Saturn is the sixth planet from the Sun. Saturn is a gas giant. Saturn is also known as a Jovian planet, after the planet Jupiter.
Physical characteristics of Saturn.
Saturn: Solar System Planet.
|Saturn Orbital characteristics.|
|Semi-major axis||1,426,725,413 km|
9.537 070 32 AU
|Orbital circumference||8.958 Tm|
|eccentricity||0.054 150 60|
9.020 632 24 AU
10.053 508 40 AU
|Orbital period||10,756.1995 d|
|Synodic period||378.10 d|
|Avg. Orbital Speed||9.639 km/s|
|Max. orbital speed||10.183 km/s|
|Min. orbital speed||9.137 km/s|
(5.51º to Sun's equator)
|Longitude of the |
|Argument of the |
|Number of Satellites||56 confirmed|
|Equatorial diameter||120,536 km|
|Polar diameter||108,728 km|
|Surface area||4.27×1010 km2|
|Mean density||0.6873 g/cm3|
(less than water)
|Equatorial gravity||8.96 m/s2|
|escape velocity||35.49 km/s|
|Rotation period||0.449 375 d|
(10 h 47 min 6 s)
|Rotation velocity||9.87 km/s = 35,500 km/h|
(at the equator)
|Right ascension |
of North pole
|40.59º (2 h 42 min 21 s)|
|Avg. cloudtop temp.||93 K|
|Surface temp.|| |
|Atmospheric pressure||140 kPa|
Saturn is the second-largest planet in the solar system after Jupiter. Saturn has a prominent system of rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Saturn was named after the Roman god Saturn (the Greek equivalent is Kronos, father of Zeus). Saturn's symbol is a stylized representation of the god's sickle.
Saturn is an oblate spheroid. Saturn is flattened at the poles and bulging at the equator. Saturn's equatorial and polar diameters vary by almost 10% (120,536 km vs. 108,728 km). This is the result of its rapid rotation and fluid state. The other gas planets are also oblate, but to a lesser degree. Saturn is the only one of the Solar System's planets that is less dense than water, with an average specific density of 0.69. This is a mean value; Saturn's upper atmosphere is less dense and its core is considerably more dense than water.
Saturn's interior is similar to Jupiter's, having a rocky core at the center, a liquid metallic hydrogen layer above that, and a molecular hydrogen layer above that. Traces of various ices are also present. Saturn has a very hot interior, reaching 12,000 Kelvin (11,700ºC) at the core, and it radiates more energy into space than it receives from the Sun. Most of the extra energy is generated by the Kelvin-Helmholtz mechanism (slow gravitational compression), but this alone may not be sufficient to explain Saturn's heat production. An additional proposed mechanism by which Saturn may generate some of its heat is the "raining out" of droplets of helium deep in Saturn's interior, the droplets of helium releasing heat by friction as they fall down through the lighter hydrogen.
Saturn's atmosphere exhibits a banded pattern similar to Jupiter's (in fact, the nomenclature is the same), but Saturn's bands are much fainter and are also much wider near the equator. Saturn's winds are among the Solar System's fastest; Voyager data indicates peak easterly winds of 500 m/s (1116 mph). Saturn's finer cloud patterns were not observed until the Voyager flybys. Since then, however, Earth-based telescopy has improved to the point where regular observations can be made.
Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter; in 1990 the Hubble Space Telescope observed an enormous white cloud near Saturn's equator which was not present during the Voyager encounters and in 1994 another, smaller storm was observed. The 1990 storm was an example of a Great White Spot, a unique but short-lived Saturnian phenomenon with a roughly 30-year periodicity. Previous Great White Spots were observed in 1876, 1903, 1933, and 1960, with the 1933 storm being the most famous. The careful study of these episodes reveals interesting patterns; if it holds another storm will occur in about 2020.(Kidger 1992)
Recent images from the Cassini spacecraft show that Saturn's northern hemisphere is changing colors. It now appears a bright blue, similar to Uranus, as can be seen in the image below. This blue color cannot currently be observed from earth, because Saturn's rings are currently blocking its northern hemisphere. One theory is that this shocking color change is a result of colder temperatures, as the shadows cast by Saturn's rings are blocking out sunlight. This would result in the yellow clouds sinking and Saturn's deeper blue atmosphere being revealed.
