Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Saturn shopping experience:
1. Compare - without doubt the biggest advantage that the Saturn offers shoppers today is the ability to compare thousands of Saturn at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Saturn? Wrong! If the Saturn is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Saturn then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Saturn? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Saturn and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Saturn wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Saturn then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Saturn site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Saturn, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Saturn, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
{{Infobox Planet| bgcolour = #FFCC66| name = Saturn| symbol = | image = | caption = Saturn, as seen by
Cassini–Huygens| orbit_ref = {{cite web| last = Yeomans | first = Donald K. | date = 2006-07-13
| url = http://ssd.jpl.nasa.gov/?horizons
| title = HORIZONS System | publisher = NASA JPL
| accessdate = 2007-08-08 --> — At the site, go to the "web interface" then select "Ephemeris Type: ELEMENTS", "Target Body: Saturn Barycenter" and "Center: Sun".Orbital elements refer to the barycenter of the Saturn system, and are the instantaneous [osculating orbit values at the precise [J2000 epoch. Barycenter quantities are given because, in contrast to the planetary centre, they do not experience appreciable changes on a day-to-day basis from to the motion of the moons.
| epoch = Epoch (astronomy)#J2000.0| aphelion = 1,513,325,783 km
10.11595804
Astronomical unit| perihelion = 1,353,572,956 km
9.04807635 AU| semimajor = 1,433,449,370 km
9.58201720 AU| eccentricity = 0.055723219| period = 10,832.327
days
29.657 296
Julian year (astronomy)| synodic_period = 378.09 days| avg_speed = 9.69 km/s| inclination = 2.485240°
5.51° to Sun's equator| asc_node = 113.642811°| arg_peri = 336.013862°| mean_anomaly = 320.347750°| satellites =
Saturn's natural satellites(up to 63 seen)| physical_characteristics = yes| flattening = 0.09796 ± 0.00018 | equatorial_radius = 60,268 ± 4 kmRefers to the level of 1 bar atmospheric pressure
9.4492 Earths| polar_radius = 54,364 ± 10 km
8.5521 Earths| surface_area = 4.27×1010 km² NASA: Solar System Exploration: Planets: Saturn: Facts & Figures
83.703 Earths| volume = 8.2713×1014 km³{{cite web|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html|title = Saturn Fact Sheet|publisher = NASA|last = Williams|first = Dr. David R.|accessdate = 2007-07-31|date = September 07, 2006-->
763.59 Earths| mass = 5.6846×1026 kg
95.152 Earths| density = 0.687 g/cm³
(less than water)]
0.914 g-force| escape_velocity = 35.5 km/s| sidereal_day = 0.439 – 0.449 day{{cite web|url = http://www.space.com/scienceastronomy/070906_saturn_day.html|title = Length of Saturn's Day Revised|publisher = Space.com|last = Than|first = Ker|accessdate = 2007-09-06|date = September 06, 2007-->
(10 h 32 – 47 min)| rot_velocity = 9.87 km/s
35,500 km/h| axial_tilt = 26.73°| right_asc_north_pole = 2 h 42 min 21 s
40.589°| declination = 83.537°| albedo = 0.342 (
Bond albedo)0.47 (Geometric albedo)| magnitude = +1.2 to -0.24 {{cite web|url = http://findarticles.com/p/articles/mi_qa4015/is_200101/ai_n8933308|title = Wideband photoelectric magnitude measurements of Saturn in 2000|accessdate = 2007-10-14|last = Schmude|first = Richard W Jr|date = 2001|publisher = Georgia Journal of Science-->| angular_size = 14.5" — 20.1"
(excludes rings)| temperatures = yes| temp_name1 = 1 bar level| min_temp_1 =| mean_temp_1 = 134
Kelvin| max_temp_1 =| temp_name2 = 0.1 bar| min_temp_2 =| mean_temp_2 = 84 K| max_temp =| adjectives = Saturnian| atmosphere = yes| atmosphere_ref = | scale_height = 59.5 km| atmosphere_composition =~96%
Hydrogen (H2)~3%Helium~0.4%Methane~0.01%
Ammonia~0.01%
Hydrogen deuteride (HD)0.0007%
EthaneIces:Ammoniawater
ammonium hydrosulfide(NH4SH)-->
Saturn () is the sixth planet from the
Sun and the second largest planet in the Solar System, after
Jupiter. Along with the planets Jupiter,
Uranus, and Neptune, it is classified as a
gas giant (also known as a Jovian planet, after the planet Jupiter). It was named after the Roman god
Saturn (mythology), equated to the
Greek mythology Cronus (the Titan father of
Zeus) and the Babylonian Ninurta. Saturn's symbol represents the god's sickle (Unicode: ). The day in the week Saturday gets its name from the planet.
The planet Saturn is primarily composed of
hydrogen, with small proportions of
helium and trace elements. The interior consists of a small core of rock and ice, surrounded by a thick layer of metallic hydrogen and a gaseous outer layer. 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 a planetary
magnetic field intermediate in strength between that of Earth and the more powerful field around Jupiter.
Saturn has a prominent system of Rings of Saturn, consisting mostly of
ice particles with a smaller amount of rocky
debris and cosmic dust. Sixty known moons orbit the planet. Titan (moon), Saturn's largest and the
Solar System's second largest moon (after
Ganymede (moon)), is larger than the planet
Mercury (planet) and is the only moon in the Solar System to possess a significant atmosphere.{{cite web|url = http://saturn.jpl.nasa.gov/news/features/saturn-story/moons.cfm|title = The Story of Saturn|accessdate = 2007-07-07|last = Munsell|first = Kirk|date = April 6, 2005|publisher = NASA Jet Propulsion Laboratory; California Institute of Technology-->
Physical characteristics
Due to a combination of its low density, rapid rotation, and fluid state, Saturn is an oblate
spheroid; that is, it is flattened at the
geographical pole and bulges at the
equator. Its equatorial and polar radii differ by almost 10%— 60268 km vs. 54364 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
density than water. Although Saturn's planetary core is considerably denser than water, the average relative 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{{cite web|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html|title = Jupiter Fact Sheet|publisher = NASA|last = Williams|first = Dr. David R.|date = November 16, 2004|accessdate = 2007-08-02--> but only about 20% larger than Saturn.{{cite web|url = http://ase.arc.nasa.gov/projects/bayes-group/Atlas/size/Jupiter/Saturn.html|title = Jupiter compared to Saturn|publisher = NASA|accessdate = 2007-07-15-->
Composition
The outer atmosphere of Saturn consists of about 93.2% molecular hydrogen and 6.7% 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.{{cite web
| last = Martinez
| first = Carolina
| date =September 5, 2005
| url = http://www.nasa.gov/mission_pages/cassini/whycassini/cassini-090505-clouds.html
| title =Cassini Discovers Saturn's Dynamic Clouds Run Deep
| publisher =NASA
| accessdate = 2007-04-29
--> 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 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.
Internal structure
Saturn's interior is similar to that of Jupiter, having a small rocky core surrounded mostly by
hydrogen and
helium. The rocky core is similar in composition to the Earth, but denser. Above this, there is a thicker liquid metallic hydrogen layer, followed by a layer of liquid hydrogen and helium, and in the outermost 1,000 km a gaseous atmosphere. Traces of various ices are also present. The core region is estimated to be about 9–22 times the mass of the Earth. Saturn has a very hot interior, reaching 11,700 °C at the core, and it radiates 2.5 times more energy into space than it receives from the Sun. Most of the extra energy is generated by the [Kelvin-Helmholtz mechanism (slow gravitational compression), but this alone may not be sufficient to explain Saturn's heat production. An additional proposed mechanism by which Saturn may generate some of its heat is the "raining out" of droplets of [helium deep in Saturn's interior, the droplets of helium releasing heat by [friction as they fall down through the lighter hydrogen.{{cite web
|url = http://www.nasa.gov/worldbook/saturn_worldbook.html|title = NASA - Saturn|publisher = NASA|accessdate = 2007-07-27|date = 2004-->
Cloud layers
Saturn's celestial body atmosphere exhibits a banded pattern similar to Jupiter's (the nomenclature is the same), but Saturn's bands are much fainter and are also much wider near the equator. At the bottom, extending for 10 km and with a temperature of -23 °C, is a layer made up of water ice. After that comes a layer of ammonium hydrosulfide ice, which extends for another 50 km and is approximately at -93 °C. Eighty kilometers above that are ammonia ice clouds, where the temperatures are about -153 °C. Near the top, extending for some 200 km to 270 km above the clouds, come layers of visible cloud tops and a hydrogen and helium atmosphere.{{cite web] data indicate peak easterly winds of 500 m/s (1,800 km/h).{{cite web|title = Voyager Saturn Science Summary|url = http://www.solarviews.com/eng/vgrsat.htm|first = Calvin|middle = J.|last = Hamilton|accessdate = 2007-07-05|date = 1997|publisher = Solarviews--> Saturn's finer cloud patterns were not observed until the Voyager flybys. Since then, however,
Earth-based
telescope has improved to the point where regular observations can be made.
Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. In 1990, the
Hubble Space Telescope observed an enormous white cloud near Saturn's equator which 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 which occurs once every Saturnian year, or 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 most famous. If the periodicity is maintained, another storm will occur in about 2020.
Patrick Moore, ed.,
1993 Yearbook of Astronomy, (London: W.W. Norton & Company, 1992), Mark Kidger, "The 1990 Great White Spot of Saturn", pp. 176-215.
In recent images from the
Cassini-Huygens spacecraft, Saturn's northern hemisphere appears a bright blue, similar to Uranus, as can be seen in the image below. This blue color cannot currently be observed from Earth, because Saturn's rings are currently blocking its northern hemisphere. The color is most likely caused by
Rayleigh scattering.
and confirmed in 2006 by
Cassini-Huygens.{{cite web|url = http://www.nasa.gov/mission_pages/cassini/multimedia/pia09188.html|title = Saturn's Strange Hexagon|accessdate = 2007-07-06|date = March 27, 2007|last = Watanabe|first = Susan|publisher =
NASA-->
Astronomers using infrared imaging have shown that Saturn has a warm polar vortex and that it is the only such planet known in the solar system. This, they say, is the warmest spot on Saturn. Whereas temperatures on Saturn are normally -185 °C, temperatures on the vortex often reach as high as -122 °C.{{cite web]al wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.{{cite web|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1988Icar...76..335G&db_key=AST&data_type=HTML&format=|title = A hexagonal feature around Saturn's North Pole|last = Godfrey|publisher = Icarus|accessdate = 2007-07-09-->{{cite web|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993Sci...260..329S&db_key=AST&data_type=HTML&format=|title = Ground-based observations of Saturn's north polar SPOT and hexagon|last = Sanchez-Lavega|first = A.|accessdate = 2007-07-30|publisher = Bulletin of the American Astronomical Society--> Unlike the north pole, HST imaging of the south polar region indicates the presence of a
jet stream, but no strong polar vortex nor any
hexagonal standing wave.{{cite web|url = http://www.aas.org/publications/baas/v34n3/dps2002/10.htm|title = Hubble Space Telescope Observations of the Atmospheric Dynamics in Saturn's South Pole from 1997 to 2002|accessdate = 2007-07-06|publisher = The American Astronomical Society|date = October 8, 2002--> However, NASA reported in November 2006 that the Cassini spacecraft observed a '
hurricane-like' storm locked to the south pole that had a clearly defined eyewall.{{cite web] of Jupiter by the Galileo (spacecraft) spacecraft).{{cite web|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=703|title = NASA Sees into the Eye of a Monster Storm on Saturn|publisher = [NASA|date = May 19, 2006|accessdate=April 27|accessyear=2007--> Bizarre geometric shapes that appear at the centre of swirling vortices in planetary atmospheres might be explained by a simple experiment with a bucket of water but correlating this to saturn's pattern is by no means certain.
Magnetic field and magnetosphere
Saturn has an intrinsic magnetic field that has a simple, symmetric shape—a magnetic
dipole. Its strength at the equator—0.2
Gauss (unit)—is approximately one twentieth than that of the field around Jupiter and slightly weaker than Earth's magnetic field. As a result the cronian magnetosphere is much smaller than jovian and extends slightly beyond the orbit of
Titan (moon).{{cite web|url = http://library.thinkquest.org/C005921/Saturn/satuAtmo.htm|title = Saturn: Atmosphere and Magnetosphere|publisher = Thinkquest Internet Challenge|accessdate = 2007-07-15|last = McDermott|first = Matthew|date = 2000--> Most probably, the magnetic field is generated similarly to that of Jupiter—by currents in the metallic-hydrogen layer, which is called a metallic-hydrogen dynamo. Similarly to the those of other planets, 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.{{cite web| author=Russell, C. T.; Luhmann, J. G.
| year=1997
| url =http://www-ssc.igpp.ucla.edu/personnel/russell/papers/sat_mag.html
| title =Saturn: Magnetic Field and Magnetosphere
| publisher =UCLA - IGPP Space Physics Center
| accessdate = 2007-04-29
-->
Orbit and rotation
The average distance between Saturn and the
Sun is over 1,400,000,000 km (9 astronomical unit). With an average orbital speed of 9.69 km/s, it takes Saturn 10,759 Earth days (or about 29½ years), to finish one revolution around the Sun. The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth. Because of an eccentricity of 0.056, the distance between Saturn and the Sun varies by approximately 155,000,000 km between perihelion and aphelion, which are the nearest and most distant points of the planet along its orbital path, respectively.
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):
System I has a period of 10 h 14 min 00 s (844.3°/d) and encompasses the Equatorial Zone, which extends from the northern edge of the South Equatorial Belt to the southern edge of the North Equatorial Belt. All other Saturnian latitudes have been assigned a rotation period of 10 h 39 min 24 s (810.76°/d), which is
System II.
System III, based on
radio astronomy emissions from the planet in the period of the Voyager flybys, has a period of 10 h 39 min 22.4 s (810.8°/d); because it is very close to System II, it has largely superseded it.
However, a precise value for the rotation period of the interior remains elusive. While approaching Saturn in 2004, the Cassini spacecraft found that the radio rotation period of Saturn had increased appreciably, to approximately 10 h 45 m 45 s (± 36 s).{{cite web|url = http://www.nasa.gov/mission_pages/cassini/media/cassini-062804.html|title = Scientists Find That Saturn's Rotation Period is a Puzzle|date = June 28, 2004|publisher = NASA|accessdate = 2007-03-22--> The cause of the change is unknown—it was thought to be due to a movement of the radio source to a different latitude inside Saturn, with a different rotational period, rather than because of a change in Saturn's rotation.
Later, in March 2007, it was found that the rotation of the radio emissions did not trace the rotation of the planet, but rather is produced by convection of the plasma disc, which is dependent also on other factors besides the planet's rotation. It was reported that the variance in measured rotation periods may be caused by geyser activity on Saturn's moon Enceladus (moon). The water vapor emitted into Saturn's orbit by this activity becomes charged and "weighs down" Saturn's magnetic field, slowing its rotation slightly relative to the rotation of the planet itself. At the time it was stated that there is no currently known method of determining the rotation rate of Saturn's core.{{cite press release|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=733|title = Enceladus Geysers Mask the Length of Saturn's Day|date = March 22, 2007|publisher = NASA Jet Propulsion Laboratory|accessdate=2007-03-22-->{{cite web| url = http://www.sciencemag.org/cgi/content/abstract/316/5823/442|title = The Variable Rotation Period of the Inner Region of Saturn's Plasma Disk|date = March 22, 2007|publisher =
Science (journal)|accessdate = 2007-04-24-->{{cite web| url = http://www.sciencemag.org/cgi/content/abstract/316/5823/442|title = A New Spin on Saturn's Rotation|date = April 20, 2007|publisher=
Science (journal)|accessdate=2007-04-24-->
The latest estimate of Saturn's rotation based on a compilation of various measurements from the Cassini, Voyager and Pioneer probes was reported in September 2007 is 10 hours, 32 minutes, 35 seconds.
