Francais | English | Espanõl

From Wikipedia, the free encyclopedia

Saturn has 56 confirmed natural satellites.

Contents 1 Introduction 2 Table of known moons 3 Grouping the moons 3.1 The ring shepherds 3.2 The co-orbitals 3.3 The inner large moons 3.4 The Trojan moons 3.5 The outer large moons 3.6 Irregular satellites 3.6.1 The Inuit group 3.6.2 The Norse group 3.6.3 The Gallic group 4 Naming notes 5 See also 6 References

[edit] Introduction

Image:PIA08235.jpg Saturn is currently known to have 56 moons, many of which were discovered very recently, and 3 additional un-confirmed, hypothetical moons. However, a precise number of moons can never be given, as there is no objective dividing line between the anonymous orbiting fragments that form Saturn's ring system and the larger objects that have already been named as moons.

Before the advent of telescopic photography, eight moons of Saturn were discovered by direct observation using an optical telescope:

• Titan, discovered in 1655 by Christiaan Huygens;
• Tethys, Dione, Rhea and Iapetus (the "Sidera Lodoicea") discovered 1671-1684 by Giovanni Domenico Cassini;
• Mimas and Enceladus, discovered 1789 by William Herschel;
• Hyperion, discovered 1848 by W.C. Bond, G.P. Bond and Lassell.

The use of long-exposure photographic plates made it possible to discover additional moons:

• Phoebe was the first satellite discovered by telescopic photograph in 1899 by W.H. Pickering.
• In 1966, the satellites Janus and Epimetheus were observed, but not confirmed, and it was not realized that there were two distinct moons sharing an orbit.

The study of the outer planets has since been revolutionized, first by the use of unmanned space probes, and then by advances in telescopy:

• From 1980, when the first of the the Voyager space probes arrived at Saturn, to 1990, analysis of Voyager images revealed 8 more moons in the inner Saturnian system. The last discovered was Pan.
• A survey starting in late 2000 found 13 new moons orbiting Saturn at a great distance in orbits that suggest they are fragments of larger bodies captured by Saturn's gravitational pull (Nature vol. 412, pp. 163–166).
• The Cassini mission, which arrived at Saturn in the summer of 2004, discovered three small moons in the inner Saturnian system as well as three suspected but unconfirmed moons in the F Ring. This increased the total to 37 moons, confirmed and unconfirmed.
• On November 16, 2004, Cassini scientists announced that the structure of Saturn's rings indicates the presence of several more moons orbiting within the rings, but only one, Daphnis, has been visually confirmed so far (its confirmation was announced on May 6, 2005).[1].
• On May 3, 2005, astronomers using the Mauna Kea Observatory announced the discovery of 12 more small outer moons [2][3].
• On June 30, 2006, astronomers using the Subaru 8.2 m telescope announced the discovery of 9 more small outer moons [4].

The spurious satellite Chiron, "discovered" in 1861, is now known not to exist. Themis, "discovered" in 1905, also was later proven not to exist.

[edit] Table of known moons

The Saturnian moons are listed here by orbital period, from shortest to longest. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in light purple. Titan, which is planetary in size, has darker highlighting. The irregular (captured) moons are indicated in grey: light grey for prograde satellites, darker grey for retrograde satellites.

