HOME

TheInfoList




Saturn is the sixth
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
from the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
and the second-largest in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
, after
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

Jupiter
. It is a
gas giant A gas giant is a giant planet The giant planets constitute a diverse type of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilib ...
with an average radius of about nine and a half times that of
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
. It only has one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive. Saturn is named after the
Roman Roman or Romans most often refers to: *, the capital city of Italy *, Roman civilization from 8th century BC to 5th century AD *, the people of ancient Rome *', shortened to ''Romans'', a letter in the New Testament of the Christian Bible Roman ...
god of wealth and agriculture. Its
astronomical symbol Astronomical symbols are abstract pictorial symbols used to represent astronomical objects, theoretical constructs and observational events in Western culture, European astronomy. The earliest forms of these symbols appear in Greek papyrus tex ...
( 16px, ♄) has been traced back to the Greek
Oxyrhynchus Papyri The Oxyrhynchus Papyri are a group of manuscripts discovered during the late nineteenth and early twentieth centuries by papyrology, papyrologists Bernard Pyne Grenfell and Arthur Surridge Hunt at an ancient Landfill, rubbish dump near Oxyrhync ...
, where it can be seen to be a Greek
kappa Kappa (uppercase Κ, lowercase κ or cursive Cursive (also known as script, among other names) is any style of penmanship in which some characters are written joined together in a flowing manner, generally for the purpose of making writin ...

kappa
-
rho Rho (uppercase Ρ, lowercase ρ or ; el, ῥῶ) is the 17th letter of the Greek alphabet The Greek alphabet has been used to write the Greek language since the late ninth or early eighth century BC. It is derived from the earlier Phoenician ...
with a cross-bar, as an abbreviation for ''Κρονος'' (Cronos), the Greek name for the planet. It later came to look like a lower-case Greek
eta Eta (uppercase , lowercase ; grc, ἦτα ''ē̂ta'' or ell, ήτα ''ita'' ) is the seventh letter of the Greek alphabet The Greek alphabet has been used to write the Greek language since the late ninth or early eighth century BC. It is ...

eta
, with the cross added at the top in the 16th century. The Romans named the seventh day of the week
Saturday Saturday is the day of the week File:Heptagram of the celestial bodies of the weekdays.png, Heptagram of the seven celestial bodies of the week The names of the days of the week in many languages are derived from the names of the classica ...
, ''Sāturni diēs'' ("Saturn's Day") for the planet Saturn. Saturn's interior is most likely composed of a core of iron–nickel and rock (
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
compounds). Its core is surrounded by a deep layer of
metallic hydrogen Metallic hydrogen is a phase of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest element in the periodic table. Hydrogen is t ...
, an intermediate layer of
liquid hydrogen Liquid hydrogen (LH2 or LH2) is the liquid state A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers to a fluid flow, flow in which ...
and
liquid helium Liquid helium is a physical state of helium, at very low temperatures if it is at standard atmospheric pressures. Liquid helium may show superfluidity. At standard pressure, the chemical element Image:Simple Periodic Table Chart-blocks.svg, ...

liquid helium
, and finally a gaseous outer layer. Saturn has a pale yellow hue due to
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
crystals in its upper atmosphere. An
electrical current Electricity is the set of physical phenomena A phenomenon (; plural phenomena) is an observable fact or event. The term came into its modern philosophical Philosophy (from , ) is the study of general and fundamental questions, ...
within the metallic hydrogen layer is thought to give rise to Saturn's planetary
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
, which is weaker than the Earth's, but which has a
magnetic moment The magnetic moment is the magnetic strength and orientation of a or other object that produces a . Examples of objects that have magnetic moments include: loops of (such as s), permanent magnets, s (such as s), various s, and many astronomical ...

magnetic moment
580 times that of Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth of Jupiter's. The outer
atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in ...

atmosphere
is generally bland and lacking in contrast, although long-lived features can appear.
Wind speed In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mode ...

Wind speed
s on Saturn can reach , higher than on Jupiter but not as high as on
Neptune Neptune is the eighth and farthest-known Solar planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly mo ...

