======================================================================
= Saturn =
======================================================================
Introduction
======================================================================
Saturn is the sixth planet from the Sun and the second largest in the
Solar System, after Jupiter. It is a gas giant, with an average radius
of about 9 times that of Earth. It has an eighth the average density
of Earth, but is over 95 times more massive. Even though Saturn is
almost as big as Jupiter, Saturn has less than a third its mass.
Saturn orbits the Sun at a distance of 1434 e6km, with an orbital
period of 29.45 years.
Saturn's interior is thought to be composed of a rocky core,
surrounded by a deep layer of metallic hydrogen, an intermediate layer
of liquid hydrogen and liquid helium, and an outer layer of gas.
Saturn has a pale yellow hue, due to ammonia crystals in its upper
atmosphere. An electrical current in the metallic hydrogen layer is
thought to give rise to Saturn's planetary magnetic field, which is
weaker than Earth's, but has a magnetic moment 580 times that of Earth
because of Saturn's greater size. Saturn's magnetic field strength is
about a twentieth that of Jupiter. The outer atmosphere is generally
bland and lacking in contrast, although long-lived features can
appear. Wind speeds on Saturn can reach 1800 km/h.
The planet has a bright and extensive system of rings, composed mainly
of ice particles, with a smaller amount of rocky debris and dust. At
least 274 moons orbit the planet, of which 63 are officially named;
these do not include the hundreds of moonlets in the rings. Titan,
Saturn's largest moon and the second largest in the Solar System, is
larger (but less massive) than the planet Mercury and is the only moon
in the Solar System that has a substantial atmosphere.
Name and symbol
======================================================================
Saturn is named after the Roman god of wealth and agriculture, who was
the father of the god Jupiter. Its astronomical symbol has been
traced back to the Greek Oxyrhynchus Papyri, where it can be seen to
be a Greek kappa-rho ligature with a horizontal stroke, as an
abbreviation for 'Κρονος' (Cronus), the Greek name for the planet
(class=skin-invert). It later came to look like a lower-case Greek
eta, with the cross added at the top in the 16th century to
Christianize this pagan symbol.
The Romans named the seventh day of the week Saturday, 'Sāturni diēs',
"Saturn's Day", for the planet Saturn.
Physical characteristics
======================================================================
Saturn is a gas giant, composed predominantly of hydrogen and helium.
It lacks a definite surface, though it is likely to have a solid core.
The planet's rotation makes it an oblate spheroid--a ball flattened at
the poles and bulging at the equator. Its equatorial radius is more
than 10% larger than the polar radius: 60,268 km versus 54,364 km
(37,449 mi versus 33,780 mi).
Jupiter, Uranus, and Neptune, the other giant planets in the Solar
System, are less oblate. The combination of the bulge and the rotation
rate means that the effective surface gravity along the equator, , is
74% of what it is at the poles and is lower than the surface gravity
of Earth. However, the equatorial escape velocity, nearly , is much
higher than that of Earth.
Saturn is the only planet of the Solar System that is less dense than
water--about 30% less. Although Saturn's core is considerably denser
than water, the average specific density of the planet is , because of
the atmosphere. Jupiter has 318 times Earth's mass, and Saturn is 95
times Earth's mass. Together, Jupiter and Saturn hold 92% of the total
planetary mass in the Solar System.
Internal structure
====================
Despite consisting mostly of hydrogen and helium, most of Saturn's
mass is not in the gas phase, because hydrogen becomes a non-ideal
liquid when the density is above , which is reached at a radius
containing 99.9% of Saturn's mass. The temperature, pressure, and
density inside Saturn all rise steadily toward the core, which causes
hydrogen to be a metal in the deeper layers.
Standard planetary models suggest that the interior of Saturn is
similar to that of Jupiter, having a small rocky core surrounded by
hydrogen and helium, with trace amounts of various volatiles. Analysis
of the distortion shows that Saturn is substantially more centrally
condensed than Jupiter and therefore contains much more material
denser than hydrogen near its center. Saturn's central regions are
about 50% hydrogen by mass, and Jupiter's are about 67% hydrogen.
This core is similar in composition to Earth, but is more dense. The
examination of Saturn's gravitational moment, in combination with
physical models of the interior, has allowed constraints to be placed
on the mass of Saturn's core. In 2004, scientists estimated that the
core must be 9-22 times the mass of Earth, which corresponds to a
diameter of about . Measurements of Saturn's rings suggest a much more
diffuse core, with a mass equal to about 17 Earths and a radius equal
to about 60% of Saturn's entire radius. This is surrounded by a
thicker, liquid metallic hydrogen layer, followed by a liquid layer of
helium-saturated molecular hydrogen, which gradually transitions to a
gas as altitude increases. The outermost layer spans about and
consists of gas.
