Saturn

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 about nine times that of Earth.[13][14] It has only one-eighth the average density of Earth, but with its larger volume Saturn is over 95 times more massive.[15][16][17] Saturn is named after the Roman god of agriculture; its astronomical symbol (♄) represents the god's sickle.

Saturn's interior is probably composed of a core of iron–nickel and rock (silicon and oxygen compounds). This 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. 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 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.[18] 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 those on Neptune.[19] In January 2019, astronomers reported that a day on the planet Saturn has been determined to be  10h 33m 38s + 1m 52s
− 1m 19s
, based on studies of the planet's C Ring.[7][8]

The planet's most famous feature is its prominent ring system that is composed mostly of ice particles, with a smaller amount of rocky debris and dust. At least 62 moons[20] are known to orbit Saturn, of which 53 are officially named. This does not include the hundreds of moonlets in the 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.[21]

Saturn Saturn symbol.svg
Saturn during Equinox
Pictured in natural color approaching equinox, photographed by Cassini in July 2008; the dot in the bottom left corner is Titan
Designations
Pronunciation/ˈsætərn/ (listen)[1]
Named after
Saturn
AdjectivesSaturnian, Cronian
Orbital characteristics[5]
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
378.09 days
9.68 km/s (6.01 mi/s)
317.020°[3]
Inclination
113.665°
339.392°[3]
Known satellites62 with formal designations; innumerable additional moonlets.[5]
Physical characteristics[5]
Mean radius
58,232 km (36,184 mi)[a]
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
  • 4.27×1010 km2 (1.65×1010 sq mi)[6][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)
0.210 I/MR2 estimate
35.5 km/s (22.1 mi/s)[a]
 10h 33m 38s + 1m 52s
− 1m 19s
[7][8]
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. min mean max
1 bar 134 K (−139 °C)
0.1 bar 84 K (−189 °C)
−0.55[11] to +1.17[11]
14.5″ to 20.1″ (excludes rings)
Atmosphere[5]
Surface pressure
140 kPa[12]
59.5 km (37.0 mi)
Composition by volumeby volume:
96.3%±2.4%hydrogen (H
2
)
3.25%±2.4%helium (He)
0.45%±0.2%methane (CH
4
)
0.0125%±0.0075%ammonia (NH
3
)
0.0110%±0.0058%hydrogen deuteride (HD)
0.0007%±0.00015%ethane (C
2
H
6
)
Ices:

Physical characteristics

Saturn, Earth size comparison
Composite image comparing the sizes of Saturn and Earth

Saturn is a gas giant because it is predominantly composed of hydrogen and helium. It lacks a definite surface, though it may have a solid core.[22] 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.[5] 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% that 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 for Earth.[23]

Saturn is the only planet of the Solar System that is less dense than water—about 30% less.[24] 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,[25] and Saturn is 95 times Earth's mass.[5] Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System.[26]

Internal structure

Saturn diagram
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.[26]

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.[27] This core is similar in composition to Earth, but more dense. 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,[28][29] which corresponds to a diameter of about 25,000 km.[30] 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.[31][32][33]

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. 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.[34][35] These descending droplets may have accumulated into a helium shell surrounding the core.[27] Rainfalls of diamonds have been suggested to occur within Saturn, as well as in Jupiter[36] and ice giants Uranus and Neptune.[37]

Atmosphere

PIA18354-Saturn-MethaneBands-20150906
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.[38] The proportion of helium is significantly deficient compared to the abundance of this element in the Sun.[27] 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.[39]

Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been detected in Saturn's atmosphere.[40][41][42] The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH
4
SH) or water.[43] 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.[42]

Cloud layers

Saturn Storm
A global storm girdles the planet in 2011. The head of the storm (bright area) passes the tail circling around the left limb.

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.[44]

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 185–270 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.[45]

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.[46] 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.[47]

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).[48] 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.[49] 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.[50] 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.[50]

North pole hexagonal cloud pattern

Rotatingsaturnhexagon
Saturn's north pole (IR animation)
Looking saturn in the eye
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.[51][52][53] The sides of the hexagon are each about 13,800 km (8,600 mi) long, which is longer than the diameter of the Earth.[54] 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.[55] The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere.[56] 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.[57][58]

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.[59] NASA reported in November 2006 that Cassini had observed a "hurricane-like" storm locked to the south pole that had a clearly defined eyewall.[60][61] 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.[62]

The south pole storm may have been present for billions of years.[63] This vortex is comparable to the size of Earth, and it has winds of 550 km/h.[63]

Other features

Cassini observed a series of cloud features nicknamed "String of Pearls" found in northern latitudes. These features are cloud clearings that reside in deeper cloud layers.[64]

Magnetosphere

Saturn's double aurorae (captured by the Hubble Space Telescope)
Polar aurorae on Saturn
Hubble sees a flickering light display on Saturn
Auroral lights at Saturn's north pole[65]
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.[18] As a result, Saturn's magnetosphere is much smaller than Jupiter's.[66] 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),[67] although it enlarged within several hours, and remained so for about three days.[68] 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.[66] 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.[18] Saturn's magnetosphere, like Earth's, produces aurorae.[69]

Orbit and rotation

PIA20517-Saturn&Rings-CassiniSpacecraftScene-20161028
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,[5] it takes Saturn 10,759 Earth days (or about ​29 12 years)[70] to finish one revolution around the Sun.[5] As a consequence, it forms a near 5:2 mean-motion resonance with Jupiter.[71] The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth.[5] The perihelion and aphelion distances are, respectively, 9.195 and 9.957 AU, on average.[5][72] 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 10 hr 14 min 00 sec (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 10 hr 38 min 25.4 sec (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,[73] System III has a rotation period of 10 hr 39 min 22.4 sec (810.8°/d). System III has largely superseded System II.[74]

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 10 hr 45 min 45 sec (± 36 sec).[75][76] 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 hr 32 min 35 sec.[77]

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.[78][79][80]

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.[81]

Natural satellites

Saturn System Montage - GPN-2000-000439
A montage of Saturn and its principal moons (Dione, Tethys, Mimas, Enceladus, Rhea and Titan; Iapetus not shown). This famous image was created from photographs taken in November 1980 by the Voyager 1 spacecraft.

Saturn has 62 known moons, 53 of which have formal names.[82][83] In addition, there is evidence of dozens to hundreds of moonlets with diameters of 40–500 meters in Saturn's rings,[84] 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.[85] Saturn's second-largest moon, Rhea, may have a tenuous ring system of its own,[86] along with a tenuous atmosphere.[87][88][89]

PIA18078-PossibleBeginning-NewMoonOfPlanetSaturn-20130415
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.[90] 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,[91][92] in which a complex organic chemistry occurs. It is the only satellite with hydrocarbon lakes.[93][94]

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.[95] 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.[96]

Saturn's moon Enceladus, which seems similar in chemical makeup to comets,[97] has often been regarded as a potential habitat for microbial life.[98][99][100][101] 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.[102][103][104] A 2015 flyby by Cassini through a plume on Enceladus found most of the ingredients to sustain life forms that live by methanogenesis.[105]

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.[106]

Planetary rings

Saturn from Cassini Orbiter (2007-01-19)
The rings of Saturn (imaged here by Cassini in 2007) are the most massive and conspicuous in the Solar System.[32]
Saturn's A Ring From the Inside Out
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.[32] 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.[107] The particles that make up the rings range in size from specks of dust up to 10 m.[108] 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 formed. Some ice in the E ring comes from the moon Enceladus's geysers.[109][110][111][112] The water abundance of the rings vary radially, with the outermost ring A being the most pure in ice water. This abundance variance may be explained by meteor bombardment.[113]

Beyond the main rings at a distance of 12 million km from the planet is the sparse Phoebe ring, which is tilted at an angle of 27° to the other rings and, like Phoebe, orbits in retrograde fashion.[114]

Some of the moons of Saturn, including Pandora and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out.[115] Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses.[116]

History of observation and exploration

Galileo.arp.300pix
Galileo Galilei first observed the rings of Saturn in 1610

The observation and exploration of Saturn can be divided into three main phases. The first era was ancient observations (such as with the naked eye), before the invention of the modern telescopes. Starting in the 17th century, progressively more advanced telescopic observations from Earth have been made. The third phase is visitation by space probes, by either orbiting or flyby. In the 21st century, 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[117] and in early recorded history it was a major character in various mythologies. Babylonian astronomers systematically observed and recorded the movements of Saturn.[118] In ancient Greek, the planet was known as Phainon, and in Roman times it was known as the "star of Saturn".[119] In ancient Roman mythology, the planet Phainon was sacred to this agricultural god, from which the planet takes its modern name.[120] The Romans considered the god Saturnus the equivalent of the Greek god Cronus; in modern Greek, the planet retains the name Cronus—Κρόνος: Kronos.)[121]

The Greek scientist Ptolemy based his calculations of Saturn's orbit on observations he made while it was in opposition.[122] 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.[120][122] 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.[123][124][125]