Neptune
. The planet's most famous feature is its prominent
ring system A ring system is a disc or ring, orbiting an astronomical object In , an astronomical object or celestial object is a naturally occurring , association, or structure that exists in the . In , the terms ''object'' and ''body'' are often u ...

ring system
, which is composed mostly of ice particles, with a smaller amount of rocky debris and
dust Dust is made of s of solid . On Earth, it generally consists of particles in the that come from various sources such as lifted by wind (an ), , and . Dust in homes is composed of about 20–50% dead . The rest, and in offices, and other ...
. At least 83
moons A natural satellite, or moon, is, in the most common usage, an astronomical body that orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet around a star or ...
are known to orbit Saturn, of which 53 are officially named; this does not include the hundreds of
moonlet A moonlet, minor moon, minor natural satellite, or minor satellite is a particularly small natural satellite orbiting a planet, dwarf planet, or other minor planet. Up until 1995, moonlets were only hypothetical components of Saturn's F-ring ...
s in its rings.
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictional ...
, Saturn's largest moon and the second largest in the Solar System, is larger than the planet
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

Mercury
, although less massive, and is the only moon in the Solar System to have a substantial atmosphere.


Physical characteristics

Saturn is a
gas giant A gas giant is a giant planet The giant planets constitute a diverse type of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilib ...
composed predominantly of hydrogen and helium. It lacks a definite surface, though it may have a solid core. Saturn's rotation causes it to have the shape of an
oblate spheroid A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric In mathematics, a quadric or quadric surface (quadric hypersurface in higher dimension thumb , 236px , The first four spatial dimensions, repres ...
; that is, it is flattened at the
poles The Poles,, ; singular masculine: ''Polak'', singular feminine: ''Polka'' or Polish people, are a nation A nation is a community A community is a social unitThe term "level of analysis" is used in the social sciences to point to the loc ...
and bulges at its
equator The Equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the N ...

equator
. Its equatorial and polar radii differ by almost 10%: 60,268 km versus 54,364 km. Jupiter,
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus, who, according to Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and ...

Uranus
, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. The combination of the bulge and 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 #REDIRECT Escape velocity#REDIRECT Escape velocity In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matt ...
of 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 Core or cores may refer to: Science and technology * Core (anatomy) In common parlance, the core of the body is broadly considered to be the torso. Functional movements are highly dependent on this part of the body, and lack of core muscular dev ...
is considerably denser than water, the average specific density of the planet is due to 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 Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

gas
phase Phase or phases may refer to: Science * State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter) In the physical sciences, a phase is a region of space (a thermodynamic system A thermodynamic system is a ...
, 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 Volatiles are the group of chemical elements and chemical compounds that can be readily Volatility (chemistry), vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as Refractory (planetary scien ...
. 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 25,000 km. However, measurements of Saturn's rings suggest a much more diffuse core with a mass equal to about 17 Earths and a radius equal to around 60% of Saturn's entire radius. This is surrounded by a thicker liquid
metallic hydrogen Metallic hydrogen is a phase of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest element in the periodic table. Hydrogen is t ...
layer, followed by a liquid layer of helium-saturated
molecular hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the sam ...
that gradually transitions to a gas with increasing altitude. The outermost layer spans 1,000 km and consists of gas. Saturn has a hot interior, reaching 11,700 °C at its core, and radiates 2.5 times more energy into space than it receives from the Sun. Jupiter's
thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concepts, such as the internal energy of a system; heat or sensible heat, which are defined as types of energy transfer (as is ...
is generated by the
Kelvin–Helmholtz mechanism The Kelvin–Helmholtz mechanism is an astronomy, astronomical process that occurs when the surface of a star or a planet cools. The cooling causes the internal pressure to drop, and the star or planet shrinks as a result. This compression, in turn ...
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 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 Friction is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mass to change its velocity (e.g. moving from a Newton's first law, st ...

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
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At Standard conditions for temperature and pressure, room temperature and pressure, another solid form of ...

diamond
s have been suggested to occur within Saturn, as well as in Jupiter and
ice giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest el ...
s 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 In astronomy, metallicity is the Abundance of the chemical elements, abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astron ...
) is not known precisely, but the proportions are assumed to match the primordial abundances from the
formation of the Solar System The formation and evolution of the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all indi ...
. The total mass of these heavier elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region. Trace amounts of ammonia,
acetylene Acetylene (systematic nameA systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is ...

acetylene
,
ethane Ethane ( or ) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living ...
,
propane Propane () is a three-carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's ...

propane
,
phosphine Phosphine (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science ...

phosphine
, and
methane Methane (, ) is a chemical compound with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes a ...
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 Ammonium hydrosulfide is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togeth ...
() or water.
Ultraviolet radiation Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...
from the Sun causes methane
photolysis Photodissociation, photolysis, or photodecomposition is a chemical reaction in which a chemical compound is broken down by photons. It is defined as the interaction of one or more photons with one target molecule. Photodissociation is not limited ...
in the upper atmosphere, leading to a series of
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
chemical reactions with the resulting products being carried downward by
eddies In fluid dynamics, an eddy is the swirling of a fluid and the reverse current (water), current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the o ...
and
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...

diffusion
. This photochemical cycle is modulated by Saturn's annual seasonal cycle.


