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[[Saturn (planet)|Saturn]] has 60 named<!--- confirmation = naming and numbering, last one as of May 2007 is Saturn XLVIII (Surtur) ---> '''[[natural satellite]]s'''.
[[Saturn (planet)|Saturn]] has 60 named<!--- confirmation = naming and numbering, last one as of May 2007 is Saturn XLVIII (Surtur) ---> '''[[natural satellite]]s'''.
<!---16 moons, three of which are especially doubtful---><!--- 57 + 3 marked "*", minus 48 --->
<!---16 moons, three of which are especially doubtful---><!--- 57 + 3 marked "*", minus 48 --->


== Saturn ==
was discovered by Lillian on September 17, 146435432 BC.



==Introduction==
==Introduction==

Revision as of 17:57, 13 March 2008

File:Saturn system.jpg
The Saturnian system (photographic montage)
Moons of Saturn (photographic montage)

Saturn has 60 named natural satellites.


Saturn

was discovered by Lillian on September 17, 146435432 BC.


Introduction

Saturn's rings cut across a scene that is ruled by Titan's luminous crescent and globe-encircling haze, broken by the small moon Enceladus, whose icy jets are dimly visible at its south pole. North is up.

Saturn is known to have sixty moons, many of which were discovered only recently and may be as small as two-to-three kilometers across. Seven are large enough to have achieved hydrostatic equilibrium and so would be considered dwarf planets if they were in orbit about the Sun; indeed one of these, Titan, is massive enough to retain an atmosphere denser than our own. There have also been sightings of three objects which may be moons, as well as eight "moonlets" only a few hundred meters across in a belt within the A Ring that is estimated to contain thousands of such objects.[1] A precise number of moons can not be given, as there is no objective boundary between the countless small anonymous objects that form Saturn's ring system and the larger objects that have been named as moons.

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

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.
  • Themis, "discovered" in 1905, also was later proven not to exist.
  • 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 Voyager space probes arrived at Saturn, to 1990, analysis of Voyager images revealed eight more moons in the inner Saturnian system. The last discovered was Pan.
  • A survey starting in late 2000 found thirteen 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 thirty-seven 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).[2].
  • On May 3, 2005, astronomers using the Mauna Kea Observatory announced the discovery of twelve more small outer moons [3] [4].
  • On June 30, 2006, astronomers using the Subaru 8.2 m telescope announced the discovery of nine more small outer moons [5].
  • On April 13, 2007, Tarqeq was announced.
  • On May 1, 2007, S/2007 S 2 and S/2007 S 3 were announced.
  • On July 18, 2007, Anthe was announced.
  • On March 6, 2008, it was announced that Cassini observations of a depletion of energetic electrons in Saturn's magnetosphere near Rhea might be the signature of a tenuous ring system around Saturn's second largest moon.[1]