In ancient Hebrew, Saturn is called 'Shabbathai'.[126] Its angel is Cassiel. Its intelligence or beneficial spirit is 'Agȋȇl (Hebrew: עֲזָאזֵל‎, translit. ʿAgyal),[127] and its darker spirit (demon) is Zȃzȇl (Hebrew: זאזל‎, translit. Zazl).[127][128][129] Zazel has been described as a great angel, invoked in Solomonic magic, who is "effective in love conjurations".[130][131] In Ottoman Turkish, Urdu and Malay, the name of Zazel is 'Zuhal', derived from the Arabic language (Arabic: زحل‎, translit. Zuhal).[128]

European observations (17th–19th centuries)

Saturn Robert Hooke 1666
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[132] to resolve and thus were not known to exist until Galileo first saw them in 1610.[133][134] He thought of them as two moons on Saturn's sides.[135][136] It was not until Christiaan Huygens used greater telescopic magnification that this notion was refuted. Huygens 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.[137]

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.[138]

In 1899 William Henry Pickering discovered Phoebe, a highly irregular satellite that does not rotate synchronously with Saturn as the larger moons do.[138] 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.[139]

Modern NASA and ESA probes

Pioneer 11 flyby

P11saturnb
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.[140]

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.[141]

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.[141]

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 probe on 25 December 2004. Huygens descended onto the surface of Titan on 14 January 2005.[142]

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.[143]

Enceladus geysers June 2009
At Enceladus's south pole geysers spray water from many locations along the tiger stripes.[144]

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.[145] Over 100 geysers have been identified on Enceladus.[144] 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".[146][147]

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.[148] 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.[149] In October 2006, the probe detected an 8,000 km diameter cyclone-like storm with an eyewall at Saturn's south pole.[150]

From 2004 to 2 November 2009, the probe discovered and confirmed eight new satellites.[151] 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).[152] 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.[153][154] 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 an atmospheric entry probe and possible investigations into the habitability and possible discovery of life on Saturn's moons Titan and Enceladus.[155]

Observation

Saturn-27-03-04.jpeg
Amateur telescopic view of Saturn

Saturn is the most distant of the five planets easily visible to the naked eye from Earth, the other four being Mercury, Venus, Mars and Jupiter. (Uranus and occasionally 4 Vesta are visible to the naked eye in dark skies.) Saturn appears to the naked eye in the night sky as a bright, yellowish point of light. The mean apparent magnitude of Saturn is 0.46 with a standard deviation of 0.34.[11] 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.[11] 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.[32][132] Twice every Saturnian year (roughly every 15 Earth years), the rings briefly disappear from view, due to the way in which they are angled and because they are so thin. Such a "disappearance" will next occur in 2025, but Saturn will be too close to the Sun for any ring-crossing observation to be possible.[156]

Saturnoppositions-animated
Simulated appearance of Saturn as seen from Earth (at opposition) during an orbit of Saturn, 2001-2029
Saturn eclipse
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,[157] even though Saturn was closer to the Earth and Sun in late 2003.[157]

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 12 or more times over a 12-month period, followed by about a five-year period in which no such activity is registered.[158] Australian astronomy experts Hill and Horner explain the seasonal nature of Saturnian occultations:

This is the result of the fact that the moon’s orbit around the Earth is tilted to the orbit of the Earth around the Sun – and so most of the time, the moon will pass above or below Saturn in the sky, and no occultation will occur. It is only when Saturn lies near the point that the moon’s orbit crosses the "plane of the ecliptic" that occultations can happen – and then they occur every time the moon swings by, until Saturn moves away from the crossing point.[158]

PIA17218 – A Farewell to Saturn, Annotated Version
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