Order	Name (spheroidal moons in bold) (Pronunciation key)			Image	Diameter (km)	Semi-major axis (km)	Orbital period (d)	Inclination (°) (to Saturn's equator)	Position	Discovered
1	XVIII	Pan	ˈpæn		30 (35 × 35 × 23) <ref name="Porco06">C.C. Porco et al. (2006). "Physical characteristics and possible accretionary origins for Saturn's small satellites". Bulletin of the American Astronomical Society 37: 768.</ref>	133,584 <ref name="Spitale06">J.N. Spitale et al (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132: 692.</ref>	+0.57505 <ref name="Spitale06" />	0.000°	in Encke Division	1990
2	XXXV	Daphnis	ˈdæfnɪs	Image:PIA06237.jpg	6 − 8	136,505 <ref name="Spitale06" />	+0.59408 <ref name="Spitale06" />	0.000°	in Keeler Gap	2005
3	XV	Atlas	ˈætləs		31 (46 × 38 × 19) <ref name="Porco06" />	137,670 <ref name="Spitale06" />	+0.60169 <ref name="Spitale06" />		outer A Ring shepherd	1980
4	XVI	Prometheus	proʊˈmiθiəs		86 (119 × 87 × 61) <ref name="Porco06"/>	139,380 <ref name="Spitale06" />	+0.61299 <ref name="Spitale06" />	0.000°	inner F Ring shepherd	1980
*		S/2004 S 6 <ref name="note_2">It is not yet clear if these are real satellites or merely persistent clumps within the F Ring</ref>		Image:S2004 S6.jpg	~3−5	140,130 <ref name="Spitale06" />	+0.61801 <ref name="Spitale06" />		*Uncertain objects around the F-ring	2004
*		S/2004 S 4 <ref name="note_2a">S/2004 S4 was most likely a transient clump − it has not been recovered since the first sighting.</ref>			~3−5	~140,100 <ref name="PGJ"> PGJ Astronomie webpage (Gilbert Javaux). Note that the F ring is centered at ~140,180 km </ref>	+0.619 <ref name="note_1">Computed from the semi-major axis using the IAU-MPC Natural Satellites Ephemeris Service µ value</ref>			2004
*		S/2004 S 3 <ref name="note_2" />			~3−5	~140,300 <ref name="see S3"> See references in S/2004 S 3</ref>	~ +0.62			2004
5	XVII	Pandora	pænˈdoʊrə		81 (103 × 80 × 64) <ref name="Porco06" />	141,720 <ref name="Spitale06"/>	+0.62850 <ref name="Spitale06"/>		outer F Ring Shepherd	1980
6	XI	Epimetheus	ˌɛpɪˈmiθiəs		113 (135 × 108 × 105) <ref name="Porco06" />	151,422 <ref name="Spitale06"/>	+0.69433 <ref name="Spitale06"/>	0.335°	co-orbitals	1980
7	X	Janus	ˈdʒeɪnəs		179 (193 × 173 × 137) <ref name="Porco06" />	151,472 <ref name="Spitale06"/>	+0.69466 <ref name="Spitale06"/>	0.165°		1966
8	I	Mimas	ˈmaɪməs		397 (415 × 394 × 381) <ref name="note_10">Source: Thomas et al. 2006</ref>	185,404 <ref name="note_3">Computed from the period using the IAU-MPC Natural Satellites Ephemeris Service µ value</ref>	+0.942422 <ref name="note_4">Source: NASA</ref>	1.566°		1789
9	XXXII	Methone	mɪˈθoʊni		3	194,440 <ref name="Spitale06" />	+1.00957 <ref name="Spitale06" />			2004
10	XXXIII	Pallene	pæˈlini		4	212,280 <ref name="Spitale06" />	+1.15375 <ref name="Spitale06" />			2004
11	II	Enceladus	ɛnˈsɛlədəs	Image:Enceladus from Voyager.jpg	504 (513 × 503 × 497) <ref name="note_10" />	237,950 <ref name="note_3" />	+1.370218 <ref name="note_4" />	0.010°	In the thick of E ring	1789
12	III	Tethys	ˈtiθɪs	Image:Tethys cassini.jpg	1066 (1081 × 1062 × 1055) <ref name="note_10" />	294,619 <ref name="note_3" />	+1.887802 <ref name="note_4" />	0.168°		1684
12a	XIII	Telesto	tɪˈlɛstoʊ		24 (29 × 22 × 20) <ref name="Porco06" />			1.158°	leading Tethys trojan	1980
12b	XIV	Calypso	kəˈlɪpsoʊ		21 (30 × 23 × 14) <ref name="Porco06" />			1.473°	trailing Tethys trojan	1980
15	IV	Dione	daɪˈoʊni		1123 (1128 × 1122 × 1121) <ref name="note_10" />	377,396 <ref name="note_3" />	+2.736915 <ref name="note_4" />	0.002°		1684
15a	XII	Helene	ˈhɛlɪni		33 (36 × 32 × 30)			0.212°	leading Dione trojan	1980
15b	XXXIV	Polydeuces	ˌpɒlɪˈdjusiz	Image:Polydeuces.jpg	3.5 <ref name="note_11">Source: Porco et al. 2005</ref>				trailing Dione trojan	2004
18	V	Rhea	ˈriə		1529 (1535 × 1525 × 1526) <ref name="note_10" />	527,108 <ref name="note_5">Source: IAU-MPC Natural Satellites Ephemeris Service</ref>	+4.518212 <ref name="note_5" />	0.327°		1672
19	VI	Titan	ˈtaɪtən	Image:Titan in natural color Cassini.jpg	5151	1,221,930 <ref name="note_3" />	+15.94542	1.634°		1655
20	VII	Hyperion	haɪˈpiriən	Image:Hyperion true.jpg	292 (360 × 280 × 225)	1,481,010 <ref name="note_3" />	+21.27661	0.568°		1848
21	VIII	Iapetus	aɪˈæpɪtəs	Image:Iapetus true.jpg	1472 (1494 × 1498 × 1425) <ref name="note_10" />	3,560,820	+79.3215 <ref name="note_1" />	7.570°		1671
