Saturn

Saturn is the sixth planet from the Sun and the second largest.

Saturn is the sixth planet from the Sun. It is a gas giant, the second-largest planet in the solar system after Jupiter. Saturn has large rings consisting of mostly ice particles with a smaller amount of rocky debris. It was named after the Roman god Saturn. Its symbol is a stylized representation of the god's sickle.

Physical Characteristics

Saturn's shape is visibly flattened at the poles and bulging at the equator (an oblate spheroid); its 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 also the only one of the Solar System's planets less dense than water, with an average specific density of 0.69. This is only an average value, however; 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 12000 K 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, but Saturn's bands are much fainter and they're also much wider near the equator. Saturn's 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 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. 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.

Rotational Behaviour

Since Saturn does not rotate on its axis at a uniform rate, two rotation periods have been assigned to it, like in Jupiter's case: System I has a period of 10 h 14 min 00 s (844.3°/d) and encompasses the Equatorial Zone, which extends from the northern edge of the South Equatorial Belt to the southern edge of the North Equatorial Belt. All other Saturnian latitudes have been assigned a rotation period of 10 h 39 min 24 s (810.76°/d), which is System II. System III, based on radio emissions from the planet, has a period of 10 h 39 min 22.4 s (810.8°/d); because it is very close in value 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 (ą 36 s). [2] The cause of the change is unknown.

Saturn's Rings

Saturn is probably best known for its planetary rings, which make it one of the most visually remarkable objects in the solar system. See rings of Saturn for a list of the planet's rings.

The rings were first observed by Galileo Galilei in 1610 with his telescope, but he clearly did not know what to make of them. He wrote to the Grand Duke of Tuscany that "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.

The riddle of the rings was not solved until 1655 by Christiaan Huygens, using a telescope much more powerful than the ones available to Galileo in his time.

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.

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, 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 Edouard 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. 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, could be seen from Earth, the Voyagers 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 undiscovered, 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) and is thought to be a product of the disintegration of water ice from the rings into its components, oxygen and hydrogen.

The side of Saturn's rings that is lit by the Sun looks very different to the backlit side, which is darker overall and appears almost black in the thick B ring. From Earth, we cannot appreciate this because the Earth cannot view Saturn from an angle that displays the backlit side of the rings, and our only views of it are from spacecraft. In 2004, the Cassini spacecraft revealed the first views of the backlit side in 25 years.

Until 1980, the structure of the rings of Saturn was explained exclusively as the action of gravitational forces. The Voyager spacecraft found dark 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. 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.

As of February 2005, the Cassini spacecraft has not observed any spokes in the rings, despite possessing imaging equipment of higher quality than the Voyagers'. It is possible that the spokes appear and disappear seasonally.

Saturn's moons

Saturn has a large number of moons, 49 are currently confirmed, 34 of which have names. The precise figure will never be certain 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. Saturn's most noteworthy moon is Titan, the only moon in the solar system to have a dense atmosphere.

Due to the tidal forces of Saturn, the moons are currently not at the same position as they were when they were first formed.

Exploration of Saturn

Saturn was first visited by Pioneer 11 in 1979. It flew within 20,000 km the planet's cloudtops. 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.

In November, 1980, 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 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 camera stuck 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.

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 flood of data during the atmospheric descent and after the landing. As of 2005, Cassini is conducting multiple flybys of Titan and icy satellites. The primary mission ends in 2008 when the spacecraft has completed 74 orbits around the planet.

Wikipedia

Cassini Website News Updates

Saturn In the News ...

Sunlight Glints off Liquid Lake on Titan Space.com - December 22, 2009

Fog Seen on Saturn Moon Titan--A First National Geographic - December 22, 2009

Saturn's Eccentric Orbit Could Explain Moon's Lopsided Lakes Space.com - December 14, 2009

Scientists discover fog on Titan PhysOrg - December 18, 2009

Saturn's Hexagon Comes to Light NASA December 14, 2009
Saturnšs Hexagon May Be Solar Systemšs Coolest Mystery Wired - December 10, 2009
Saturn's Mysterious Hexagon Emerges from Winter Darkness Science Daily - December 10, 2009

Saturn's North Pole

A Mysterious Hexagonal Cloud System on Saturn NASA - March 27, 2007
Cassini Images Bizarre Hexagon On Saturn Science Daily - March 27, 2007
Hexagon Spied Around Saturn's Pole National Geographic - March 28, 2007

Dark Side of a Saturnian Moon: Iapetus Is Coated With Foreign Dust Science Daily - December 11, 2009

Scientists explain puzzling lake asymmetry on Titan PhysOrg - November 29, 2009

Water geysers on Saturn moon take center stage MSNBC - November 4, 2009

New 8th ring detected around Saturn BBC - October 7, 2009
New Saturn Ring Is Largest Known; May Solve Moon Puzzle National Geographic - October 7, 2009

Saturn Lightning Storm Breaks Solar System Record National Geographic - September 15, 2009

Saturn's moon Titan has a foggy bottom New Scientist - September 15, 2009

Saturn's Raging Storms Thunderbolts - April 28, 2009

Subterranean oceans on Saturn's moon Titan PhysOrg - April 6, 2009

Saturn's New Moon in Transit NASA - March 19, 2009

New Saturn Moon: Tiny Gem Found in Outer Ring National Geographic - March 3, 2009
Mysterious Moon Flashes Signs of "Last Gasps"? National Geographic - March 2, 2009

New lakes materialize on Saturn moon New Scientist - February 2, 2009

Methane Rain Formed New Lake on Saturn Moon National Geographic - January 30, 2009