References

  1. ^ Walter, Elizabeth (21 April 2003). Cambridge Advanced Learner's Dictionary (Second ed.). Cambridge University Press. ISBN 978-0-521-53106-1.
  2. ^ Seligman, Courtney. "Rotation Period and Day Length". Archived from the original on 11 August 2011. Retrieved 13 August 2009.
  3. ^ a b c d Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.; Francou, G.; Laskar, J. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics. 282 (2): 663–683. Bibcode:1994A&A...282..663S.
  4. ^ "The MeanPlane (Invariable plane) of the Solar System passing through the barycenter". 3 April 2009. Archived from the original on 14 May 2009. Retrieved 10 April 2009. (produced with Solex 10 Archived 29 April 2009 at WebCite written by Aldo Vitagliano; see also Invariable plane)
  5. ^ a b c d e f g h i j Williams, David R. (23 December 2016). "Saturn Fact Sheet". NASA. Archived from the original on 12 October 2017. Retrieved 12 October 2017.
  6. ^ "NASA: Solar System Exploration: Planets: Saturn: Facts & Figures". Solarsystem.nasa.gov. 22 March 2011. Archived from the original on 6 October 2011. Retrieved 8 August 2011.
  7. ^ a b McCartney, Gretchen; Wendel, JoAnna (18 January 2019). "Scientists Finally Know What Time It Is on Saturn". NASA. Retrieved 18 January 2019.
  8. ^ a b Mankovich, Christopher; et al. (17 January 2019). "Cassini Ring Seismology as a Probe of Saturn's Interior. I. Rigid Rotation". The Astrophysical Journal. 871 (1): 1. doi:10.3847/1538-4357/aaf798.
  9. ^ Hanel, R.A.; et al. (1983). "Albedo, internal heat flux, and energy balance of Saturn". Icarus. 53 (2): 262–285. Bibcode:1983Icar...53..262H. doi:10.1016/0019-1035(83)90147-1.
  10. ^ Mallama, Anthony; Krobusek, Bruce; Pavlov, Hristo (2017). "Comprehensive wide-band magnitudes and albedos for the planets, with applications to exo-planets and Planet Nine". Icarus. 282: 19–33. arXiv:1609.05048. Bibcode:2017Icar..282...19M. doi:10.1016/j.icarus.2016.09.023.
  11. ^ a b c d Mallama, A.; Hilton, J.L. (2018). "Computing Apparent Planetary Magnitudes for The Astronomical Almanac". Astronomy and Computing. 25: 10–24. arXiv:1808.01973. Bibcode:2018A&C....25...10M. doi:10.1016/j.ascom.2018.08.002.
  12. ^ Knecht, Robin (24 October 2005). "On The Atmospheres Of Different Planets" (PDF). Archived from the original (PDF) on 14 October 2017. Retrieved 14 October 2017.
  13. ^ Brainerd, Jerome James (24 November 2004). "Characteristics of Saturn". The Astrophysics Spectator. Archived from the original on 5 October 2011. Retrieved 5 July 2010.
  14. ^ "General Information About Saturn". Scienceray. 28 July 2011. Archived from the original on 6 October 2011. Retrieved 17 August 2011.
  15. ^ Brainerd, Jerome James (6 October 2004). "Solar System Planets Compared to Earth". The Astrophysics Spectator. Archived from the original on 6 October 2011. Retrieved 5 July 2010.
  16. ^ Dunbar, Brian (29 November 2007). "NASA – Saturn". NASA. Archived from the original on 6 October 2011. Retrieved 21 July 2011.
  17. ^ Cain, Fraser (3 July 2008). "Mass of Saturn". Universe Today. Retrieved 17 August 2011.
  18. ^ a b c Russell, C. T.; et al. (1997). "Saturn: Magnetic Field and Magnetosphere". Science. 207 (4429): 407. Bibcode:1980Sci...207..407S. doi:10.1126/science.207.4429.407. Archived from the original on 5 October 2011. Retrieved 29 April 2007.
  19. ^ "The Planets ('Giants')". Science Channel. 8 June 2004.
  20. ^ Piazza, Enrico. "Saturn's Moons". Cassini, Equinox Mission. JPL NASA. Archived from the original on 5 October 2011. Retrieved 22 June 2010.
  21. ^ Munsell, Kirk (6 April 2005). "The Story of Saturn". NASA Jet Propulsion Laboratory; California Institute of Technology. Archived from the original on 22 August 2011. Retrieved 7 July 2007.
  22. ^ Melosh, H. Jay (2011). Planetary Surface Processes. Cambridge Planetary Science. 13. Cambridge University Press. p. 5. ISBN 978-0-521-51418-7.
  23. ^ Gregersen, Erik, ed. (2010). Outer Solar System: Jupiter, Saturn, Uranus, Neptune, and the Dwarf Planets. The Rosen Publishing Group. p. 119. ISBN 978-1615300143.
  24. ^ "Saturn – The Most Beautiful Planet of our solar system". Preserve Articles. 23 January 2011. Archived from the original on 5 October 2011. Retrieved 24 July 2011.
  25. ^ Williams, David R. (16 November 2004). "Jupiter Fact Sheet". NASA. Archived from the original on 5 October 2011. Retrieved 2 August 2007.
  26. ^ a b Fortney, Jonathan J.; Nettelmann, Nadine (May 2010). "The Interior Structure, Composition, and Evolution of Giant Planets". Space Science Reviews. 152 (1–4): 423–447. arXiv:0912.0533. Bibcode:2010SSRv..152..423F. doi:10.1007/s11214-009-9582-x.
  27. ^ a b c Guillot, Tristan; et al. (2009). "Saturn's Exploration Beyond Cassini-Huygens". In Dougherty, Michele K.; Esposito, Larry W.; Krimigis, Stamatios M. Saturn from Cassini-Huygens. Springer Science+Business Media B.V. p. 745. arXiv:0912.2020. Bibcode:2009sfch.book..745G. doi:10.1007/978-1-4020-9217-6_23. ISBN 978-1-4020-9216-9.
  28. ^ Fortney, Jonathan J. (2004). "Looking into the Giant Planets". Science. 305 (5689): 1414–1415. doi:10.1126/science.1101352. PMID 15353790.
  29. ^ Saumon, D.; Guillot, T. (July 2004). "Shock Compression of Deuterium and the Interiors of Jupiter and Saturn". The Astrophysical Journal. 609 (2): 1170–1180. arXiv:astro-ph/0403393. Bibcode:2004ApJ...609.1170S. doi:10.1086/421257.
  30. ^ "Saturn". BBC. 2000. Archived from the original on 21 August 2011. Retrieved 19 July 2011.
  31. ^ Faure, Gunter; Mensing, Teresa M. (2007). Introduction to planetary science: the geological perspective. Springer. p. 337. ISBN 978-1-4020-5233-0.
  32. ^ a b c d "Saturn". National Maritime Museum. 2015-08-20. Archived from the original on 6 October 2011. Retrieved 6 July 2007.
  33. ^ "Structure of Saturn's Interior". Windows to the Universe. Archived from the original on 21 August 2011. Retrieved 19 July 2011.
  34. ^ de Pater, Imke; Lissauer, Jack J. (2010). Planetary Sciences (2nd ed.). Cambridge University Press. pp. 254–255. ISBN 978-0-521-85371-2.
  35. ^ "NASA – Saturn". NASA. 2004. Archived from the original on 21 August 2011. Retrieved 27 July 2007.
  36. ^ Kramer, Miriam (9 October 2013). "Diamond Rain May Fill Skies of Jupiter and Saturn". Space.com. Retrieved 27 August 2017.
  37. ^ Kaplan, Sarah (25 August 2017). "It rains solid diamonds on Uranus and Neptune". The Washington Post. Retrieved 27 August 2017.
  38. ^ "Saturn". Universe Guide. Retrieved 29 March 2009.
  39. ^ Guillot, Tristan (1999). "Interiors of Giant Planets Inside and Outside the Solar System". Science. 286 (5437): 72–77. Bibcode:1999Sci...286...72G. doi:10.1126/science.286.5437.72. PMID 10506563.
  40. ^ Courtin, R.; et al. (1967). "The Composition of Saturn's Atmosphere at Temperate Northern Latitudes from Voyager IRIS spectra". Bulletin of the American Astronomical Society. 15: 831. Bibcode:1983BAAS...15..831C.
  41. ^ Cain, Fraser (22 January 2009). "Atmosphere of Saturn". Universe Today. Archived from the original on 5 October 2011. Retrieved 20 July 2011.
  42. ^ a b Guerlet, S.; Fouchet, T.; Bézard, B. (November 2008). Charbonnel, C.; Combes, F.; Samadi, R., eds. "Ethane, acetylene and propane distribution in Saturn's stratosphere from Cassini/CIRS limb observations". SF2A-2008: Proceedings of the Annual Meeting of the French Society of Astronomy and Astrophysics: 405. Bibcode:2008sf2a.conf..405G.
  43. ^ Martinez, Carolina (5 September 2005). "Cassini Discovers Saturn's Dynamic Clouds Run Deep". NASA. Archived from the original on 5 October 2011. Retrieved 29 April 2007.
  44. ^ Orton, Glenn S. (September 2009). "Ground-Based Observational Support for Spacecraft Exploration of the Outer Planets". Earth, Moon, and Planets. 105 (2–4): 143–152. Bibcode:2009EM&P..105..143O. doi:10.1007/s11038-009-9295-x.
  45. ^ Dougherty, Michele K.; Esposito, Larry W.; Krimigis, Stamatios M. (2009). Dougherty, Michele K.; Esposito, Larry W.; Krimigis, Stamatios M., eds. Saturn from Cassini-Huygens. Saturn from Cassini-Huygens. Springer. p. 162. Bibcode:2009sfch.book.....D. doi:10.1007/978-1-4020-9217-6. ISBN 978-1-4020-9216-9.
  46. ^ Pérez-Hoyos, S.; Sánchez-Laveg, A.; French, R. G.; J. F., Rojas (2005). "Saturn's cloud structure and temporal evolution from ten years of Hubble Space Telescope images (1994–2003)". Icarus. 176 (1): 155–174. Bibcode:2005Icar..176..155P. doi:10.1016/j.icarus.2005.01.014.
  47. ^ Kidger, Mark (1992). "The 1990 Great White Spot of Saturn". In Moore, Patrick. 1993 Yearbook of Astronomy. 1993 Yearbook of Astronomy. London: W.W. Norton & Company. pp. 176–215. Bibcode:1992ybas.conf.....M.
  48. ^ Hamilton, Calvin J. (1997). "Voyager Saturn Science Summary". Solarviews. Archived from the original on 5 October 2011. Retrieved 5 July 2007.
  49. ^ Watanabe, Susan (27 March 2007). "Saturn's Strange Hexagon". NASA. Archived from the original on 1 February 2010. Retrieved 6 July 2007.