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 blue. 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
0 (moonlets) 0.06 to 0.14 130,000 a 3000-km band within the A ring 2007[2]
1 XVIII Pan ˈpæn
30 (35 × 35 × 23) [3] 133,584 [4] +0.57505 [4] 0.001° in Encke Division 1990
2 XXXV Daphnis ˈdæfnɨs
6 − 8 136,505 [4] +0.59408 [4] ≈ 0° in Keeler Gap 2005
3 XV Atlas ˈætləs
31 (46 × 38 × 19) [3] 137,670 [4] +0.60169 [4] 0.003° outer A Ring shepherd 1980
4 XVI Prometheus proʊˈmiːθiəs
86 (119 × 87 × 61) [3] 139,380 [4] +0.61299 [4] 0.008° inner F Ring shepherd 1980
5 XVII Pandora pænˈdɔərə
81 (103 × 80 × 64) [3] 141,720 [4] +0.62850 [4] 0.050° outer F Ring Shepherd 1980
6 XI Epimetheus ˌɛpɨˈmiːθiəs 113 (135 × 108 × 105) [3] 151,422 [4] +0.69433 [4] 0.335° co-orbitals 1980
7 X Janus ˈdʒeɪnəs
179 (193 × 173 × 137) [3] 151,472 [4] +0.69466 [4] 0.165° 1966
8 I Mimas ˈmaɪməs
397 (415 × 394 × 381) [5] 185,404 [6] +0.942422 [7] 1.566°   1789
9 XXXII Methone mɨˈθoʊni 3 194,440 [4] +1.00957 [4] 0.007° (Alkyonides) 2004
10 XLIX Anthe ˈænθi ~2 197,700 1.03650 0.1° 2007
11 XXXIII Pallene pəˈliːni
4 212,280 [4] +1.15375 [4] 0.181° 2004
12 II Enceladus ɛnˈsɛlədəs
504 (513 × 503 × 497) [5] 237,950 [6] +1.370218 [7] 0.010° In the thick of E ring 1789
13 III Tethys ˈtiːθɨs
1066 (1081 × 1062 × 1055) [5] 294,619 [6] +1.887802 [7] 0.168°   1684
13a XIII Telesto tɨˈlɛstoʊ
24 (29 × 22 × 20) [3] 1.158° leading Tethys trojan 1980
13b XIV Calypso kəˈlɪpsoʊ
21 (30 × 23 × 14) [3] 1.473° trailing Tethys trojan 1980
16 IV Dione daɪˈoʊni
1123 (1128 × 1122 × 1121) [5] 377,396 [6] +2.736915 [7] 0.002°   1684
16a XII Helene ˈhɛlɨni
File:Cassini Helene N00086680 CL.jpg
 33 (36 × 32 × 30) 0.212° leading Dione trojan 1980
16b XXXIV Polydeuces ˌpɒlɨˈdjuːsiːz
3.5 [8] 0.177° trailing Dione trojan 2004
19 V Rhea ˈriːə
1529 (1535 × 1525 × 1526) [5] 527,108 [9] +4.518212 [9] 0.327°   1672
20 VI Titan ˈtaɪtən
5151 1,221,930 [6] +15.94542 1.634°   1655
21 VII Hyperion haɪˈpɪəriən
292 (360 × 280 × 225) 1,481,010 [6] +21.27661 0.568°   1848
22 VIII Iapetus aɪˈæpɨtəs
1472 (1494 × 1498 × 1425) [5] 3,560,820 +79.3215 [10] 7.570°   1671
23 XXIV Kiviuq ˈkɪvioʊk ~16 11 294 800 [9] +448.16 [9] 49.087° Inuit group 2000
24 XXII Ijiraq ˈiːɨrɒk ~12 11 355 316 [9] +451.77 [9] 50.212° 2000
25 IX Phoebe ˈfiːbi
220 (230 × 220 × 210) 12 869 700 −545.09[10][11] 173.047° Norse group 1899
26 XX Paaliaq ˈpɑːliɒk ~22 15 103 400 [9] +692.98 [9] 46.151° Inuit group 2000
27 XXVII Skathi ˈskɒði ~8 15 672 500 [9] −732.52 [7][11] 149.084° Norse (Skathi) Group 2000
28 XXVI Albiorix ˌælbiːˈɒrɨks ~32 16 266 700 [9] +774.58 [9] 38.042° Gallic group 2000