Saturn Moon Has Lake Effect Clouds?    National Geographic - December 16, 2008
Saturn's moon Titan has 'ice volcanoes'    BBC - December 16, 2008
Saturn: Titan's Volcanoes Give Cassini Chilly Reception    PhysOrg - December 16, 2008
Saturn: Enceladus has 'spreading surface' - very Earth-like    BBC - December 16, 2008

Cassini Finds Mysterious New Aurora on Saturn Science Daily - November 12, 2008

Beneath the South Pole of Saturn NASA - October 27, 2008

Mysterious Cyclones Seen at Both of Saturn's Poles National Geographic - October 15, 2008

Photo: Saturn Moon "Mother Lode": Icy Jets Located National Geographic - August 15, 2008
Cassini returns close-up images of moon's 'tiger stripes' New Scientist - August 13, 2008
Probe gets close up to Enceladus BBC - August 13, 2008

Jupiter and Saturn full of liquid metal helium PhysOrg - August 6, 2008

Giant Lake Confirmed on Saturn's Moon Titan National Geographic - July 31, 2008

"Pinball" Collisions Seen in Saturn Ring National Geographic - June 4, 2008

Nonstop "Hurricane" Raging on Saturn's South Pole National Geographic - March 27, 2008

Dive Into Saturn Moon's Jets Shows Ingredients for Life National Geographic - March 27, 2008

Saturn: Icy Moon Tethys Had Ancient Underground Ocean National Geographic - March 24, 2008

Saturn Moon Titan May Have Underground Ocean National Geographic - March 21, 2008
Saturn moon may have hidden ocean BBC - March 20, 2008

Saturn moon 'once had ocean' BBC - March 14, 2008

Saturn Moon May Have Rings -- A First National Geographic - March 7, 2008

Saturn's Rings as Old as Solar System, Study Says National Geographic - December 13, 2007

Saturn's "Flying Saucer" Moons Made Mainly of Ring Dust National Geographic - December 6, 2007

Moonlet Study Sheds Light on Origins of Saturn's Rings National Geographic - October 24, 2007

Titan: It's raining Methane ABC - October 12, 2007

New Lakes Discovered on Titan NASA - October 12, 2007

Source of Saturn moon Enceladus' mysterious jets pinpointed New Scientist - October 10, 2007

Iapetus

This false-color mosaic shows the entire hemisphere of Iapetus.
The Strange Tailing Side of Saturn's Iapetus NASA - October 10, 2007
2-Tone Saturn Moon Caught in Hi-Res National Geographic - October 9, 2007
The Strange Tailing Side of Saturn's Iapetus NASA - October 9, 2007
'Black and white moon' less grey BBC - October 9, 2007
Iapetus' mysterious dark side unveiled Science Daily - October 10, 2007
Sun to blame for mysterious blemishes on Saturn moon New Scientist - October 9, 2007

Saturn's Moon Iapetus Is The Yin-yang Of The Solar System Science Daily - September 18, 2007

Iapetus: 3D Equatorial Ridge NASA - September 15, 2007

Iapetus in Black and White NASA - September 14, 2007

Saturn's Mysterious G-ring Explained Space.com - August 4, 2007

Saturn's sixtieth moon discovered BBC - July 20, 2007

Saturn's "Walnut Moon" Mystery Solved National Geographic - July 19, 2007

Saturn "Sponge Moon" Has Ingredients for Life? National Geographic - July 5, 2007

Probe reveals seas on Saturn moon BBC - March 14, 2007
Saturn's Icy Moon May Have Been Hot Enough for Life, Study Finds National Geographic - March 14, 2007

Awesome image of Saturn from above NASA - March 6, 2007

Saturn Moon's Ice Geysers Create "Cosmic Graffiti" National Geographic - February 9, 2007

Liquid Lakes on Saturn's Titan NASA - February 7, 2007

'Proof' of methane (liquid) lakes on Titan BBC - January 4, 2007
Saturn Moon Has Lakes, "Water" Cycle Like Earth's, Scientists Say National Geographic - January 5, 2007

Mountain range spotted on Titan BBC - December 13, 2006

Huge 'hurricane' rages on Saturn BBC - November 10, 2006

NASA hurricane story with enlarged Image NASA
Monster "Hurricane" Spotted on Saturn National Geographic - November 14, 2006

Faint new ring discovered around Saturn BBC - September 21, 2006

'Great lakes' seen on Titan moon BBC - July 25, 2006

Methane Rain Possible on Titan NASA - August 2, 2006

Saturn Moon Has Seas of Sand, Images Reveal National Geographic - May 7, 2006

Encore For Enceladus! Saturn Moon Ripe For Astrobiology Exploration Space.com - April 3, 2006
The discovery of apparent liquid water reservoirs erupting in Yellowstone-like geysers on Saturn's moon Enceladus has produced a gusher of questions.

Saturn Moon Has Water Geysers and May Support Life National Geographic - March 11, 2006

Saturn's rings gave birth to moons News in Science - December 22, 2005

Saturn Surprise: One Ring is Actually a Spiral Space.com - November 28, 2005

Shoreline Spotted on Saturn's Moon Titan Space.com - September 19, 2005

Titan moon occupies 'sweet spot' BBC - September 9, 2005

Saturn ring particles 'fluffy' BBC - September 5, 2005

Saturn moon Titan 'dry as a bone' BBC - August 4, 2005

Eerie-sounding Radio Emissions NASA - July 27, 2005