22	XXIV	Kiviuq	ˈkiviuk		~16	11 294 800 <ref name="note_5" />	+448.16 <ref name="note_5" />	49.087°	Inuit group	2000
23	XXII	Ijiraq	ˈijirak		~12	11 355 316 <ref name="note_5" />	+451.77 <ref name="note_5" />	50.212°		2000
24	IX	Phoebe	ˈfibi		220 (230 × 220 × 210)	12 869 700	-545.09<ref name="note_1" /><ref name="note_6">Negative orbital periods indicate a retrograde orbit around Saturn (opposite to the planet's rotation)</ref>	173.047°	Norse group	1899
25	XX	Paaliaq	ˈpaliak		~22	15 103 400 <ref name="note_5" />	+692.98 <ref name="note_5" />	46.151°	Inuit group	2000
26	XXVII	Skathi	ˈskaði		~8	15 672 500 <ref name="note_5" />	-732.52 <ref name="note_4" /><ref name="note_6" />	149.084°	Norse (Skathi) Group	2000
27	XXVI	Albiorix	ælˈbaɪʊrɪks		~32	16 266 700 <ref name="note_5" />	+774.58 <ref name="note_5" />	38.042°	Gallic group	2000
28	XXXVII	S/2004 S 11	-		~6	17 153 520 <ref name="note_5" />	+838.77 <ref name="note_5" />	40.484°	Inuit group	2004
29	XXVIII	Erriapo	ˈɛriˌæpoʊ		~10	17 236 900 <ref name="note_5" />	+844.89 <ref name="note_5" />	38.109°	Gallic group	2000
30	XLVII	S/2006 S 8	-		~6	17 473 800 <ref name="note_3" />	-862.37 <ref name="note_5" />	155.624°	Norse group	2006
31	XXIX	Siarnaq	ˈsiarnak		~40	17 776 600 <ref name="note_5" />	+884.88 <ref name="note_5" />	45.798°	Inuit group	2000
32		S/2004 S 13	-		~6	18 056 300 <ref name="note_5" />	-905.85 <ref name="note_4" /><ref name="note_6" />	167.379°	Norse group	2004
33		S/2006 S 4	-		~6	18 065 700 <ref name="note_3" />	-906.56 <ref name="note_5" />	172.666°		2006
34	XLIV	S/2004 S 19	-		~8	18 168 300 <ref name="note_3" />	-914.29 <ref name="note_5" />	153.272°		2006
35		S/2006 S 6	-		~6	18 556 900 <ref name="note_3" />	-943.78 <ref name="note_5" />	162.861°		2006
36	XXI	Tarvos	ˈtarvɒs		~15	18 562 800 <ref name="note_5" />	+944.23 <ref name="note_5" />	34.679°	Gallic group	2000
37	XXV	Mundilfari	ˈmʊndɪlˌfari		~7	18 725 800 <ref name="note_5" />	-956.70 <ref name="note_4" /><ref name="note_6" />	169.378°	Norse group	2000
38		S/2006 S 1	-		~6	18 930 200 <ref name="note_3" />	-972.41 <ref name="note_5" />	154.232°		2006
39		S/2004 S 17	-		~4	19 099 200 <ref name="note_5" />	-985.45 <ref name="note_4" /><ref name="note_6" />	166.881°		2004
40	XXXVIII	S/2004 S 15	-		~6	19 104 000 <ref name="note_5" />	-985.83 <ref name="note_4" /><ref name="note_6" />	157.384°	Norse (Skathi) group	2004
41	XXXI	Narvi	ˈnarvi		~7	19 395 200 <ref name="note_5" />	-1008.45 <ref name="note_4" /><ref name="note_6" />	137.292°	Norse group	2003
42	XXIII	Suttungr	ˈsʊtʊŋgər		~7	19 579 000 <ref name="note_5" />	-1022.82 <ref name="note_4" /><ref name="note_6" />	174.321°		2000
43	XLIII	S/2004 S 14	-		~6	19 709 300 <ref name="note_5" />	-1033.05 <ref name="note_4" /><ref name="note_6" />	163.131°		2004
44		S/2004 S 12	-		~5	19 905 900 <ref name="note_5" />	-1048.54 <ref name="note_4" /><ref name="note_6" />	164.042°		2004
45	XL	S/2004 S 9	-		~5	19 984 800 <ref name="note_5" />	-1054.78 <ref name="note_4" /><ref name="note_6" />	158.361°	Norse (Skathi) group	2004
46	XXX	Thrymr	ˈθrɪmər		~7	20 278 100 <ref name="note_5" />	-1078.09 <ref name="note_4" /><ref name="note_6" />	174.524°	Norse group	2000
47	XXXVI	S/2004 S 10	-		~6	20 482 900 <ref name="note_5" />	-1094.46 <ref name="note_4" /><ref name="note_6" />	167.425°		2004
48	XXXIX	S/2004 S 18	-		~7	20 570 000 <ref name="note_5" />	-1101.45 <ref name="note_4" /><ref name="note_6" />	147.395°	Norse (Skathi) group	2004
49		S/2004 S 7	-		~6	20 576 700 <ref name="note_5" />	-1101.99 <ref name="note_4" /><ref name="note_6" />	165.596°	Norse group	2004
50		S/2006 S 3	-		~6	21 076 300 <ref name="note_3" />	-1142.37 <ref name="note_5" />	150.817°		2006
51	XLI	S/2004 S 16	-		~4	21 930 644 <ref name="note_5" />	-1212.53 <ref name="note_4" /><ref name="note_6" />	162.832°		2004
52	XLVIII	S/2006 S 7	-		~6	22 288 916 <ref name="note_3" />	-1242.36 <ref name="note_5" />	166.918°		2006
53	XLV	S/2006 S 2	-		~7	22 321 200 <ref name="note_3" />	-1245.06 <ref name="note_5" />	148.384°		2006
54	XIX	Ymir	ˈɪmɪr		~18	22 429 673 <ref name="note_5" />	-1254.15 <ref name="note_4" /><ref name="note_6" />	172.143°		2000
55	XLVI	S/2006 S 5	-		~6	22 984 322 <ref name="note_3" />	-1300.95 <ref name="note_5" />	166.539°		2006
56	XLII	S/2004 S 8	-		~6	24 504 879 <ref name="note_5" />	-1432.16 <ref name="note_4" /><ref name="note_6" />	167.886°		2004