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 Voyager may refer to: Computing and communications * LG Voyager The LG VX10000, also known as the Verizon Voyager or LG VX10K, is an Internet-enabled multimedia phone designed by LG Electronics and carried by Verizon Wireless, Telus, and Bel ...
'' spacecraft during the 1980s. Since then, Earth-based 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 the temperature in the range 100–160 K and pressures extending between 0.5–2
bar Bar or BAR may refer to: Food *Bar (establishment) A bar is a long raised narrow table or bench designed for dispensing beer or other alcoholic beverage, alcoholic drinks. They were originally chest high, and a bar, often brass, ran the len ...
, the clouds consist of ammonia ice. Water
ice cloud An ice cloud is a colloid A colloid is a mixture In chemistry, a mixture is a material made up of two or more different chemical substances which are not chemically combined. A mixture is the physical combination of two or more substances in ...
s 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. Finally, 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 The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first ...

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 unique but short-lived phenomenon that occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere's
summer solstice The summer solstice, also known as estival solstice or midsummer, occurs when one of Earth's geographical pole, poles has its maximum tilt toward the Sun. It happens twice yearly, once in each Hemispheres of Earth, hemisphere (Northern and Souther ...

summer solstice
. Previous Great White Spots were observed in 1876, 1903, 1933 and 1960, with the 1933 storm being the most famous. If the periodicity is maintained, another storm will occur in about 2020. The winds on Saturn are the second fastest among the Solar System's planets, after Neptune's. ''Voyager'' data indicate peak easterly winds of . 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 Rayleigh scattering ( ), named after the nineteenth-century British physicist Lord Rayleigh (John William Strutt), is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength o ...

Rayleigh scattering
.
Thermography Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a Thermographic camera, thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are e ...
has shown that Saturn's south pole has a warm
polar vortex ''Polar Vortex'' is a 2020 novel by Canadian author Shani Mootoo. This domestic drama deals with the complexities of modern love. A love triangle develops between Priya, Alexandra and Prakash. The novel was shortlisted for the Giller Prize T ...
, 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.


North pole hexagonal cloud pattern

A persisting
hexagon In geometry, a hexagon (from Ancient Greek, Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon or 6-gon. The total of the internal angles of any simple polygon, simple (non-self-intersecting) hexagon is 720°. Regul ...

hexagon
al 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 In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Ph ...

standing wave
pattern in the atmosphere. Polygonal shapes have been replicated in the laboratory through differential rotation of fluids. Laboratory experiment of spinning disks in a liquid solution forms vortices around a stable hexagonal pattern similar to that of Saturn's.


South pole vortex

imaging of the south polar region indicates the presence of a
jet stream Jet streams are fast flowing, narrow, meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse the s of an outer, concave bank () and deposits sedimen ...
, but no strong polar vortex nor any hexagonal standing wave.
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agency A regulatory agency or regulatory authority, is a Public benefit corporation Public-benefit corporation is a term that has different meanings in differen ...

NASA
reported in November 2006 that ''Cassini'' had observed a "
hurricane A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation Atmospheric circulation is the large-scale movement of Atmosphere of Earth, air and together with oc ...

hurricane
-like" storm locked to the south pole that had a clearly defined
eyewall The eye is a region of mostly calm weather at the center of tropical cyclone A tropical cyclone is a rapidly rotating storm, storm system characterized by a Low-pressure area, low-pressure center, a closed low-level atmospheric circulation, ...
. Eyewall clouds had not previously been seen on any planet other than Earth. For example, images from the ''
Galileo Galileo di Vincenzo Bonaiuti de' Galilei ( , ; 15 February 1564 – 8 January 1642), commonly referred to as Galileo, was an astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific qu ...
'' spacecraft did not show an eyewall in the
Great Red Spot The Great Red Spot is a persistent high-pressure region in the atmosphere of Jupiter The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System. It is mostly made of molecular hydrogen and helium in roughly Sun#Compositi ...
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.


Other features

''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.