Planetary rings
(here: as imaged by Cassini in 2007) are the most spectacular in the
Solar System.Saturn is probably best known for its system of
planetary rings, which makes it the most visually remarkable object in the solar system.{{cite web|title = Saturn|url = http://www.nmm.ac.uk/server/show/conWebDoc.286|publisher = National Maritime Museum|accessdate = 2007-07-06-->
History
The rings were first observed by Galileo Galilei in 1610 with his telescope, but he was unable to identify them as such. He wrote to the
Cosimo II de' Medici, Grand Duke of Tuscany that "The planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the zodiac, and the middle one (Saturn itself) is about three times the size of the lateral ones edges of the rings." He also described Saturn as having "ears." In 1612 the plane of the rings was oriented directly at the Earth and the rings appeared to vanish. Mystified, Galileo wondered, "Has Saturn swallowed his children?", referring to the myth of the god Saturn eating his own children to prevent them from overthrowing him. Then, in 1613, they reappeared again, further confusing Galileo.
In 1655, Christiaan Huygens became the first person to suggest that Saturn was surrounded by a ring. Using a telescope that was far superior to those available to Galileo, Huygens observed Saturn and wrote that "It is surrounded by a thin, flat, ring, nowhere touching, inclined to the ecliptic."
In 1675, Giovanni Domenico Cassini determined that Saturn's ring was composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the
Rings of Saturn#Cassini Division. This division in itself is a 4,800 km wide region between the Rings of Saturn#A_Ring and
Rings of Saturn#B_Ring.{{cite web|title = Saturn's Cassini Division|url = http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/cassini_division.html|accessdate = 2007-07-06|publisher = StarChild-->
In 1859,
James Clerk Maxwell demonstrated that the rings could not be solid or they would become unstable and break apart. He proposed that the rings must be composed of numerous small particles, all independently orbiting Saturn.{{cite web] of Lick Observatory.
Physical characteristics
, whose
cryovolcanos are dimly visible at its south pole. North is up. Imaged by Cassini in 2006.The rings can be viewed using a quite modest modern telescope or with good binoculars. They extend from 6,630 km to 120,700 km above Saturn's equator, average approximately one kilometer in thickness, and are composed of 93 percent water
ice with a smattering of tholin impurities, and 7 percent amorphous carbon. They range in size from specks of dust to the size of a small automobile.{{cite web] in the 19th century, is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by
tidal forces (see Roche limit). A variation of this theory is that the moon disintegrated after being struck by a large comet or asteroid. The second theory is that the rings were never part of a moon, but are instead left over from the original
nebular material from which Saturn formed. This theory is not widely accepted today, since Saturn's rings are thought to be unstable over periods of millions of years and therefore of relatively recent origin.
While the largest gaps in the rings, such as the Cassini Division and Rings of Saturn#Encke Division, can be seen from Earth, the Voyager spacecrafts discovered the rings to have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise from the gravitational pull of Saturn's many moons in several different ways. Some gaps are cleared out by the passage of tiny moonlets such as
Pan (moon), many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small
shepherd satellites such as Prometheus (moon) and Pandora (moon). Other gaps arise from
orbital resonance between the orbital period of particles in the gap and that of a more massive moon further out; Mimas (moon) maintains the Cassini division in this manner. Still more structure in the rings consists of spiral waves raised by the moons' periodic gravitational perturbations.
Data from the Cassini space probe indicate that the rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular oxygen gas (O2) produced when ultraviolet light from the Sun disintegrates water ice in the rings. Chemical reactions between water molecule fragments and further
ultraviolet stimulation create and eject, among other things O2. According to models of this atmosphere, H2 is also present. The O2 and H2 atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be on the order of one atom thick.{{cite web]-->The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O2, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic
ions that bombard water molecules ejected by Saturn's moon
Enceladus (moon). This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope.{{cite web|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006ApJ...644L.137J&db_key=AST&data_type=HTML&format=&high=42bf06f4d906731|title = The Enceladus and OH Tori at Saturn|last = Johnson|first = R. E.|accessdate = 2007-07-07|date = 2006|publisher = The
American Astronomical Society-->
Saturn shows complex patterns in its brightness. Most of the variability is due to the changing aspect of the rings,{{cite web]|accessdate=2007-07-07|year = 2003|month = February-->
In 1980, Voyager I made a fly-by of Saturn that showed the F-ring to be composed of three narrow rings that appeared to be braided in a complex structure; it is now known that the outer two rings consist of knobs, kinks and lumps that give the illusion of braiding, with the less bright third ring lying inside them.
Spokes of the rings
in 1981
Until 1980, the structure of the rings of Saturn was explained exclusively as the action of
gravitational forces. The Voyager spacecraft found radial features in the
Rings of Saturn#B ring, called
spokes, which could not be explained in this manner, as their persistence and rotation around the rings were not consistent with orbital mechanics.{{cite web] interactions, as they rotate almost synchronously with the
magnetosphere of Saturn. However, the precise mechanism generating the spokes is still unknown.{{cite web
Twenty-five years later, the spokes were observed again, this time by Cassini. They appear to be a seasonal phenomenon, disappearing in the Saturnian midwinter/midsummer and reappearing as Saturn comes closer to equinox. The spokes were not visible when Cassini arrived at Saturn in early 2004. Some scientists speculated that the spokes would not be visible again until 2007, based on models attempting to describe spoke formation. Nevertheless, the Cassini imaging team kept looking for spokes in images of the rings, and the spokes reappeared in images taken on September 5,
2005.{{cite web|url = http://www.space.com/scienceastronomy/050915_cassini_spokes.html|title = Cassini Probe Spies Spokes in Saturn's Rings|accessdate = 2007-07-06|date = 2005-09-15|publisher = Imaginova Corp.|first = Tarig|last = Malik-->
Natural satellites
, Titan (moon),
Prometheus (moon) (edge of rings), Telesto (moon) (top center)
Saturn has a large number of natural satellite. The precise figure is uncertain, as the orbiting chunks of ice in Saturn's rings are all technically moons, and it is difficult to draw a distinction between a large ring particle and a tiny moon. As of 2007, a total of 60 individual moons have been identified, plus 3 unconfirmed moons that could be small dust clumps in the rings. Out of those, 48 have been named. Many of the moons are very small: out of 60, 34 are less than 10 km in diameter, and another 13 less than 50 km.{{cite web|url = http://www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html|title=www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html|title = Saturn's Known Satellites|accessdate=2007-05-23--> Only seven of them are massive enough to have collapsed into spheroids under their own gravitation. These are compared with Earth's moon in the table below.
Titan (moon), Saturn's largest moon, is the only moon in the Solar System to have a dense atmosphere. While most of the moons in the Saturnian system are small in size, Titan is, relatively speaking, gigantic. After the Sun, the eight planets and Jupiter's moon Ganymede (moon), Titan is the most massive object in the Solar System. Titan comprises more than 90 percent of the mass in orbit around Saturn, including the rings, and the other moons range from one hundredth to one hundred millionth its mass.
Traditionally, most of Saturn's other moons are named after
Titan (mythology) of Greek mythology. This started because
John Herschel—son of
William Herschel, discoverer of Mimas and Enceladus—suggested doing so in his 1847 publication
Results of Astronomical Observations made at the Cape of Good Hope,Herschel, J.;
Results of Astronomical Observations made at the Cape of Good Hope, 1847 —as reported by Lassell, W.; Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 3 (
January 14, 1848), pp. 42–43 because they were the sisters and brothers of Cronus (the Greek Saturn).
For a timeline of discovery dates, see Timeline of discovery of Solar System planets and their natural satellites.
History and exploration
/European Space Agency.
Ancient times and observation
Saturn has been known since prehistoric times.{{cite web|title = Saturn > Observing Saturn|url = http://www.nmm.ac.uk/server/show/conWebDoc.13852/viewPage/5|publisher =
National Maritime Museum, the god [Saturn (mythology), from which the planet takes its name, was the god of the agricultural and harvest sector. The Romans considered Saturnus the equivalent of the Greek mythology Kronos. The Greeks had made the outermost planet sacred to Kronos, and the Romans followed suit.
