Moons of Saturn

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Artist's concepts of the Saturnian ring–moon system

A spherical yellow-brownish body (Saturn) can be seen on the left. It is viewed at an oblique angle of to its equatorial plane. Around Saturn there are rings and small ring moons. Further to the right large round moons are shown in order of their distance.
Saturn, its rings and major icy moons—from Mimas to Rhea
In the foreground there are six round fully illuminated bodies and some small irregular objects. A large half-illuminated body is shown in the background with circular cloud bands around the partially darkened north pole visible.
Images of several moons of Saturn. From left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and irregularly shaped Hyperion (bottom). Some small moons are also shown. All to scale.

The moons of Saturn are numerous and diverse ranging from tiny moonlets less than 1 kilometer across to the enormous Titan which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, 53 of which have names and only 13 of which have diameters larger than 50 kilometers.[1][2][3] Saturn has seven moons that are large enough to be ellipsoidal in shape (though only two, Titan and Rhea, are currently in hydrostatic equilibrium), as well as dense rings with complex orbital motions of their own. Particularly notable among Saturn's moons are Titan, the second-largest moon in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape including hydrocarbon lakes and dry river networks;[4] and Enceladus, which emits jets of gas and dust and may harbor liquid water under its south pole region. [5]

Twenty-four of Saturn's moons are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane. [6] They include the seven major satellites, four small moons which exist in a trojan orbit with larger moons, two mutually co-orbital moons and two moons which act as shepherds of Saturn's F Ring. Two other known regular satellites orbit within gaps in Saturn's rings. The relatively large Hyperion is locked in a resonance with Titan. The remaining regular moons orbit near the outer edge of the A Ring, within G Ring and between the major moons Mimas and Enceladus. The regular satellites are traditionally named after Titans and Titanesses or other figures associated with the mythological Saturn.

The remaining 38, all small except one, are irregular satellites, whose orbits are much farther from Saturn, have high inclinations, and are mixed between prograde and retrograde. These moons are probably captured minor planets, or debris from the breakup of such bodies after they were captured, creating collisional families. The irregular satellites have been classified by their orbital characteristics into the Inuit, Norse, and Gallic groups, and their names are chosen from the corresponding mythologies. The largest of the irregular moons is Phoebe, the ninth moon of Saturn, and was discovered at the end of the 19th century.

The rings of Saturn are made up of objects ranging in size from microscopic to moonlets hundreds of meters across, each in its own orbit about the planet.[7] Thus a precise number of Saturnian moons cannot 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. Over 150 moonlets embedded in the rings have been detected by the disturbance they create in the surrounding ring material, though this is thought to be only a small sample of the total population of such objects.[8]

Discovery and naming[edit]

A large bright circle in the center is surrounded by small circles.
Saturn (overexposed) and the moons Iapetus, Titan, Dione, Hyperion, and Rhea viewed through a 12.5-inch telescope

Early observations[edit]

Before the advent of telescopic photography, eight moons of Saturn were discovered by direct observation using optical telescopes. Saturn's largest moon, Titan, was discovered in 1655 by Christiaan Huygens using a 57-millimeter (2.2 in) objective lens[9] on a refracting telescope of his own design.[10] Tethys, Dione, Rhea and Iapetus (the "Sidera Lodoicea") were discovered between 1671 and 1684 by Giovanni Domenico Cassini.[11] Mimas and Enceladus were discovered in 1789 by William Herschel.[11] Hyperion was discovered in 1848 by W.C. Bond, G.P. Bond[12] and William Lassell.[13]

The use of long-exposure photographic plates made possible the discovery of additional moons. The first to be discovered in this manner, Phoebe, was found in 1899 by W.H. Pickering.[14] In 1966 the tenth satellite of Saturn was discovered by Audouin Dollfus, when the rings were observed edge-on near an equinox.[15] It was later named Janus. A few years later it was realized that all observations of 1966 could only be explained if another satellite had been present and that it had an orbit similar to that of Janus.[15] This object is now known as Epimetheus, the eleventh moon of Saturn. It shares the same orbit with Janus—the only known example of co-orbitals in the Solar System.[16] In 1980 three additional Saturnian moons were discovered from the ground and later confirmed by the Voyager probes. They are trojan moons of Dione (Helene) and Tethys (Telesto and Calypso).[16]

Observations by spacecraft[edit]

Circular complex rings of Saturn are seen at the low angle. The rings look like two grayish bands running parallel to each other from the left to right and connecting at the far right. Half illuminated Titan and Dione are visible slightly below the rings in the foreground. Two bright dots: one at the lower edge of rings and another above the rings can be seen. They are Prometheus and Telepso.
Four moons of Saturn can be seen on this image by the Cassini spacecraft: Huge Titan and Dione at the bottom, small Prometheus (under the rings) and tiny Telesto above center.
Five moons in another Cassini image: Rhea bisected in the foreground, Mimas behind it, bright Enceladus above and beyond the rings, Pandora eclipsed by the F Ring, and Janus off to the left.