Astronomers using Infrared imaging have shown that Saturn has a warm polar vortex, and is the only planet in the solar system known to do so.
An apparently permanent hexagonal wave pattern around the polar vortex in the atmosphere at about 78ºN was first noted in the Voyager images . HST imaging of the south polar region indicates the presence of a jet stream, but no strong polar vortex nor any hexagonal standing wave. However, NASA reported in November of 2006 that the Cassini spacecraft observed a 'hurricane-like' storm locked to the south pole that had a clearly defined eyewall. This observation is particularly notable because eyewall clouds have not been seen on any planet other than Earth (including a failure to observe an eyewall in the Great Red Spot of Jupiter by the Galileo spacecraft).
Rotational behavior of Saturn.
Since Saturn does not rotate on its axis at a uniform rate, two rotation periods have been assigned to it (as in Jupiter's case): System I has a period of 10 h 14 min 00 s (844.3º/d) and encompasses the Equatorial Zone, which extends from the northern edge of the South Equatorial Belt to the southern edge of the North Equatorial Belt. All other Saturnian latitudes have been assigned a rotation period of 10 h 39 min 24 s (810.76º/d), which is System II. System III, based on radio emissions from the planet, has a period of 10 h 39 min 22.4 s (810.8º/d); because it is very close to System II, it has largely superseded it.
While approaching Saturn in 2004, the Cassini spacecraft found that the radio rotation period of Saturn had increased slightly, to approximately 10 h 45 m 45 s (± 36 s). The cause of the change is unknown - however, it is thought that this is due to a movement of the radio source to a different latitude inside Saturn, with a different rotational period, rather than an actual change in Saturn's rotation.
Planetary rings of Saturn.
Saturn is probably best known for its planetary rings, which make it one of the most visually remarkable objects in the solar system.
History of Saturn.
The rings were first observed by Galileo Galilei in 1610 with his telescope, but he was unable to identify them as such. He wrote to the Duke of Tuscany that "The planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the Zodiac, and the middle one (Saturn itself) is about three times the size of the lateral ones [the edges of the rings]." He also described Saturn as having "ears." In 1612 the plane of the rings was oriented directly at the Earth and the rings appeared to vanish, and then in 1613 they reappeared again, further confusing Galileo.
In 1655, Christiaan Huygens became the first person to suggest that Saturn was surrounded by a ring. Using a telescope that was far superior to those available to Galileo, Huygens observed Saturn and wrote that "It [Saturn] is surrounded by a thin, flat, ring, nowhere touching, inclined to the ecliptic."
In 1675, Giovanni Domenico Cassini determined that Saturn's ring was actually composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the Cassini Division.
In 1859, James Clerk Maxwell demonstrated that the rings could not be solid or they would become unstable and break apart. He proposed that the rings must be composed of numerous small particles, all independently orbiting Saturn. Maxwell's theory was proven correct in 1895 through spectroscopic studies of the rings carried out by James Keeler of Lick Observatory.
Physical characteristics of Saturn.
The rings can be viewed using a quite modest modern telescope or with a good pair of binoculars. They extend from 6,630 km to 120,700 km above Saturn's equator, average close to one kilometre in thickness and are composed of silica rock, iron oxide, and ice particles ranging in size from specks of dust to the size of a small automobile. There are two main theories regarding the origin of Saturn's rings. One theory, originally proposed by Édouard Roche in the 19th century, is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by tidal forces (see Roche limit). A variation of this theory is that the moon disintegrated after being struck by a large comet or asteroid. The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material that Saturn formed out of. This theory is not widely accepted today, since Saturn's rings are thought to be unstable over periods of millions of years and therefore of relatively recent origin.