Saturn has a hot interior, reaching at its core, and radiates 2.5
times more energy into space than it receives from the Sun. Jupiter's
thermal energy is generated by the Kelvin-Helmholtz mechanism of slow
gravitational compression; but such a process alone may not be
sufficient to explain heat production for Saturn, because it is less
massive. An alternative or additional mechanism may be the generation
of heat through the "raining out" of droplets of helium deep in
Saturn's interior. As the droplets descend through the lower-density
hydrogen, the process releases heat by friction and leaves Saturn's
outer layers depleted of helium. These descending droplets may have
accumulated into a helium shell surrounding the core. Rainfalls of
diamonds have been suggested to occur within Saturn, as well as in
Jupiter and ice giants Uranus and Neptune.
Atmosphere
============
The outer atmosphere of Saturn contains 96.3% molecular hydrogen and
3.25% helium by volume. The proportion of helium is significantly
deficient compared to the abundance of this element in the Sun. The
quantity of elements heavier than helium (metallicity) is 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 heavier elements is estimated to be 19-31 times the mass of
Earth, with a significant fraction located in Saturn's core region.
Trace amounts of ammonia, acetylene, ethane, propane, phosphine, and
methane have been detected in Saturn's atmosphere. The upper clouds
are composed of ammonia crystals, while the lower level clouds appear
to consist of either ammonium hydrosulfide () or water. Ultraviolet
radiation from the Sun causes methane photolysis in the upper
atmosphere, leading to a series of hydrocarbon chemical reactions with
the resulting products being carried downward by eddies and diffusion.
This photochemical cycle is modulated by Saturn's annual seasonal
cycle. 'Cassini' observed a series of cloud features found in northern
latitudes, nicknamed the "String of Pearls". These features are cloud
clearings that reside in deeper cloud layers.
Cloud layers
==============
Saturn's atmosphere exhibits a banded pattern similar to Jupiter's,
but Saturn's bands are much fainter and are much wider near the
equator. The nomenclature used to describe these bands is the same as
on Jupiter. Saturn's finer cloud patterns were not observed until the
flybys of the 'Voyager' spacecraft during the 1980s. Since then,
Earth-based telescopy has improved to the point where regular
observations can be made.
The composition of the clouds varies with depth and increasing
pressure. In the upper cloud layers, with temperatures in the range of
100-160 K and pressures extending between 0.5-2 bar, the clouds
consist of ammonia ice. Water ice clouds begin at a level where the
pressure is about 2.5 bar and extend down to 9.5 bar, where
temperatures range from 185 to 270 K. Intermixed in this layer is a
band of ammonium hydrosulfide ice, lying in the pressure range 3-6 bar
with temperatures of 190-235 K. The lower layers, where pressures are
between 10 and 20 bar and temperatures are 270-330 K, contains a
region of water droplets with ammonia in aqueous solution.
Saturn's usually bland atmosphere occasionally exhibits long-lived
ovals and other features common on Jupiter. In 1990, the Hubble Space
Telescope imaged an enormous white cloud near Saturn's equator that
was not present during the 'Voyager' encounters, and in 1994 another
smaller storm was observed. The 1990 storm was an example of a Great
White Spot, a short-lived phenomenon that occurs once every Saturnian
year, roughly every 30 Earth years, around the time of the northern
hemisphere's summer solstice.
Previous Great White Spots were observed in 1876, 1903, 1933, and
1960, with the 1933 storm being the best observed. The latest giant
storm was observed in 2010. In 2015, researchers used Very Large Array
telescope to study Saturnian atmosphere, and reported that they found
"long-lasting signatures of all mid-latitude giant storms, a mixture
of equatorial storms up to hundreds of years old, and potentially an
unreported older storm at 70°N".
The winds on Saturn are the second fastest among the Solar System's
planets, after Neptune's. 'Voyager' data indicate peak easterly winds
of 500 m/s. In images from the 'Cassini' spacecraft during 2007,
Saturn's northern hemisphere displayed a bright blue hue, similar to
Uranus. The color was most likely caused by Rayleigh scattering.