The study of the outer planets has since been revolutionized by the use of unmanned space probes. The arrival of the Voyager spacecraft at Saturn in 1980–1981 resulted in the discovery of three additional moons—Atlas, Prometheus and Pandora, bringing the total to 17.[16] In addition, Epimetheus was confirmed as distinct from Janus. In 1990, Pan was discovered in archival Voyager images.[16]

The Cassini mission, which arrived at Saturn in the summer of 2004, initially discovered three small inner moons including Methone and Pallene between Mimas and Enceladus as well as the second Lagrangian moon of Dione—Polydeuces. It also observed three suspected but unconfirmed moons in the F Ring.[17] In November 2004 Cassini scientists announced that the structure of Saturn's rings indicates the presence of several more moons orbiting within the rings, although only one, Daphnis, has been visually confirmed so far (in 2005).[18] In 2007 Anthe was announced.[19] In 2008 it was reported 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.[20] In March 2009, Aegaeon, a moonlet within the G Ring, was announced.[21] In July of the same year, S/2009 S 1, the first moonlet within the B Ring, was observed.[3]

Outer moons[edit]

Quadruple Saturn moon transit captured by the Hubble Space Telescope

Study of Saturn's moons has also been aided by advances in telescope instrumentation, primarily the introduction of digital charge-coupled devices which replaced photographic plates. For the entire 20th century, Phoebe stood alone among Saturn's known moons with its highly irregular orbit. Beginning in 2000, however, three dozen additional irregular moons have been discovered using ground-based telescopes.[22] A survey starting in late 2000 and conducted using three medium-size telescopes found thirteen new moons orbiting Saturn at a great distance, in eccentric orbits, which are highly inclined to both the equator of Saturn and the ecliptic.[23] They are probably fragments of larger bodies captured by Saturn's gravitational pull.[22][23] In 2005, astronomers using the Mauna Kea Observatory announced the discovery of twelve more small outer moons.[24][25] In 2006, astronomers using the Subaru 8.2 m telescope reported the discovery of further nine irregular moons.[26] In April 2007, Tarqeq (S/2007 S 1) was announced. In May of the same year S/2007 S 2 and S/2007 S 3 were reported.[27]

Naming[edit]

The modern names for Saturnian moons were suggested by John Herschel in 1847.[11] He proposed to name them after mythological figures associated with the Roman god of agriculture and harvest, Saturn (equated to the Greek Cronus).[11] In particular, the then known seven satellites were named after Titans and Titanesses—brothers and sisters of Saturn.[14] In 1848 Lassell proposed that the eighth satellite of Saturn was named Hyperion after another Titan.[13] When in the 20th century the names of Titans were exhausted, the moons were named after different characters of the Greco-Roman mythology or giants from other mythologies.[28] All the irregular moons (except Phoebe) are named after Inuit and Gallic gods and after Norse ice giants.[29]

Some asteroids share the same names as moons of Saturn: 55 Pandora, 106 Dione, 577 Rhea, 1809 Prometheus, 1810 Epimetheus, and 4450 Pan. In addition, two more asteroids previously shared the names of Saturnian moons until spelling differences were made permanent by the International Astronomical Union (IAU): Calypso and asteroid 53 Kalypso; and Helene and asteroid 101 Helena.

Sizes[edit]

A pie chart
The relative masses of Saturn's moons. Mimas, the rings, and the small moons are invisible at this scale.

