SATURN

Data from Wikipedia and NASA (C)

Saturn is the sixth planet of the solar system in order of distance from the Sun. It is a gaseous giant, the second after Jupiter. In the nocturnal sky of the Earth appears like a star of first magnitude of yellowish color

History

Saturn is the last of the easy visible planets to nacked eye, therefore it was known sin from the antiquity. However the first astronomer to observe of a lengthened shape was Galileo Galilei, than with still imperfect lens saw only an oblong object. In the time then, the variation of the visual angle of rings, showed it a various aspect, for this reason he defined it as a planet "bizzarro". The furthest observations will reveal a planet with rings and satellites that rotates around.

Observation from Earth

The better moment in order to observe Saturn and its rings is the opposition (when the elongation of the planet is 180°, and it finds itself therefore in the opposite part of sky to the Sun). In all these cases the diameter of Saturn is too much small for being able to perceive it to eye knot, and the planet will always appears like a point. A binoculars or a telescope of modest power for being able are necessary to distinguish the disc of the planet and rings. With a telescope of a diameter greater of 150 milimeter, Saturn shows perfectly the structure of rings with the division of Cassini and in the best atmospheric conditions also the division of Encke. The surface of the planet shows a series of regular bands, lacking in an appearing activity. They show to the maximum a colour variation in the course of the time, or a irregular presence of WOS. It is the much spectacular periodic observation of rings hiding, a perfect alignment with the Earth that happens every 14 or 16 years. In these occasions the planet temporary loses the visibility of rings, showing entire its disc. Moreover it is possible to observe the satellites inside of the structure of rings, otherwise hidden from the extreme vicinity.

Orbital parameters

Saturn appear visibly crushed to the poles: its diameters equatorial and polar defer nearly 10% (120 536 km against 108 728 km). This shape is the result of its fast rotation and its composition fluid, easy to become deformed itself. Also the other gaseous giants are deform in analogous way, but in way the much less obvious one. Saturn is also the only planet of the solar system with a medium density inferior to that one of the water: only 0,69 g/cm3. In truth the medium value is a combination of density many lowlands, in the atmosphere of the planet, and elevated to the inside, sure greater density more of that one of the water. Saturn orbit around the Sun to a medium distance of 1,427 billions of km, covering a complete revolution in 29,458 earth’s years. Its orbit is tilted of 2,488° regarding the ecliptic and is eccentric of a factor 0,0560. To its distance, the sunlight appears 100 times less intense regarding the measures carried out from Earth. With an equal mass to 95 times and an equal volume to 700 times that earthling, Saturn is the second planet of the solar system after Jupiter. The axis of rotation is tilted of 26,73 degrees, giving to the planet a cycle of seasons analogous to that earthling and Martian, but much longer. The period of rotation of Saturn on itself varied to second of the quota; the superior layers, in the equatorial regions, employ 10,233 hours to complete a complete turn, while nucleus and cape rotate in 10,675 hours.

Atmosphere

The atmosphere of Saturn shows bands similar to those of Jupiter, but many more weak and close to the Equator. They are so that never not to have been observed before the arrival of the Voyager probes. From then the telescopes to Earth are improved the point of being able to lead regular observations of the atmospheric characteristics of Saturn. They have been found oval storms of long life and much similar to those of Jupiter. In 1990 the Telescope Spaces Hubble observed an enormous white cloud close to the Equator of the planet, and an other was observed in 1994. The atmosphere is composed mainly of hydrogen and helium; that one of Saturn contains however a greater percentage of hydrogen, beyond to an amount of phosphorus and arsenic approximately 10 times. Also in the case of Saturn, like for Jupiter, it has been possible to characterize through the infrared spectroscopy the presence of infinitesimal concentrations of carbon monoxide, fosfina, idruro of germanium and arsine. Perhaps these chemical compounds, than normally could not exist in an atmosphere made up of hydrogen and helium, are originated in chemistries reactions and then are pushes until the visible atmospheric level of the planet from strong convettivei motions. A substantial difference between atmospheres of Jupiter and Saturn is the presence of clear and dark bands, especially near the Equator, much obvious in the first one but extremely soffuse and little contrasted in the other. The reason is probably the smaller atmospheric temperature of Saturn (130 K in the high atmosphere), that it favors the cloud formation to a greater depth regarding Jupiter. The saturnian atmosphere is covered from strong winds, that blow until 1800 km/h near the Equator. They are moreover present cyclones, above all to the high latitudes, from the relatively short duration and the maximum dimensions of approximately 1200 km.