Thermography has shown that Saturn's south pole has a warm polar
vortex, the only known example of such a phenomenon in the Solar
System. Whereas temperatures on Saturn are normally −185 °C,
temperatures on the vortex often reach as high as −122 °C, suspected
to be the warmest spot on Saturn.
Hexagonal cloud patterns
==========================
A persisting hexagonal wave pattern around the north polar vortex in
the atmosphere at about 78°N was first noted in the 'Voyager' images.
The sides of the hexagon are each about long, which is longer than
the diameter of the Earth. The entire structure rotates with a period
of (the same period as that of the planet's radio emissions) which is
assumed to be equal to the period of rotation of Saturn's interior.
The hexagonal feature does not shift in longitude like the other
clouds in the visible atmosphere. The pattern's origin is a matter of
much speculation. Most scientists think it is a standing wave pattern
in the atmosphere. Polygonal shapes have been replicated in the
laboratory through differential rotation of fluids.
HST imaging of the south polar region indicates the presence of a jet
stream, but no strong polar vortex nor any hexagonal standing wave.
NASA reported in November 2006 that 'Cassini' had observed a
"hurricane-like" storm locked to the south pole that had a clearly
defined eyewall. Eyewall clouds had not previously been seen on any
planet other than Earth. For example, images from the 'Galileo'
spacecraft did not show an eyewall in the Great Red Spot of Jupiter.
The south pole storm may have been present for billions of years. This
vortex is comparable to the size of Earth, and it has winds of 550
km/h.
Magnetosphere
===============
Saturn has an intrinsic magnetic field that has a simple, symmetric
shape--a magnetic dipole. Its strength at the equator--0.2 gauss (20
μT)--is approximately one twentieth of that of the field around
Jupiter and slightly weaker than Earth's magnetic field. As a result,
Saturn's magnetosphere is much smaller than Jupiter's.
When 'Voyager 2' entered the magnetosphere, the solar wind pressure
was high and the magnetosphere extended only 19 Saturn radii, or 1.1
million km (684,000 mi), although it enlarged within several hours,
and remained so for about three days. Most probably, the magnetic
field is generated similarly to that of Jupiter--by currents in the
liquid metallic-hydrogen layer called a metallic-hydrogen dynamo. This
magnetosphere is efficient at deflecting the solar wind particles from
the Sun. The moon Titan orbits within the outer part of Saturn's
magnetosphere and contributes plasma from the ionized particles in
Titan's outer atmosphere. Saturn's magnetosphere, like Earth's,
produces aurorae.
Orbit and rotation
======================================================================
The average distance between Saturn and the Sun is over 1.4 billion
kilometers (9 AU). With an average orbital speed of 9.68 km/s, it
takes Saturn 10,759 Earth days (or about years) to finish one
revolution around the Sun. As a consequence, it forms a near 5:2
mean-motion resonance with Jupiter. The elliptical orbit of Saturn is
inclined 2.48° relative to the orbital plane of the Earth. The
perihelion and aphelion distances are, respectively, 9.195 and 9.957
AU, on average. The visible features on Saturn rotate at different
rates depending on latitude, and multiple rotation periods have been
assigned to various regions (as in Jupiter's case).
Astronomers use three different systems for specifying the rotation
rate of Saturn. 'System I' has a period of (844.3°/d) and encompasses
the Equatorial Zone, the South Equatorial Belt, and the North
Equatorial Belt. The polar regions are considered to have rotation
rates similar to 'System I'. All other Saturnian latitudes, excluding
the north and south polar regions, are indicated as 'System II' and
have been assigned a rotation period of (810.76°/d). 'System III'
refers to Saturn's internal rotation rate. Based on radio emissions
from the planet detected by 'Voyager 1' and 'Voyager 2', System III
has a rotation period of (810.8°/d). System III has largely
superseded System II.
A precise value for the rotation period of the interior remains
elusive. While approaching Saturn in 2004, 'Cassini' found that the
radio rotation period of Saturn had increased appreciably, to
approximately . An estimate of Saturn's rotation (as an indicated
rotation rate for Saturn as a whole) based on a compilation of various
measurements from the 'Cassini', 'Voyager', and 'Pioneer' probes is .
Studies of the planet's C Ring yield a rotation period of .
In March 2007, it was found that the variation in radio emissions from
the planet did not match Saturn's rotation rate. This variance may be
caused by geyser activity on Saturn's moon Enceladus. The water vapor
emitted into Saturn's orbit by this activity becomes charged and
creates a drag upon Saturn's magnetic field, slowing its rotation
slightly relative to the rotation of the planet.