The Saturnian moon system is very lopsided: one moon, Titan, comprises more than 96% of the mass in orbit around the planet. The six other planemo (ellipsoidal) moons constitute roughly 4%, while the remaining 55 small moons, together with the rings, comprise only 0.04%.[a]

Saturn's major satellites, compared to Earth's Moon
Name
Diameter
(km)[30]
Mass
(kg)[31]
Orbital radius
(km)[32]
Orbital period
(days)[32]
Mimas396
(12% Moon)
0.4×1020
(0.05% Moon)
185,000
(50% Moon)
0.9
(3% Moon)
Enceladus504
(14% Moon)
1.1×1020
(0.2% Moon)
238,000
(60% Moon)
1.4
(5% Moon)
Tethys1,062
(30% Moon)
6.2×1020
(0.8% Moon)
295,000
(80% Moon)
1.9
(7% Moon)
Dione1,123
(32% Moon)
11×1020
(1.5% Moon)
377,000
(100% Moon)
2.7
(10% Moon)
Rhea1,527
(44% Moon)
23×1020
(3% Moon)
527,000
(140% Moon)
4.5
(20% Moon)
Titan5,150
(148% Moon)
(75% Mars)
1,350×1020
(180% Moon)
1,222,000
(320% Moon)
16
(60% Moon)
Iapetus1,470
(42% Moon)
18×1020
(2.5% Moon)
3,560,000
(930% Moon)
79
(290% Moon)

Orbital groups[edit]

Although the boundaries may be somewhat vague, Saturn's moons can be divided into ten groups according to their orbital characteristics. Many of them, such as Pan and Daphnis, orbit within Saturn's ring system and have orbital periods only slightly longer than the planet's rotation period.[33] The innermost moons and most regular satellites all have mean orbital inclinations ranging from less than a degree to about 1.5 degrees (except Iapetus, which has an inclination of 7.57 degrees) and small orbital eccentricities.[34] On the other hand, irregular satellites in the outermost regions of Saturn's moon system, in particular the Norse group, have orbital radii of millions of kilometers and orbital periods lasting several years. The moons of the Norse group also orbit in the opposite direction to Saturn's rotation.[29]

Ring moonlets[edit]

Daphnis in the Keeler gap

During late July 2009, a moonlet was discovered in the B Ring,[3] 480 km from the outer edge of the ring, by the shadow it cast. It is estimated to be 300 m in diameter. Unlike the A Ring moonlets (see below), it does not induce a 'propeller' feature, probably due to the density of the B Ring.[35]

In 2006, four tiny moonlets were found in Cassini images of the A Ring.[36] Before this discovery only two larger moons had been known within gaps in the A Ring: Pan and Daphnis. These are large enough to clear continuous gaps in the ring.[36] In contrast, a moonlet is only massive enough to clear two small—about 10 km across—partial gaps in the immediate vicinity of the moonlet itself creating a structure shaped like an airplane propeller.[37] The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly.[8] In 2007, the discovery of 150 more moonlets revealed that they (with the exception of two that have been seen outside the Encke gap) are confined to three narrow bands in the A Ring between 126,750 and 132,000 km from Saturn's center. Each band is about a thousand kilometers wide, which is less than 1% the width of Saturn's rings.[8] This region is relatively free from the disturbances related to resonances with larger satellites,[8] although other areas of the A Ring without disturbances are apparently free of moonlets. The moonlets were probably formed from the breakup of a larger satellite.[37] It is estimated that the A Ring contains 7,000–8,000 propellers larger than 0.8 km in size and millions larger than 0.25 km.[8]

Similar moonlets may reside in the F Ring.[8] There, "jets" of material may be due to collisions, initiated by perturbations from the nearby small moon Prometheus, of these moonlets with the core of the F Ring. One of the largest F-Ring moonlets may be the as-yet unconfirmed object S/2004 S 6. The F Ring also contains transient "fans" which are thought to result from even smaller moonlets, about 1 km in diameter, orbiting near the F Ring core.[38]

One of the recently discovered moons, Aegaeon, resides within the bright arc of G Ring and is trapped in the 7:6 mean motion resonance with Mimas.[21] This means that it makes exactly seven revolutions around Saturn while Mimas makes exactly six. The moon is the largest among the population of bodies that are sources of dust in this ring.[39]

Ring shepherds[edit]

Shepherd satellites are small 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 (Encke gap), Daphnis (Keeler gap), Atlas (A Ring), Prometheus (F Ring) and Pandora (F Ring).[17][21] These moons together with co-orbitals (see below) probably formed as a result of accretion of the friable ring material on preexisting denser cores. The cores with sizes from one-third to one-half the present day moons may be themselves collisional shards formed when a parental satellite of the rings disintegrated.[33]

Co-orbitals[edit]

Janus and Epimetheus are called co-orbital moons.[16] They are of roughly equal size, with Janus being slightly larger than Epimetheus.[33] Janus and Epimetheus have orbits with only a few kilometers difference in semi-major axis, 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.[40]

Inner large moons[edit]

The innermost large moons of Saturn orbit within its tenuous E Ring, along with three smaller moons of the Alkyoniods group.