Magnetosphere

Saturn has an intrinsic
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
that has a simple, symmetric shape – a magnetic
dipole In electromagnetism Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electric charge, electrically charged particles. The electromagnetic force is c ...

dipole
. Its strength at the equator – 0.2 
gauss Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician This is a List of German mathematician A mathematician is someone who uses an extensive knowledge of m ...
(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 In astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses m ...

magnetosphere
is much smaller than Jupiter's. When ''
Voyager 2 ''Voyager 2'' is a space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe may approach the Moon; travel thro ...
'' entered the magnetosphere, the
solar wind The solar wind is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...

solar wind
pressure was high and the magnetosphere extended only 19 Saturn radii, or 1.1 million km (712,000 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 The solar wind is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...

solar wind
particles from the Sun. The moon Titan orbits within the outer part of Saturn's magnetosphere and contributes plasma from the
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
ized particles in Titan's outer atmosphere. Saturn's magnetosphere, like Earth's, produces
aurora An aurora (plural: auroras or aurorae), sometimes referred to as polar lights (aurora polaris), northern lights (aurora borealis), or southern lights (aurora australis), is a natural light display in the Earth's sky, predominantly seen in high-l ...

aurora
e.


Orbit and rotation

The average distance between Saturn and the Sun is over 1.4 billion kilometers (9 ). 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 . Conjunctions are highlighted by brief color changes. There are two Io-Europa conjunctions (green) and three Io-Ganymede conjunctions (grey) for each Europa-Ganymede conjunction (magenta). This diagram is not to scale. In celestial mechanics, ...
with Jupiter. The elliptical orbit of Saturn is inclined 2.48° relative to the Orbital plane (astronomy), orbital plane of the Earth. The apsis, 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 astronomy, 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 Rings of Saturn#C Ring, C Ring yield a rotation period of . In March 2007, it was found that the variation of 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 (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. An apparent oddity for Saturn is that it does not have any known trojan asteroids. These are minor planets that orbit the Sun at the stable Lagrangian points, designated L4 and L5, located at 60° angles to the planet along its orbit. Trojan asteroids have been discovered for Mars, Jupiter, Uranus, and Neptune. Orbital resonance mechanisms, including secular resonance, are believed to be the cause of the missing Saturnian trojans.


Natural satellites

Saturn has 83 known natural satellite, moons, 53 of which have formal names. In addition, there is evidence of dozens to hundreds of
moonlet A moonlet, minor moon, minor natural satellite, or minor satellite is a particularly small natural satellite orbiting a planet, dwarf planet, or other minor planet. Up until 1995, moonlets were only hypothetical components of Saturn's F-ring ...
s with diameters of 40–500 meters in Saturn's rings, which are not considered to be true moons.
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictional ...
, the largest moon, comprises more than 90% of the mass in orbit around Saturn, including the rings. Saturn's second-largest moon, Rhea (moon), Rhea, may have a tenuous Rings of Rhea, ring system of its own, along with a tenuous
atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in ...

atmosphere
. Many of the other moons are small: 34 are less than 10 km in diameter and another 14 between 10 and 50 km in diameter. Traditionally, most of Saturn's moons have been named after Titan (mythology), Titans of Greek mythology. Titan is the only satellite in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
with a major Atmosphere of Titan, atmosphere, in which a complex organic chemistry occurs. It is the only satellite with Lakes of Titan, hydrocarbon lakes. On 6 June 2013, scientists at the Instituto de Astrofísica de Andalucía, IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan, a PAH world hypothesis, 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 Planetary habitability, habitat for Microorganism, 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 Rings of Saturn#A Ring, 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 outward from Saturn's equator and average approximately 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 giant A gas giant is a giant planet The giant planets constitute a diverse type of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilib ...
s also have ring systems, Saturn's is the largest and most visible. There are two main hypotheses regarding the origin of the rings. One hypothesis is that the rings are remnants of a destroyed moon of Saturn. The second hypothesis is that the rings are left over from the original nebular material from which Saturn was formed. Some ice in the E ring comes from the moon Enceladus's geysers. The water abundance of the rings varies radially, with the outermost ring A being the most pure in ice water. This abundance variance may be explained by meteor bombardment. Beyond the main rings, at a distance of 12 million km from the planet is the sparse Phoebe ring. It is tilted at an angle of 27° to the other rings and, like Phoebe (moon), Phoebe, orbits in Retrograde motion, retrograde fashion. Some of the moons of Saturn, including Pandora (moon), Pandora and Prometheus (moon), Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out. Pan (moon), Pan and Atlas (moon), 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. The first phase is ancient observations (such as with the naked eye), before the invention of modern telescopes. The second phase began in the 17th century, with telescopic observations from Earth, which improved over time. The third phase is visitation by space probes, in orbit or on planetary flyby, flyby. In the 21st century, telescopic observations continue from Earth (including Earth orbit, Earth-orbiting space telescope, observatories like the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first ...