  50. ^ a b "Warm Polar Vortex on Saturn". Merrillville Community Planetarium. 2007. Archived from the original on 5 October 2011. Retrieved 25 July 2007.
  51. ^ Godfrey, D. A. (1988). "A hexagonal feature around Saturn's North Pole". Icarus. 76 (2): 335. Bibcode:1988Icar...76..335G. doi:10.1016/0019-1035(88)90075-9.
  52. ^ Sanchez-Lavega, A.; et al. (1993). "Ground-based observations of Saturn's north polar SPOT and hexagon". Science. 260 (5106): 329–32. Bibcode:1993Sci...260..329S. doi:10.1126/science.260.5106.329. PMID 17838249.
  53. ^ Overbye, Dennis (6 August 2014). "Storm Chasing on Saturn". New York Times. Retrieved 6 August 2014.
  54. ^ "New images show Saturn's weird hexagon cloud". MSNBC. 12 December 2009. Archived from the original on 5 October 2011. Retrieved 29 September 2011.
  55. ^ Godfrey, D. A. (9 March 1990). "The Rotation Period of Saturn's Polar Hexagon". Science. 247 (4947): 1206–1208. Bibcode:1990Sci...247.1206G. doi:10.1126/science.247.4947.1206. PMID 17809277.
  56. ^ Baines, Kevin H.; et al. (December 2009). "Saturn's north polar cyclone and hexagon at depth revealed by Cassini/VIMS". Planetary and Space Science. 57 (14–15): 1671–1681. Bibcode:2009P&SS...57.1671B. doi:10.1016/j.pss.2009.06.026.
  57. ^ Ball, Philip (19 May 2006). "Geometric whirlpools revealed". Nature. doi:10.1038/news060515-17. Bizarre geometric shapes that appear at the center of swirling vortices in planetary atmospheres might be explained by a simple experiment with a bucket of water but correlating this to Saturn's pattern is by no means certain.
  58. ^ Aguiar, Ana C. Barbosa; et al. (April 2010). "A laboratory model of Saturn's North Polar Hexagon". Icarus. 206 (2): 755–763. Bibcode:2010Icar..206..755B. doi:10.1016/j.icarus.2009.10.022. Retrieved 20 February 2013. Laboratory experiment of spinning disks in a liquid solution forms vortices around a stable hexagonal pattern similar to that of Saturn's.
  59. ^ Sánchez-Lavega, A.; et al. (8 October 2002). "Hubble Space Telescope Observations of the Atmospheric Dynamics in Saturn's South Pole from 1997 to 2002". Bulletin of the American Astronomical Society. 34: 857. Bibcode:2002DPS....34.1307S. Retrieved 6 July 2007.
  60. ^ "NASA catalog page for image PIA09187". NASA Planetary Photojournal. Archived from the original on 5 October 2011. Retrieved 23 May 2007.
  61. ^ "Huge 'hurricane' rages on Saturn". BBC News. 10 November 2006. Archived from the original on 5 October 2011. Retrieved 29 September 2011.
  62. ^ "NASA Sees into the Eye of a Monster Storm on Saturn". NASA. 9 November 2006. Archived from the original on 5 October 2011. Retrieved 20 November 2006.
  63. ^ a b Nemiroff, R.; Bonnell, J., eds. (13 November 2006). "A Hurricane Over the South Pole of Saturn". Astronomy Picture of the Day. NASA. Retrieved 1 May 2013.
  64. ^ "Cassini Image Shows Saturn Draped in a String of Pearls" (Press release). Carolina Martinez, NASA. 10 November 2006. Retrieved 3 March 2013.
  65. ^ "Hubble sees a flickering light display on Saturn". ESA/Hubble Picture of the Week. Retrieved 20 May 2014.
  66. ^ a b McDermott, Matthew (2000). "Saturn: Atmosphere and Magnetosphere". Thinkquest Internet Challenge. Archived from the original on 5 October 2011. Retrieved 15 July 2007.
  67. ^ "Voyager – Saturn's Magnetosphere". NASA Jet Propulsion Laboratory. 18 October 2010. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  68. ^ Atkinson, Nancy (14 December 2010). "Hot Plasma Explosions Inflate Saturn's Magnetic Field". Universe Today. Archived from the original on 6 October 2011. Retrieved 24 August 2011.
  69. ^ Russell, Randy (3 June 2003). "Saturn Magnetosphere Overview". Windows to the Universe. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  70. ^ Cain, Fraser (26 January 2009). "Orbit of Saturn". Universe Today. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  71. ^ Michtchenko, T. A.; Ferraz-Mello, S. (February 2001). "Modeling the 5 : 2 Mean-Motion Resonance in the Jupiter-Saturn Planetary System". Icarus. 149 (2): 357−374. Bibcode:2001Icar..149..357M. doi:10.1006/icar.2000.6539.
  72. ^ Jean Meeus, Astronomical Algorithms (Richmond, VA: Willmann-Bell, 1998). Average of the nine extremes on p 273. All are within 0.02 AU of the averages.
  73. ^ Kaiser, M. L.; Desch, M. D.; Warwick, J. W.; Pearce, J. B. (1980). "Voyager Detection of Nonthermal Radio Emission from Saturn". Science. 209 (4462): 1238–40. Bibcode:1980Sci...209.1238K. doi:10.1126/science.209.4462.1238. hdl:2060/19800013712. PMID 17811197.
  74. ^ Benton, Julius (2006). Saturn and how to observe it. Astronomers' observing guides (11th ed.). Springer Science & Business. p. 136. ISBN 978-1-85233-887-9.
  75. ^ "Scientists Find That Saturn's Rotation Period is a Puzzle". NASA. 28 June 2004. Archived from the original on 21 August 2011. Retrieved 22 March 2007.
  76. ^ Cain, Fraser (30 June 2008). "Saturn". Universe Today. Archived from the original on 6 October 2011. Retrieved 17 August 2011.
  77. ^ Anderson, J. D.; Schubert, G. (2007). "Saturn's gravitational field, internal rotation and interior structure". Science. 317 (5843): 1384–1387. Bibcode:2007Sci...317.1384A. doi:10.1126/science.1144835. PMID 17823351.
  78. ^ "Enceladus Geysers Mask the Length of Saturn's Day" (Press release). NASA Jet Propulsion Laboratory. 22 March 2007. Archived from the original on 6 October 2011. Retrieved 22 March 2007.
  79. ^ Gurnett, D. A.; et al. (2007). "The Variable Rotation Period of the Inner Region of Saturn's Plasma Disc". Science. 316 (5823): 442–5. Bibcode:2007Sci...316..442G. doi:10.1126/science.1138562. PMID 17379775.
  80. ^ Bagenal, F. (2007). "A New Spin on Saturn's Rotation". Science. 316 (5823): 380–1. doi:10.1126/science.1142329. PMID 17446379.
  81. ^ Hou, X. Y.; et al. (January 2014). "Saturn Trojans: a dynamical point of view". Monthly Notices of the Royal Astronomical Society. 437 (2): 1420−1433. Bibcode:2014MNRAS.437.1420H. doi:10.1093/mnras/stt1974.
  82. ^ "Solar System Dynamics - Planetary Satellite Discovery Circumstances". NASA. 9 March 2015. Retrieved 26 February 2016.
  83. ^ Wall, Mike (21 June 2011). "Saturn's 'Ice Queen' Moon Helene Shimmers in New Photo". Space.com. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  84. ^ Tiscareno, Matthew (17 July 2013). "The population of propellers in Saturn's A Ring". The Astronomical Journal. 135 (3): 1083–1091. arXiv:0710.4547. Bibcode:2008AJ....135.1083T. doi:10.1088/0004-6256/135/3/1083.
  85. ^ Brunier, Serge (2005). Solar System Voyage. Cambridge University Press. p. 164. ISBN 978-0-521-80724-1.
  86. ^ Jones, G. H.; et al. (7 March 2008). "The Dust Halo of Saturn's Largest Icy Moon, Rhea". Science. 319 (5868): 1380–1384. Bibcode:2008Sci...319.1380J. doi:10.1126/science.1151524. PMID 18323452.
  87. ^ Atkinson, Nancy (26 November 2010). "Tenuous Oxygen Atmosphere Found Around Saturn's Moon Rhea". Universe Today. Archived from the original on 6 October 2011. Retrieved 20 July 2011.
  88. ^ NASA (30 November 2010). "Thin air: Oxygen atmosphere found on Saturn's moon Rhea". ScienceDaily. Archived from the original on 6 October 2011. Retrieved 23 July 2011.
  89. ^ Ryan, Clare (26 November 2010). "Cassini reveals oxygen atmosphere of Saturn′s moon Rhea". UCL Mullard Space Science Laboratory. Archived from the original on 6 October 2011. Retrieved 23 July 2011.
  90. ^ "Saturn's Known Satellites". Department of Terrestrial Magnetism. Archived from the original on 6 October 2011. Retrieved 22 June 2010.
  91. ^ "Cassini Finds Hydrocarbon Rains May Fill Titan Lakes". ScienceDaily. 30 January 2009. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  92. ^ "Voyager – Titan". NASA Jet Propulsion Laboratory. 18 October 2010. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  93. ^ "Evidence of hydrocarbon lakes on Titan". MSNBC. Associated Press. 25 July 2006. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  94. ^ "Hydrocarbon lake finally confirmed on Titan". Cosmos Magazine. 31 July 2008. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  95. ^ López-Puertas, Manuel (6 June 2013). "PAH's in Titan's Upper Atmosphere". CSIC. Retrieved 6 June 2013.
  96. ^ Dyches, Preston; et al. (23 June 2014). "Titan's Building Blocks Might Pre-date Saturn". NASA. Retrieved 24 June 2014.
  97. ^ Battersby, Stephen (26 March 2008). "Saturn's moon Enceladus surprisingly comet-like". New Scientist. Retrieved 16 April 2015.
  98. ^ NASA (21 April 2008). "Could There Be Life On Saturn's Moon Enceladus?". ScienceDaily. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  99. ^ Madrigal, Alexis (24 June 2009). "Hunt for Life on Saturnian Moon Heats Up". Wired Science. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  100. ^ Spotts, Peter N. (28 September 2005). "Life beyond Earth? Potential solar system sites pop up". USA Today. Archived from the original on 6 October 2011. Retrieved 21 July 2011.