A circular part of a grayish surface, which is intersected from the top-left to the bottom-right by four wide sinuous groves. Smaller and shorter grooves can be seen between them running either parallel to the large grooves or criss-crossing them. There is a rough terrain in the top-left corner.
Tiger stripes on Enceladus

Alkyonides[edit]

Three small moons orbit between Mimas and Enceladus: Methone, Anthe, and Pallene. Named after the Alkyonides of Greek mythology, they are some of the smallest moons in the Saturn system. Anthe and Methone possess very faint ring arcs along their orbits while Pallene possesses a faint complete ring.[47] Of these three moons, only Methone has been photographed at close range, showing it to be egg-shaped with very few or no craters. [48]

Trojan moons[edit]

Trojan moons are a unique feature only known from the Saturnian system. A trojan body orbits at either the leading L4 or trailing L5 Lagrange point of a much larger object, such as a large moon or planet. Tethys has two trojan moons, Telesto (leading) and Calypso (trailing), and Dione also has two, Helene (leading) and Polydeuces (trailing).[17] Helene is by far the largest trojan moon,[41] while Polydeuces is the smallest and has the most chaotic orbit.[40] These moons are coated with dusty material that has smoothened out their surfaces. [49]

Outer large moons[edit]

These moons all orbit beyond the E Ring. They are:

A spherical body is almost fully illuminated. Its grayish surface is covered by numerous circular craters. The terminator is located near the upper-right limb. A large crater can be seen near the limb in the upper-left part of the body. Another smaller bright crater can be seen in the center. It is surrounded by a large bright patch having the shape of a five-pointed star.
Inktomi or "The Splat", a relatively young crater with prominent butterfly-shaped ejecta on Rhea's leading hemisphere
A part of a spherical body illuminated from the above and behind. The convex limb runs from the lower-left to the upper-right corner. The black outer space is in the upper-left corner. The terminator is near the bottom. The surface of the body is covered with numerous craters. A large ridge runs in the center from the top to bottom.
Equatorial ridge on Iapetus

Irregular moons[edit]

Diagram illustrating the orbits of the irregular satellites of Saturn. The inclination and semi-major axis are represented on the Y and X-axis, respectively. The eccentricity of the orbits is shown by the segments extending from the pericenter to apocenter. The satellites with positive inclinations are prograde, those with negative are retrograde. The X-axis is labeled in km. The prograde Inuit and Gallic groups and the retrograde Norse group are identified.

Irregular moons are small satellites with large-radii, inclined, and frequently retrograde orbits, believed to have been acquired by the parent planet through a capture process. They often occur as collisional families or groups.[22] The precise size as well as albedo of the irregular moons are not known for sure because the moons are very small to be resolved by a telescope, although the latter is usually assumed to be quite low—around 6% (albedo of Phoebe) or less.[23] The irregulars generally have featureless visible and near infrared spectra dominated by water absorption bands.[22] They are neutral or moderately red in color—similar to C-type, P-type, or D-type asteroids,[29] though they are much less red than Kuiper belt objects.[22][c]

Inuit group[edit]

The Inuit group includes five prograde outer moons that are similar enough in their distances from the planet (186–297 radii of Saturn), their orbital inclinations (45–50°) and their colors that they can be considered a group.[23][29] The moons are Ijiraq, Kiviuq, Paaliaq, Siarnaq, and Tarqeq.[29] The largest among them is Siarnaq with an estimated size of about 40 km.

Gallic group[edit]

The Gallic group are four prograde outer moons that are similar enough in their distance from the planet (207–302 radii of Saturn), their orbital inclination (35–40°) and their color that they can be considered a group.[23][29] They are Albiorix, Bebhionn, Erriapus, and Tarvos.[29] Tarvos, as of 2009, is the most distant of Saturn's moons with a prograde orbit. The largest among these moons is Albiorix with an estimated size of about 32 km.