Saturn only has one known trojan asteroid, designated , whose trojan
configuration was announced in September 2024, orbiting the Sun at the
stable L4 Lagrange point 60° ahead of the planet along its orbit. This
discovery leaves only Mercury without any known trojans at all.
Orbital resonance mechanisms, including secular resonance, are
believed to be the cause of the low number of known Saturnian trojans.
Natural satellites
======================================================================
Saturn has 274 known moons, 63 of which have formal names. There is
evidence of dozens to hundreds of moonlets with diameters of 40-500
meters in Saturn's rings, which are not considered to be true moons.
Titan, the largest moon, comprises more than 90% of the mass in orbit
around Saturn, including the rings. Saturn's second-largest moon,
Rhea, may have a tenuous ring system of its own, along with a tenuous
atmosphere.
Many of the other moons are small: 131 are less than 50 km in
diameter. Traditionally, most of Saturn's moons have been named after
Titans of Greek mythology. Titan is the only satellite in the Solar
System with a major atmosphere, in which a complex organic chemistry
occurs. It is the only satellite with hydrocarbon lakes.
On 6 June 2013, scientists at the IAA-CSIC reported the detection of
polycyclic aromatic hydrocarbons in the upper atmosphere of Titan, a
possible precursor for life. On 23 June 2014, NASA claimed to have
strong evidence that nitrogen in the atmosphere of Titan came from
materials in the Oort cloud, associated with comets, and not from the
materials that formed Saturn in earlier times.
Saturn's moon Enceladus, which seems similar in chemical makeup to
comets, has often been regarded as a potential habitat for microbial
life. Evidence of this possibility includes the satellite's salt-rich
particles having an "ocean-like" composition that indicates most of
Enceladus's expelled ice comes from the evaporation of liquid salt
water.
A 2015 flyby by 'Cassini' through a plume on Enceladus found most of
the ingredients to sustain life forms that live by methanogenesis.
In April 2014, NASA scientists reported the possible beginning of a
new moon within the A Ring, which was imaged by 'Cassini' on 15 April
2013.
Planetary rings
======================================================================
Saturn is probably best known for the system of planetary rings that
makes it visually unique. The rings extend from 6630 to outward from
Saturn's equator and average approximately 20 m in thickness. They are
composed predominantly of water ice, with trace amounts of tholin
impurities and a peppered coating of approximately 7% amorphous
carbon. The particles that make up the rings range in size from specks
of dust up to 10 m. While the other gas giants also have ring systems,
Saturn's is the largest and most visible.
There is a debate on the age of the rings. One side supports that they
are ancient, and were created simultaneously with Saturn from the
original nebular material (around 4.6 billion years ago), or shortly
after the LHB (around 4.1 to 3.8 billion years ago). The other side
supports that they are much younger, created around 100 million years
ago. An MIT research team, supporting the latter theory, proposed that
the rings are remnant of a destroyed moon of Saturn, named
″Chrysalis″.
Beyond the main rings, at a distance of 12 million km (7.5 million mi)
from the planet is the sparse Phoebe ring. It is tilted at an angle of
27° to the other rings and, like Phoebe, orbits in retrograde fashion.
Some of the moons of Saturn, including Pandora and Prometheus, act as
shepherd moons to confine the rings and prevent them from spreading
out. Pan and Atlas cause weak, linear density waves in Saturn's rings
that have yielded more reliable calculations of their masses.
History of observation and exploration
======================================================================
The observation and exploration of Saturn can be divided into three
phases: (1) pre-modern observations with the naked eye, (2) telescopic
observations from Earth beginning in the 17th century, and (3)
visitation by space probes, in orbit or on flyby. In the 21st century,
telescopic observations continue from Earth (including Earth-orbiting
observatories like the Hubble Space Telescope) and, until its 2017
retirement, from the 'Cassini' orbiter around Saturn.
Pre-telescopic observation
============================
Saturn has been known since prehistoric times, and in early recorded
history it was a major character in various mythologies. Babylonian
astronomers systematically observed and recorded the movements of
Saturn. In ancient Greek, the planet was known as 'Phainon', and in
Roman times it was known as the "star of Saturn" or the "star of the
Sun (i.e. Helios)". In ancient Roman mythology, the planet Phainon was
sacred to this agricultural god, from which the planet takes its
modern name. The Romans considered the god Saturnus the equivalent of
the Greek god Cronus. In modern Greek, the planet retains the name
'Cronus'--: 'Kronos'.