In
Jyotisha, there are nine astrological objects, known as Navagrahas. Saturn, one of them, is known as "Sani" or "Shani," the Judge among all the planets, and determines everyone according to their own performed deeds bad or good.{{cite web] and Japanese culture designated the planet Saturn as the
earth star (土星). This was based on Five elements (Chinese philosophy) which were traditionally used to classify natural elements. In ancient Hebrew language, Saturn is called 'Shabbathai'. Its angel is Cassiel. Its intelligence, or beneficial spirit, is
Agiel (layga), and its spirit (darker aspect) is Zazel (lzaz). In
Ottoman Turkish and in
Malay language, its name is 'Zuhal', derived from Arabic language زحل.
Saturn's rings require at least a 75 mm diameter
telescope to resolve and thus were not known to exist until
Galileo first saw them in 1610.{{cite web] used greater telescopic magnification that the rings were assumed to be rings. Huygens also discovered Saturn's moon
Titan (moon). Some time later, Jean-Dominique Cassini discovered four other moons: Iapetus (moon), Rhea (moon),
Tethys (moon), and
Dione (moon). In 1675, Cassini also discovered the gap now known as the Cassini Division.{{cite web|url = http://huygensgcms.gsfc.nasa.gov/Shistory.htm|title = Saturn: History of Discoveries|accessdate = 2007-07-15|last = Micek|last = Catherine-->
No further discoveries of significance were made until 1789 when
William Herschel discovered two further moons,
Mimas (moon) and Enceladus (moon). The irregularly shaped satellite
Hyperion (moon), which has a
orbital resonance with Titan, was discovered in 1848 by a British team.
In 1899 William Henry Pickering discovered Phoebe (moon), 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 twentieth 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
Saturn was first visited by
Pioneer 11 on September 1979. It flew within 20,000 km of the planet's cloud tops. Low resolution images were acquired of the planet and a few of its moons; the resolution of the images was not good enough to discern surface features. The spacecraft also studied the rings; among the discoveries were the thin F-ring and the fact that dark gaps in the rings are bright when viewed towards the Sun, or in other words, they are not empty of material. Pioneer 11 also measured the temperature of Titan.{{cite web|url = http://web.archive.org/web/20060130100401/http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PN10&11.html|title = The Pioneer 10 & 11 Spacecraft|accessdate=2007-07-05|publisher = Mission Descriptions-->
Voyager flybys
In November 1980, the
Voyager 1 probe visited the Saturn system. It sent back the first high-resolution images of the planet, rings, and satellites. Surface features of various moons were seen for the first time. Voyager 1 performed a close flyby of Titan, greatly increasing our knowledge of the atmosphere of the moon. However, it also proved that Titan's atmosphere is impenetrable in visible wavelengths; so, no surface details were seen. The flyby also changed the spacecraft's trajectory out from the plane of the solar system.{{cite web] 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. They also discovered the small Rings of Saturn#Maxwell_Gap gap (a gap within the Rings of Saturn#C_Ring) and Rings of Saturn#Keeler_Gap gap (a 42 km wide gap in the Rings of Saturn#A_Ring).
Cassini orbiter
On July 1 2004, the Cassini–Huygens spacecraft performed the SOI (Saturn Orbit Insertion) maneuver and entered into orbit around Saturn. Before the SOI, Cassini had already studied the system extensively. In June 2004, it had conducted a close flyby of Phoebe (moon), sending back high-resolution images and data.
Cassini's flyby of Saturn's largest moon,
Titan (moon), has 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
December 25, 2004. Huygens descended onto the surface of Titan on
January 14,
2005, sending a flood of data during the atmospheric descent and after the landing. During 2005, Cassini conducted multiple flybys of Titan and icy satellites. Cassini's last Titan flyby was scheduled for July 19, 2007.
Since early 2005, scientists have been tracking lightning on Saturn, primarily found by Cassini. The power of the lightning is said to be approximately 1000 times than that of the lightning on Earth. In addition, scientists believe that this storm is the strongest of its kind ever seen.{{cite web],
2006, NASA reported that, through images, the Cassini probe found evidence of liquid water reservoirs that erupt in geysers on Saturn's moon Enceladus (moon). Images had also shown particles of water in its liquid state being emitted by icy jets and towering plumes. According to Dr. Andrew Ingersoll, California Institute of Technology, "Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust. What's different here is that pockets of liquid water may be no more than tens of meters below the surface."{{cite web|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=639|title = NASA's Cassini Discovers Potential Liquid Water on Enceladus|accessdate = 2007-07-08|date = March 9, 2006|publisher = NASA Jet Propulsion Laboratory|first = Michael|last = Pence-->
On
September 20,
2006, a Cassini probe photograph revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. Apparently, the source of this ring is the result of the crashing of a meteoroid off two of the moons of Saturn. {{cite web].{{cite web|url = http://news.bbc.co.uk/2/hi/science/nature/6449081.stm|title = Probe reveals seas on Saturn moon|publisher = BBC|last =|first =|accessdate = 2007-09-26|date = March 14, 2007-->
In October 2006, the probe detected a 5,000 km diameter hurricane with an eyewall at Saturn's South Pole.{{cite web|url = http://news.bbc.co.uk/2/hi/science/nature/6135450.stm|title = Huge 'hurricane' rages on Saturn|publisher = BBC|last = Rincon|first = Paul|accessdate = 2007-07-12|date = November 10, 2006-->
As of 2006, the probe has discovered and confirmed 4 new satellites. Its primary mission will end in 2008 when the spacecraft will be expected to have completed 74 orbits around the planet. The probe, however, is expected to have at least one mission extension.
Best viewing
Saturn is the most distant of the five planets easily visible to the naked eye, the other four being
Mercury (planet),
Venus,
Mars, and Jupiter (Uranus and occasionally 4 Vesta are visible to the naked eye in very dark skies), and was the last planet known to early astronomers until Uranus was discovered in 1781. Saturn appears to the naked eye in the night sky as a bright, yellowish star varying usually between magnitude +1 and 0 and takes approximately 29½ years to make a complete circuit of the ecliptic against the background constellations of the
zodiac. Optical aid (large binoculars or a telescope) magnifying at least 20X is required to clearly resolve Saturn's rings for most people.
While it is a rewarding target for observation for most of the time it is visible in the sky, Saturn and its rings are best seen when the planet is at or near
opposition (astronomy) (the configuration of a planet when it is at an elongation of 180° and thus appears opposite the Sun in the sky). During the opposition of
December 17 2002, Saturn appeared at its brightest due to a favorable orientation of the rings relative to the
Earth.{{cite web|url = http://findarticles.com/p/articles/mi_qa4015/is_200301/ai_n9338203|title = SATURN IN 2002-03|accessdate = 2007-10-14|last = Schmude|first = Richard W Jr|date = 2003|publisher = Georgia Journal of Science-->
See also
References
External links
- Introduction to Saturn by NASA's Solar System Exploration
- Saturn Fact Sheet, by NASA
- Cassini-Huygens mission to Saturn, by NASA
- Research News about Saturn
- General information about Saturn
- Studies on the Rings of Saturn
{{Infobox Planet| bgcolour = #FFCC66| name = Saturn| symbol = | image = | caption = Saturn, as seen by Cassini–Huygens| orbit_ref = {{cite web| last = Yeomans | first = Donald K. | date = 2006-07-13
| url = http://ssd.jpl.nasa.gov/?horizons
| title = HORIZONS System | publisher = NASA JPL
| accessdate = 2007-08-08 --> — At the site, go to the "web interface" then select "Ephemeris Type: ELEMENTS", "Target Body: Saturn Barycenter" and "Center: Sun".Orbital elements refer to the barycenter of the Saturn system, and are the instantaneous [osculating orbit values at the precise [J2000 epoch. Barycenter quantities are given because, in contrast to the planetary centre, they do not experience appreciable changes on a day-to-day basis from to the motion of the moons.