Norse group[edit]

The Norse (or Phoebe) group consists of 29 retrograde outer moons.[23][29] They are Aegir, Bergelmir, Bestla, Farbauti, Fenrir, Fornjot, Greip, 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.[29] After Phoebe, Ymir is the largest of the known retrograde irregular moons, with an estimated diameter of only 18 km. The Norse group may itself consist of several smaller subgroups.[29]

Tables of moons[edit]

Confirmed moons[edit]

The Saturnian moons are listed here by orbital period (or semi-major axis), from shortest to longest. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in bold, while the irregular moons are listed in red, orange and gray background.
Key

Major icy moons

Titan

Inuit group

Gallic group

Norse group


OrderLabel
[d]
NamePronunciation (key)ImageDiameter (km)[e]Mass
(×1015 kg) [f]
Semi-major axis (km) [g]Orbital period (d)[g][h]Inclination [g][i]EccentricityPositionDiscovery
year
[28]
Discoverer
[28]
0S/2009 S/2009 S 1PIA11665 moonlet in B Ring.jpg≈ 0.3< 0.0001≈ 117000≈ 0.47≈ 0°≈ 0outer B Ring2009Cassini–Huygens[3]
0(moonlets)A noisy image showing a few bright dots marked by circles0.04 to 0.4 (Earhart)< 0.0001≈ 130000≈ 0.55≈ 0°≈ 0Three 1000 km bands within A Ring2006Cassini–Huygens
1XVIIIPan PanˈpænA bright fuzzy band (rings of Saturn) is running from the left to right. In the center a bright irregularity shaped body is superimposed on its upper edge. A narrow grayish band, which is a part of the main band, partially covers the body.28.2±2.6
(34 × 31 × 20)
4.95±0.75133584+0.575050.001°0.000035in Encke Division1990M. Showalter
2XXXVDaphnis DaphnisˈdæfnɨsTwo bright bands run from the left to right. In the narrow gap between them (Keeler gap), which has wavy edges, a small oblong object can be seen.7.6±1.6
(9 × 8 × 6)
0.084±0.012136505+0.59408≈ 0°≈ 0in Keeler Gap2005Cassini–Huygens
3XVAtlas AtlasˈætləsAn irregularly shaped body is half illuminated from the right. The terminator runs from the top to bottom. The body, which looks like a cone viewed from the vertex, is elongated in the direction perpendicular to the image.30.2±1.8
(41 × 35 × 19)
6.6±0.045137670+0.601690.003°0.0012outer A Ring shepherd1980Voyager 2
4XVIPrometheus PrometheusproʊˈmiːθiːəsAn irregularly shaped oblong body is fully illuminated. It is elongated in the direction from the right to left. Its surface is covered by craters. There is valley at the top.86.2±5.4
(136 × 79 × 59)
159.5±1.5139380+0.612990.008°0.0022inner F Ring shepherd1980Voyager 2
5XVIIPandora PandorapænˈdɔərəAn irregularly shaped body is half illuminated from the bottom. The terminator runs from the left to right. The surface is covered by numerous craters.81.4±3.0
(104 × 81 × 64)
137.1±1.9141720+0.628500.050°0.0042outer F Ring Shepherd1980Voyager 2
6aXIEpimetheus EpimetheusˌɛpɨˈmiːθiːəsA fully illuminated irregular body, which has a shape remotely resembling a cube. One vertex with a large crater is at the right side of the image pointing towards the light source. The body's surface consists of ridges and valleys and is covered by craters.116.2±3.6
(130 × 114 × 106)
526.6±0.6151422+0.694330.335°0.0098co-orbital with Janus1977J. Fountain, and S. Larson
6bXJanus JanusˈdʒeɪnəsAn irregular body, whose outline looks like an approximate circle in this image. It is illuminated from the bottom-left. The terminator runs from the top-left to bottom-right. The surface is covered by craters.179.0±2.8
(203 × 185 × 153)
1897.5±0.6151472+0.694660.165°0.0068co-orbital with Epimetheus1966A. Dollfus
8LIIIAegaeon AegaeoniːˈdʒiːənThere images of a ring's segment are stacked together from the right to left. They shows motion of a moon along the ring.≈ 0.5≈ 0.0001167500+0.808120.001°0.0002G Ring moonlet2008Cassini–Huygens
