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*On [[June 30]], [[2006]], astronomers using the [[Subaru (telescope)|Subaru 8.2-m telescope]] announced the discovery of 9 more small outer moons [http://www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html].
*On [[June 30]], [[2006]], astronomers using the [[Subaru (telescope)|Subaru 8.2-m telescope]] announced the discovery of 9 more small outer moons [http://www.ifa.hawaii.edu/~sheppard/satellites/satsatdata.html].


The spurious satellite [[Themis (moon)|Themis]], "discovered" in [[1905]], does not exist.
The spurious satellite [[Chiron (hypothetical moon)|Chiron]], "discovered" in [[1861]], is now known not exist. [[Themis (moon)|Themis]], "discovered" in [[1905]], also was later proven not to exist.


==Table of known moons==
==Table of known moons==

Revision as of 15:33, 16 October 2006

File:Saturn sat.jpg
Saturn Rings and Satellites. ESA

Saturn has 56 confirmed natural satellites.

Introduction

Saturn's rings cut across an eerie 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 currently known to have 56 moons, many of which were discovered very recently, and 3 additional un-confirmed 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 Space Age, 9 moons were known to orbit Saturn: Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus, and Phoebe.
  • 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.
  • In 1980, the Voyager space probes discovered 8 more moons in the inner Saturnian system, the last of which, Pan, was identified ten years later.
  • 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 exist. Themis, "discovered" in 1905, also was later proven not to exist.

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)

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

Grouping the moons

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

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

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.

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.

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).

The Trojan moons

Main article: Trojan moon

Trojan moons are another kind of co-orbitals. Like 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 has also two, Helene and Polydeuces. All four of these moons orbit in the larger moons' Lagrangian points, one in each point.

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, Hyperion (which is relatively small and very irregular), Titan and Iapetus.

Irregular satellites

Irregular satellites of Saturn.

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.

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.

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.

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.

See also

References

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