| epoch = Epoch (astronomy)#J2000.0| aphelion = 1,513,325,783 km
10.11595804
Astronomical unit| perihelion = 1,353,572,956 km
9.04807635 AU| semimajor = 1,433,449,370 km
9.58201720 AU| eccentricity = 0.055723219| period = 10,832.327 days
29.657 296
Julian year (astronomy)| synodic_period = 378.09 days| avg_speed = 9.69 km/s| inclination = 2.485240°
5.51° to Sun's equator| asc_node = 113.642811°| arg_peri = 336.013862°| mean_anomaly = 320.347750°| satellites =
Saturn's natural satellites(up to 63 seen)| physical_characteristics = yes| flattening = 0.09796 ± 0.00018 | equatorial_radius = 60,268 ± 4 kmRefers to the level of 1 bar atmospheric pressure
9.4492 Earths| polar_radius = 54,364 ± 10 km
8.5521 Earths| surface_area = 4.27×1010 km² NASA: Solar System Exploration: Planets: Saturn: Facts & Figures
83.703 Earths| volume = 8.2713×1014 km³{{cite web|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html|title = Saturn Fact Sheet|publisher = NASA|last = Williams|first = Dr. David R.|accessdate = 2007-07-31|date = September 07, 2006-->
763.59 Earths| mass = 5.6846×1026 kg
95.152 Earths| density = 0.687 g/cm³
(less than
water)]
0.914 g-force| escape_velocity = 35.5 km/s| sidereal_day = 0.439 – 0.449 day{{cite web|url = http://www.space.com/scienceastronomy/070906_saturn_day.html|title = Length of Saturn's Day Revised|publisher = Space.com|last = Than|first = Ker|accessdate = 2007-09-06|date = September 06, 2007-->
(10 h 32 – 47 min)| rot_velocity = 9.87 km/s
35,500 km/h| axial_tilt = 26.73°| right_asc_north_pole = 2 h 42 min 21 s
40.589°| declination = 83.537°| albedo = 0.342 (
Bond albedo)0.47 (Geometric albedo)| magnitude = +1.2 to -0.24 {{cite web|url = http://findarticles.com/p/articles/mi_qa4015/is_200101/ai_n8933308|title = Wideband photoelectric magnitude measurements of Saturn in 2000|accessdate = 2007-10-14|last = Schmude|first = Richard W Jr|date = 2001|publisher = Georgia Journal of Science-->| angular_size = 14.5" — 20.1"
(excludes rings)| temperatures = yes| temp_name1 = 1 bar level| min_temp_1 =| mean_temp_1 = 134 Kelvin| max_temp_1 =| temp_name2 = 0.1 bar| min_temp_2 =| mean_temp_2 = 84 K| max_temp =| adjectives = Saturnian| atmosphere = yes| atmosphere_ref = | scale_height = 59.5 km| atmosphere_composition =~96%Hydrogen (H2)~3%
Helium~0.4%Methane~0.01%
Ammonia~0.01%
Hydrogen deuteride (HD)0.0007%Ethane
Ices:
Ammoniawaterammonium hydrosulfide(NH4SH)-->
Saturn () is the sixth planet from the Sun and the second largest planet in the
Solar System, after Jupiter. Along with the planets Jupiter, Uranus, and Neptune, it is classified as a gas giant (also known as a Jovian planet, after the planet Jupiter). It was named after the Roman god Saturn (mythology), equated to the
Greek mythology Cronus (the Titan father of
Zeus) and the Babylonian Ninurta. Saturn's symbol represents the god's sickle (Unicode: ). The day in the week Saturday gets its name from the planet.
The planet Saturn is primarily composed of hydrogen, with small proportions of helium and trace elements. The interior consists of a small core of rock and ice, surrounded by a thick layer of
metallic hydrogen and a gaseous outer layer. 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 a planetary
magnetic field intermediate in strength between that of Earth and the more powerful field around Jupiter.
Saturn has a prominent system of
Rings of Saturn, consisting mostly of ice particles with a smaller amount of rocky
debris and cosmic dust. Sixty known moons orbit the planet.
Titan (moon), Saturn's largest and the
Solar System's second largest moon (after Ganymede (moon)), is larger than the planet
Mercury (planet) and is the only moon in the Solar System to possess a significant atmosphere.{{cite web|url = http://saturn.jpl.nasa.gov/news/features/saturn-story/moons.cfm|title = The Story of Saturn|accessdate = 2007-07-07|last = Munsell|first = Kirk|date = April 6, 2005|publisher = NASA Jet Propulsion Laboratory; California Institute of Technology-->
Physical characteristics
Due to a combination of its low density, rapid rotation, and fluid state, Saturn is an oblate
spheroid; that is, it is flattened at the geographical pole and bulges at the equator. Its equatorial and polar radii differ by almost 10%— 60268 km vs. 54364 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
density than water. Although Saturn's planetary core is considerably denser than water, the average
relative 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{{cite web|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html|title = Jupiter Fact Sheet|publisher = NASA|last = Williams|first = Dr. David R.|date = November 16, 2004|accessdate = 2007-08-02--> but only about 20% larger than Saturn.{{cite web|url = http://ase.arc.nasa.gov/projects/bayes-group/Atlas/size/Jupiter/Saturn.html|title = Jupiter compared to Saturn|publisher = NASA|accessdate = 2007-07-15-->
Composition
The outer atmosphere of Saturn consists of about 93.2% molecular hydrogen and 6.7% 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.{{cite web
| last = Martinez
| first = Carolina
| date =September 5, 2005
| url = http://www.nasa.gov/mission_pages/cassini/whycassini/cassini-090505-clouds.html
| title =Cassini Discovers Saturn's Dynamic Clouds Run Deep
| publisher =NASA
| accessdate = 2007-04-29
--> 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 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.
Internal structure
Saturn's interior is similar to that of Jupiter, having a small rocky core surrounded mostly by
hydrogen and
helium. The rocky core is similar in composition to the Earth, but denser. Above this, there is a thicker liquid metallic hydrogen layer, followed by a layer of liquid hydrogen and helium, and in the outermost 1,000 km a gaseous atmosphere. Traces of various ices are also present. The core region is estimated to be about 9–22 times the mass of the Earth. Saturn has a very hot interior, reaching 11,700 °C at the core, and it radiates 2.5 times more energy into space than it receives from the Sun. Most of the extra energy is generated by the [Kelvin-Helmholtz mechanism (slow gravitational compression), but this alone may not be sufficient to explain Saturn's heat production. An additional proposed mechanism by which Saturn may generate some of its heat is the "raining out" of droplets of [helium deep in Saturn's interior, the droplets of helium releasing heat by [friction as they fall down through the lighter hydrogen.{{cite web
|url = http://www.nasa.gov/worldbook/saturn_worldbook.html|title = NASA - Saturn|publisher = NASA|accessdate = 2007-07-27|date = 2004-->
Cloud layers
Saturn's celestial body atmosphere exhibits a banded pattern similar to Jupiter's (the nomenclature is the same), but Saturn's bands are much fainter and are also much wider near the equator. At the bottom, extending for 10 km and with a temperature of -23 °C, is a layer made up of water ice. After that comes a layer of ammonium hydrosulfide ice, which extends for another 50 km and is approximately at -93 °C. Eighty kilometers above that are ammonia ice clouds, where the temperatures are about -153 °C. Near the top, extending for some 200 km to 270 km above the clouds, come layers of visible cloud tops and a hydrogen and helium atmosphere.{{cite web] data indicate peak easterly winds of 500 m/s (1,800 km/h).{{cite web|title = Voyager Saturn Science Summary|url = http://www.solarviews.com/eng/vgrsat.htm|first = Calvin|middle = J.|last = Hamilton|accessdate = 2007-07-05|date = 1997|publisher = Solarviews--> Saturn's finer cloud patterns were not observed until the Voyager flybys. Since then, however, Earth-based telescope has improved to the point where regular observations can be made.
Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. In 1990, the Hubble Space Telescope observed an enormous white cloud near Saturn's equator which 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 which occurs once every Saturnian year, or 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 most famous. If the periodicity is maintained, another storm will occur in about 2020.Patrick Moore, ed.,
1993 Yearbook of Astronomy, (London: W.W. Norton & Company, 1992), Mark Kidger, "The 1990 Great White Spot of Saturn", pp. 176-215.
In recent images from the
Cassini-Huygens spacecraft, Saturn's northern hemisphere appears a bright blue, similar to
Uranus, as can be seen in the image below. This blue color cannot currently be observed from Earth, because Saturn's rings are currently blocking its northern hemisphere. The color is most likely caused by Rayleigh scattering.
and confirmed in 2006 by
Cassini-Huygens.{{cite web|url = http://www.nasa.gov/mission_pages/cassini/multimedia/pia09188.html|title = Saturn's Strange Hexagon|accessdate = 2007-07-06|date = March 27, 2007|last = Watanabe|first = Susan|publisher =
NASA-->
Astronomers using
infrared imaging have shown that Saturn has a warm polar vortex and that it is the only such planet known in the solar system. This, they say, is the warmest spot on Saturn. Whereas temperatures on Saturn are normally -185 °C, temperatures on the vortex often reach as high as -122 °C.{{cite web]al wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.{{cite web|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1988Icar...76..335G&db_key=AST&data_type=HTML&format=|title = A hexagonal feature around Saturn's North Pole|last = Godfrey|publisher = Icarus|accessdate = 2007-07-09-->{{cite web|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993Sci...260..329S&db_key=AST&data_type=HTML&format=|title = Ground-based observations of Saturn's north polar SPOT and hexagon|last = Sanchez-Lavega|first = A.|accessdate = 2007-07-30|publisher = Bulletin of the American Astronomical Society--> Unlike the north pole, HST imaging of the south polar region indicates the presence of a
jet stream, but no strong polar vortex nor any
hexagonal standing wave.{{cite web|url = http://www.aas.org/publications/baas/v34n3/dps2002/10.htm|title = Hubble Space Telescope Observations of the Atmospheric Dynamics in Saturn's South Pole from 1997 to 2002|accessdate = 2007-07-06|publisher = The American Astronomical Society|date = October 8, 2002--> However, NASA reported in November 2006 that the Cassini spacecraft observed a '
hurricane-like' storm locked to the south pole that had a clearly defined eyewall.{{cite web] of Jupiter by the Galileo (spacecraft) spacecraft).{{cite web|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=703|title = NASA Sees into the Eye of a Monster Storm on Saturn|publisher = [NASA|date = May 19, 2006|accessdate=April 27|accessyear=2007--> Bizarre geometric shapes that appear at the centre of swirling vortices in planetary atmospheres might be explained by a simple experiment with a bucket of water but correlating this to saturn's pattern is by no means certain.
Magnetic field and magnetosphere
Saturn has an intrinsic magnetic field that has a simple, symmetric shape—a magnetic
dipole. Its strength at the equator—0.2
Gauss (unit)—is approximately one twentieth than that of the field around Jupiter and slightly weaker than Earth's magnetic field. As a result the cronian magnetosphere is much smaller than jovian and extends slightly beyond the orbit of
Titan (moon).{{cite web|url = http://library.thinkquest.org/C005921/Saturn/satuAtmo.htm|title = Saturn: Atmosphere and Magnetosphere|publisher = Thinkquest Internet Challenge|accessdate = 2007-07-15|last = McDermott|first = Matthew|date = 2000--> Most probably, the magnetic field is generated similarly to that of Jupiter—by currents in the metallic-hydrogen layer, which is called a metallic-hydrogen dynamo. Similarly to the those of other planets, 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.{{cite web| author=Russell, C. T.; Luhmann, J. G.
| year=1997
| url =http://www-ssc.igpp.ucla.edu/personnel/russell/papers/sat_mag.html
| title =Saturn: Magnetic Field and Magnetosphere
| publisher =UCLA - IGPP Space Physics Center
| accessdate = 2007-04-29
-->
Orbit and rotation
The average distance between Saturn and the
Sun is over 1,400,000,000 km (9 astronomical unit). With an average orbital speed of 9.69 km/s, it takes Saturn 10,759 Earth days (or about 29½ years), to finish one revolution around the Sun. The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth. Because of an
eccentricity of 0.056, the distance between Saturn and the Sun varies by approximately 155,000,000 km between
perihelion and aphelion, which are the nearest and most distant points of the planet along its orbital path, respectively.
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):
System I has a period of 10 h 14 min 00 s (844.3°/d) and encompasses the Equatorial Zone, which extends from the northern edge of the South Equatorial Belt to the southern edge of the North Equatorial Belt. All other Saturnian latitudes have been assigned a rotation period of 10 h 39 min 24 s (810.76°/d), which is
System II.
System III, based on radio astronomy emissions from the planet in the period of the Voyager flybys, has a period of 10 h 39 min 22.4 s (810.8°/d); because it is very close to System II, it has largely superseded it.
However, a precise value for the rotation period of the interior remains elusive. While approaching Saturn in 2004, the Cassini spacecraft found that the radio rotation period of Saturn had increased appreciably, to approximately 10 h 45 m 45 s (± 36 s).{{cite web|url = http://www.nasa.gov/mission_pages/cassini/media/cassini-062804.html|title = Scientists Find That Saturn's Rotation Period is a Puzzle|date = June 28, 2004|publisher = NASA|accessdate = 2007-03-22--> The cause of the change is unknown—it was thought to be due to a movement of the radio source to a different latitude inside Saturn, with a different rotational period, rather than because of a change in Saturn's rotation.
Later, in March 2007, it was found that the rotation of the radio emissions did not trace the rotation of the planet, but rather is produced by convection of the plasma disc, which is dependent also on other factors besides the planet's rotation. It was reported that the variance in measured rotation periods may be caused by geyser activity on Saturn's moon
Enceladus (moon). The water vapor emitted into Saturn's orbit by this activity becomes charged and "weighs down" Saturn's magnetic field, slowing its rotation slightly relative to the rotation of the planet itself. At the time it was stated that there is no currently known method of determining the rotation rate of Saturn's core.{{cite press release|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=733|title = Enceladus Geysers Mask the Length of Saturn's Day|date = March 22, 2007|publisher = NASA Jet Propulsion Laboratory|accessdate=2007-03-22-->{{cite web| url = http://www.sciencemag.org/cgi/content/abstract/316/5823/442|title = The Variable Rotation Period of the Inner Region of Saturn's Plasma Disk|date = March 22, 2007|publisher =
Science (journal)|accessdate = 2007-04-24-->{{cite web| url = http://www.sciencemag.org/cgi/content/abstract/316/5823/442|title = A New Spin on Saturn's Rotation|date = April 20, 2007|publisher=
Science (journal)|accessdate=2007-04-24-->
The latest estimate of Saturn's rotation based on a compilation of various measurements from the Cassini, Voyager and Pioneer probes was reported in September 2007 is 10 hours, 32 minutes, 35 seconds.
Planetary rings
(here: as imaged by
Cassini in 2007) are the most spectacular in the
Solar System.Saturn is probably best known for its system of planetary rings, which makes it the most visually remarkable object in the solar system.{{cite web|title = Saturn|url = http://www.nmm.ac.uk/server/show/conWebDoc.286|publisher = National Maritime Museum|accessdate = 2007-07-06-->
History
The rings were first observed by
Galileo Galilei in 1610 with his
telescope, but he was unable to identify them as such. He wrote to the Cosimo II de' Medici, Grand Duke of Tuscany that "The planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the
zodiac, and the middle one (Saturn itself) is about three times the size of the lateral ones edges of the rings." He also described Saturn as having "ears." In 1612 the plane of the rings was oriented directly at the Earth and the rings appeared to vanish. Mystified, Galileo wondered, "Has Saturn swallowed his children?", referring to the myth of the god Saturn eating his own children to prevent them from overthrowing him. Then, in 1613, they reappeared again, further confusing Galileo.