<references />

[edit] Grouping the moons

Although the borders may be somewhat nebulous, Saturn's moons can be divided into eight groups.

[edit] The ring shepherds

Shepherd satellites are moons that orbit within, or just beyond, a planet's ring system. They have the effect of sculpting the rings: giving them sharp edges, and creating gaps between them. Saturn's shepherd moons are Pan, Daphnis, Atlas, Prometheus, Pandora, S/2004 S 3, in addition to the unconfirmed moons S/2004 S 4 and S/2004 S 6.

[edit] The co-orbitals

Janus and Epimetheus are co-orbital moons. These two moons are of roughly equal size and have orbits with only a few kilometers difference in diameter, close enough that they would collide if they attempted to pass each other. Instead of colliding, however, their gravitational interaction causes them to swap orbits every four years. See Epimetheus' article for a more detailed explanation of this arrangement.

[edit] The inner large moons

The innermost large moons of Saturn orbit within its tenuous E Ring. They are Mimas, Enceladus, Tethys and Dione.

Two recently discovered tiny moons also orbit within this group: Methone and Pallene. So too do the co-orbital moons that form a group of their own (see below).

[edit] The Trojan moons

Main article: Trojan moon

Trojan moons are another kind of co-orbital. Like the other co-orbitals, they are a feature unique to the Saturnian system. They are moons that orbit at exactly the same distance from Saturn as another moon, but at such a distance from the other moon that they never collide. Tethys has two tiny co-orbitals Telesto and Calypso, and Dione also has two, Helene and Polydeuces. All four of these moons orbit in the larger moons' L4 or L5 Lagrangian points, one in each point.

