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Saturn's natural satellites

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The Saturnian System (photographic montage)
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The Saturnian System (photographic montage)
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Saturn Rings and Satellites. ESA

Saturn has 48 confirmed natural satellites.

Contents

Introduction

Saturn is currently known to have 48 moons (plus 2 unconfirmed), many of which were discovered very recently. However, the precise number of Saturn's moons will never be certain 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.

  • Before the Space Age, 9 moons were known to orbit Saturn.
  • In 1980, the Voyager space probes discovered 9 more moons in the inner Saturnian system.
  • A survey starting in late 2000 found 12 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, p.163-166).
  • The Cassini mission, which arrived at Saturn in the summer of 2004, discovered three small moons in the inner Saturnian system. In addition three other moons in the F Ring are suspected, two of which remain unconfirmed. This increased the suspected number of moons to 37.
  • 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 (S/2005 S 1) has been visually confirmed so far [1] (http://www.space.com/scienceastronomy/saturn_update_041116.html).
  • On May 3, 2005, astronomers using the Mauna Kea Observatory announced the discovery of 12 more small outer moons [2] (http://www.ifa.hawaii.edu/~jewitt/saturn2005.html)[3] (http://www.planetary.org/news/2005/saturn_12newmoons_0503.html).
  • On May 6, 2005, the Cassini imagining team announced the discovery of a small moon orbiting within the rings, S/2005 S 1.

The latest announcement thus brings the total number of confirmed moons to 48 (excluding the two unconfirmed moons S/2004 S 4 and 6 in the F Ring).

The spurious satellite Themis, "discovered" in 1905, does not exist.

Table of known moons

Name

(Pronunciation key)