The Greek scientist Ptolemy based his calculations of Saturn's orbit
on observations he made while it was in opposition. In Hindu
astrology, there are nine astrological objects, known as Navagrahas.
Saturn is known as "Shani" and judges everyone based on the good and
bad deeds performed in life. Ancient Chinese and Japanese culture
designated the planet Saturn as the "earth star" (). This was based on
Five Elements which were traditionally used to classify natural
elements.
In Hebrew, Saturn is called 'Shabbathai'. Its angel is Cassiel. Its
intelligence or beneficial spirit is 'Agȋȇl (), and its darker spirit
(demon) is Zȃzȇl (). Zazel has been described as a great angel,
invoked in Solomonic magic, who is "effective in love conjurations".
In Ottoman Turkish, Urdu, and Malay, the name of Zazel is 'Zuhal',
derived from the Arabic language ().
Telescopic pre-spaceflight observations
=========================================
Saturn's rings require at least a 15-mm-diameter telescope to resolve
and were not known to exist until Christiaan Huygens saw them in 1655
and published his observations in 1659. Galileo, with his primitive
telescope in 1610, incorrectly thought of Saturn's appearing not quite
round as two moons on Saturn's sides.
When Huygens used greater telescopic magnification this notion was
refuted, and the rings were truly seen for the first time. Huygens
discovered Saturn's moon Titan. Giovanni Domenico Cassini later
discovered four other moons: Iapetus, Rhea, Tethys, and Dione. In
1675, Cassini 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 took 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.
''Pioneer 11'' flyby
======================
'Pioneer 11' made the first flyby of Saturn in September 1979, when it
passed within of the planet's cloud tops. Images were taken of the
planet and a few of its moons, although their resolution was too low
to discern surface detail. The spacecraft also studied Saturn's rings,
revealing the thin F-ring and the fact that dark gaps in the rings are
bright when viewed at a high phase angle (towards the Sun), meaning
that they contain fine light-scattering material. In addition,
'Pioneer 11' measured the temperature of Titan.
''Voyager'' flybys
====================
In November 1980, the 'Voyager 1' probe visited the Saturn system. It
sent back the first high-resolution images of the planet, its rings
and satellites. Surface features of various moons were seen for the
first time. 'Voyager 1' performed a close flyby of Titan, increasing
knowledge of the atmosphere of the moon. It proved that Titan's
atmosphere is impenetrable at visible wavelengths; therefore no
surface details were seen. The flyby changed the spacecraft's
trajectory out of the plane of the Solar System.
Almost a year later, in August 1981, 'Voyager 2' continued the study
of the Saturn system. More close-up images of Saturn's moons were
acquired, as well as evidence of changes in the atmosphere and the
rings. During the flyby, the probe's turnable camera platform stuck
for a couple of days and some planned imaging was lost. Saturn's
gravity was used to direct the spacecraft's trajectory towards Uranus.
The probes discovered and confirmed several new satellites orbiting
near or within the planet's rings, as well as the small Maxwell Gap (a
gap within the C Ring) and Keeler gap (a 42 km-wide gap in the A
Ring).
''Cassini–Huygens'' spacecraft
================================
tiger stripes.]
The 'Cassini-Huygens' space probe entered orbit around Saturn on 1
July 2004. In June 2004, it conducted a close flyby of Phoebe, sending
back high-resolution images and data. 'Cassini' flyby of Saturn's
largest moon, Titan, captured radar images of large lakes and their
coastlines with numerous islands and mountains. The orbiter completed
two Titan flybys before releasing the 'Huygens' probe on 25 December
2004. 'Huygens' descended onto the surface of Titan on 14 January
2005.
Starting in early 2005, scientists used 'Cassini' to track lightning
on Saturn. The power of the lightning is approximately 1,000 times
that of lightning on Earth.
'Cassini' photographs have revealed a previously undiscovered
planetary ring, outside the brighter main rings of Saturn and inside
the G and E rings. The source of this ring is hypothesized to be the
crashing of a meteoroid off Janus and Epimetheus. In July 2006, images
were returned of hydrocarbon lakes near Titan's north pole, the
presence of which were confirmed in January 2007. In March 2007,
hydrocarbon seas were found near the North pole, the largest of which
is almost the size of the Caspian Sea. In October 2006, the probe
detected an diameter cyclone-like storm with an eyewall at Saturn's
south pole.
