Saturn is the sixth planet from the Sun
and the second largest planet in the
Solar System, after Jupiter. Saturn is
named after the Roman god Saturn,
equated to the Greek Cronus (the Titan
father of Zeus), the Babylonian Ninurta and the Hindu Shani. Saturn's symbol
represents the Roman god's sickle. Saturn, along with Jupiter, Uranus and
Neptune, is classified as a gas giant.
Together, these four planets are
sometimes referred to as the Jovian,
meaning "Jupiter-like", planets. Saturn
has an average radius about 9 times larger than the Earth's. While only 1/8
the average density of Earth, due to its
larger volume, Saturn's mass is just
over 95 times greater than Earth's. Because of Saturn's large mass and
resulting gravitation, the conditions
produced on Saturn are extreme if
compared to Earth. The interior of
Saturn is probably composed of a core
of iron, nickel, silicon and oxygen compounds, surrounded by a deep
layer of metallic hydrogen, an
intermediate layer of liquid hydrogen
and liquid helium and finally, an outer
gaseous layer. Electrical current within the metallic-
hydrogen layer is thought to give rise
to Saturn's planetary magnetic field,
which is slightly weaker than Earth's
magnetic field and approximately
one-twentieth the strength of the field around Jupiter. 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 nine rings, consisting
mostly of ice particles with a smaller
amount of rocky debris and dust.
Sixty-two known moons orbit the
planet; fifty-three are officially named.
This is not counting hundreds of "moonlets" within the rings. 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.
Saturn's magnificent ring system - a
huge disc resembling an old
gramophone record - turns out to
share another property with the LP: it
constantly emits a melodic series of
musical notes. The surprising discovery was made by radio and
plasma wave detectors on board the
Cassini spacecraft as it passed over
Saturn's rings during its arrival at the
planet in July. The tones are emitted as
radio waves. Don Gurnett of the University of Iowa says his team
reduced their frequencies by a factor
of five to bring them into the range of
human hearing. Gurnett says he was
"completely astonished" when he
heard the musical notes. The tones are short, typically lasting
between one and three seconds, and
unlike the ethereal sliding tones
associated with other cosmic
processes, every one is quite distinct.
The evidence suggests that each tone is produced by the impact of a
meteoroid on the icy chunks that
make up the rings. Each hit, Gurnett says, creates a pulse
of energy that is focused along the
surface of a cone from the point of
impact. By estimating the energy
involved, he calculates that the
impacting objects are about 1 centimetre across - although he
cautions that his estimate could be out
by as much as a factor of 10.
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% - 60,268 km versus 54,364 km. 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,
compared to Jupiter, which is 318
times the mass of the Earth but only
about 20% larger than Saturn.
Saturn's rings require at least a 15 mm
diameter telescope to resolve and thus
were not known to exist until Galileo first saw them in 1610. He thought of
them as two moons on Saturn's sides.
It was not until Christian Huygens
used greater telescopic magnification
that this notion was refuted. Huygens
also discovered Saturn's moon Titan. Some time later, Giovanni Domenico
Cassini discovered four other moons:
Iapetus, Rhea, Tethys and Dione. In 1675, Cassini also discovered the
gap now known as the Cassini
Division. No further discoveries of significance
were made until 1789 when William
Herschel discovered two further
moons, Mimas and Enceladus. The
irregularly shaped satellite Hyperion,
which has a resonance with Titan, was discovered in 1848 by a British team. In 1899 William Henry Pickering
discovered Phoebe, a highly irregular
satellite that does not rotate
synchronously with Saturn as the
larger moons do. Phoebe was the first
such satellite found and it takes more than a year to orbit Saturn in a
retrograde orbit. During the early 20th century,
research on Titan led to the
confirmation in 1944 that it had a thick
atmosphere - a feature unique among
the solar system's moons.