  101. ^ Pili, Unofre (9 September 2009). "Enceladus: Saturn′s Moon, Has Liquid Ocean of Water". Scienceray. Archived from the original on 6 October 2011. Retrieved 21 July 2011.
  102. ^ "Strongest evidence yet indicates Enceladus hiding saltwater ocean". Physorg. 22 June 2011. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  103. ^ Kaufman, Marc (22 June 2011). "Saturn′s moon Enceladus shows evidence of an ocean beneath its surface". Washington Post. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  104. ^ Greicius, Tony; et al. (22 June 2011). "Cassini Captures Ocean-Like Spray at Saturn Moon". NASA. Archived from the original on 6 October 2011. Retrieved 17 September 2011.
  105. ^ Chou, Felicia; Dyches, Preston; Weaver, Donna; Villard, Ray (13 April 2017). "NASA Missions Provide New Insights into 'Ocean Worlds' in Our Solar System". NASA. Retrieved 20 April 2017.
  106. ^ Platt, Jane; et al. (14 April 2014). "NASA Cassini Images May Reveal Birth of a Saturn Moon". NASA. Retrieved 14 April 2014.
  107. ^ Poulet F.; et al. (2002). "The Composition of Saturn's Rings". Icarus. 160 (2): 350. Bibcode:2002Icar..160..350P. doi:10.1006/icar.2002.6967.
  108. ^ Porco, Carolyn. "Questions about Saturn's rings". CICLOPS web site. Retrieved 18 June 2017.
  109. ^ Spahn, F.; et al. (2006). "Cassini Dust Measurements at Enceladus and Implications for the Origin of the E Ring" (PDF). Science. 311 (5766): 1416–1418. Bibcode:2006Sci...311.1416S. CiteSeerX 10.1.1.466.6748. doi:10.1126/science.1121375. PMID 16527969.
  110. ^ "Finger-like Ring Structures In Saturn's E Ring Produced By Enceladus' Geysers". CICLOPS web site.
  111. ^ "Icy Tendrils Reaching into Saturn Ring Traced to Their Source". CICLOPS web site (Press release). 14 April 2015.
  112. ^ "The Real Lord of the Rings". Science@NASA. 12 February 2002. Archived from the original on 19 August 2016. Retrieved 8 February 2018.
  113. ^ Esposito, Larry W.; et al. (February 2005). "Ultraviolet Imaging Spectroscopy Shows an Active Saturnian System". Science. 307 (5713): 1251−1255. Bibcode:2005Sci...307.1251E. doi:10.1126/science.1105606. PMID 15604361.
  114. ^ Cowen, Rob (7 November 1999). "Largest known planetary ring discovered". Science News. Archived from the original on 6 October 2011. Retrieved 9 April 2010.
  115. ^ Russell, Randy (7 June 2004). "Saturn Moons and Rings". Windows to the Universe. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  116. ^ NASA Jet Propulsion Laboratory (3 March 2005). "NASA's Cassini Spacecraft Continues Making New Discoveries". ScienceDaily. Archived from the original on 6 October 2011. Retrieved 19 July 2011.
  117. ^ "Observing Saturn". National Maritime Museum. 2015-08-20. Archived from the original on 22 April 2007. Retrieved 6 July 2007.
  118. ^ Sachs, A. (2 May 1974). "Babylonian Observational Astronomy". Philosophical Transactions of the Royal Society of London. 276 (1257): 43–50. Bibcode:1974RSPTA.276...43S. doi:10.1098/rsta.1974.0008. JSTOR 74273.
  119. ^ Cicero, De Natura Deorum.
  120. ^ a b "Starry Night Times". Imaginova Corp. 2006. Archived from the original on 21 August 2011. Retrieved 5 July 2007.
  121. ^ "Greek Names of the Planets". 2010-04-25. Retrieved 14 July 2012. The Greek name of the planet Saturn is Kronos. The Titan Cronus was the father of Zeus, while Saturn was the Roman God of agriculture. See also the Greek article about the planet.
  122. ^ a b Corporation, Bonnier (April 1893). "Popular Miscellany – Superstitions about Saturn". The Popular Science Monthly: 862.
  123. ^ De Groot, Jan Jakob Maria (1912). Religion in China: universism. a key to the study of Taoism and Confucianism. American lectures on the history of religions. 10. G. P. Putnam's Sons. p. 300. Retrieved 8 January 2010.
  124. ^ Crump, Thomas (1992). The Japanese numbers game: the use and understanding of numbers in modern Japan. Nissan Institute/Routledge Japanese studies series. Routledge. pp. 39–40. ISBN 978-0415056090.
  125. ^ Hulbert, Homer Bezaleel (1909). The passing of Korea. Doubleday, Page & company. p. 426. Retrieved 8 January 2010.
  126. ^ Cessna, Abby (15 November 2009). "When Was Saturn Discovered?". Universe Today. Archived from the original on 6 October 2011. Retrieved 21 July 2011.
  127. ^ a b "The Magus, Book I: The Celestial Intelligencer: Chapter XXVIII". Sacred-Text.com. Retrieved 4 August 2018.
  128. ^ Beyer, Catherine (8 March 2017). "Planetary Spirit Sigils - 01 Spirit of Saturn". ThoughtCo.com. Retrieved 3 August 2018.
  129. ^ "Meaning and Origin of: Zazel". FamilyEducation.com. 2014. Retrieved 3 August 2018. Latin: Angel summoned for love invocations
  130. ^ "Angelic Beings". Hafapea.com. 1998. Retrieved 3 August 2018. a Solomonic angel of love rituals
  131. ^ a b Eastman, Jack (1998). "Saturn in Binoculars". The Denver Astronomical Society. Archived from the original on 21 August 2011. Retrieved 3 September 2008.
  132. ^ Chan, Gary (2000). "Saturn: History Timeline". Archived from the original on 21 August 2011. Retrieved 16 July 2007.
  133. ^ Cain, Fraser (3 July 2008). "History of Saturn". Universe Today. Archived from the original on 6 October 2011. Retrieved 24 July 2011.
  134. ^ Cain, Fraser (7 July 2008). "Interesting Facts About Saturn". Universe Today. Archived from the original on 6 October 2011. Retrieved 17 September 2011.
  135. ^ Cain, Fraser (27 November 2009). "Who Discovered Saturn?". Universe Today. Archived from the original on 6 October 2011. Retrieved 17 September 2011.
  136. ^ Micek, Catherine. "Saturn: History of Discoveries". Archived from the original on 21 August 2011. Retrieved 15 July 2007.
  137. ^ a b Barton, Samuel G. (April 1946). "The names of the satellites". Popular Astronomy. Vol. 54. pp. 122–130. Bibcode:1946PA.....54..122B.
  138. ^ Kuiper, Gerard P. (November 1944). "Titan: a Satellite with an Atmosphere". Astrophysical Journal. 100: 378–388. Bibcode:1944ApJ...100..378K. doi:10.1086/144679.
  139. ^ "The Pioneer 10 & 11 Spacecraft". Mission Descriptions. Archived from the original on 30 January 2006. Retrieved 5 July 2007.
  140. ^ a b "Missions to Saturn". The Planetary Society. 2007. Archived from the original on 21 August 2011. Retrieved 24 July 2007.
  141. ^ Lebreton, Jean-Pierre; et al. (December 2005). "An overview of the descent and landing of the Huygens probe on Titan". Nature. 438 (7069): 758–764. Bibcode:2005Natur.438..758L. doi:10.1038/nature04347. PMID 16319826.
  142. ^ "Astronomers Find Giant Lightning Storm At Saturn". ScienceDaily LLC. 2007. Archived from the original on 21 August 2011. Retrieved 27 July 2007.
  143. ^ a b Dyches, Preston; et al. (28 July 2014). "Cassini Spacecraft Reveals 101 Geysers and More on Icy Saturn Moon". NASA. Retrieved 29 July 2014.
  144. ^ Pence, Michael (9 March 2006). "NASA's Cassini Discovers Potential Liquid Water on Enceladus". NASA Jet Propulsion Laboratory. Archived from the original on 21 August 2011. Retrieved 3 June 2011.
  145. ^ Lovett, Richard A. (31 May 2011). "Enceladus named sweetest spot for alien life". Nature. doi:10.1038/news.2011.337. Archived from the original on 6 October 2011. Retrieved 3 June 2011.
  146. ^ Kazan, Casey (2 June 2011). "Saturn's Enceladus Moves to Top of "Most-Likely-to-Have-Life" List". The Daily Galaxy. Archived from the original on 21 August 2011. Retrieved 3 June 2011.
  147. ^ Shiga, David (20 September 2007). "Faint new ring discovered around Saturn". NewScientist.com. Archived from the original on 21 August 2011. Retrieved 8 July 2007.
  148. ^ Rincon, Paul (14 March 2007). "Probe reveals seas on Saturn moon". BBC. Archived from the original on 6 October 2011. Retrieved 26 September 2007.
  149. ^ Rincon, Paul (10 November 2006). "Huge 'hurricane' rages on Saturn". BBC. Archived from the original on 6 October 2011. Retrieved 12 July 2007.
  150. ^ "Mission overview – introduction". Cassini Solstice Mission. NASA / JPL. 2010. Archived from the original on 21 August 2011. Retrieved 23 November 2010.
  151. ^ "Massive storm at Saturn's north pole". 3 News NZ. 30 April 2013.
  152. ^ Brown, Dwayne; Cantillo, Laurie; Dyches, Preston (15 September 2017). "NASA's Cassini Spacecraft Ends Its Historic Exploration of Saturn". NASA. Retrieved 15 September 2017.
  153. ^ Chang, Kenneth (14 September 2017). "Cassini Vanishes Into Saturn, Its Mission Celebrated and Mourned". The New York Times. Retrieved 15 September 2017.
  154. ^ Foust, Jeff (8 January 2016). "NASA Expands Frontiers of Next New Frontiers Competition". SpaceNews. Retrieved 20 April 2017.
  155. ^ "Saturn's Rings Edge-On". Classical Astronomy. 2013. Archived from the original on 5 November 2013. Retrieved 4 August 2013.
  156. ^ a b Schmude Jr., Richard W. (Winter 2003). "Saturn in 2002–03". Georgia Journal of Science. 61 (4). ISSN 0147-9369. Retrieved 29 June 2015.
  157. ^ a b Tanya Hill; et al. (9 May 2014). "Bright Saturn will blink out across Australia – for an hour, anyway". The Conversation. Retrieved 11 May 2014.

