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SATURN
Taken by Voyager 1 -- false color
Saturn ([ˈsætɚn] [9]) is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Along with the planets Jupiter, Uranus and Neptune it is classified as a gas giant (also known as a Jovian planet, after the planet Jupiter). It was named after the Roman god Saturnus, equated to the Greek Kronos (the Titan father of Zeus) and the Babylonian Ninurta. Saturn's symbol represents the god's sickle (Unicode: ♄).
The planet Saturn is composed of hydrogen, with small proportions of helium and trace elements.[10] The interior consists of a small core of rock and ice, surrounded by a thick layer of metallic hydrogen and a gaseous outer layer. The outer atmosphere is generally bland in appearance, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h, significantly faster than those on Jupiter. Saturn has a planetary magnetic field intermediate in strength between that of Earth and the more powerful field around Jupiter.
Saturn has a prominent system of rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Sixty known moons orbit the planet. Titan, Saturn's largest and the Solar System's second largest moon (after Jupiter's Ganymede), is larger than the planet Mercury and is the only moon in the Solar System to possess a significant atmosphere.[11]
Saturn compared to Earth
Due to a combination of its lower density, rapid rotation, and fluid state, Saturn is an oblate spheroid; that is, it is flattened at the poles and bulges at the equator. Its equatorial and polar radii differ by almost 10% – 60268 km vs. 54364 km.[3] The other gas planets are also oblate, but to a lesser extent. Saturn is the only planet of the Solar System that is less dense than water. Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm³ due to the gaseous atmosphere. Saturn is only 95 Earth masses,[3] compared to Jupiter, which is 318 times the mass of the Earth[12] but only about 20% larger than Saturn.[13]
Composition
The outer atmosphere of Saturn consists of about 93.2% molecular hydrogen and 6.7% helium. Trace amounts of ammonia, acetylene, ethane, phosphine, and methane have also been detected.[14] The upper clouds on Saturn are composed of ammonia crystals, while the lower level clouds appear to be composed of either ammonium hydrosulfide (NH4SH) or water.[15] The atmosphere of Saturn is significantly deficient in helium relative to the abundance of the elements in the Sun.
The quantity of elements heavier than helium are 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 elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.[16]
Though there is little direct information about Saturn's internal structure, it is thought that its interior is similar to that of Jupiter, having a small rocky core surrounded mostly by hydrogen and helium. The rocky core is similar in composition to the Earth, but denser. Above this, there is a thicker liquid metallic hydrogen layer, followed by a layer of liquid hydrogen and helium, and in the outermost 1,000 km a gaseous atmosphere.[17] Traces of various ices are also present. The core region is estimated to be about 9–22 times the mass of the Earth.[18] Saturn has a very hot interior, reaching 11,700 °C at the core, and it radiates 2.5 times 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.[19]
Rings of Saturn captured by Cassini
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. Mystified, Galileo wondered, "Has Saturn swallowed his children?", referring to the myth of the god Saturn eating his own children to prevent them from overthrowing him.[39] Then, in 1613, they reappeared again, further confusing Galileo.[40]
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."[40]
In 1675, Giovanni Domenico Cassini determined that Saturn's ring was composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the Cassini Division. This division in itself is a 4,800 km wide region between the A Ring and B Ring.[41]
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.[42] Maxwell's theory was proven correct in 1895 through spectroscopic studies of the rings carried out by James Keeler of Lick Observatory.
MORE: http://en.wikipedia.org/wiki/Saturn
Takn by Hubbel Telescope
This image of Saturn was taken by Voyager I in 1980
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Like the inner planets and Jupiter, Saturn is clearly visible in the night sky. The ancient Greeks named the planet after the god of agriculture and time. It wasn't until 1655, however, that we knew Saturn had rings. Galileo saw two lumps on either side of Saturn, be he didn't know what they were. The astronomer Christian Huygens later found out they were rings.
Much of what we now know about the second largest planet in our solar system comes from the Voyager spacecrafts. Voyager took close-up pictures of Saturn and its rings. They clearly show the large gaps in between the rings, called the Cassini Division and Encke Division.
Recently, a lot of research has been devoted to Saturn's moons. Huygens discovered Saturn's largest moon, Titan, in 1655. Six other satellites were discovered by various astronomers before 1800. Many smaller moons were found by the Voyager spacecraft.
Cassini is the newest mission to Saturn. If all goes as planned, it will reach the planet in 2004. Cassini will study Saturn and its largest moon, Titan.
MORE: http://www.windows.ucar.edu/tour/link=/saturn/discover.html
A montage of images: Saturn and its satellites
MORE: http://www.windows.ucar.edu/tour/link=/saturn/images/satsats_image.html
MOONS OF SATURN
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This is an image of Rhea.
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The gas giant planet Saturn has a large group of 59 moons. It also has the largest, most complex, and best-known ring system in our Solar System.
Saturn's moon Titan is one of the few moons in the Solar System with much of an atmosphere. It is also one of the largest moons in the Solar System.