Inner structure

The inside of Saturn is similar to that one of Jupiter, with a full of rocks nucleus, a liquid metallic hydrogen layer over of it, and a molecular hydrogen layer still more over. They are present iced traces of several elements. The inside of Saturn is much warmth (12 000 K in the nucleus), and the entire planet emits in the space more energy than that one that it receives from the Sun. The greater part of this energy comes from a slow gravitational jam called mechanism of Kelvin-Helmholtz, but it seems that such phenomenon pack-saddles not to explain the amount of observed energy. A proposal in order to explain the heat in more is the reduction than helium drops a lot to the inside of Saturn, that it would generate heat for clutch against surrounding hydrogen. Saturn is much similar one in the structure to Jupiter and the composition to the Sun being composed for 75% of hydrogen and 25% of helium, with traces of water, methane and ammonia. In the external layer is present an atmosphere where clear and dark parallels bands are alternated to the Equator with cyclonic perturbations and cloud formations; all it degrades in the below zone, the liquid molecular hydrogen and helium ocean that covering between 0,2 and 0,5 planetary radius to a pressure of 3 million atmospheres where it dominates the liquid metallic hydrogen to a temperature of approximately 20 000°C. Subsequently, to the center of the planet, the nucleus is present, than measure 0,2 planetary radii, approximately the dimensions of the Earth, with a temperature of approximately 12 000°C and a pressure of 8 million atmospheres, formed from silicati ferrous and ice. Saturn like Jupiter, irradiates a double energy of that it receives from the Sun, is believed that the helium being heavier of hydrogen compresses and of consequence free heat that for high convection migrates in the atmosphere.

Natural satellites

Saturn possess an elevated number of natural satellites: they know 50 between confirmed and probable, of which 12 discoveries in 2005 thanks to the Japanese telescope Subaru; only 30 are named. It will not be never possible to quantify with precision their number, because technically all the small iced bodies that compose rings of Saturn are from considering satellites. The saturnian satellite more interesting is Titano, the only satellite of the solar system to possess a dense atmosphere. The great number of satellites and the presence of rings render very complex the dynamics of the system of Saturn. The rings are influence from the movements of the satellites, that cause marked divisions, and the tidial interaction with Saturn provocates effects disturbing the orbits of the smaller satellites.

