this notion was refuted, and the rings were truly seen for the first time. Saturn_sentence_171

Huygens also discovered Saturn's moon Titan; Giovanni Domenico Cassini later discovered four other moons: Iapetus, Rhea, Tethys and Dione. Saturn_sentence_172

In 1675, Cassini discovered the gap now known as the Cassini Division. Saturn_sentence_173

No further discoveries of significance were made until 1789 when William Herschel discovered two further moons, Mimas and Enceladus. Saturn_sentence_174

The irregularly shaped satellite Hyperion, which has a resonance with Titan, was discovered in 1848 by a British team. Saturn_sentence_175

In 1899 William Henry Pickering discovered Phoebe, a highly irregular satellite that does not rotate synchronously with Saturn as the larger moons do. Saturn_sentence_176

Phoebe was the first such satellite found and it takes more than a year to orbit Saturn in a retrograde orbit. Saturn_sentence_177

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. Saturn_sentence_178

Modern NASA and ESA probes Saturn_section_14

Main article: Exploration of Saturn Saturn_sentence_179

Pioneer 11 flyby Saturn_section_15

Pioneer 11 made the first flyby of Saturn in September 1979, when it passed within 20,000 km of the planet's cloud tops. Saturn_sentence_180

Images were taken of the planet and a few of its moons, although their resolution was too low to discern surface detail. Saturn_sentence_181

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. Saturn_sentence_182

In addition, Pioneer 11 measured the temperature of Titan. Saturn_sentence_183

Voyager flybys Saturn_section_16

In November 1980, the Voyager 1 probe visited the Saturn system. Saturn_sentence_184

It sent back the first high-resolution images of the planet, its rings and satellites. Saturn_sentence_185

Surface features of various moons were seen for the first time. Saturn_sentence_186

Voyager 1 performed a close flyby of Titan, increasing knowledge of the atmosphere of the moon. Saturn_sentence_187

It proved that Titan's atmosphere is impenetrable in visible wavelengths; therefore no surface details were seen. Saturn_sentence_188

The flyby changed the spacecraft's trajectory out from the plane of the Solar System. Saturn_sentence_189

Almost a year later, in August 1981, Voyager 2 continued the study of the Saturn system. Saturn_sentence_190

More close-up images of Saturn's moons were acquired, as well as evidence of changes in the atmosphere and the rings. Saturn_sentence_191

Unfortunately, during the flyby, the probe's turnable camera platform stuck for a couple of days and some planned imaging was lost. Saturn_sentence_192

Saturn's gravity was used to direct the spacecraft's trajectory towards Uranus. Saturn_sentence_193

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). Saturn_sentence_194

Cassini–Huygens spacecraft Saturn_section_17

Main article: Cassini–Huygens Saturn_sentence_195

The Cassini–Huygens space probe entered orbit around Saturn on 1 July 2004. Saturn_sentence_196

In June 2004, it conducted a close flyby of Phoebe, sending back high-resolution images and data. Saturn_sentence_197

Cassini's flyby of Saturn's largest moon, Titan, captured radar images of large lakes and their coastlines with numerous islands and mountains. Saturn_sentence_198

The orbiter completed two Titan flybys before releasing the Huygens probe on 25 December 2004. Saturn_sentence_199

Huygens descended onto the surface of Titan on 14 January 2005. Saturn_sentence_200

Starting in early 2005, scientists used Cassini to track lightning on Saturn. Saturn_sentence_201

The power of the lightning is approximately 1,000 times that of lightning on Earth. Saturn_sentence_202

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. Saturn_sentence_203

These jets of icy particles are emitted into orbit around Saturn from vents in the moon's south polar region. Saturn_sentence_204

Over 100 geysers have been identified on Enceladus. Saturn_sentence_205

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". Saturn_sentence_206

Cassini photographs have revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. Saturn_sentence_207

The source of this ring is hypothesized to be the crashing of a meteoroid off Janus and Epimetheus. Saturn_sentence_208

In July 2006, images were returned of hydrocarbon lakes near Titan's north pole, the presence of which were confirmed in January 2007. Saturn_sentence_209

In March 2007, hydrocarbon seas were found near the North pole, the largest of which is almost the size of the Caspian Sea. Saturn_sentence_210

In October 2006, the probe detected an 8,000 km diameter cyclone-like storm with an eyewall at Saturn's south pole. Saturn_sentence_211

From 2004 to 2 November 2009, the probe discovered and confirmed eight new satellites. Saturn_sentence_212

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). Saturn_sentence_213

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. Saturn_sentence_214

The atmospheric entry of Cassini ended the mission. Saturn_sentence_215

Possible future missions Saturn_section_18

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. Saturn_sentence_216

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. Saturn_sentence_217

Observation Saturn_section_19

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. Saturn_sentence_218

(Uranus, and occasionally 4 Vesta, are visible to the naked eye in dark skies.) Saturn_sentence_219

Saturn appears to the naked eye in the night sky as a bright, yellowish point of light. Saturn_sentence_220

The mean apparent magnitude of Saturn is 0.46 with a standard deviation of 0.34. Saturn_sentence_221

Most of the magnitude variation is due to the inclination of the ring system relative to the Sun and Earth. Saturn_sentence_222

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. Saturn_sentence_223

It takes approximately 29.5 years for the planet to complete an entire circuit of the ecliptic against the background constellations of the zodiac. Saturn_sentence_224

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. Saturn_sentence_225

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. Saturn_sentence_226

Such a "disappearance" will next occur in 2025, but Saturn will be too close to the Sun for observations. Saturn_sentence_227

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. Saturn_sentence_228

A Saturnian opposition occurs every year—approximately every 378 days—and results in the planet appearing at its brightest. Saturn_sentence_229

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_sentence_230

Saturn also appears brighter when the rings are angled such that they are more visible. Saturn_sentence_231

For example, during the opposition of 17 December 2002, Saturn appeared at its brightest due to a favorable relative to the Earth, even though Saturn was closer to the Earth and Sun in late 2003. Saturn_sentence_232

From time to time, Saturn is occulted by the Moon (that is, the Moon covers up Saturn in the sky). Saturn_sentence_233

As with all the planets in the Solar System, occultations of Saturn occur in "seasons". Saturn_sentence_234

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. Saturn_sentence_235

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). Saturn_sentence_236

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