[edit] The outer large moons

Saturn's largest moons all orbit beyond its E Ring and can thus be considered a distinct group. They are Rhea, Titan, Hyperion (which is relatively small and very irregular), and Iapetus.

[edit] Irregular satellites

Image:TheIrregulars SATURN.svg

[edit] The Inuit group

Main article: Saturn's Inuit group of satellites

The Inuit group are five prograde outer moons that are similar enough in their distances from Saturn and their orbital inclinations that they can be considered a group. They are Kiviuq, Ijiraq, Paaliaq, Siarnaq, and S/2004 S 11.

[edit] The Norse group

Main article: Saturn's Norse group of satellites

The Norse group are 18 retrograde outer moons that are similar enough in their distance from Saturn to be considered a group. They are Phoebe, Skathi, Narvi, Mundilfari, Suttungr, Thrymr, Ymir, S/2004 S 7 through S/2004 S 10, S/2004 S 12 through S/2004 S 19, and S/2006 S 1 through S/2006 S 8. All of these moons orbit Saturn in a retrograde direction.

[edit] The Gallic group

Main article: Saturn's Gallic group of satellites

The Gallic group are three prograde outer moons that are similar enough in their distance from Saturn and their orbital inclination that they can be considered a group. They are Albiorix, Erriapo and Tarvos.

The diagram illustrates the orbits of the irregular satellites of Saturn discovered so far¹. The eccentricity of the orbits is represented by the segments (extending from the pericentre to the apocentre) with the inclination represented on Y axis. The satellites above the axis are prograde, the satellites beneath are retrograde. The X axis is labelled in Gm (milion km) and the fraction of the Hill sphere's (gravitational influence) radius (~65 Gm for Saturn). Prograde groups: Inuit and Gallic and the retrograde Norse group are clearly identifiable (from top to bottom).

¹Named satellites are plotted in yellow; the unnamed satellites S/2004 Sxx (announced in 2005 and 2006) are plotted in white and S/2006 Sxx in grey.

[edit] Naming notes

Some asteroids share the same names as moons of Saturn: 55 Pandora, 106 Dione, 577 Rhea, 1809 Prometheus, 1810 Epimetheus, 4450 Pan. See also Name conflicts of solar system bodies.

[edit] See also

• Saturn's moons in fiction

Solar System Natural Satellites v • d • e</div>
Planetary satellites:	Terran • Martian • Jovian • Saturnian • Uranian • Neptunian
Other satellite systems:	Plutonian • Eridian • Asteroid satellites
Largest satellites:	Ganymede • Titan • Callisto • Io • Earth's Moon • Europa • Triton Titania • Rhea • Oberon • Iapetus • Charon • Umbriel • Ariel • Dione • Tethys
See also: inner satellites • trojans • irregulars • list by diameter • discovery timeline • naming

The Solar System v • d • e</div>
Image:Solar System XXVII.png
The Sun · Mercury · Venus · Earth · Mars · Ceres · Jupiter · Saturn · Uranus · Neptune · Pluto · Eris
Planets · Dwarf planets · Moons: Terran · Martian · Asteroidal · Jovian · Saturnian · Uranian · Neptunian · Plutonian · Eridian
Small bodies:   Meteoroids · Asteroids (Asteroid belt) · Centaurs · TNOs (Kuiper belt/Scattered disc) · Comets (Oort cloud)
See also astronomical objects and the solar system's list of objects, sorted by radius or mass.

[edit] References

• Saturnian Satellites Fact Sheetbg:Естествени спътници на Сатурн

br:loarennoù Sadorn (planedenn) bs:Saturnovi prirodni sateliti ca:Satèl·lits de Saturn cs:Saturnovy měsíce da:Saturns måner de:Liste der Saturnmonde es:Satélites de Saturno fr:Satellites naturels de Saturne it:Satelliti naturali di Saturno ja:土星の衛星と環 nl:Manen van Saturnus ms: Satelit semulajadi Zuhal uk:Супутники Сатурна ro:Sateliţii naturali ai lui Saturn ru:Спутники Сатурна sk:Mesiace Saturnu sv:Saturnus naturliga satelliter tr:Satürn'ün doğal uyduları zh:土星的卫星