Nome		Diametro medio	Massa	Raggio orbitale medio	Periodo orbitale	Scoperta	Gruppo
Saturno XVIII	Pan	35×35×23 km	2,7×10¹⁵ kg	133 583 km	0,575 giorni	1990
Saturno XXXV	Dafni	7 km	?	136 505 km	0,59537 giorni	2005
Saturno XV	Atlante	40×20 km	?	137 670 km	0,6019 giorni	1980
Saturno XVI	Prometeo	145×85×62 km	0,270×10¹⁸ kg	139 350 km	0,6130 giorni	1980
Saturno XVII	Pandora	114×84×62 km	0,220×10¹⁸ kg	141 700 km	0,6285 giorni	1980
Saturno XI	Epimeteo	144×108×98 km	0,560×10¹⁸ kg	151 422 km	0,6942 giorni	1980
Saturno X	Giano	196×192×150 km	2,01×10¹⁸ kg	151 472 km	0,6945 giorni	1966
Saturno I	Mimante	397 km	38,0×10¹⁸ kg	185 520 km	0,942422 giorni	1789
Saturno XXXII	Metone	3 km	?	194 000 km	1,01 giorni	2004
Saturno XXXIII	Pallene	4 km	?	211 000 km	1,14 giorni	2004
Saturno II	Encelado	499 km	73,0×10¹⁸ kg	238 020 km	1,370218 giorni	1789
Saturno XIII	Telesto	34×28×36 km	?	294 660 km	1,887802 giorni	1980
Saturno III	Teti	1 060 km	0,622×10²¹ kg	294 660 km	1,887802 giorni	1684
Saturno XIV	Calipso	34×22×22 km	?	294 660 km	1,887802 giorni	1980
Saturno XII	Elena	36×32×30 kg	?	377 400 km	2,736915 giorni	1980
Saturno IV	Dione	1 118 km	1,05×10²¹ kg	377 400 km	2,736915 giorni	1684
Saturno XXXIV	Polluce	13 km	?	377 400 km	2,736915 giorni	2004
Saturno V	Rea	1 528 km	2,49×10²¹ kg	527 040 km	4,5175 giorni	1672
Saturno VI	Titano	5 151 km	135×10²¹ kg	1 221 850 km	15,94542 giorni	1655
Saturno VII	Iperione	410×260×220 km	17,7×10¹⁸ kg	1 481 100 km	21,27661 giorni	1848
Saturno VIII	Giapeto	1 460 km	1,88×10²¹ kg	3 561 300 km	79,33018 giorni	1671
Saturno XXIV	Kiviuq	16 km	3,3×10¹⁵ kg	11 365 000 km	1,2298 anni	2000	Gruppo Inuit
Saturno XXII	Ijiraq	12 km	?	11 442 000 km	1,2361 anni	2000	Gruppo Inuit
Saturno IX	Febe	220 km	4,00×10¹⁸ kg	12 944 300 km	-1,5009 anni	1899	Gruppo Nordico
Saturno XX	Paaliaq	22 km	?	15 199 000 km	1,8806 anni	2000	Gruppo Inuit
Saturno XXVII	Skadi	8 km	?	15 647 000 km	-1,9956 anni	2000	Gruppo Nordico
Saturno XXVI	Albiorix	32 km	?	16 404 000 km	2,1451 anni	2000	Gruppo Gallico
Saturno XXXVII	Bebhionn	6 km	?	16 950 000 km	2,25 anni	2004	Gruppo Inuit
Saturno XLVII	Skoll	6 km		17 610 000 km	-2,3792 anni	2006
Saturno XXVIII	Erriapo	10 km	?	17 616 000 km	2,3871 anni	2000	Gruppo Gallico
S/2007 S 1		7 km	?	17 910 600 km	-2,44 anni	2007	Gruppo Inuit
S/2006 S 4		6 km		18 105 000 km	-2,4778 anni	2006
Saturno XXIX	Siarnaq	40 km	?	18 160 000 km	2,4452 anni	2000	Gruppo Inuit
Saturno XLIV	Hyrokkin	8 km		18 217 125 km	-2,4970 anni	2004
Saturno XXI	Tarvos	15 km	?	18 247 000 km	2,5342 anni	2000	Gruppo Gallico
S/2004 S 13		6 km	?	18 450 000 km	-2,48 anni	2004	Gruppo Nordico
S/2006 S 6		6 km		18 600 000 km	-2,5791 anni	2006
S/2004 S 17		4 km	?	18 600 000 km	-2,70 anni	2004	Gruppo Nordico
Saturno XXV	Mundilfari	7 km	?	18 722 000 km	-2,6048 anni	2000	Gruppo Nordico
Saturno XXXVIII	Bergelmir	6 km	?	18 750 000 km	-2,76 anni	2004	Gruppo Nordico
S/2006 S 1		6 km		18 981 135 km	-2,6558 anni	2006
Saturno XXXVI	Ægir	6 km	?	19 350 000 km	-2,81 anni	2004	Gruppo Nordico
Saturno XXXI	Narvi	7 km	?	19 370 700 km	-2,7558 anni	2003	Gruppo Nordico
S/2004 S 12		5 km	?	19 650 000 km	-2,87 anni	2004	Gruppo Nordico
Saturno XXXIX	Bestla	7 km	?	19 650 000 km	-2,88 anni	2004	Gruppo Nordico
Saturno XXIII	Suttungr	7 km	?	19 666 700 km	-2,8192 anni	2000	Gruppo Nordico
Saturno XL	Farbauti	5 km	?	19 800 800 km	-2,95 anni	2004	Gruppo Nordico
S/2004 S 7		6 km	?	19 800 000 km	-3,02 anni	2004	Gruppo Nordico
Saturno XLIII	Hati	6 km	?	19 950 000 km	-2,96 anni	2004	Gruppo Nordico
Saturno XXX	Thrymr	7 km	?	20 810 300 km	-3,07 anni	2000	Gruppo Nordico
S/2006 S 3		6 km		21 132 000 km	-3,13 anni	2006
Saturno XLI	Fenrir	4 km	?	22 200 000 km	-3,48 anni	2004	Gruppo Nordico
Saturno XLII	Fornjot	6 km	?	22 200 000 km	-3,71 anni	2004	Gruppo Nordico
Saturno XLVIII	Surtur	6 km		22 290 000 km	-3,39 anni	2006
Saturno XLV	Kari	7 km		22 350 000 km	-3,41 anni	2006
Saturno XIX	Ymir	18 km	?	23 174 600 km	-3,61 anni	2000	Gruppo Nordico
Saturno XLVI	Loge	6 km		23 190 000 km	-3,60 anni	2006