Diameter (km) Mean orbital
radius (km)
Orbital period (d) Position Discovered
XVIII Pan pan' 20 133,583 0.576(1) in Encke Division 1990
  S/2005 S 1   ~7 136,505(8) 0.59537(1) in Keeler Gap 2005
XV Atlas at'-lus 33 (37 × 34 × 27) 137,670 0.603(1) outer A Ring shepherd 1980
XVI Prometheus proe-mee'-thee-us 106 (148 × 100 × 68) 139,350 0.614(1) inner F Ring shepherds 1980
  S/2004 S 6(2)   ~5 140,000 0.61 2004
  S/2004 S 4(2)   ~5 140,100 0.619(1) 2004
  S/2004 S 3   ~5 140,580 0.62095 outer F Ring Shepherds 2004
XVII Pandora pan-dor'-a 87 (110 × 88 × 62) 141,520 (3) 0.6285(7) 1980
XI Epimetheus ep'-i-mee'-thee-us 119 (138 × 110 × 110) 151,422(7) 0.6956(1) co-orbitals 1980
X Janus jay'-nus 179 (194 × 190 × 154) 151,472(7) 0.6960(1) 1966
I Mimas mye'-mus 397 (418 × 392 × 382) 185,404(3) 0.942422(4)   1789
XXXII Methone me-thoe'-nee 3 194,000 1.01(1)   2004
XXXIII Pallene pa-lee'-nee 4 211,000 1.14(1)   2004
II Enceladus en-sel'-a-dus 499 (512 × 494 × 490) 237,950(3) 1.370218(4) In the thick of E ring 1789
XIII Telesto te-les'-toe 23 (30 × 25 × 15) 294,619(3) 1.887802(4) leading Tethys trojan 1980
III Tethys tee'-this 1060 (1072 × 1056 × 1052)   1684
XIV Calypso ka-lip'-soe 21 (30 × 16 × 16) trailing Tethys trojan 1980
XII Helene hel'-e-nee 33 (36 × 32 × 30) 377,396(3) 2.736915(4) leading Dione trojan 1980
IV Dione dye-oe'-nee 1120   1684
XXXIV Polydeuces pol'-ee-dew'-seez 3.5 trailing Dione trojan 2004
V Rhea ree'-a 1528 527,108(5) 4.518212(5)   1672
VI Titan tye'-tun 5151 1,221,930(3) 15.94542   1655
VII Hyperion hye-peer'-ee-on 292 (370 × 280 × 226) 1,481,010(3) 21.27661   1848
VIII Iapetus eye-ap'-i-tus 1436 3,560,820 79.3215(1)   1671
XXIV Kiviuq kee'-vee-oek ~16 11,333,200(5) 450.444(5) Inuit group 2000
XXII Ijiraq ee'-ye-raak ~12 11,372,000(5) 452.760(5) 2000
IX Phoebe fee'-bee 220 (230 × 220 × 210) 12,944,300 -549.834(1,6) Norse group 1899
XX Paaliaq paw'-lee-aak ~22 14,923,800(5) 680.667(5) Inuit group 2000
XXVII Skathi skaadh'-ee ~8 15,576,200(5) -725.784(4,6) Norse (Skathi) Group 2000
XXVI Albiorix al'-bee-or'-iks ~32 16,401,600(5) 784.226(5) Gallic group 2000
  S/2004 S 11 - ~6 16,898,400(5) 820.130(5) Inuit group 2004
XXVIII Erriapo air'-ee-ap'-oe ~10 17,408,700(5) 857.556(5) Gallic group 2000
XXIX Siarnaq see'-ar-naak ~40 17,905,700(5) 894.542(5) Inuit group 2000
  S/2004 S 13 - ~6 18,056,300(5) -905.848(4,6) Norse group 2004
XXI Tarvos tar'-vus ~15 18,160,200(5) 913.685(5) Gallic group 2000
XXV Mundilfari moon'-dil-fair'-ee ~7 18,360,100(5) -928.806(4,6) Norse group 2000
  S/2004 S 17 - ~4 19,099,200(5) -985.453(4,6) 2004
XXXI Narvi nar'-vee ~7 19,370,700(5) -1006.541(4,6) 2003
  S/2004 S 15 - ~6 19,372,200(5) -1006.659(4,6) Norse (Skathi) group 2004
  S/2004 S 10 - ~6 19,618,400(5) -1025.908(4,6) Norse group 2004
XXIII Suttungr soot'-oong-ur ~7 19,666,700(5) -1029.703(4,6) 2000
  S/2004 S 12 - ~5 19,905,900(5) -1048.541(4,6) Norse group 2004
  S/2004 S 18 - ~7 19,958,700(5) -1052.722(4,6) Norse (Skathi) group 2004
  S/2004 S 9 - ~5 20,290,800(5) -1079.099(4,6) Norse (Skathi) group 2004
  S/2004 S 14 - ~6 20,303,300(5) -1080.099(4,6) Norse group 2004
  S/2004 S 7 - ~6 20,576,700(5) -1101.989(4,6) 2004
XXX Thrymr thrim'-ur ~7 20,810,300(5) -1120.809(4,6) 2000
  S/2004 S 16 - ~4 22,610,700(5) -1269.362(4,6) 2004
XIX Ymir ee'-mur ~18 23,174,600(5) -1317.137(4,6) 2000
  S/2004 S 8 - ~6 23,608,900(5) -1354.342(4,6) 2004
  • (1) Computed from the semi-major axis using the IAU-MPC Natural Satellites Ephemeris Service value
  • (2) It is not yet clear if these are real satellites or merely persistent clumps within the F Ring
  • (3) Computed from the period using the IAU-MPC Natural Satellites Ephemeris Service value
  • (4) Source: NASA (http://exp.arc.nasa.gov/downloads/celestia/data/solarsys.ssc)
  • (5) Source: IAU-MPC Natural Satellites Ephemeris Service (http://cfa-www.harvard.edu/iau/NatSats/NaturalSatellites.html)
  • (6) Negative orbital periods indicate a retrograde orbit around Saturn (opposite to the planet's rotation)
  • (7) Source: NASA/JPL (http://sse.jpl.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Moons)
  • (8) Source: [4] (http://www.nasa.gov/mission_pages/cassini/media/cassini-051005.html)

Grouping the moons

Although the borders may be somewhat nebulous, Saturn's moons can be divided into six 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, S/2005 S 1, 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 kilometer's 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

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.

The Inuit group

The Inuit group are five 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

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

The Gallic group

The Gallic group are three 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.

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

References

Template:Saturn Full Footerbg:Естествени спътници на Сатурн bs:Saturnovi prirodni sateliti de:Saturn (Planet)#Monde es:Satlites de Saturno fr:Satellites naturels de Saturne it:Satelliti naturali di Saturno ja:土星の衛星 ru:Спутники Сатурна sk:Mesiace Saturnu tr:Satrn'n doğal uyduları zh:土星的衛星

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