FREE ESSAY ON SATURN

SATURN

Saturn
Saturn is one of the most interesting planets in the solar system. It is the sixth planet
in the solar system, and is most famous for its stunning array of rings. It is a very
easy planet to pick out in the sky because it is one of the brightest lights in the shy.
It also has a very faint greenish color that makes it stand out from the rest of the
objects in the sky ("Astronomy for Kids"). Saturn is the second largest planet in the
solar system, Jupiter being the only planet that is bigger. It also has at least eighteen
moons, more than any other planet in the solar system. There have been three voyages to
this extraordinary planet, and one is still in process today. The Pioneer II traveled to
Saturn in September of 1979, the Voyager missions took place in the 1980's and the
Cassini probe began it's voyage in October of 1997 (Kuhn 280-282). There are many aspects
of Saturn that make it one of the most extraordinary planets in this solar system.
Galileo Galilei was the first to view Saturn's system of rings in the year 1610. Because
he happened to be viewing their edge, he failed to recognize them as rings. In fact, he
mistakenly interpreted the rings to be two moons similar to those he had discovered near
the planet Jupiter. In 1655, a Dutch astronomer named Christiaan Huygens was able to
discern what Galileo had thought to be moons as rings. Huygens benefited from a much
improved telescope than that used by Galileo. A second moon of Saturn called Iapetus was
found by the Italian astronomer Cassini in 1671. He also discovered, in 1675, that Saturn
had more than one ring, i.e. a concentric pair of rings. A third ring was discovered by
Johann Franz Encke in 1837 using a telescope at the Berlin observatory. Until Pioneer II
approached Saturn in September of 1979, the planet was thought to have but three rings
(Yenne 125).
Saturn is the sixth planet in the solar system, located between Jupiter and Uranus. Its
average distance from the Sun is over 850 million miles, compared to Earth's which is 93
million miles. Saturn's orbit, the path it follows around the Sun, is nearly a circle.
The closest the planet has come to the Sun is around 840 million miles, while the
furthest away it gets is 930 million miles. Since Saturn is so far away from the Sun, it
takes a very long time for it to complete its orbit of the Sun. Saturn's year equals 29
and one-half Earth years. A day on Saturn, though, is much shorter than an Earth day; it
rotates around once every ten and one-half hours (Kuhn 280-282).
Saturn is the second largest planet in the solar system. Jupiter is the only planet that
is larger. The gas giant is 72 thousand miles in diameter, almost ten times the size of
Earth. In spite of its huge size, though, Saturn weighs very little. It is a very light
gas planet. Saturn is the least dense planet in the solar system-- so light, in fact,
that it would float in water. This planet is mostly composed of hydrogen and helium, like
Jupiter, but it is much less dense. The combination of its light weight and fast rotation
causes Saturn to spread out, or oblate, its center. Since Saturn is a gas planet, it does
not have a solid surface. Spacecraft are unable to land on this type of surface. The
clouds that are seen when looking at Saturn are just the top layer of a very deep layer
that covers a center of liquid hydrogen. The clouds are blown by constant winds that
reach speeds up to one thousand miles per hour at the equator of the planet ("Great Space
Place"). 
The rings of Saturn are more spectacular than those of any other planet. Although this
planet's rings are very wide, extending from the top of its atmosphere to well beyond the
orbits of its closest moons, they are very thin, measuring no more than a few kilometers
(about a mile) in thickness ("Great Space Place"). The Pioneer 11 flyby made several
discoveries about the rings. The rings are made of particles that are dust-sized up to
large mountain-sized masses, with the average size being in the marble to basketball
range - about 10 centimeters (four inches). These particles are extremely cold and are
possibly composed of frozen water and other ices. An extensive cloud of hydrogen was also
discovered around the rings. The rings might have resulted when a moon or a passing body
ventured too close to Saturn. The unlucky object would have been torn apart by great
tidal forces on its surface and in its interior. In addition, the object may not have
been fully formed to begin with and disintegrated under the influence of Saturn's
gravity. A third possibility is that the object was shattered by collisions with larger
objects orbiting the planet ("Pioneer 10, 11").
Voyager I provided much more detail on the beauty, complexity, and sometimes baffling
nature of the rings. The six known rings are actually composed of hundreds of tiny, thin
ringlets with intervening spaces, so that the whole ring system looks something like the
grooves in a phonograph record. Even the Cassini division, once thought to be empty space
between the A and B rings, contains several dozen ringlets. There are far too many rings
to be explained by the present theories of how planetary rings form and remain stable.
The thin outer F-ring, discovered by Pioneer 11, was resolved into three distinct but
intertwined ringlets. This braided ring structure is very difficult to explain; it seems
likely that both electrical and gravitational forces are at work. This voyage also helped
to discovered that two of Saturn's small moons, one on each side of the F-ring, may act
as "shepherds," their gravitational attraction keeping the ring particles on track
between the orbits of the moon (Yenne 126).