Further reading

  • Alexander, Arthur Francis O'Donel (1980) [1962]. The Planet Saturn - A History of Observation, Theory and Discovery. Dover. ISBN 978-0-486-23927-9.
  • Gore, Rick (July 1981). "Voyager 1 at Saturn: Riddles of the Rings". National Geographic. Vol. 160 no. 1. pp. 3–31. ISSN 0027-9358. OCLC 643483454.
  • Lovett, L.; et al. (2006). Saturn: A New View. Harry N. Abrams. ISBN 978-0-8109-3090-2.
  • Karttunen, H.; et al. (2007). Fundamental Astronomy (5th ed.). Springer. ISBN 978-3-540-34143-7.
  • Seidelmann, P. Kenneth; et al. (2007). "Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006". Celestial Mechanics and Dynamical Astronomy. 98 (3): 155–180. Bibcode:2007CeMDA..98..155S. doi:10.1007/s10569-007-9072-y.
  • de Pater, Imke; Lissauer, Jack J. (2015). Planetary Sciences (2nd updated ed.). Cambridge University Press. p. 250. ISBN 978-0-521-85371-2.

External links

Apollo program

The Apollo program, also known as Project Apollo, was the third United States human spaceflight program carried out by the National Aeronautics and Space Administration (NASA), which succeeded in landing the first humans on the Moon from 1969 to 1972. First conceived during Dwight D. Eisenhower's administration as a three-man spacecraft to follow the one-man Project Mercury which put the first Americans in space, Apollo was later dedicated to President John F. Kennedy's national goal of "landing a man on the Moon and returning him safely to the Earth" by the end of the 1960s, which he proposed in an address to Congress on May 25, 1961. It was the third US human spaceflight program to fly, preceded by the two-man Project Gemini conceived in 1961 to extend spaceflight capability in support of Apollo.

Kennedy's goal was accomplished on the Apollo 11 mission when astronauts Neil Armstrong and Buzz Aldrin landed their Apollo Lunar Module (LM) on July 20, 1969, and walked on the lunar surface, while Michael Collins remained in lunar orbit in the command and service module (CSM), and all three landed safely on Earth on July 24. Five subsequent Apollo missions also landed astronauts on the Moon, the last in December 1972. In these six spaceflights, twelve men walked on the Moon.

Apollo ran from 1961 to 1972, with the first manned flight in 1968. It achieved its goal of manned lunar landing, despite the major setback of a 1967 Apollo 1 cabin fire that killed the entire crew during a prelaunch test. After the first landing, sufficient flight hardware remained for nine follow-on landings with a plan for extended lunar geological and astrophysical exploration. Budget cuts forced the cancellation of three of these. Five of the remaining six missions achieved successful landings, but the Apollo 13 landing was prevented by an oxygen tank explosion in transit to the Moon, which destroyed the service module's capability to provide electrical power, crippling the CSM's propulsion and life support systems. The crew returned to Earth safely by using the lunar module as a "lifeboat" for these functions. Apollo used Saturn family rockets as launch vehicles, which were also used for an Apollo Applications Program, which consisted of Skylab, a space station that supported three manned missions in 1973–74, and the Apollo–Soyuz Test Project, a joint US-Soviet Union Earth-orbit mission in 1975.

Apollo set several major human spaceflight milestones. It stands alone in sending manned missions beyond low Earth orbit. Apollo 8 was the first manned spacecraft to orbit another celestial body, while the final Apollo 17 mission marked the sixth Moon landing and the ninth manned mission beyond low Earth orbit. The program returned 842 pounds (382 kg) of lunar rocks and soil to Earth, greatly contributing to the understanding of the Moon's composition and geological history. The program laid the foundation for NASA's subsequent human spaceflight capability and funded construction of its Johnson Space Center and Kennedy Space Center. Apollo also spurred advances in many areas of technology incidental to rocketry and manned spaceflight, including avionics, telecommunications, and computers.

Cassini–Huygens

The Cassini–Huygens mission ( kə-SEE-nee HOY-gənz), commonly called Cassini, was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class robotic spacecraft comprised both NASA's Cassini probe, and ESA's Huygens lander which landed on Saturn's largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. The craft were named after astronomers Giovanni Cassini and Christiaan Huygens.

Launched aboard a Titan IVB/Centaur on October 15, 1997, Cassini was active in space for nearly 20 years, with 13 years spent orbiting Saturn, studying the planet and its system after entering orbit on July 1, 2004. The voyage to Saturn included flybys of Venus (April 1998 and July 1999), Earth (August 1999), the asteroid 2685 Masursky, and Jupiter (December 2000). Its mission ended on September 15, 2017, when Cassini's trajectory took it into Saturn's upper atmosphere and it burned up in order to prevent any risk of contaminating Saturn's moons, which might have offered habitable environments to stowaway terrestrial microbes on the spacecraft. The mission is widely perceived to have been successful beyond expectation. Cassini-Huygens has been described by NASA's Planetary Science Division Director as a "mission of firsts", that has revolutionized human understanding of the Saturn system, including its moons and rings, and our understanding of where life might be found in the Solar System.

Cassini's original mission was planned to last for four years, from June 2004 to May 2008. The mission was extended for another two years until September 2010, branded the Cassini Equinox Mission. The mission was extended a second and final time with the Cassini Solstice Mission, lasting another seven years until September 15, 2017, on which date Cassini was de-orbited to burn up in Saturn's upper atmosphere.

The Huygens module traveled with Cassini until its separation from the probe on December 25, 2004; it was landed by parachute on Titan on January 14, 2005. It returned data to Earth for around 90 minutes, using the orbiter as a relay. This was the first landing ever accomplished in the outer Solar System and the first landing on a moon other than our own.

At the end of its mission, the Cassini spacecraft executed the "Grand Finale" of its mission: a number of risky passes through the gaps between Saturn and Saturn's inner rings. The purpose of this phase was to maximize Cassini's scientific outcome before the spacecraft was disposed. The atmospheric entry of Cassini ended the mission, but analyses of the returned data will continue for many years.

Guillermo del Toro

Guillermo del Toro Gómez (Spanish: [ɡiˈʝeɾmo ðel ˈtoɾo]; born October 9, 1964) is a Mexican filmmaker, author, actor, and former special effects makeup artist. He is best known for the Academy Award-winning fantasy films Pan's Labyrinth (2006) and The Shape of Water (2017), winning the Academy Award for Best Director and the Academy Award for Best Picture for the latter.

Throughout his career, del Toro has shifted between personal, lower-budget Spanish language films, such as Cronos (1993) and The Devil's Backbone (2001), and Hollywood tentpoles, including Mimic (1997), Blade II (2002), Hellboy (2004), Hellboy II: The Golden Army (2008), and Pacific Rim (2013). He also directed the gothic romance film Crimson Peak (2015). As a producer, he worked on the films The Orphanage (2007), Don't Be Afraid of the Dark (2010), The Hobbit film series (2012–14), Mama (2013), The Book of Life (2014), and Pacific Rim Uprising (2018).

With Chuck Hogan, he co-authored The Strain trilogy of novels (2009–2011), later adapted into a comic-book series (2011–15) and a live-action television series (2014–17). With DreamWorks Animation, he created the Netflix animated series Trollhunters (2016–18), the first installment of the Tales of Arcadia trilogy, based on the 2015 novel he co-wrote with Daniel Kraus. Working with DreamWorks he also executive produced Kung Fu Panda 2 (2011), Puss in Boots (2011), Rise of the Guardians (2012), and Kung Fu Panda 3 (2016).

Del Toro's work has been characterized by a strong connection to fairy tales and horror, with an effort to infuse visual or poetic beauty in the grotesque. He has had a lifelong fascination with monsters, which he considers symbols of great power. He is also known for his use of insectile and religious imagery, the themes of Catholicism and celebrating imperfection, underworld and clockwork motifs, practical special effects, dominant amber lighting and his frequent collaborations with actors Ron Perlman and Doug Jones. He is good friends with fellow Mexican filmmakers Alfonso Cuarón and Alejandro G. Iñárritu, collectively known as "The Three Amigos of Cinema".

List of Apollo missions

The Apollo program was the third United States human spaceflight program carried out by the National Aeronautics and Space Administration (NASA), which accomplished landing the first humans on the Moon from 1969 to 1972. During the Apollo 11 mission, astronauts Neil Armstrong and Buzz Aldrin landed their lunar module (LM) and walked on the lunar surface, while Michael Collins remained in lunar orbit in the command and service module (CSM), and all three landed safely on Earth on July 24, 1969. Five subsequent Apollo missions also landed astronauts on the Moon, the last in December 1972. In these six spaceflights, twelve men walked on the Moon.Apollo ran from 1961 to 1972, with the first manned flight in 1968. It achieved its goal of manned lunar landing, despite the major setback of a 1967 Apollo 1 cabin fire that killed the entire crew during a prelaunch test. After the first landing, sufficient flight hardware remained for nine follow-up landings with a plan for extended lunar geological and astrophysical exploration. Budget cuts forced the cancellation of three of these. Five of the remaining six missions achieved successful landings, but the Apollo 13 landing was prevented by an oxygen tank explosion in transit to the Moon, which damaged the CSM's propulsion and life support. The crew returned to Earth safely by using the Lunar Module as a "lifeboat" for these functions. Apollo used Saturn family rockets as launch vehicles, which were also used for an Apollo Applications Program, which consisted of Skylab, a space station that supported three manned missions from 1973 through 1974, and the Apollo–Soyuz Test Project, a joint Earth orbit mission with the Soviet Union in 1975.