Hubble Space Telescope
) and, until Cassini retirement, its 2017 retirement, from the '' Cassini'' orbiter around Saturn.


Ancient observations

Saturn has been known since prehistoric times, and in early recorded history it was a major character in various mythologies. Babylonian astronomy, 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 (mythology), Saturn". In Roman mythology, 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 mythology, Greek god Cronus; in modern Greek language, 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 (planets), opposition. In Jyotisha, 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 astrology, Chinese and Japanese culture designated the planet Saturn as the "earth star" (). This was based on Five elements (Chinese philosophy), Five Elements which were traditionally used to classify natural elements. In ancient Hebrew language, Hebrew, Saturn is called 'Shabbathai'. Its angel is Cassiel. Its intelligence or beneficial spirit is Agiel, 'Agȋȇl ( he, אגיאל, ʿAgyal), and its darker spirit (demon) is Zazel (spirit), Zȃzȇl ( he, זאזל, Zazl). Zazel has been described as a Angel, great angel, invoked in Solomon#Angels and magic, Solomonic magic, who is "effective in Evocation, love conjurations". In Ottoman Turkish language, Ottoman Turkish, Urdu and Malay language, Malay, the name of Zazel is 'Zuhal', derived from the Arabic language ( ar, زحل, Zuhal).


European observations (17th–19th centuries)

Saturn's rings require at least a 15-mm-diameter telescope to resolve and thus were not known to exist until Christiaan Huygens saw them in 1655 and published about this 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. It was not until Huygens used greater telescopic magnification that this notion was refuted, and the rings were truly seen for the first time. Huygens also discovered Saturn's moon Titan; Giovanni Domenico Cassini later discovered four other moons: Iapetus (moon), Iapetus, Rhea (moon), Rhea, Tethys (moon), Tethys and Dione (moon), 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 (moon), Mimas and Enceladus. The irregularly shaped satellite Hyperion (moon), Hyperion, which has a orbital resonance, 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.


Modern NASA and ESA probes


''Pioneer 11'' flyby

''Pioneer 11'' made the first flyby of Saturn in September 1979, when it passed within 20,000 km 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 high Phase angle (astronomy), 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 in visible wavelengths; therefore no surface details were seen. The flyby changed the spacecraft's trajectory out from the plane of the Solar System. Almost a year later, in August 1981, ''
Voyager 2 ''Voyager 2'' is a space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe may approach the Moon; travel thro ...
'' 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. Unfortunately, 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 Rings of Saturn#C Ring, C Ring) and Keeler gap (a 42 km-wide gap in the A Ring).


''Cassini–Huygens'' spacecraft

The ''Cassini–Huygens'' space probe entered orbit around Saturn on 1 July 2004. In June 2004, it conducted a close flyby of Phoebe (moon), 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, ''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. In 2006, NASA reported that ''Cassini'' had found evidence of liquid water reservoirs no more than tens of meters below the surface that erupt in geysers on Saturn's moon Enceladus (moon), Enceladus. These jets of icy particles are emitted into orbit around Saturn from vents in the moon's south polar region. Over 100 geysers have been identified on Enceladus. In May 2011, NASA scientists reported that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it". ''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 (moon), Janus and Epimetheus (moon), 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 8,000 km 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 . 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 (spacecraft), Dragonfly''.


Observation

Saturn is the most distant of the five planets easily visible to the naked eye from Earth, the other four being
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

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 in time to 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 29.5 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 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 (planets), opposition, the configuration of a planet when it is at an Elongation (astronomy), 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 a favorable :File:Saturnoppositions.jpg, 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 Occultation, 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 Lunar precession#Nodal precession, nodal precession period of the Moon's orbit influence the periodicity).


Notes


References


Further reading

* * * * * *


See also

* List_of_gravitationally_rounded_objects_of_the_Solar_System#Planets, Stats of planets in the Solar System


External links


Saturn overview
by NASA's Science Mission Directorate
Saturn fact sheet
at the NASA Space Science Data Coordinated Archive
Saturnian System terminology
by the IAU Gazetteer of Planetary Nomenclature
''Cassini-Huygens'' legacy website
by the Jet Propulsion Laboratory
Saturn
at SolarViews.com
Interactive 3D gravity simulation of the Cronian system
{{Featured article Saturn, Astronomical objects known since antiquity Gas giants Outer planets