The first spacecraft flyby accomplished by Pioneer 11 in 1979 accomplished many findings
of Saturn's composition. The planet has an internal heat source like Jupiter and radiates
about twice as much energy as it receives from the Sun. As suspected, Saturn must have
internal shells of liquid and metallic hydrogen, small amounts of helium, ammonia, water,
and perhaps a small rocky core. A magnetic field was also discovered around Saturn,
larger than the Earth's, but smaller than that of Jupiter. It is five times as weak as
predicted by theory. The axis of this magnetic field is aligned parallel to the planet's
rotation axis, contrary to the circumstances in both Jupiter and Earth. The boundary of
the magnetic field varies due to changes in the pressure of the solar wind on the sunward
side, as was found in the case of Jupiter. The atmosphere of Saturn has weak bonds and
there is a high haze, perhaps composed of crystals of ammonia ice, above the clouds.
Apparent high-speed jet streams were also detected in the atmosphere. Confirming
ground-based measurements, the cloud-top temperatures were measured at about -200 degrees
Celsius (-330 degrees Fahrenheit), and only about 73 degrees Celsius (130 degrees
Fahrenheit) above absolute zero. The Pioneer 11 voyage also discovered radiation belts
that are weaker than those of Jupiter. The radiation is absorbed by the rings and moons
of Saturn. Cutoffs in the radiation data were used to infer the presence of additional
rings and moons beyond those already known from visual observations ("Pioneer 10, 11"). 
Saturn has more moons than any other planet in the solar system. Nine (possibly ten) of
these moons have been detected from Earth. Voyager 1's encounter to Saturn provided
several new discoveries about Saturn's moons. Six, tiny unnamed moons were photographed
on this mission, some of them for the first time. Satellites 10 and 11 share the same
orbit and must frequently undergo some orbital "evasive actions" to avoid colliding.
Satellite 12 shares the orbit of the larger moon Dione. The shepherd Satellites13 and 14,
on either side of the thin F-ring, may exert gravitational forces to keep the ring in
place, while Satellite 15, located just outside the large A-ring, likewise may help keep
that ring in place.
The inner moons Mimas, Tethys, Dione, and Rhea all have heavily cratered surfaces like
those of the Moon and Mercury, although Saturn's moons are composed largely of water and
ice. This shows that meteorite bombardment, even as far out as Saturn, has been a major
process in shaping the solar system. Mimas is marked by a huge impact crater called
Herschel that is fully one-fourth the diameter of Mimas itself. This crater makes Mimas
look like a staring eyeball, giving it the nickname "Death Star." The impact that formed
it was almost intense enough to blast Mimas into fragments. This moon is the innermost of
Saturn's large moons, orbiting outside the rings of its parent planet. Herschek is 140
kilometers (90 miles) across and 10 kilometers (6 miles) deep. It is one of the largest
craters, with respect to planetary diameter, in the solar system ("Great Space Place").
Enceladus, another of Saturn's moons, is located in the center of this planet's E-ring.
The tiny droplets of frozen water that make up the E-ring have coated the surface of
Enceladus and made it the most reflective moon in the solar system. Heavily cratered
areas are cut by linear grooves and relatively smooth, cratered regions. Tidal forces may
be generating the internal energy necessary to drive the faulting and volcanism observed
on Enceladus. In fact, ice particles in the E-ring may be produces by active water
volcanism on this moon. 
Titan is the largest moon of Saturn, and the second largest moon in the solar system,
after Ganymede. Titan is unique in the solar system - it is the only satellite with its
own rich atmosphere of nitrogen, more like Earth's atmosphere than any other world.
Traces of methane and other hydrocarbons ("the building blocks of life") have also been
detected. Like Venus, the thick atmosphere of Titan completely obscured its surface from
view. Scientists have guessed at what Titan's surface may be like. Some have suggested it
is a "bizarre, murky swamp of liquid nitrogen and hydrocarbon muck." Others have proposed
a global ocean of liquid hydrocarbons, with rains of frozen gasoline. Radar signals
bounced off Titan indicate no global oceans, but did produce signals that could be due to
local lakes and swamps (Yenne 127).
Three American spacecraft have visited Saturn. Pioneer 11 sped by the planet and its moon
Titan in September 1979, returning the first close-up images. Voyager 1 followed in
November 1980, sending back breathtaking photographs that revealed for the first time the
complexities of Saturn's ring system and moons. Voyager 2 flew by the planet and its
moons in August 1981. As of now, the Cassini-Huygens probe began its 6.7-year voyage to
Saturn on Wednesday, October 15, 1997. A U.S. Air Force Titan 4B rocket blasted off with
the multi-billion dollar space probe ("Yenne 127").