From 2004 to 2 November 2009, the probe discovered and confirmed eight
new satellites. In April 2013, 'Cassini' sent back images of a
hurricane at the planet's north pole 20 times larger than those found
on Earth, with winds faster than 530 km/h. On 15 September 2017, the
'Cassini-Huygens' spacecraft performed the "Grand Finale" of its
mission: a number of passes through gaps between Saturn and Saturn's
inner rings. The atmospheric entry of 'Cassini' ended the mission.
Possible future missions
==========================
The continued exploration of Saturn is still considered to be a viable
option for NASA as part of their ongoing New Frontiers program of
missions. NASA previously requested for plans to be put forward for a
mission to Saturn that included the Saturn Atmospheric Entry Probe,
and possible investigations into the habitability and possible
discovery of life on Saturn's moons Titan and Enceladus by
'Dragonfly'.
Observation
======================================================================
Saturn is the most distant of the five planets easily visible to the
naked eye from Earth, the other four being Mercury, Venus, Mars, and
Jupiter. (Uranus, and occasionally 4 Vesta, are visible to the naked
eye in dark skies.) Saturn appears to the naked eye in the night sky
as a bright, yellowish point of light. The mean apparent magnitude of
Saturn is 0.46 with a standard deviation of 0.34. Most of the
magnitude variation is due to the inclination of the ring system
relative to the Sun and Earth. The brightest magnitude, −0.55, occurs
near the time when the plane of the rings is inclined most highly, and
the faintest magnitude, 1.17, occurs around the time when they are
least inclined.
It takes approximately 29.4 years for the planet to complete an entire
circuit of the ecliptic against the background constellations of the
zodiac. Most people will require an optical aid (very large binoculars
or a small telescope) that magnifies at least 30 times to achieve an
image of Saturn's rings in which a clear resolution is present.
When Earth passes through the ring plane, which occurs twice every
Saturnian year (roughly every 15 Earth years), the rings briefly
disappear from view because they are so thin. Such a "disappearance"
will next occur in 2025, but Saturn will be too close to the Sun for
observations.
Saturn and its rings are best seen when the planet is at, or near,
opposition, the configuration of a planet when it is at an elongation
of 180°, and thus appears opposite the Sun in the sky. A Saturnian
opposition occurs every year--approximately every 378 days--and
results in the planet appearing at its brightest. Both the Earth and
Saturn orbit the Sun on eccentric orbits, which means their distances
from the Sun vary over time, and therefore so do their distances from
each other, hence varying the brightness of Saturn from one opposition
to the next. Saturn also appears brighter when the rings are angled
such that they are more visible. For example, during the opposition of
17 December 2002, Saturn appeared at its brightest due to the
favorable orientation of its rings relative to the Earth, even though
Saturn was closer to the Earth and Sun in late 2003.
From time to time, Saturn is occulted by the Moon (that is, the Moon
covers up Saturn in the sky). As with all the planets in the Solar
System, occultations of Saturn occur in "seasons". Saturnian
occultations will take place monthly for about a 12-month period,
followed by about a five-year period in which no such activity is
registered. The Moon's orbit is inclined by several degrees relative
to Saturn's, so occultations will only occur when Saturn is near one
of the points in the sky where the two planes intersect (both the
length of Saturn's year and the 18.6-Earth-year nodal precession
period of the Moon's orbit influence the periodicity).
In fiction
======================================================================
Saturn has frequently appeared in fiction since at least 1752, when
Voltaire published his novel 'Micromégas'. Early works generally
depicted it as solid, whereas Saturn is later correctly described as a
gaseous planet. Saturn's moons are also featured in fiction,
especially Titan.
See also
======================================================================
* Moons of Saturn
* Statistics of planets in the Solar System
* Outline of Saturn
External links
======================================================================
* [
https://solarsystem.nasa.gov/planets/saturn/overview/ Saturn
overview] by NASA's Science Mission Directorate
* [
https://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html
Saturn fact sheet] at the NASA Space Science Data Coordinated Archive
*
[
https://web.archive.org/web/20180219090345/https://planetarynames.wr.usgs.gov/Page/SATURN/system
Saturnian System terminology] by the IAU Gazetteer of Planetary
Nomenclature
*
[
https://web.archive.org/web/20020330192909/http://saturn.jpl.nasa.gov/
'Cassini-Huygens' legacy website] by the Jet Propulsion Laboratory
* [
https://gravitysimulator.org/solar-system/the-cronian-system
Interactive 3D gravity simulation of the Cronian system]
License
=========
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Original Article:
http://en.wikipedia.org/wiki/Saturn
