Moons of Saturn: Difference between revisions
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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'''. |
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<!---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 ---> |
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== Lillian Marie == |
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was here |
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==Introduction== |
==Introduction== |
Revision as of 17:55, 13 March 2008
Saturn has 60 named natural satellites.
Lillian Marie
was here
Introduction
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:
- 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 spurious satellite Chiron, "discovered" in 1861, is now known not to exist.
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 | 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 |
- ^ 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.
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suggested) (help) - ^ Miodrag Sremčević; et al. (2007). " A belt of moonlets in Saturn's A ring". Nature. 449: 1019–1021.
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(help) - ^ 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.
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(help) - ^ 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.
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(help) - ^ a b c d e f Source: Thomas et al. 2006
- ^ 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
- ^ a b c d e f g h i j k l m n o p q r s t u Source: NASA
- ^ Source: Porco et al. 2005
- ^ 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
- ^ a b c Computed from the semi-major axis using the IAU-MPC Natural Satellites Ephemeris Service µ value
- ^ 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)
- ^ MPEC 2007-G38
- ^ a b It is not yet clear if these are real satellites or merely persistent clumps within the F Ring
- ^ S/2004 S4 was most likely a transient clump − it has not been recovered since the first sighting.
- ^ PGJ Astronomie webpage (Gilbert Javaux). Note that the F ring is centered at ~140,180 km
- ^ 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
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
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 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
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
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
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
- Saturn's moons in fiction
- Natural satellites of Mars · Jupiter · Uranus · Neptune · Pluto
- Timeline of discovery of Solar System planets and their natural satellites
- Naming of natural satellites
- Carolyn Porco: Fly me to the moons of Saturn
References
- Saturnian Satellites Fact Sheet
- Saturn's Rings by NASA's Solar System Exploration
- USGS Astrogeology: Gazetteer of Planetary Names - Planetary Body Names and Discoverers
- ^ 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) - ^ 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) - ^ 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)