While the largest gaps in the rings, such as the Cassini Division and Encke division, can be seen from Earth, the Voyager spacecrafts discovered the rings to have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise from the gravitational pull of Saturn's many moons in several different ways. Some gaps are cleared out by the passage of tiny moonlets such as Pan, many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small shepherd satellites such as Prometheus and Pandora. Other gaps arise from resonances between the orbital period of particles in the gap and that of a more massive moon further out; Mimas maintains the Cassini division in this manner. Still more structure in the rings actually consists of spiral waves raised by the moons' periodic gravitational perturbations.
Data from the Cassini space probe indicates that the rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular Oxygen gas (O2) produced when ultraviolet light from the Sun disintegrates water ice in the rings. Chemical reactions between water molecule fragments and further ultraviolet stimulation create and eject, among other things O2. According to models of this atmosphere, H2 is also present. The O2 and H2 atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be on the order of 1 atom thick. The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O2, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic ions that bombard water molecules ejected by Saturn's moon Enceladus. This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope.
Saturn shows complex patterns in its brightness. Most of the variability is due to the changing aspect of the rings, and this goes through two cycles every orbit. However, superimposed on this is variability due to the eccentricity of the planet’s orbit that causes the planet to display brighter oppositions in the northern hemisphere than it does in the southern. (Henshaw, C., 2003).
Saturn: Spokes of the rings.
Until 1980, the structure of the rings of Saturn was explained exclusively as the action of gravitational forces. The Voyager spacecraft found radial features in the B ring, called spokes, which could not be explained in this manner, as their persistence and rotation around the rings were not consistent with orbital mechanics. The spokes appear dark against the lit side of the rings, and light when seen against the unlit side. It is assumed that they are connected to electromagnetic interactions, as they rotate almost synchronously with the magnetosphere of Saturn. However, the precise mechanism behind the spokes is still unknown.
Twenty-five years later, Cassini observed the spokes again. They appear to be a seasonal phenomenon, disappearing in the Saturnian midwinter/midsummer and reappearing as Saturn comes closer to equinox. The spokes were not visible when Cassini arrived at Saturn in early 2004. Some scientists speculated that the spokes would not be visible again until 2007, based on models attempting to describe spoke formation. Nevertheless, the Cassini imaging team kept looking for spokes in images of the rings, and the spokes reappeared in images taken September 5, 2005.
Natural satellites of Saturn.
Saturn has a large number of moons. The precise figure is uncertain as the orbiting chunks of ice in Saturn's rings are all technically moons, and it is difficult to draw a distinction between a large ring particle and a tiny moon. As of 2006, a total of 56 individual moons have been identified, many of them quite small. Seven of the moons are massive enough to have collapsed into spheroids under their own gravitation. These are compared to Earth's moon in the table below. Saturn's most noteworthy moon is Titan, the only moon in the solar system to have a dense atmosphere.
Traditionally, most of Saturn's other moons are named after actual Titans of Greek mythology. This started because John Herschel - son of William Herschel, discoverer of Mimas and Enceladus - suggested doing so in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope, because they were the sisters and brothers of Cronos (the Greek Saturn).
|Saturn's major satellites, compared to Earth's Moon.|
|Orbital radius (km)||Orbital period (days)|
|Mimas||mee'-ms ||400 |
|Enceladus||en-sel'-ds ||500 |
|Tethys||te'-th's ||1060 |
|Dione||dye-oe'-nee ||1120 |
|Rhea||ree'- ||1530 |
|Titan||tye'-t'n ||5150 |
|Iapetus||eye-ap'-ts ||1440 |
Exploration of Saturn.
Pioneer 11 flyby of Saturn.
Saturn was first visited by Pioneer 11 in September 1979. It flew within 20,000 km of the planet's cloud tops. Low-resolution images were acquired of the planet and few of its moons. Resolution was not good enough to discern surface features, however. The spacecraft also studied the rings; among the discoveries were the thin F-ring and the fact that dark gaps in the rings are bright when viewed towards the Sun, or in other words, they are not empty of material. It also measured the temperature of Titan.