29   S/2007 S 2 — ~6 16 560 000 −792.96 176.68° Norse group 2007
30 XXXVII Bebhionn ˈbɛviːn ~6 17 153 520 [9] +838.77 [9] 40.484° Gallic group 2004
31 XXVIII Erriapus ˌɛriːˈæpəs ~10 17 236 900 [9] +844.89 [9] 38.109° 2000
32 XLVII Skoll ˈskɔːl, ˈskɜːl ~6 17 473 800 [6] −862.37 [9] 155.624° Norse (Skathi) group 2006
33 XXIX Siarnaq ˈsiːɑrnək ~40 17 776 600 [9] +884.88 [9] 45.798° Inuit group 2000
34 LII Tarqeq ˈtɑrkeɪk ? ~7 17 910 600 [12] +894.86 [9] 49.904° 2007
35   S/2004 S 13 — ~6 18 056 300 [9] −905.85 [7][11] 167.379° Norse group 2004
36 LI Greip ˈɡreɪp ~6 18 065 700 [6] −906.56 [9] 172.666° 2006
37 XLIV Hyrrokkin hɨˈrɒkɨn ~8 18 168 300 [6] −914.29 [9] 153.272° Norse (Skathi) group 2006
38 L Jarnsaxa jɑrnˈsɒksə ~6 18 556 900 [6] −943.78 [9] 162.861° Norse group 2006
39 XXI Tarvos ˈtɑrvəs ~15 18 562 800 [9] +944.23 [9] 34.679° Gallic group 2000
40 XXV Mundilfari ˌmʊndəlˈvɛri ~7 18 725 800 [9] −956.70 [7][11] 169.378° Norse group 2000
41   S/2006 S 1 — ~6 18 930 200 [6] −972.41 [9] 154.232° Norse (Skathi) group 2006
42   S/2004 S 17 — ~4 19 099 200 [9] −985.45 [7][11] 166.881° Norse group 2004
43 XXXVIII Bergelmir bɛrˈjɛlmɪr ~6 19 104 000 [9] −985.83 [7][11] 157.384° Norse (Skathi) group 2004
44 XXXI Narvi ˈnɑrvi ~7 19 395 200 [9] −1008.45 [7][11] 137.292° Norse (Narvi) group 2003
45 XXIII Suttungr ˈsʊtʊŋɡɚ ~7 19 579 000 [9] −1022.82 [7][11] 174.321° Norse group 2000
46 XLIII Hati ˈhɑːti ~6 19 709 300 [9] −1033.05 [7][11] 163.131° 2004
47   S/2004 S 12 — ~5 19 905 900 [9] −1048.54 [7][11] 164.042° 2004
48 XL Farbauti fɑrˈbaʊti ~5 19 984 800 [9] −1054.78 [7][11] 158.361° Norse (Skathi) group 2004
49 XXX Thrymr ˈθrɪmɚ ~7 20 278 100 [9] −1078.09 [7][11] 174.524° Norse group 2000
50 XXXVI Aegir ˈaɪɚ ~6 20 482 900 [9] −1094.46 [7][11] 167.425° 2004
51   S/2007 S 3 — ~5 20 518 500 ~ −1100 177.22° 2007
52 XXXIX Bestla ˈbɛstlə ~7 20 570 000 [9] −1101.45 [7][11] 147.395° Norse (Narvi) group 2004
53   S/2004 S 7 — ~6 20 576 700 [9] −1101.99 [7][11] 165.596° Norse group 2004
54   S/2006 S 3 — ~6 21 076 300 [6] −1142.37 [9] 150.817° Norse (Skathi) group 2006
55 XLI Fenrir ˈfɛnrɪr ~4 21 930 644 [9] −1212.53 [7][11] 162.832° Norse group 2004
56 XLVIII Surtur ˈsʊərtɚ ~6 22 288 916 [6] −1242.36 [9] 166.918° 2006
57 XLV Kari ˈkɑːri ~7 22 321 200 [6] −1245.06 [9] 148.384° Norse (Skathi) group 2006
58 XIX Ymir ˈɪmɪr ~18 22 429 673 [9] −1254.15 [7][11] 172.143° Norse group 2000
59 XLVI Loge ˈlɔɪeɪ ~6 22 984 322 [6] −1300.95 [9] 166.539° 2006
60 XLII Fornjot ˈfɔrnjɒt ~6 24 504 879 [9] −1432.16 [7][11] 167.886° 2004