Pioneers 10 and 11 were the first spacecraft to visit Jupiter (Pioneer 10 and 11) and
Saturn (Pioneer 11 only). Acting as pathfinders for the Voyager missions, the vehicles
provided first up-close science observations of these planets, as well as information
about the environments that would be encountered by the Voyagers. Instruments abroad the
two spacecraft studied Jupiter and Saturn's atmospheres, magnetic fields, moons, and
rings, as well as the interplanetary magnetic and dust particle environment, the solar
wind, and cosmic rays. Following their planetary encounters, some experiments abroad both
spacecraft were turned off to save power as the vehicle's RTG power output degraded.
Pioneer 11's mission ended on September 30, 1995 when its PTG power level was
insufficient to operate any experiments and the spacecraft could no longer be controlled.

The Voyager 1 flyby of Saturn took place on November 12, 1980 and Voyager 2 flew by
Saturn and its moons in August 1981. The Voyager 1 spacecraft reached as close as184, 300
kilometers from the center of the planet. Among the highlights of the encounter were the
separate encounter of Titan, discovery of intricate patterns within the ring system, and
observations of variations among the many moons of the planet. Radio emissions quite
similar to the static heard on an AM car radio during an electrical storm were detected
by the Voyager spacecraft. These emissions are typical of lightning but are believed to
be coming from Saturn's ring system rather than its atmosphere, where no lightning was
observed. As they had at Jupiter, the Voyagers saw a version of Earth's auroras near
Saturn's poles. The Voyagers discovered new moons and found several satellites that share
the same orbit. Saturn's 18th moon was discovered in 1990 from images taken by Voyager 2
in 1981. Voyager 1 determined that Titan has a nitrogen-based atmosphere. Unfortunately,
Voyager 1's cameras could not penetrate the moon's dense clouds. The Voyagers 1 and 2
were not the last spacecraft to visit the planet ("great Space Place").
The most recent spacecraft to visit Saturn is the Cassini-Huygens probe. Cassini is the
biggest and most complicated mission that NASA has ever built, and is maybe the last of
the big spacecraft which will explore the outer solar system for decades to come. Cassini
is a joint mission sponsored by NASA, the US space agency, and ESA, the European Space
Energy. NASA had help from ESA, which built the Huygens probes, and from many other
American and European companies and scientific organizations which built other
instruments. Cassini has 27 different instruments on it, and weighs almost 5,300 kg at
launch, more than half of which is fuel which will help send it all the way to Saturn.
Cassini is over 2 stories tall fully assembled, and the probe itself is only 2.7 meters
in diameter. It is named after the 17th century astronomer, Jean Dominique Cassini, who
discovered a large dark gap in the Saturn's rings, and the Huygens probe is named after
the Dutch scientist Christiaan Huygens, who discovered Titan in 1655. Scientists are
excited about studying Titan in more detail because its thick clouds completely hid its
think surface from view during the Voyager's flyby's. The probe's 2.2 billion mile
roundabout journey to Saturn will take it by Venus twice, the Earth, and Jupiter.
Cassini's mission to explore Saturn, its icy rings, the moon Titan, other moons and the
huge magnetic bubble that surrounds them is being described as the most ambitious
planetary mission ever mounted. The mission also entails the first descent of a probe to
a moon of another planet, sending the Huygens probe to the surface of Titan - by far the
most distant landing ever attempted on another object in the solar system ("Astronomy
Now").
There is no other planet in the solar system that is adorned like Saturn. Its exquisite
ring system is unrivaled. Like Jupiter, Saturn is composed mostly of hydrogen. In
contrast to the vivid colors and wild turbulence found in the clouds, Saturn's atmosphere
has a more subtle hue, and its markings are hidden by the high-altitude haze. Three
American spacecraft have visited Saturn, and the Cassini mission is in orbit now. Pioneer
11 sped by the planet returning the first close-up images. Voyager 1 followed in November
1980, sending back photographs that revealed for the first time Saturn's ring system and
moons. Voyager 2 flew by the planet and its moons in August 1981. The Cassini probe is
exploring many of Saturn's characteristics from its icy rings to the magnetic field,
which is a very ambitious mission. The mission also entails the first decent of a probe
to a moon of another planet - the most distant landing ever attempted on another object
in the solar system ("Great Space Place"). These discoveries and close-ups of the
exquisite characteristics of Saturn are what make this planet the most interesting and
amazing of the solar system. 
Bibliography
Bibliography
"Astronomy for Kids-Saturn," Altavista, http://www.dustbunny.com/afk/planets/saturn.
htm, November 20, 1998.
"Astronomy Now: Cassini - Mission to Saturn," Altavista, http://www.astronomynow.
com/cassini/ November 10, 1998,
"Great Space Place," Altavista, http://www.transatlantech.com/TPS/gsp-starssaturn.html
November 15, 1998.
Kuhn, Karl F., "In Quest of the Universe," Jones and Bartlett Publishers, Inc. Copyright
1998.
Pioneer 10, 11 Quicklook," Altavista, http://leonardo.jpl.nasa.gov/msl/QuickLooks/
pioneer10QL.html, November 10, 1998.
Yenne, Bill, "The Atlas of the Solar System," Brompton Books Corp., Greenwich, 1987, 
125-128.