Voyager flybys of Saturn.
In November 1980, the Voyager 1 probe visited the Saturn system. It sent back the first high-resolution images of the planet, rings, and the satellites. Surface features of various moons were seen for the first time. Voyager 1 performed a close flyby of Titan, greatly increasing our knowledge of the atmosphere of the moon. However, it also proved that Titan's atmosphere is impenetrable in visible wavelengths, so no surface details were seen. The flyby also changed the spacecraft's trajectory out from the plane of the solar system.
Almost a year later, in August 1981, Voyager 2 continued the study of the Saturn system. 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.
The probes discovered and confirmed several new satellites orbiting near or within the planet's rings. They also discovered the small Maxwell and Keeler gaps.
Saturn: Cassini orbiter.
On July 1, 2004, the Cassini-Huygens spacecraft performed the SOI (Saturn Orbit Insertion) maneuver and entered into orbit around Saturn. Before the SOI, Cassini had already studied the system extensively. In June 2004, it had conducted a close flyby of Phoebe sending back high-resolution images and data. The orbiter completed two Titan flybys before releasing the Huygens probe on December 25, 2004. Huygens descended onto the surface of Titan on January 14, 2005, sending a flood of data during the atmospheric descent and after the landing. As of 2005, Cassini is conducting multiple flybys of Titan and icy satellites. On March 10, 2006, NASA reported that the Cassini probe found evidence of liquid water reservoirs that erupt in geysers on Saturn's moon Enceladus . On September 20, 2006, a Cassini probe photograph revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. The primary mission ends in 2008 when the spacecraft has completed 74 orbits around the planet.
Best viewing of Saturn.
Saturn has been known since prehistoric times. It is the most distant of the five planets visible to the naked eye (the other four are Mercury, Venus, Mars, and Jupiter) and was the last planet known to early astronomers until Uranus was discovered in 1781. Saturn appears to the naked eye in the night sky as a bright, yellowish star varying usually between magnitude +1 and 0 and takes approximately 29 and a half years to make a complete circuit of the ecliptic against the background constellations of the Zodiac. Optical aid (a large pair of binoculars or a telescope) magnifying at least 20X is required to clearly resolve Saturn's rings for most people.
While it is a rewarding target for observation for most of the time it is visible in the sky, Saturn and its rings are best seen when the planet is at or near opposition (the configuration of a planet when it is at an elongation of 180º and thus appears opposite the Sun in the sky.) In the opposition on January 13, 2005, Saturn appeared at its brightest until 2031, mostly due to a favorable orientation of the rings relative to the Earth.
Saturn in various cultures.
Saturn is known as "Sani" or "Shani" in Hindu Astrology. Hindus believe in the existence of Nine Planets - known as Navagraha(s). These Navagrahas were propitiated as planetary influences govern the life of individuals. Sani is identified as an inauspicious planet, and is worshipped by individuals going through a "bad" phase in their life. Sani's father is the Sun God "Surya".
Chinese and Japanese culture designate the planet Saturn as the earth star (??). This is based on Five Elements which was traditionally used to classify natural elements.
In Hebrew, Saturn is called 'Shabbathai'. Its Angel is Cassiel. Its Intelligence, or beneficial spirit, is Agiel (layga), and its spirit (darker aspect) is Zazel (lzaz). See: Kabbalah.
In Ottoman Turkish and in Bahasa Malaysia (the Malay language), its name is 'Zuhal'.
Ithaca Chasma on Tethys
Dec 28, 2005 - In this image of Saturn's moon Tethys, it's possible to see the giant Ithaca Chasma cutting a swath across its surface. The chasm is 100 km (60 miles) long and 4 km (2 miles) deep in places. Cassini took this photograph on November 28, 2005 when the spacecraft was approximately 1.1 million km (700,000 miles) away from Tethys.
