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Saturn is the second largest planet.
Only Jupiter is larger. Saturn has seven thin, flat rings around it. The
rings consist of numerous narrow ringlets, which are made up of ice
particles that travel around the planet. The gleaming rings make Saturn
one of the most beautiful objects in the solar system. Jupiter, Neptune,
and Uranus are the only other planets known to have rings. Their rings are
much fainter than those around Saturn.
Saturn's diameter at its equator is
about 74,900 miles (120,540 kilometers), almost 10 times that of Earth.
The planet can be seen from Earth with the unaided eye, but its rings
cannot. Saturn was the farthest planet from Earth that the ancient
astronomers knew about. They named it for the Roman god of
agriculture.
Saturn travels around the sun in an
elliptical (oval-shaped) orbit. Its distance from the sun varies from
about 941,070,000 miles (1,514,500,000 kilometers) at its farthest point
to about 840,440,000 miles (1,352,550,000 kilometers) at its closest
point. The planet takes about 10,759 Earth days, or about 29 1/2 Earth
years, to go around the sun, compared with 365 days, or one year, for
Earth.
 Rotation
As Saturn travels around the sun, it
spins on its axis, an imaginary line drawn through its center. Saturn's
axis is not perpendicular (at an angle of 90 degrees) to the planet's path
around the sun. The axis tilts at an angle of about 27 degrees from the
perpendicular position.
Saturn rotates faster than any other
planet except Jupiter. Saturn spins around once in only 10 hours 39
minutes, compared to about 24 hours, or one day, for Earth. The rapid
rotation of Saturn causes the planet to bulge at its equator and flatten
at its poles. The planet's diameter is 8,000 miles (13,000 kilometers)
larger at the equator than between the poles.
Surface and atmosphere
Most scientists believe Saturn is a giant ball of
gas that has no solid surface. However, the planet seems to have a hot
solid inner core of iron and rocky material. Around this dense central
part is an outer core that probably consists of ammonia, methane, and
water. A layer of highly compressed, liquid metallic hydrogen surrounds
the outer core. Above this layer lies a region composed of hydrogen and
helium in a viscous (syruplike) form. The hydrogen and helium become
gaseous near the planet's surface and merge with its atmosphere, which
consists chiefly of the same two elements.
 A dense layer of clouds covers Saturn.
Photographs of the planet show a series of belts and zones of varied
colors on the cloud tops. This banded appearance seems to be caused by
differences in the temperature and altitude of atmospheric gas masses.
The plants and animals that live on Earth could
not live on Saturn. Scientists doubt that any form of life exists on the
planet.
Temperature
The tilt of Saturn's axis causes the sun to heat
the planet's northern and southern halves unequally, resulting in seasons
and temperature changes. Each season lasts about 7 1/2 Earth years,
because Saturn takes about 29 times as long to go around the sun as Earth
does. Saturn's temperature is always much colder than Earth's, because
Saturn is so far from the sun. The temperature at the top of Saturn's
clouds averages -285 degrees F (-175 degrees C).
The temperatures below Saturn's clouds are much
higher than those at the top of the clouds. The planet gives off about 2
1/2 times as much heat as it receives from the sun. Many astronomers
believe that much of Saturn's internal heat comes from energy generated by
the sinking of helium slowly through the liquid hydrogen in the planet's
interior.
Density and mass
Saturn has a lower density than any other planet.
It is only about one-tenth as dense as Earth, and about two-thirds as
dense as water. That is, a portion of Saturn would weigh much less than an
equal portion of Earth, and would float in water.
Although Saturn has a low density, it has a
greater mass than any other planet except Jupiter. Saturn is about 95
times as massive as Earth. The force of gravity is a little higher on
Saturn than on Earth. A 100-pound object on Earth would weigh about 107
pounds on Saturn.
Rings
 The rings of Saturn surround the planet at its
equator. They do not touch Saturn. As Saturn orbits the sun, the rings
always tilt at the same angle as the equator.