Apollo set several major human spaceflight milestones. It stands alone in sending manned missions beyond low Earth orbit. Apollo 8 was the first manned spacecraft to orbit another celestial body, while the final Apollo 17 mission marked the sixth Moon landing and the ninth manned mission beyond low Earth orbit. The program returned 842 pounds (382 kg) of lunar rocks and soil to Earth, greatly contributing to the understanding of the Moon's composition and geological history. The program laid the foundation for NASA's subsequent human spaceflight capability. Apollo also spurred advances in many areas of technology incidental to rocketry and manned spaceflight, including avionics, telecommunications, and computers.The Apollo program used four types of launch vehicles. The first was the Little Joe II, which was used for unmanned suborbital launch escape system development. The second is the Saturn I, which was used for unmanned suborbital and orbital hardware development. The third is the Saturn IB which was used for preparatory unmanned missions and Apollo 7. Last, the Saturn V which was used for unmanned and manned earth orbit and lunar missions. The Marshall Space Flight Center, which designed the Saturn rockets, referred to the flights as Saturn-Apollo (SA), while Kennedy Space Center referred to the flights as Apollo-Saturn (AS). This is why the unmanned Saturn I flights are referred to as SA and the unmanned Saturn IB are referred to as AS.

Moons of Saturn

The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, 53 of which have names and only 13 of which have diameters larger than 50 kilometers, as well as dense rings with complex orbital motions of their own. Seven Saturnian moons are large enough to be ellipsoidal in shape, yet only two of those, Titan and Rhea, are currently in hydrostatic equilibrium. Particularly notable among Saturn's moons are Titan, the second-largest moon in the Solar System (after Jupiter's Ganymede), with a nitrogen-rich Earth-like atmosphere and a landscape featuring dry river networks and hydrocarbon lakes found nowhere else in the solar system; and Enceladus since its chemical composition is similar to that of comets. In particular, Enceladus emits jets of gas and dust, which could indicate the presence of liquid water under its south pole region, and may have a global ocean below its surface.Twenty-four of Saturn's moons are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane. They include the seven major satellites, four small moons that exist in a trojan orbit with larger moons, two mutually co-orbital moons and two moons that act as shepherds of Saturn's F Ring. Two other known regular satellites orbit within gaps in Saturn's rings. The relatively large Hyperion is locked in a resonance with Titan. The remaining regular moons orbit near the outer edge of the A Ring, within G Ring and between the major moons Mimas and Enceladus. The regular satellites are traditionally named after Titans and Titanesses or other figures associated with the mythological Saturn.

The remaining 38, with mean diameters ranging from 4 to 213 km, are irregular satellites, whose orbits are much farther from Saturn, have high inclinations, and are mixed between prograde and retrograde. These moons are probably captured minor planets, or debris from the breakup of such bodies after they were captured, creating collisional families. The irregular satellites have been classified by their orbital characteristics into the Inuit, Norse, and Gallic groups, and their names are chosen from the corresponding mythologies. The largest of the irregular moons is Phoebe, the ninth moon of Saturn, discovered at the end of the 19th century.

The rings of Saturn are made up of objects ranging in size from microscopic to moonlets hundreds of meters across, each in its own orbit around Saturn. Thus a precise number of Saturnian moons cannot be given, because there is no objective boundary between the countless small anonymous objects that form Saturn's ring system and the larger objects that have been named as moons. Over 150 moonlets embedded in the rings have been detected by the disturbance they create in the surrounding ring material, though this is thought to be only a small sample of the total population of such objects.

Natural satellite

A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet (or sometimes another small Solar System body).

In the Solar System there are six planetary satellite systems containing 185 known natural satellites. Four IAU-listed dwarf planets are also known to have natural satellites: Pluto, Haumea, Makemake, and Eris. As of September 2018, there are 334 other minor planets known to have moons.The Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System (although there are minor-planet systems with even greater ratios, notably the Pluto–Charon system). At 3,474 km (2,158 miles) across, the Moon is 0.27 times the diameter of Earth.

Perry Saturn

Perry Arthur Satullo (born October 25, 1966) is an American professional wrestler known by his ring name, Perry Saturn. Since debuting in 1990, Saturn has wrestled for promotions including Extreme Championship Wrestling (ECW), World Championship Wrestling (WCW), the World Wrestling Federation (WWF) and Total Nonstop Action Wrestling (TNA). He is a former ECW World Tag Team Champion, WCW World Tag Team Champion, WCW World Television Champion, WWF European Champion and WWF Hardcore Champion.

Rings of Saturn

The rings of Saturn are the most extensive ring system of any planet in the Solar System. They consist of countless small particles, ranging from μm to m in size, that orbit about Saturn. The ring particles are made almost entirely of water ice, with a trace component of rocky material. There is still no consensus as to their mechanism of formation. Although theoretical models indicated that the rings were likely to have formed early in the Solar System's history, new data from Cassini suggest they formed relatively late.Although reflection from the rings increases Saturn's brightness, they are not visible from Earth with unaided vision. In 1610, the year after Galileo Galilei turned a telescope to the sky, he became the first person to observe Saturn's rings, though he could not see them well enough to discern their true nature. In 1655, Christiaan Huygens was the first person to describe them as a disk surrounding Saturn. Although many people think of Saturn's rings as being made up of a series of tiny ringlets (a concept that goes back to Laplace), true gaps are few. It is more correct to think of the rings as an annular disk with concentric local maxima and minima in density and brightness. On the scale of the clumps within the rings there is much empty space.

The rings have numerous gaps where particle density drops sharply: two opened by known moons embedded within them, and many others at locations of known destabilizing orbital resonances with the moons of Saturn. Other gaps remain unexplained. Stabilizing resonances, on the other hand, are responsible for the longevity of several rings, such as the Titan Ringlet and the G Ring.

Well beyond the main rings is the Phoebe ring, which is presumed to originate from Phoebe and thus to share its retrograde orbital motion. It is aligned with the plane of Saturn's orbit. Saturn has an axial tilt of 27 degrees, so this ring is tilted at an angle of 27 degrees to the more visible rings orbiting above Saturn's equator.

Saturn (mythology)

Saturn (Latin: Saturnus pronounced [saˈtʊr.nʊs]) is a god in ancient Roman religion, and a character in myth as a god of generation, dissolution, plenty, wealth, agriculture, periodic renewal and liberation. In later developments, he also came to be a god of time. His reign was depicted as a Golden Age of plenty and peace. The Temple of Saturn in the Roman Forum housed the state treasury. In December, he was celebrated at what is perhaps the most famous of the Roman festivals, the Saturnalia, a time of feasting, role reversals, free speech, gift-giving and revelry. Saturn the planet and Saturday are both named after the god.

Saturn Award

The Saturn Award is an American award presented annually by the Academy of Science Fiction, Fantasy and Horror Films; it was initially created to honor science fiction, fantasy, and horror on film, but has since grown to reward other films belonging to genre fiction, as well as on television and home media releases.

The award was originally referred to as a Golden Scroll. The Saturn Awards were created in 1973.

Saturn Corporation

The Saturn Corporation, also known as Saturn LLC, was an American automobile manufacturer, a registered trademark established on January 7, 1985, as a subsidiary of General Motors. The company marketed itself as a "different kind of car company" and operated somewhat independently from its parent company for a time with its own assembly plant in Spring Hill, Tennessee, unique models, and a separate retailer network, and was GM's attempt to compete with Japanese automakers.

Following the withdrawal of a bid by Penske Automotive to acquire Saturn in September 2009, General Motors discontinued the Saturn brand and ended its outstanding franchises on October 31, 2010. All new production was halted on October 7, 2009.

Saturn IB

The Saturn IB (pronounced "one B", also known as the uprated Saturn I) was an American launch vehicle commissioned by the National Aeronautics and Space Administration (NASA) for the Apollo program. It replaced the S-IV second stage of the Saturn I with the much more powerful S-IVB, able to launch a partially fueled Apollo command and service module (CSM) or a fully fueled lunar module (LM) into low Earth orbit for early flight tests before the larger Saturn V needed for lunar flight was ready.

By sharing the S-IVB upper stage, the Saturn IB and Saturn V provided a common interface to the Apollo spacecraft. The only major difference was that the S-IVB on the Saturn V burned only part of its propellant to achieve Earth orbit, so it could be restarted for trans-lunar injection. The S-IVB on the Saturn IB needed all of its propellant to achieve Earth orbit.

The Saturn IB launched two unmanned CSM suborbital flights, one unmanned LM orbital flight, and the first manned CSM orbital mission (first planned as Apollo 1, later flown as Apollo 7). It also launched one orbital mission, AS-203, without a payload so the S-IVB would have residual liquid hydrogen fuel. This mission supported the design of the restartable version of the S-IVB used in the Saturn V, by observing the behavior of the liquid hydrogen in weightlessness.

In 1973, the year after the Apollo lunar program ended, three Apollo CSM/Saturn IBs ferried crews to the Skylab space station. In 1975, one last Apollo/Saturn IB launched the Apollo portion of the joint US-USSR Apollo–Soyuz Test Project (ASTP). A backup Apollo CSM/Saturn IB was assembled and made ready for a Skylab rescue mission, but never flown.

The remaining Saturn IBs in NASA's inventory were scrapped after the ASTP mission, as no use could be found for them and all heavy lift needs of the US space program could be serviced by the cheaper and more versatile Titan III family.