Titan's Purple Halo
Dec 23, 2005 - Cassini took this beautiful image of Titan with its orange surface shining against the purple halo of its atmosphere. The photograph was made by using separate blue, green and red spectral filters and then combining this with an ultraviolet image. This image was taken by Cassini's narrow-angle camera on the May 5, 2005, at a distance of approximately 1.4 million kilometers (900,000 miles) from Titan.
Mimas and Tiny Helene
Dec 21, 2005 - Cassini has captured this amazing image of two Saturian moons: Mimas and Helene, hiding behind the planet's ringplane. The large, bright moon is Mimas, illuminated on its right side by the Sun. The tiny dot to its left is the tiny Trojan moon Helene. This moonlet is only 32 kilometers (20 miles) across, and shares the same orbit as Dione. This image was taken on November 2, 2005.
Rhea Hiding Behind the Rings
Dec 19, 2005 - This beautiful photograph shows Saturn's moon Rhea, partially obscured by the rings. The material surrounding the ring is probably on the planet's equatorial plane, extending farther out from the ring's main core. This image was taken on Oct. 30, 2005, at a distance of approximately 689,000 kilometers (428,000 miles) from Saturn.
Enceladus is Creating one of Saturn's Rings
Dec 19, 2005 - Instruments on board Cassini have confirmed that Saturn's faintest ring is being created by particles emitted by its icy moon Enceladus. Scientists are amazed that this tiny, supposedly dead moon has such active volcanoes. Some unknown process is heating up the interior of Enceladus, especially near the southern pole, causing this plume of ejected material. Most of the larger particles probably reimpact the moon, but the smaller ones are pushed into orbit around Saturn by sunlight.
Prometheus and Pandora
Dec 15, 2005 - This photograph shows two of Saturn's ring shepherd moons surrounded by halos of icy particles: Prometheus (at left) and Pandora (at right). Prometheus tugs at Saturn's rings pulling a stream of particles towards it as it orbits the giant planet. Cassini took this image on October 29, 2005 when it was approximately 459,000 kilometers (285,000 miles) from Pandora and 483,500 kilometers (300,500 miles) from Prometheus.
Gaps in Saturn's Rings
Dec 14, 2005 - In this Cassini image, Saturn's rings cast dark shadows across the face of the giant planet. The three bright arcs in the image are the three well-known gaps in Saturn's rings: the Cassini Division, the Encke Gap and the Keeler Gap. Cassini took this image on October 29, 2005 when it was 446,000 kilometers (277,000 miles) from Saturn.
Strange Bulge in Saturn's Rings
Dec 13, 2005 - NASA's Cassini spacecraft took this surprising photograph of Saturn's rings precisely edge-on. What's unusual is the strange bulge right at the edge of the rings. It's possible this bulge is created by a kilometer-sized chunk of material that's disrupting the ring material with its gravity. It could also be an effect of viewing the rings perfectly edge-on; normally faint material becomes visible when viewed at this angle.
Dione and Rhea in the Same Frame
Dec 11, 2005 - Two of Saturn's moons, Rhea and Dione posed for Cassini in this photograph. The lower moon is Dione, which has been much more geologically active in the past than Rhea. Dione has a smoother surface and linear depressions, while Rhea looks quite pummeled by impacts, like our own Moon. When Cassini took this image, Rhea was 1.8 million kilometers (1.1 million miles) away, and Dione was 1.2 million kilometers (800,000 miles) away.
Saturn's Graceful Crescent
Dec 8, 2005 - This beautiful photograph of Saturn was taken when Cassini was lined up directly with the planet's rings. The black line near the top of the photograph are the rings. It's possible to see the intricate cloud patterns across the planet's surface, especially right at the terminator, which separates day from night. Cassini took this image on October 31, 2005 when it was 1.2 million kilometers (800,000 miles) from Saturn.
New Views of Saturn's Moons
Dec 7, 2005 - NASA's Cassini spacecraft has wrapped up a successful year exploring Saturn's icy moons, and scientists have released a new set of images to celebrate. New images of Rhea were taken during Cassini's November 26th flyby, when the spacecraft dipped within 500 km (310 miles) of Rhea's surface. Other images include "zoomable" mosaics of Rhea and Hyperion taken at high resolution.
