The Saturnian System (photographic montage)
Saturn has a large number of natural satellites.
Introduction
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.
To date, 34 moons have been confirmed and named. Many of these were discovered very recently; 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-Huygens mission, which arrived at Saturn in the summer of 2004, has 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 these have not yet been visually confirmed [1].
The spurious satellite Themis, supposedly discovered in 1905, does not exist.
Name
(Pronunciation key)
| Diameter (km)
| Mean orbital
radius (km)
| Orbital period
| Position
| Disc.
|
| XVIII | Pan | pan' | 20 | 133,583 | 0.575 days | in Encke Division | 1990
|
| XV | Atlas | at'-lus | 33 (37 × 34 × 27) | 137,670 | 0.6019 days | outer A Ring shepherd | 1980
|
| XVI | Prometheus | proh-mee'-thee-us | 106 (148 × 100 × 68) | 139,350 | 0.6130 days | inner F Ring shepherd | 1980
|
| | S/2004 S 4*** | | ~5 | 140,000 | 0.618 days | inner F Ring shepherd | 2004
|
| | S/2004 S 3*** | | ~5 | 141,000 | 0.624 days | outer F Ring shepherd | 2004
|
| | S/2004 S 6*** | | ~5 | 141,000 | 0.622 days | outer F Ring Shepherd | 2004
|
| XVII | Pandora | pan-dor'-a | 87 (110 × 88 × 62) | 141,700 | 0.6285 days | outer F Ring shepherd | 1980
|
| XI | Epimetheus | ep'-i-mee'-thee-us | 119 (138 × 110 × 110) | 151,422 | 0.6942 days | co-orbitals | 1980
|
| X | Janus | jay'-nus | 179 (194 × 190 × 154) | 151,472 | 0.6945 days | 1966
|
| I | Mimas | mye'-mus | 397 (418 × 392 × 382) | 185,520 | 0.942422 days | | 1789
|
| XXXII | Methone | me-thoh'-nee | 3 | 194,000 | 1.01 days | | 2004
|
| XXXIII | Pallene | pa-lee'-nee | 4 | 211,000 | 1.14 days | | 2004
|
| II | Enceladus | en-sel'-a-dus | 499 (512 × 494 × 490) | 238,020 | 1.370218 days | In the thick of E ring | 1789
|
| III | Tethys | tee'-this | 1060 (1072 × 1056 × 1052) | 294,660 | 1.887802 days | | 1684
|
| XIII | Telesto | te-les'-toh | 23 (30 × 25 × 15) | 294,660 | 1.887802 days | leading Tethys trojan | 1980
|
| XIV | Calypso | ka-lip'-soh | 21 (30 × 16 × 16) | 294,660 | 1.887802 days | trailing Tethys trojan | 1980
|
| XXXIV | Polydeuces | pol'-ee-dew'-seez | 3.5 | 377,000 | 2.737 days | trailing Dione trojan | 2004
|
| IV | Dione | dye-oh'-nee | 1120 | 377,400 | 2.736915 days | | 1684
|
| XII | Helene | hel'-e-nee | 33 (36 × 32 × 30) | 377,400 | 2.736915 days | leading Dione trojan | 1980
|
| V | Rhea | ree'-a | 1528 | 527,040 | 4.5175 days | | 1672
|
| VI | Titan | tye'-tun | 5151 | 1,221,850 | 15.94542 days | | 1655
|
| VII | Hyperion | hye-peer'-ee-on | 292 (370 × 280 × 226) | 1,481,100 | 21.27661 days | | 1848
|
| VIII | Iapetus | eye-ap'-i-tus | 1436 | 3,561,300 | 79.33018 days | | 1671
|
| XXIV | Kiviuq | kee'-vee-ohk | ~16 | 11,365,000 | 449.2 days | Inuit Group | 2000
|
| XXII | Ijiraq | ee'-ye-rahk | ~12 | 11,442,000 | 451.5 days | Inuit Group | 2000
|
| IX | Phoebe | fee'-bee | 220 (230 × 220 × 210) | 12,944,300 | -548.2 days** | Norse Group | 1899
|
| XX | Paaliaq | paw'-lee-ahk | ~22 | 15,199,000 | 686.9 days | Inuit Group | 2000
|
| XXVII | Skathi | skahdh'-ee | ~8 | 15,647,000 | -728.9 days** | Norse Group | 2000
|
| XXVI | Albiorix | al'-bee-or'-iks | ~32 | 16,404,000 | 783.5 days | Gallic Group | 2000
|
| XXVIII | Erriapo | air'-ee-ap'-oh? | ~10 | 17,616,000 | 871.9 days | Gallic Group | 2000
|
| XXIX | Siarnaq | see'-ar-nahk | ~40 | 18,160,000 | 893.1 days | Inuit Group | 2000
|
| XXI | Tarvos | tar'-vohs | ~15 | 18,247,000 | 925.6 days | Gallic Group | 2000
|
| XXXI | Narvi | nar'-vee | ~7 | 18,719,000 | -956.2 days** | Norse Group | 2003
|
| XXV | Mundilfari | moon'-dil-fair'-ee | ~7 | 18,722,000 | -951.4 days** | Norse Group | 2000
|
| XXIII | Suttungr | soot'-oong-ur | ~7 | 19,463,000 | -1016.3 days** | Norse Group | 2000
|
| XXX | Thrymr | thrim'-ur | ~7 | 20,382,000 | -1086.9 days** | Norse Group | 2000
|
| XIX | Ymir | ee'-mur | ~18 | 23,096,000 | -1312.4 days** | Norse Group | 2000
|
* Awaiting confirmation and naming
** Negative orbital periods indicate a retrograde orbit around Saturn (opposite to the planet's rotation)
*** It is not yet clear if these are real satellites or persistent clumps in the F Ring
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, Atlas, Prometheus, Pandora, in addition to the unconfirmed moons S/2004 S 4, S/2004 S 3, 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 four 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 and Siarnaq.
The Norse group
The Norse group are seven 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 and Ymir. 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