In 1655, Christiaan Huygens became the first person to suggest that Saturn was surrounded by a ring. Using a telescope that was far superior to those available to Galileo, Huygens observed Saturn and wrote that "It is surrounded by a thin, flat, ring, nowhere touching, inclined to the ecliptic."
In 1675,
Giovanni Domenico Cassini determined that Saturn's ring was composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the Rings of Saturn#Cassini Division. This division in itself is a 4,800 km wide region between the Rings of Saturn#A_Ring and Rings of Saturn#B_Ring.{{cite web|title = Saturn's Cassini Division|url = http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/cassini_division.html|accessdate = 2007-07-06|publisher = StarChild-->
In 1859, James Clerk Maxwell demonstrated that the rings could not be solid or they would become unstable and break apart. He proposed that the rings must be composed of numerous small particles, all independently orbiting Saturn.{{cite web] of
Lick Observatory.
Physical characteristics
, whose cryovolcanos are dimly visible at its south pole. North is up. Imaged by Cassini in 2006.The rings can be viewed using a quite modest modern telescope or with good
binoculars. They extend from 6,630 km to 120,700 km above Saturn's equator, average approximately one kilometer in thickness, and are composed of 93 percent water
ice with a smattering of
tholin impurities, and 7 percent amorphous
carbon. They range in size from specks of dust to the size of a small automobile.{{cite web] in the 19th century, is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by
tidal forces (see
Roche limit). A variation of this theory is that the moon disintegrated after being struck by a large comet or
asteroid. The second theory is that the rings were never part of a moon, but are instead left over from the original
nebular material from which Saturn formed. This theory is not widely accepted today, since Saturn's rings are thought to be unstable over periods of millions of years and therefore of relatively recent origin.
While the largest gaps in the rings, such as the Cassini Division and
Rings of Saturn#Encke Division, can be seen from Earth, the Voyager spacecrafts discovered the rings to have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise from the gravitational pull of Saturn's many moons in several different ways. Some gaps are cleared out by the passage of tiny moonlets such as
Pan (moon), many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small
shepherd satellites such as Prometheus (moon) and Pandora (moon). Other gaps arise from orbital resonance between the orbital period of particles in the gap and that of a more massive moon further out; Mimas (moon) maintains the Cassini division in this manner. Still more structure in the rings consists of spiral waves raised by the moons' periodic gravitational perturbations.
Data from the Cassini space probe indicate that the rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular oxygen gas (O2) produced when ultraviolet light from the Sun disintegrates water ice in the rings. Chemical reactions between water molecule fragments and further
ultraviolet stimulation create and eject, among other things O2. According to models of this atmosphere, H2 is also present. The O2 and H2 atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be on the order of one atom thick.{{cite web]-->The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O2, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic
ions that bombard water molecules ejected by Saturn's moon
Enceladus (moon). This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope.{{cite web|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006ApJ...644L.137J&db_key=AST&data_type=HTML&format=&high=42bf06f4d906731|title = The Enceladus and OH Tori at Saturn|last = Johnson|first = R. E.|accessdate = 2007-07-07|date = 2006|publisher = The American Astronomical Society-->
Saturn shows complex patterns in its brightness. Most of the variability is due to the changing aspect of the rings,{{cite web]|accessdate=2007-07-07|year = 2003|month = February-->
In 1980, Voyager I made a fly-by of Saturn that showed the F-ring to be composed of three narrow rings that appeared to be braided in a complex structure; it is now known that the outer two rings consist of knobs, kinks and lumps that give the illusion of braiding, with the less bright third ring lying inside them.
Spokes of the rings
in 1981
Until 1980, the structure of the rings of Saturn was explained exclusively as the action of gravitational forces. The Voyager spacecraft found radial features in the Rings of Saturn#B ring, called
spokes, which could not be explained in this manner, as their persistence and rotation around the rings were not consistent with
orbital mechanics.{{cite web] interactions, as they rotate almost synchronously with the
magnetosphere of Saturn. However, the precise mechanism generating the spokes is still unknown.{{cite web
Twenty-five years later, the spokes were observed again, this time by Cassini. They appear to be a seasonal phenomenon, disappearing in the Saturnian midwinter/midsummer and reappearing as Saturn comes closer to
equinox. The spokes were not visible when Cassini arrived at Saturn in early 2004. Some scientists speculated that the spokes would not be visible again until 2007, based on models attempting to describe spoke formation. Nevertheless, the Cassini imaging team kept looking for spokes in images of the rings, and the spokes reappeared in images taken on September 5, 2005.{{cite web|url = http://www.space.com/scienceastronomy/050915_cassini_spokes.html|title = Cassini Probe Spies Spokes in Saturn's Rings|accessdate = 2007-07-06|date = 2005-09-15|publisher = Imaginova Corp.|first = Tarig|last = Malik-->
Natural satellites
, Titan (moon),
Prometheus (moon) (edge of rings), Telesto (moon) (top center)
Saturn has a large number of
natural satellite. The precise figure is uncertain, as the orbiting chunks of ice in Saturn's rings are all technically moons, and it is difficult to draw a distinction between a large ring particle and a tiny moon. As of 2007, a total of 60 individual moons have been identified, plus 3 unconfirmed moons that could be small dust clumps in the rings. Out of those, 48 have been named. Many of the moons are very small: out of 60, 34 are less than 10 km in diameter, and another 13 less than 50 km.{{cite web|url = http://www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html|title=www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html|title = Saturn's Known Satellites|accessdate=2007-05-23--> Only seven of them are massive enough to have collapsed into spheroids under their own gravitation. These are compared with Earth's moon in the table below.
Titan (moon), Saturn's largest moon, is the only moon in the Solar System to have a dense atmosphere. While most of the moons in the Saturnian system are small in size, Titan is, relatively speaking, gigantic. After the Sun, the eight planets and Jupiter's moon Ganymede (moon), Titan is the most massive object in the Solar System. Titan comprises more than 90 percent of the mass in orbit around Saturn, including the rings, and the other moons range from one hundredth to one hundred millionth its mass.
Traditionally, most of Saturn's other moons are named after
Titan (mythology) of Greek mythology. This started because
John Herschel—son of
William Herschel, discoverer of Mimas and Enceladus—suggested doing so in his 1847 publication
Results of Astronomical Observations made at the Cape of Good Hope,Herschel, J.;
Results of Astronomical Observations made at the Cape of Good Hope, 1847 —as reported by Lassell, W.; Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 3 (January 14, 1848), pp. 42–43 because they were the sisters and brothers of Cronus (the Greek Saturn).
For a timeline of discovery dates, see Timeline of discovery of Solar System planets and their natural satellites.
History and exploration
/
European Space Agency.
Ancient times and observation
Saturn has been known since prehistoric times.{{cite web|title = Saturn > Observing Saturn|url = http://www.nmm.ac.uk/server/show/conWebDoc.13852/viewPage/5|publisher = National Maritime Museum, the god [Saturn (mythology), from which the planet takes its name, was the god of the agricultural and harvest sector. The Romans considered Saturnus the equivalent of the Greek mythology Kronos. The Greeks had made the outermost planet sacred to Kronos, and the Romans followed suit.
In Jyotisha, there are nine astrological objects, known as
Navagrahas. Saturn, one of them, is known as "Sani" or "Shani," the Judge among all the planets, and determines everyone according to their own performed deeds bad or good.{{cite web] and Japanese culture designated the planet Saturn as the
earth star (土星). This was based on Five elements (Chinese philosophy) which were traditionally used to classify natural elements. In ancient
Hebrew language, Saturn is called 'Shabbathai'. Its angel is Cassiel. Its intelligence, or beneficial spirit, is Agiel (layga), and its spirit (darker aspect) is Zazel (lzaz). In
Ottoman Turkish and in
Malay language, its name is 'Zuhal', derived from Arabic language زحل.