Saturn V

The Saturn V (pronounced "Saturn five") was an American human-rated expendable rocket used by NASA between 1967 and 1973. The three-stage liquid-propellant super heavy-lift launch vehicle was developed to support the Apollo program for human exploration of the Moon and was later used to launch Skylab, the first American space station.

The Saturn V was launched 13 times from the Kennedy Space Center in Florida with no loss of crew or payload. As of 2019, the Saturn V remains the tallest, heaviest, and most powerful (highest total impulse) rocket ever brought to operational status, and holds records for the heaviest payload launched and largest payload capacity to low Earth orbit (LEO) of 140,000 kg (310,000 lb), which included the third stage and unburned propellant needed to send the Apollo Command/Service Module and Lunar Module to the Moon.The largest production model of the Saturn family of rockets, the Saturn V was designed under the direction of Wernher von Braun and Arthur Rudolph at the Marshall Space Flight Center in Huntsville, Alabama, with Boeing, North American Aviation, Douglas Aircraft Company, and IBM as the lead contractors.

To date, the Saturn V remains the only launch vehicle to carry humans beyond low Earth orbit. A total of 15 flight-capable vehicles were built, but only 13 were flown. An additional three vehicles were built for ground testing purposes. A total of 24 astronauts were launched to the Moon, three of them twice, in the four years spanning December 1968 through December 1972.

Sega Saturn

The Sega Saturn is a 32-bit fifth-generation home video game console developed by Sega and released on November 22, 1994 in Japan, May 11, 1995 in North America, and July 8, 1995 in Europe. The successor to the successful Sega Genesis, the Saturn has a dual-CPU architecture and eight processors. Its games are in CD-ROM format, and its game library contains several arcade ports as well as original games.

Development of the Saturn began in 1992, the same year Sega's groundbreaking 3D Model 1 arcade hardware debuted. Designed around a new CPU from Japanese electronics company Hitachi, another video display processor was incorporated into the system's design in early 1994 to better compete with Sony's forthcoming PlayStation.

The Saturn was initially successful in Japan, but failed to sell in large numbers in the United States after its surprise May 1995 launch, four months before its scheduled release date. After the debut of the Nintendo 64 in late 1996, the Saturn rapidly lost market share in the U.S., where it was discontinued in 1998. Having sold 9.26 million units worldwide, the Saturn is considered a commercial failure. The failure of Sega's development teams to release a game in the Sonic the Hedgehog series, known in development as Sonic X-treme, has been considered a factor in the console's poor performance.

Although the Saturn is remembered for several well-regarded games, including Nights into Dreams, the Panzer Dragoon series, and the Virtua Fighter series, its reputation is mixed due to its complex hardware design and limited third-party support. Sega's management has been criticized for its decisions during the system's development and discontinuation.

Solar System

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.

The Solar System also contains smaller objects. The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between regions. Six of the planets, at least four of the dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.

The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way galaxy.

Titan (moon)

Titan is the largest moon of Saturn and the second-largest natural satellite in the Solar System. It is the only moon known to have a dense atmosphere, and the only object in space, other than Earth, where clear evidence of stable bodies of surface liquid have been found.

Titan is the sixth gravitationally rounded moon from Saturn. Frequently described as a planet-like moon, Titan is 50% larger than Earth's moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's moon Ganymede, and is larger than the smallest planet, Mercury, but only 40% as massive. Discovered in 1655 by the Dutch astronomer Christiaan Huygens, Titan was the first known moon of Saturn, and the sixth known planetary satellite (after Earth's moon and the four Galilean moons of Jupiter). Titan orbits Saturn at 20 Saturn radii. From Titan's surface, Saturn subtends an arc of 5.09 degrees and would appear 11.4 times larger in the sky than the Moon from Earth.

Titan is primarily composed of ice and rocky material. Much as with Venus before the Space Age, the dense opaque atmosphere prevented understanding of Titan's surface until the Cassini–Huygens mission in 2004 provided new information, including the discovery of liquid hydrocarbon lakes in Titan's polar regions. The geologically young surface is generally smooth, with few impact craters, although mountains and several possible cryovolcanoes have been found.

The atmosphere of Titan is largely nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog. The climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle is analogous to Earth's water cycle, at the much lower temperature of about 94 K (−179.2 °C; −290.5 °F).

Voyager 1

Voyager 1 is a space probe launched by NASA on September 5, 1977. Part of the Voyager program to study the outer Solar System, Voyager 1 was launched 16 days after its twin, Voyager 2. Having operated for 41 years, 6 months and 11 days as of March 16, 2019, the spacecraft still communicates with the Deep Space Network to receive routine commands and to transmit data to Earth. At a distance of 145 AU (22 billion km; 13 billion mi) from Earth as of February 22, 2019, it is the most distant human-made object from Earth.The probe's objectives included flybys of Jupiter, Saturn, and Saturn's largest moon, Titan. While the spacecraft's course could have been altered to include a Pluto encounter by forgoing the Titan flyby, exploration of the moon, which was known to have a substantial atmosphere, took priority. Voyager 1 studied the weather, magnetic fields, and rings of the two planets and was the first probe to provide detailed images of their moons.

After completing its primary mission with the flyby of Saturn on November 12, 1980, Voyager 1 became the third of five artificial objects to achieve the escape velocity required to leave the Solar System. On August 25, 2012, Voyager 1 became the first spacecraft to cross the heliopause and enter the interstellar medium.In a further testament to the robustness of Voyager 1, the Voyager team completed a successful test of the spacecraft's trajectory correction maneuver (TCM) thrusters in late 2017 (the first time these thrusters were fired since 1980), a project enabling the mission to be extended by two to three years.Voyager 1's extended mission is expected to continue until about 2025 when its radioisotope thermoelectric generators will no longer supply enough electric power to operate its scientific instruments.

Voyager 2

Voyager 2 is a space probe launched by NASA on August 20, 1977, to study the outer planets. Part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach Jupiter and Saturn but enabled further encounters with Uranus and Neptune. It is the only spacecraft to have visited either of these two ice giant planets.

Its primary mission ended with the exploration of the Neptunian system on October 2, 1989, after having visited the Uranian system in 1986, the Saturnian system in 1981, and the Jovian system in 1979. Voyager 2 is now in its extended mission to study the outer reaches of the Solar System and has been operating for 41 years, 6 months and 24 days as of 16 March 2019. It remains in contact through the NASA Deep Space Network.At a distance of 120 AU (1.80×1010 km) (about 16.5 light-hours) from the Sun as of February 25, 2019, moving at a velocity of 15.341 km/s (55,230 km/h) relative to the Sun, Voyager 2 is the fourth of five spacecraft to achieve the escape velocity that will allow them to leave the Solar System. The probe left the heliosphere for interstellar space on November 5, 2018, becoming the second artificial object to do so, and has begun to provide the first direct measurements of the density and temperature of the interstellar plasma.

Voyager program

The Voyager program is an American scientific program that employs two robotic probes, Voyager 1 and Voyager 2, to study the outer Solar System. The probes were launched in 1977 to take advantage of a favorable alignment of Jupiter, Saturn, Uranus and Neptune. Although their original mission was to study only the planetary systems of Jupiter and Saturn, Voyager 2 continued on to Uranus and Neptune. The Voyagers now explore the outer boundary of the heliosphere in interstellar space; their mission has been extended three times and they continue to transmit useful scientific data. Neither Uranus nor Neptune has been visited by a probe other than Voyager 2.

On 25 August 2012, data from Voyager 1 indicated that it had become the first human-made object to enter interstellar space, traveling "further than anyone, or anything, in history". As of 2013, Voyager 1 was moving with a velocity of 17 kilometers per second (11 mi/s) relative to the Sun.On 5 November 2018, data from Voyager 2 indicated that it also had entered interstellar space.Data and photographs collected by the Voyagers' cameras, magnetometers and other instruments, revealed unknown details about each of the four giant planets and their moons. Close-up images from the spacecraft charted Jupiter's complex cloud forms, winds and storm systems and discovered volcanic activity on its moon Io. Saturn's rings were found to have enigmatic braids, kinks and spokes and to be accompanied by myriad "ringlets". At Uranus, Voyager 2 discovered a substantial magnetic field around the planet and ten more moons. Its flyby of Neptune uncovered three rings and six hitherto unknown moons, a planetary magnetic field and complex, widely distributed auroras. Voyager 2 is the only spacecraft to have visited the two ice giants. In August 2018, NASA confirmed, based on results by the New Horizons spacecraft, of a "hydrogen wall" at the outer edges of the Solar System that was first detected in 1992 by the two Voyager spacecraft.The Voyager spacecraft were built at the Jet Propulsion Laboratory in Southern California and they were funded by the National Aeronautics and Space Administration (NASA), which also financed their launches from Cape Canaveral, Florida, their tracking and everything else concerning the probes.

The cost of the original program was $865 million, with the later-added Voyager Interstellar Mission costing an extra $30 million.

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