Although the distinction is not defined rigorously, the moons of Saturn can be divided again in six groups. The "shepherds" of rings: the satellites "shepherds" are moons that orbit immediately to the inside or to the outside of the ring system of a planet. They have the effect to model to the rings giving edges or creating discontinuity between of they. The satellites shepherds of rings of Saturn are Pan, Atlas, Prometeo, Ancient lute, Epimeteo, and Giano, beyond to the satellites not confirmed S/2004 4 S and S/2004 S 3. The great inner satellites: the satellites nearer Saturn orbit inside of the tenuous ring E;they are Mimante, Encelado, Teti and Dione. The situation is more complex; in the years 2000 the discovery of two smaller natural satellites, Metone and Pallene, that orbit inside of this group, between Mimante and Encelado. The group comprises also numerous co-orbiting satellites, that they constitute one class to himself. Co-orbiting moons: the co-orbiting moons are a prerogative only of the saturnian system. They are troiani satellites, that share the same orbit around Saturn with an other moon to a such angular distance not to never collidere with it. Teti has two co-orbiting ones: Telesto and Calipso, like pure Dione: Elena and Polideuce. Large external moons: the largest moons of Saturn orbit all beyond the ring and and can be considered a distinguished group. They are Guilty, Iperione (that it is relatively small), Titano and Giapeto.

Rings

Saturn possess a magnificent planetary ring system, composed from million small iced objects, of a kilometer or less, orbiting around the planet on its equatorial plan, and organized in a flat ring. Since the axis of rotation of Saturn is tilted regarding its orbital plan, also the rings turn out tilt. This "granular" nature of rings was demonstrated for theoretical way since the 1859 from the Scottish physicist J. C. Maxwell. The rings begin to a height of approximately 6600 kilometers from the top of clouds of Saturn and they extend until 120 000 kilometers, little less than a third party of the Earth-Moon distance. Their thickness is medium equal to 3 km. Their discovery is due to Christiaan Huygens, in 1655; previously already Galileo Galilei had noticed of the unusual swells to sides of the planet, but the insufficient power of its telescope and the particular position of Saturn to the age - with closed rings - had not allowed it to distinguish the shape with clarity. The rings are divided in seven bands, separated of divisions that are nearly empty. The organization in bands and divisions turns out from a complex dynamics still not very comprised, but the so-called shepherds satellites play sure a role. The origin of rings is disowned. There are two main hypotheses: that they are the result of the destruction of a satellite of Saturn, to work of a collision with a comet or an other satellite, or that they are a "remainder" of the material from which Saturn was formed that is not successful to assemble in an only body. The theories suggest them that the rings are unstable and have a relatively short life: a few million years would have to be dispersed or to fall on the same planet. This would favor a recent origin of rings. The greater division was discovered from Cassini in 1675, and is called division of Cassini. Subsequently Bond discovered that the inner ring was subdivided too(1850). Also the external ring is subdivided from that one that division of Enke is called. The various rings come call with letters of the alphabet. Originally the sequence left from the inner (A) towards outside (B, C, etc), but with the ring discovery new it is all mixed letters.

Nome	Distanza dal centro di Saturno (km)	Larghezza (km)	Chiamato in onore di
Anello D	60.000 - 72.600	12.600
Divisione di Guerin	72.600 - 73.800	1.200
Anello C	73.800 - 92.000	17,500
Divisione di Colombo	77.800	100
Divisione di Maxwell	87.500	270	James Clerk Maxwell
Anello B	92.000 - 117.500	25.500
Divisione di Cassini	117.500 - 122.200	4,700	Giovanni Cassini
Separazione di Huygens	117.680	285-440	Christiaan Huygens
Anello A	122.200 - 136.800	14,600
Divisione di Encke	133.570	325	Johann Encke
Divisione di Keeler	136.530	35	James Keeler
R/2004 S1	137.630	190 (?)
R/2004 S2	138.900	(?)
Anello F	140.210	30-500
Anello G	165.800 - 173.800	8.000
Anello E	180.000 - 480.000	300.000

Exploration of Saturn

Saturn was visited for the first time from the American probe Pioneer 11 in 1979, and two years following from the probes Voyager 1 and Voyager 2. All and the three probes executed the fly-by, that is they pass beside the planet and continue beyond. The Cassini-Huygens probe has as main scope the exploration of the system of Saturn and in particular of its moon Titano. It has arrived first July 2004 and is from then in orbit around the planet. The same mission has allowed to observe, in 2005, liquid methane lakes and rivers on the surface of Titano, and in the 2006 jets of vapor of water emitted from the surface of the satellite Encelado: it is the first sure water observation not iced outside of the Earth.