Some of Saturn's moons are odd. A giant crater on Mimas makes it look like the "Death Star" from the Star Wars movies. Iapetus is quite dark on one side and very bright on the other. Hyperion is shaped like a garbage can. Prometheus and Pandora are called the "shepherd moons" because they herd particles into Saturn's "F ring". Phoebe is very dark and moves in a strange orbit. It may be an asteroid or Kuiper Belt Object that Saturn's strong gravity captured long ago.
The other medium-sized moons of Saturn are Rhea, Dione, Tethys, Enceladus, Janus and Epimetheus.
Some of Saturn's moons are icy moons. Most of the others are small moons which are basically large rocks in space. Some stories from old myths include characters that some of Saturn's moons were named after.
The two tables below list all of Saturn's know moons. One table lists them in order of size (largest to smallest). The other table linsts them in order of their distance from Saturn (closest to furthest).
MORE: http://www.windows.ucar.edu/tour/link=/saturn/moons_and_rings.html
Dione was discovered by G. Cassini in 1684. Dione is the 7th farthest moon from Saturn, with a standoff distance of 377,400 km. It is a small icy moon, lightly cratered, with wispy white streaks across the surface. Dione is about as wide as the Oregon coast is long, a width of 1120 km, or 750 miles. In appearance, it looks very much like Rhea, Enceladus, and Tethys.
MORE: http://www.windows.ucar.edu/tour/link=/saturn/moons/dione.html
Tethys is has a rather heavily cratered surface, with deep trenches. In appearance, this moon looks very much like Dione, Enceladus, and Rhea.
MORE: http://www.windows.ucar.edu/tour/link=/saturn/moons/tethys.html
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Enceladus is a moon of Saturn. It is Saturn's sixth largest moon. Saturn has 59 moons. Enceladus was discovered in 1789 by William Herschel (who also discovered the planet Uranus). It is mostly made of ice. It is pretty close to Saturn. It is actually inside of one of Saturn's rings!
Most of what we know about Enceladus comes from two spacecraft - Voyager and Cassini. The icy surface of Enceladus is very bright, like fresh snow. It reflects more light than any other moon in the Solar System! Scientists think they have discovered giant geysers of ice crystals on Enceladus. Maybe the geysers keep the moon covered with fresh ice, making it shiny.
The area near the South Pole on Enceladus is strange. The ground there is cracked. Some of the cracks are called "Tiger Stripes". In some places near the pole, the ice is much warmer than on the rest of the moon. Some scientists think there is liquid water under the surface of Enceladus. They think that water shoots up through the cracks, making geysers. The geysers might be a bit like "Old Faithful" in Yellowstone Park. The geysers on Enceladus shoot out cold water or ice crystals instead of hot water, though.
Enceladus has a very thin atmosphere. The atmosphere is thickest near the South Pole. The ice geysers probably make the atmosphere. Some of the ice from the geysers flies away from Enceladus. The moon is small and doesn't have very strong gravity. The ice goes into orbit around Saturn. It makes up one of Saturn's rings.
The orbit of Enceladus is inside of a ring of Saturn! The moon orbits 238,040 km (147,911 miles) above the center of Saturn. It takes Enceladus a bit more than one day (about 33 hours) to go around Saturn. The diameter of Enceladus is 505 km (314 miles).
There are only four places in our Solar System that have volcanoes or geysers. Enceladus may be one of them. The others are Earth, Jupiter's moon Io, and maybe Neptune's moon Triton. The cracked ground on Enceladus looks like the surfaces of Europa and Ganymede. Those are two ice moons of Jupiter. Enceladus is a very interesting moon! If there is water under the surface of Enceladus, some scientists wonder whether there might even be life there!
MORE: http://www.windows.ucar.edu/tour/link=/saturn/moons/enceladus.html
Saturn and two of its moons, Tethys and Dione, were photographed by Voyager 1 at a distance of 13 million km (8 million mi). The shadows of Saturn's three bright rings are cast onto the cloud tops. The limb of the planet can be seen easily through the 3500 km (2170 mi) wide Cassini Division, which separates the A and B rings. The view through the much narrower Encke Gap, near the outer edge of the A ring is less clear. Closer to the planet is the faintest of Saturn's three main rings, the C ring or crepe ring, barely visible against the planet.
MORE: http://pds.jpl.nasa.gov/planets/captions/saturn/tethdion.htm
Mimas, the innermost of Saturn's larger moons, was nearly shattered by a cataclysmic impact. From observing Mimas' crater Herschel, scientists speculate that the inner satellites of the outer planets have, in fact, been shattered and gravitationally reassembled many times in their geologic history. Herschel's walls are approximately 5 km (3.2 mi) high, parts of its floor measure 10 km (6.2 mi) deep, and its central peak rises 6 km (3.7 mi) above the crater floor. The diameter of this moon is 394 km (244 mi).
MORE: http://pds.jpl.nasa.gov/planets/captions/saturn/mimas.htm
This global mosaic of Enceladus was assembled from images acquired by Voyager 2 during its close flyby of Saturn's second large satellite. Although Enceladus shows an abundance of impact craters in some areas, the lava flows near the center of the disk contain many fewer craters and cut some craters in half. This confirms the multiple stages or episodes of volcanism that formed and reformed the icy body's surface.
MORE: http://pds.jpl.nasa.gov/planets/captions/saturn/encelads.htm
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