The seven rings of Saturn consist of thousands of
narrow ringlets. The ringlets are made up of billions of pieces of ice.
These pieces range from ice particles that are the size of dust to chunks
of ice that measure more than 10 feet (3 meters) in diameter.
Saturn's major rings are extremely wide. The
outermost ring, for example, may measure as much as 180,000 miles (300,000
kilometers) across. However, the rings of Saturn are so thin that they
cannot be seen when they are in direct line with Earth. They vary in
thickness from about 660 to 9,800 feet (200 to 3,000 meters). A space
separates the rings from one another. Each of these gaps is about 2,000
miles (3,200 kilometers) or more in width. However, some of the gaps
between the major rings contain ringlets.
Saturn's rings were discovered in the early 1600's
by the Italian astronomer Galileo. Galileo could not see the rings clearly
with his small telescope, and thought they were large satellites. In 1656,
after using a more powerful telescope, Christiaan Huygens, a Dutch
astronomer, described a "thin, flat" ring around Saturn. Huygens thought
the ring was a solid sheet of some material. In 1675, Giovanni Domenico
Cassini, an Italian-born French astronomer, announced the discovery of two
separate rings made up of swarms of satellites. Later observations of
Saturn resulted in the discovery of more rings. The ringlets were
discovered in 1980.
Satellites
In addition to its rings, Saturn has 33 satellites
that measure at least 6 miles (10 kilometers) in diameter, and several
smaller satellites. The largest of Saturn's satellites, Titan, has a
diameter of about 3,200 miles (5,150 kilometers) -- larger than the
planets Mercury and Pluto. Titan is one of the few satellites in the solar
system known to have an atmosphere. Its atmosphere consists largely of
nitrogen.
Many of Saturn's satellites have large craters.
For example, Mimas has a crater that covers about one-third the diameter
of the satellite. Another satellite, Iapetus, has a bright side and a dark
side. The bright side of this satellite reflects about 10 times as much
sunlight as the dark side. The satellite Hyperion is shaped somewhat like
a squat cylinder rather than like a sphere. Unlike Saturn's other
satellites, Hyperion's axis does not point toward the planet. Saturn has
at least 52 moons total.
Flights to Saturn
In 1973, the United States launched a space probe
to study both Saturn and Jupiter. This craft, called Pioneer-Saturn, sped
by Jupiter in 1974 and flew within 13,000 miles (20,900 kilometers) of
Saturn on Sept. 1, 1979. The probe sent back scientific data and close-up
photographs of Saturn. The data and photographs led to the discovery of
two of the planet's outer rings.
 Pioneer-Saturn
also found that the planet has a magnetic field, which is 1,000 times as
strong as that of Earth. This field produces a large magnetosphere (zone
of strong magnetic forces) around Saturn. In addition, data from the probe
indicated the presence of radiation belts inside the planet's
magnetosphere. The belts consist of high-energy electrons and protons, and
are comparable to Earth's Van Allen belts.
In 1977, the United States launched two space
probes -- Voyager 1 and Voyager 2 -- to study Saturn and other planets.
Voyager 1 flew within 78,000 miles (126,000 kilometers) of Saturn on Nov.
12, 1980. On Aug. 25, 1981, Voyager 2 flew within 63,000 miles (101,000
kilometers) of the planet.
The Voyager probes confirmed the existence of
Saturn's seventh ring. They also found that the planet's rings are made up
of ringlets. In addition, the probes sent back data and photographs that
led to the discovery or confirmation of the existence of nine satellites.
The Voyager probes also determined that the atmosphere of Titan consists
chiefly of nitrogen. In 1997, the United States launched the Cassini probe
to study Saturn, its rings, and its satellites. The probe began orbiting
Saturn in 2004. Cassini also carried a probe called Huygens, which was to
separate from Cassini and land on Titan. Huygens was built by the European
Space Agency, an organization of European nations.
Contributor: Hyron Spinrad, Ph.D., Professor of
Astronomy, University of California, Berkeley.
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Comparing Saturn and
Earth |
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