The following objects have not been confirmed as satellites:

Order Name Image Diameter (km) Semi-major
axis (km) 		Orbital
period (d) 		Inclination Position Discovered
*   S/2004 S 6 [13]  
~3−5 140,130 [4] +0.61801 [4] uncertain objects around the F-Ring 2004
*   S/2004 S 4 [14]   ~3−5 ~140,100 [15] +0.619 [10] 2004
*   S/2004 S 3 [13]  
~3−5 ~140,300 [16] ~ +0.62 2004
  1. ^ Jones, Geraint H. (2008 March 07). "The Dust Halo of Saturn's Largest Icy Moon, Rhea". Science. 319 (5868). AAAS: 1380–1384. doi:10.1126/science.1151524. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ Miodrag Sremčević; et al. (2007). " A belt of moonlets in Saturn's A ring". Nature. 449: 1019–1021. {{cite journal}}: Explicit use of et al. in: |author= (help)
  3. ^ a b c d e f g h C.C. Porco; et al. (2006). "Physical characteristics and possible accretionary origins for Saturn's small satellites" (PDF). Bulletin of the American Astronomical Society. 37: 768. {{cite journal}}: Explicit use of et al. in: |author= (help)
  4. ^ a b c d e f g h i j k l m n o p q r s t J.N. Spitale; et al. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations" (PDF). The Astronomical Journal. 132: 692. {{cite journal}}: Explicit use of et al. in: |author= (help)
  5. ^ a b c d e f Source: Thomas et al. 2006
  6. ^ a b c d e f g h i j k l m n o Computed from the period using the IAU-MPC Natural Satellites Ephemeris Service µ value
  7. ^ a b c d e f g h i j k l m n o p q r s t u Source: NASA
  8. ^ Source: Porco et al. 2005
  9. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as Source: IAU-MPC Natural Satellites Ephemeris Service
  10. ^ a b c Computed from the semi-major axis using the IAU-MPC Natural Satellites Ephemeris Service µ value
  11. ^ a b c d e f g h i j k l m n o p q r Negative orbital periods indicate a retrograde orbit around Saturn (opposite to the planet's rotation)
  12. ^ MPEC 2007-G38
  13. ^ a b It is not yet clear if these are real satellites or merely persistent clumps within the F Ring
  14. ^ S/2004 S4 was most likely a transient clump − it has not been recovered since the first sighting.
  15. ^ PGJ Astronomie webpage (Gilbert Javaux). Note that the F ring is centered at ~140,180 km
  16. ^ See references in S/2004 S 3

Grouping the moons

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

A-Ring moonlets

In 2006, four tiny "moonlets" were found in Cassini images of the A Ring.[1] The moonlets themselves are only about a hundred meters in diameter, too small to be seen directly; what Cassini sees are the "propeller"-shaped disturbance the moonlets create, which are several km across. It is estimated that the A Ring contains thousands of such objects. In 2007, the discovery of eight more moonlets revealed that they are largely confined to a 3000-km belt, about 130,000 km from Saturn's center[2] Over 150 "propeller" moonlets have now been detected.[3]

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 the moonlets, Pan, Daphnis, Atlas, Prometheus, Pandora, in addition to the unconfirmed moons S/2004 S 4, S/2004 S 6 and S/2004 S 3.

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.

Inner large moons

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

Alkyonides

See also: Alkyonides

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

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.

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.

Irregular moons

Irregular satellites of Saturn.

Irregular moons are small satellites with large-radius, inclined, and sometimes retrograde orbits, believed to have been acquired by the parent planet through a capture process.

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 Ijiraq, Kiviuq, Paaliaq, Siarnaq, and Tarqeq.

Norse group

Main article: Saturn's Norse group of satellites

The Norse group are 29 retrograde outer moons that are similar enough in their distance from Saturn to be considered a group. They are Aegir, Bergelmir, Bestla, Farbauti, Fenrir, Fornjot, Greip (moon), Hati, Hyrrokkin, Jarnsaxa, Kari, Loge, Mundilfari, Narvi, Phoebe, Skathi, Skoll, Surtur, Suttungr, Thrymr, Ymir, S/2004 S 7, S/2004 S 12, S/2004 S 13, S/2004 S 17, S/2006 S 1, S/2006 S 3, S/2007 S 2, and S/2007 S 3.

Gallic group

Main article: Saturn's Gallic group of satellites

The Gallic group are four 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, Bebhionn, Erriapus, 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 (million 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.

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 objects.

See also

References

Template:Saturn Footer

  1. ^ Matthew S. Tiscareno; et al. (2006). "100-metre-diameter moonlets in Saturn's A ring from observations of 'propeller' structures". Nature. 440: 648–650. {{cite journal}}: Explicit use of et al. in: |author= (help)
  2. ^ Miodrag Sremčević; et al. (2007). "A belt of moonlets in Saturn's A ring". Nature. 449: 1019–1021. {{cite journal}}: Explicit use of et al. in: |author= (help)
  3. ^ Matthew S. Tiscareno; et al. (2008). "The population of propellers in Saturn's A Ring". Astronomical Journal. 135: 1083–1091. {{cite journal}}: Explicit use of et al. in: |author= (help)
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