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Saturn[Key Words] [General] [History] [Rings] [Satellites] [Unknowns]Key Words
Saturn looks just like a star, at least without the help of any special equipment. It isn't as bright as Jupiter, it is flattened at the poles, spins fast but is rather slow moving around the Sun. Saturn shines with a dull, slightly yellowish light which gives the star-gazer the impression that it is just another star, instead of being the second largest planet in the system. Sometimes Saturn is brightest when its rings are at a wide angle and it can glow brighter than any star in the sky except Sirius and Canopus.
General Saturn has a diameter of about 120,00 km, could hold more than
700 Earths (right), has a 10 hour day and takes 30 years to go
around the Sun. Its magnetic field is considerably less than
Jupiter's but still 1,000 times greater than that of the
Earth. Like Jupiter, Saturn has atmospheric bands. On Saturn, the bands are much weaker and vary with altitude. Close the surface, winds travel mostly in an easterly direction at over 1000 miles per hour. At higher altitudes, the winds vary in direction in layers but do not strictly follow the changes in color. Two adjacent layers could be going the same direction (for example). Saturn is, of course, best known for its rings that are
labeled alphabetically (A, B, C, etc.) in the order of their
discovery. It is less known for its oval spots (see image at
right) that were discovered by Voyager or for its luminous aurora
at both of its poles. Saturn's "Northern Lights" range
2,000 km (1,200 miles) above the clouds and rapidly change in
brightness. Similarly, Saturn's "Southern Lights" are
the result of charged particles from the magnetosphere colliding
with atmospheric gases.
History Saturn was thought to be the only planet with rings until well into the 20th Century. In 1977, rings were discovered around Uranus and soon after we found that Jupiter and Neptune also had them. Saturn's rings were labeled in the order they were discovered. It's not surprising then that rings A and B are the easiest to see and that only rarely can one see rings D and E. In order from the surface outward, the rings are D, C, B, A, F, G, and E rings. A and B are the easiest rings to see. The rings are actually clusters of thin rings and not the broad sections that they appear to be. There may be more than 100,000 individual rings making up the system. Like Jupiter, Saturn is primarily hydrogen (88 percent) and helium (11 percent). It's colder than Jupiter by about 50° F but its magnetosphere is much smaller. It was first visited by Pioneer 11 in 1979. Later, the Voyagers (1 and 2) flew by. The spacecraft Cassini is currently on its way to Saturn and should arrive in 2004. So stay tuned for more.
Rings
* Distance is measured from the center of Saturn. Keep in mind that the categories are not this defined. There are variations within the rings, the gaps are not totally empty, the rings are not completely circular, and everything is mixed together in a complex structure.
Satellites
Rhea and Iapetus are midsized moons (about 1000
km wide). There are likely more than the 18 moons listed below;
perhaps as many as 30 or more. Saturn is apparently a popular
place to orbit.
In 1655, the Dutch astronomer Christiaan Huygens (1629-1695) discovered Titan, the largest of Saturn's moons. It is nearly as large as Jupiter's Ganymede moon and larger than the planets Mercury and Pluto). It has its own atmosphere (mostly nitrogen, methane and acetylene) and might contain oceans or lakes of liquid methane. Giovanni Domenico Cassini (1625-1712 ) is responsible for discovering four of Saturn's moons. In 1671, Cassini discovered Iapetus, which is characterized by having one side dark red while the other is bright and nearly white. The following year, he discovered Rhea, which about 2/3 water and 1/3 rock. In 1684, Cassini found Tethys, an icy ball whose main feature is a 40 mile long trench that cuts about 3/4th of the way around it. That same year, he discovered Dione, Saturn's second densest moon (after Titan). Dione is slightly larger than Tethys, more massive, and yet still mostly made of ice. In 1789, William Herschel (1738-1822) discovered Mimas and Enceladu. Mimas is an icy, heavily crater moon with low density that orbits close to Saturn. One of its craters covers nearly a third of its surface, indicating that Mimas was struck by an object large enough to nearly smash it to pieces. Like Mimas, Enceladus is probably entirely made of ice. What's unusual about this moon is that it reflects nearly all of the light that hits it. Since it reflects light so well, the surface of Enceladus is probably around -200° C (-330° F). Although Enceladus has two heavily cratered plains, it also hosts a large smooth plain with almost no craters at all. In 1898, William Pickering (1858-1938) discovered Saturn's moon Phoebe. Phoebe doesn't reflect much light (about 6%) and is probably an asteroid captured by Saturn. Phoebe takes nearly 2 years to go around the Sun, has 9 hour days and is not synchronous. That is, its revolution period around Saturn is 550 days, and a day on Phoebe is about 9 hours.
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The magnetosphere extends out to the
orbit of Titan (one of its 18 satellites) but varies so that
Titan is sometimes inside and sometimes outside. Saturn is
inclined only about three degrees more than Earth is: at 25-26°.
(see picture at left) 
described it as a planet with a large
ring around it. In 1675, G. D. Cassini discovered a gap in a ring
(called the Cassini division). Further study let to the discovery
of more rings. 
only 1-2 km thick. At some angles they appear to
almost vanish. Rings A and B (and sometimes C) can be seen from
Earth as continuous rings. But actually the rings are composed of
independent globs of ice that orbit the planet. These particles
of ice vary in size from centimeters to kilometers and travel as
a complex system with thousands of parts. Saturn's rings also
seem to have what can best be described as "spokes"
(right) within the rings. It is not known if Saturn's rings were
there when the planet was formed. 
ore satellites than any other planet and they range
in size greatly. Titan (left), the largest moon is about 1500 km
across but Enceladus and Mimas are only about 400-500 km wide.