Detailed Cloud Features on Saturn
Dec 6, 2005 - This image of Saturn shows the giant planet's southwest edge, and a hint of thread-like cloud features. The edge of the planet looks smooth, but right at the terminator (the edge between light and dark), it's possible to see these cloud features. The long shadows make the height differences in the clouds visible. Cassini took this image on October 30, 2005 when the spacecraft was 401,000 kilometers (249,000 miles) from Saturn.
Hilly Terrain on Titan
Dec 5, 2005 - This perspective view shows the hilly terrain on Saturn's moon Titan. The image has been colour coded to show the altitude, with red being the highest areas, and blue the lowest. Stereo images were taken by Huygens as it descended into Titan's atmosphere earlier this year, and then the 3-D terrain was rendered in computer.
Dione and Enceladus
Dec 5, 2005 - This Cassini photo shows two of Saturn's moons, Dione and Enceladus floating just beneath the ringplane. Smaller Enceladus is on the right, and measures 505 kilometers (314 miles across). Dione is further away at the top left, and measures 1,126 kilometers (700 miles across). This image was taken on October 15, 2005, when Cassini was 2.1 million kilometers (1.3 million miles) from Dione and 1.5 million kilometers (900,000 miles) from Enceladus.
Huygens Sunk Into Soft Ground
Dec 5, 2005 - When ESA's Huygens probe touched down on the surface of Titan earlier this year, it hit hard, and then slumped sideways into the soft ground. After analyzing the landing in detail, ESA scientists have calculated that Huygens probably hit a surface similar to soft clay, lightly packed snow, or wet or dry sand. It penetrated about 10mm into the ground, and then settled slightly over time by a few millimetres, tilting the probe a few degrees. It's possible that Huygens landed on a Titan beach, shortly after the hydrocarbon ocean tide went out.
Titan's Atmosphere Surprised Scientists
Dec 1, 2005 - When ESA's Huygens probe passed through Titan's atmosphere on its way to a successful landing, it was buffeted by turbulence unexpected by scientists. Very little was known about Titan's atmosphere before Huygen's landing because the moon is shrouded by a thick hydrocarbon haze. Huygens found that the upper atmosphere was much thicker than expected, and broken up into several distinct layers. The probe also discovered possible evidence of lightning strikes around it.
Ice Volcanoes on Enceladus
Nov 29, 2005 - Cassini has returned amazing photographs of ice volcanoes erupting from the surface of Saturn's moon Enceladus. On a previous pass of the moon, Cassini detected particles of water vapour stretching hundreds of kilometres above its surface, and this photograph shows the ice volcanoes in action. It's believed they're spewing out material that refreshes the ice in Saturn's E-ring.
Death Star Mimas and Its Giant Crater Herschel
Nov 25, 2005 - In this Cassini image of Mimas perched in front of Saturn's moons, you can clearly see its giant crater Herschel. The 130-kilometer (80-mile) crater makes the moon look like the Death Star from Star Wars. Cassini took this image on October 13, 2005 when it was approximately 711,000 kilometers (442,000 miles) from Mimas.
Carthage Linea on Dione
Nov 24, 2005 - This photograph of a fractured and crater-scarred Dione was taken by Cassini on October 11, 2005, when the spacecraft was only 19,600 kilometers (12,200 miles) away from the moon. Most of the craters in this image have bright walls and dark deposits of material on their floors. Rock slides on the surface of Dione can reveal cleaner ice, while the darker materials accumulate in lower areas.
Good Look at Dione
Nov 23, 2005 - Cassini took this amazing image of Saturn's moon Dione on approach to its recent October 11, 2005 rendezvous; Saturn itself sits in the background. Dione is much darker on its western side in this image, and you can see the bright wispy fresh canyons right at the edge. Cassini took this image when it was approximately 24,500 kilometers (15,200 miles) from Dione.