The outer atmosphere of Saturn
consists of 96.3% molecular hydrogen
and 3.25% helium. Trace amounts of
ammonia, acetylene, ethane,
phosphine and methane have also
been detected. 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. 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 1931 times the mass of the Earth,
with a significant fraction located in
Saturn's core region.
and the second largest planet in the
Solar System, after Jupiter. Saturn is
named after the Roman god Saturn,
equated to the Greek Cronus (the Titan
father of Zeus), the Babylonian Ninurta and the Hindu Shani. Saturn's symbol
represents the Roman god's sickle. Saturn, along with Jupiter, Uranus and
Neptune, is classified as a gas giant.
Together, these four planets are
sometimes referred to as the Jovian,
meaning "Jupiter-like", planets. Saturn
has an average radius about 9 times larger than the Earth's. While only 1/8
the average density of Earth, due to its
larger volume, Saturn's mass is just
over 95 times greater than Earth's. Because of Saturn's large mass and
resulting gravitation, the conditions
produced on Saturn are extreme if
compared to Earth. The interior of
Saturn is probably composed of a core
of iron, nickel, silicon and oxygen compounds, surrounded by a deep
layer of metallic hydrogen, an
intermediate layer of liquid hydrogen
and liquid helium and finally, an outer
gaseous layer. Electrical current within the metallic-
hydrogen layer is thought to give rise
to Saturn's planetary magnetic field,
which is slightly weaker than Earth's
magnetic field and approximately
one-twentieth the strength of the field around Jupiter. 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 nine rings, consisting
mostly of ice particles with a smaller
amount of rocky debris and dust.
Sixty-two known moons orbit the
planet; fifty-three are officially named.
This is not counting hundreds of "moonlets" within the rings. 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.
Saturn's magnificent ring system - a
huge disc resembling an old
gramophone record - turns out to
share another property with the LP: it
constantly emits a melodic series of
musical notes. The surprising discovery was made by radio and
plasma wave detectors on board the
Cassini spacecraft as it passed over
Saturn's rings during its arrival at the
planet in July. The tones are emitted as
radio waves. Don Gurnett of the University of Iowa says his team
reduced their frequencies by a factor
of five to bring them into the range of
human hearing. Gurnett says he was
"completely astonished" when he
heard the musical notes. The tones are short, typically lasting
between one and three seconds, and
unlike the ethereal sliding tones
associated with other cosmic
processes, every one is quite distinct.
The evidence suggests that each tone is produced by the impact of a
meteoroid on the icy chunks that
make up the rings. Each hit, Gurnett says, creates a pulse
of energy that is focused along the
surface of a cone from the point of
impact. By estimating the energy
involved, he calculates that the
impacting objects are about 1 centimetre across - although he
cautions that his estimate could be out
by as much as a factor of 10.
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% - 60,268 km versus 54,364 km. 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,
compared to Jupiter, which is 318
times the mass of the Earth but only
about 20% larger than Saturn.
Saturn's rings require at least a 15 mm
diameter telescope to resolve and thus
were not known to exist until Galileo first saw them in 1610. He thought of
them as two moons on Saturn's sides.
It was not until Christian Huygens
used greater telescopic magnification
that this notion was refuted. Huygens
also discovered Saturn's moon Titan. Some time later, Giovanni Domenico
Cassini discovered four other moons:
Iapetus, Rhea, Tethys and Dione. In 1675, Cassini also discovered the
gap now known as the Cassini
Division. No further discoveries of significance
were made until 1789 when William
Herschel discovered two further
moons, Mimas and Enceladus. The
irregularly shaped satellite Hyperion,
which has a resonance with Titan, was discovered in 1848 by a British team. In 1899 William Henry Pickering
discovered Phoebe, a highly irregular
satellite that does not rotate
synchronously with Saturn as the
larger moons do. Phoebe was the first
such satellite found and it takes more than a year to orbit Saturn in a
retrograde orbit. During the early 20th century,
research on Titan led to the
confirmation in 1944 that it had a thick
atmosphere - a feature unique among
the solar system's moons.
The outer atmosphere of Saturn
consists of 96.3% molecular hydrogen
and 3.25% helium. Trace amounts of
ammonia, acetylene, ethane,
phosphine and methane have also
been detected. 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. 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 1931 times the mass of the Earth,
with a significant fraction located in
Saturn's core region.
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