Saturn's rings require at least a 75 mm diameter telescope to resolve and thus were not known to exist until Galileo first saw them in 1610.{{cite web] used greater telescopic magnification that the rings were assumed to be rings. Huygens also discovered Saturn's moon Titan (moon). Some time later,
Jean-Dominique Cassini discovered four other moons: Iapetus (moon), Rhea (moon),
Tethys (moon), and Dione (moon). In 1675, Cassini also discovered the gap now known as the Cassini Division.{{cite web|url = http://huygensgcms.gsfc.nasa.gov/Shistory.htm|title = Saturn: History of Discoveries|accessdate = 2007-07-15|last = Micek|last = Catherine-->
No further discoveries of significance were made until 1789 when
William Herschel discovered two further moons,
Mimas (moon) and
Enceladus (moon). The irregularly shaped satellite
Hyperion (moon), which has a orbital resonance with Titan, was discovered in 1848 by a British team.
In 1899 William Henry Pickering discovered
Phoebe (moon), 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 twentieth 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
Saturn was first visited by Pioneer 11 on September 1979. It flew within 20,000 km of the planet's cloud tops. Low resolution images were acquired of the planet and a few of its moons; the resolution of the images was not good enough to discern surface features. The spacecraft also studied the rings; among the discoveries were the thin F-ring and the fact that dark gaps in the rings are bright when viewed towards the Sun, or in other words, they are not empty of material. Pioneer 11 also measured the temperature of Titan.{{cite web|url = http://web.archive.org/web/20060130100401/http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PN10&11.html|title = The Pioneer 10 & 11 Spacecraft|accessdate=2007-07-05|publisher = Mission Descriptions-->
Voyager flybys
In November 1980, the
Voyager 1 probe visited the Saturn system. It sent back the first high-resolution images of the planet, rings, and satellites. Surface features of various moons were seen for the first time. Voyager 1 performed a close flyby of Titan, greatly increasing our knowledge of the atmosphere of the moon. However, it also proved that Titan's atmosphere is impenetrable in visible wavelengths; so, no surface details were seen. The flyby also changed the spacecraft's trajectory out from the plane of the solar system.{{cite web] 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. They also discovered the small Rings of Saturn#Maxwell_Gap gap (a gap within the
Rings of Saturn#C_Ring) and
Rings of Saturn#Keeler_Gap gap (a 42 km wide gap in the Rings of Saturn#A_Ring).
Cassini orbiter
On July 1 2004, the
Cassini–Huygens spacecraft performed the SOI (Saturn Orbit Insertion) maneuver and entered into orbit around Saturn. Before the SOI, Cassini had already studied the system extensively. In June 2004, it had conducted a close flyby of
Phoebe (moon), sending back high-resolution images and data.
Cassini's flyby of Saturn's largest moon, Titan (moon), has 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
December 25, 2004. Huygens descended onto the surface of Titan on
January 14, 2005, sending a flood of data during the atmospheric descent and after the landing. During 2005, Cassini conducted multiple flybys of Titan and icy satellites. Cassini's last Titan flyby was scheduled for
July 19,
2007.
Since early 2005, scientists have been tracking lightning on Saturn, primarily found by Cassini. The power of the lightning is said to be approximately 1000 times than that of the lightning on Earth. In addition, scientists believe that this storm is the strongest of its kind ever seen.{{cite web], 2006, NASA reported that, through images, the Cassini probe found evidence of liquid water reservoirs that erupt in
geysers on Saturn's moon Enceladus (moon). Images had also shown particles of water in its liquid state being emitted by icy jets and towering plumes. According to Dr. Andrew Ingersoll, California Institute of Technology, "Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust. What's different here is that pockets of liquid water may be no more than tens of meters below the surface."{{cite web|url = http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=639|title = NASA's Cassini Discovers Potential Liquid Water on Enceladus|accessdate = 2007-07-08|date = March 9, 2006|publisher = NASA Jet Propulsion Laboratory|first = Michael|last = Pence-->
On September 20, 2006, a Cassini probe photograph revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. Apparently, the source of this ring is the result of the crashing of a meteoroid off two of the moons of Saturn. {{cite web].{{cite web|url = http://news.bbc.co.uk/2/hi/science/nature/6449081.stm|title = Probe reveals seas on Saturn moon|publisher = BBC|last =|first =|accessdate = 2007-09-26|date = March 14, 2007-->
In October 2006, the probe detected a 5,000 km diameter hurricane with an eyewall at Saturn's South Pole.{{cite web|url = http://news.bbc.co.uk/2/hi/science/nature/6135450.stm|title = Huge 'hurricane' rages on Saturn|publisher = BBC|last = Rincon|first = Paul|accessdate = 2007-07-12|date = November 10, 2006-->
As of 2006, the probe has discovered and confirmed 4 new satellites. Its primary mission will end in 2008 when the spacecraft will be expected to have completed 74 orbits around the planet. The probe, however, is expected to have at least one mission extension.
Best viewing
Saturn is the most distant of the five planets easily visible to the naked eye, the other four being Mercury (planet),
Venus,
Mars, and
Jupiter (Uranus and occasionally
4 Vesta are visible to the naked eye in very dark skies), and was the last planet known to early astronomers until Uranus was discovered in 1781. Saturn appears to the naked eye in the night sky as a bright, yellowish star varying usually between magnitude +1 and 0 and takes approximately 29½ years to make a complete circuit of the ecliptic against the background constellations of the zodiac. Optical aid (large binoculars or a telescope) magnifying at least 20X is required to clearly resolve Saturn's rings for most people.
While it is a rewarding target for observation for most of the time it is visible in the sky, Saturn and its rings are best seen when the planet is at or near opposition (astronomy) (the configuration of a planet when it is at an
elongation of 180° and thus appears opposite the Sun in the sky). During the opposition of December 17
2002, Saturn appeared at its brightest due to a favorable orientation of the rings relative to the Earth.{{cite web|url = http://findarticles.com/p/articles/mi_qa4015/is_200301/ai_n9338203|title = SATURN IN 2002-03|accessdate = 2007-10-14|last = Schmude|first = Richard W Jr|date = 2003|publisher = Georgia Journal of Science-->
See also
References
External links
- Introduction to Saturn by NASA's Solar System Exploration
- Saturn Fact Sheet, by NASA
- Cassini-Huygens mission to Saturn, by NASA
- Research News about Saturn
- General information about Saturn
- Studies on the Rings of Saturn
BBC - Science & Nature - Space - Saturn
Sail to Saturn with BBCi's guide to the Solar System ... DEFINITION The second largest planet in the Solar System, sixth in line from the Sun.
BBC - Weather Centre - Features - The Planets - Saturn
BBC Weather Centre archive for articles and features on weather-related subjects. Information for on-line learning providing a range of detailed subject matter for all aspects of ...
SATURN
Description goes here... ... is a specialist underwriting agency formed in 1996 to provide. Professional Indemnity Insurance
Saturn the Gatekeeper
Saturn the Gatekeeper . in Esoteric Astrology. artwork by Jean-Luc Bozzoli. Esoteric ruler of Capricorn . Planet of the Third Ray. Saturn is representative of the Law of Economy on ...
Saturn - Wikipedia, the free encyclopedia
Saturn ([ˈsætɚn] (help · info) [9]) is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Along with the planets Jupiter, Uranus ...
Saturn
Saturn, the sixth planet from the Sun, has the most spectacular set of rings in the solar system. We now know that Saturn has moons in addition to its complex ring system.
Saturn - Student Administration
Register as a New User (Staff Members Only): To register as a Saturn WEB User , please follow the link below: as a Saturn WEB User For more information about the ...
Solar System Exploration: Planets: Saturn
The Solar System Exploration Home Page is part of NASA's Office of Space Science and describes NASA's program to explore the solar system.
Saturn Communications Group Ltd - Group Homepage
Saturn Communications Group Ltd - Saturn Visual Solutions Ltd - Connectvision - Wigan ... Saturn Communications Group redefines the communication channels of organisations by ...
Saturn | Homepage - New 2008 Cars, SUVs, & Crossover Vehicles
Saturn | Saturn's Official web site & home page for New Cars, SUVs & Crossover Vehicles. 2008 models include the VUE, OUTLOOK, AURA, SKY and ASTRA.