9IMimasMimasˈmaɪməsA spherical body is half illuminated from the left. The terminator runs from the top to bottom in the vicinity of the right limb. A large crater with a central peak sits on the terminator slightly to the right and above the center of the body. It makes the body look like the Death Star. There are numerous smaller craters.396.4±0.8
(416 × 393 × 381)
37493±31185404+0.9424221.566°0.0202 1789W. Herschel
10XXXIIMethone MethonemɨˈθoʊniːFrom May 2012 flyby3.2±1.2≈ 0.02194440+1.009570.007°0.0001Alkyonides2004Cassini–Huygens
11XLIXAnthe AntheˈænθiːAn animated image showing as a dot (right) moves around Saturn (left) outside the main rings (in the middle), which are viewed from a relatively low angle≈ 1≈ 0.007197700+1.036500.1°0.001Alkyonides2007Cassini–Huygens
12XXXIIIPallene PallenepəˈliːniːA dot in the glare of Saturn5.0±1.2
(6 × 6 × 4)
≈ 0.05212280+1.153750.181°0.0040Alkyonides2004Cassini–Huygens
13IIEnceladusEnceladusɛnˈsɛlədəsA spherical body is half illuminated from the left. The terminator runs from the top to bottom in the vicinity of the right limb. In the center and at the top there are heavily cratered areas. The areas to the left and at the bottom have few craters and are intersected by lots of sinuous greenish grooves. The four prominent grooves at the bottom are Tiger stripes.504.2±0.4
(513 × 503 × 497)
108022±101237950+1.3702180.010°0.0047Generates the E ring1789W. Herschel
14IIITethysTethysˈtiːθɨsA spherical heavily cratered body is illuminated from the bottom. The terminator runs from the left to right in the vicinity of the top limb. There is a wide curved graben running from the center of the body to the bottom. It is Ithaca Chasma.1062±1.2
(1077 × 1057 × 1053)
617449±132294619+1.8878020.168°0.0001 1684G. Cassini
14aXIIITelesto TelestotɨˈlɛstoʊA potato shaped body is illuminated from the right. The terminator runs from the top to bottom. There is a large crater at the bottom near the terminator. The body is elongated from the right to left.24.8±0.8
(33 × 24 × 20)
≈ 9.41294619+1.8878021.158°0.000leading Tethys trojan1980B. Smith, H. Reitsema, S. Larson, and J. Fountain
14bXIVCalypso CalypsokəˈlɪpsoʊAn oblong reddish body is seen in this low resolution image.21.4±1.4
(30 × 23 × 14)
≈ 6.3294619+1.8878021.473°0.000trailing Tethys trojan1980D. Pascu, P. Seidelmann, W. Baum, and D. Currie
17IVDioneDionedaɪˈoʊniːA spherical body is half illuminated from the right. The terminator is running from the top to bottom slightly to the left off the center. The central part of the body is smooth and has only a few craters. A heavily cratered terrain is near the right limb. A part of a large crater is intersected by the terminator in the lower-left corner. To the left of it there is a long crack running parallel to the terminator.1122.8±0.8
(1128 × 1123 × 1119)
1095452±168377396+2.7369150.002°0.0022 1684G. Cassini
17aXIIHelene HeleneˈhɛlɨniːAn irregularly shaped body illuminated from the left. Its surface is covered by numerous impact craters.35.2±0.8
(43 × 38 × 26)
≈ 24.46377396+2.7369150.212°0.0022leading Dione trojan1980P. Laques and J. Lecacheux
17bXXXIVPolydeuces PolydeucesˌpɒliˈdjuːsiːzA small oblong body is barely resolved in this image.2.6±0.8
(3 × 2 × 1)
≈ 0.03377396+2.7369150.177°0.0192trailing Dione trojan2004Cassini–Huygens
20VRheaRheaˈriːəA spherical body is almost fully illuminated. The terminator is running near the top edge. The surface is covered by numerous craters. Two partially overlapping large craters can be seen above the center. One that is younger is above and to the right from the older one.1527.0±1.2
(1530 × 1526 × 1525)
2306518±353527108+4.5182120.327°0.001258 1672G. Cassini
21VITitanTitanˈtaɪtənAn orange spherical body is half illuminated from the right. The terminator is running from the top to bottom slightly to the left off the center. Both limb and terminator are fuzzy due to light scattering in the atmosphere.5151134520000±200001221930+15.945420.3485°0.0288 1655C. Huygens
22VIIHyperionHyperionhaɪˈpɪəriənAn irregularly shaped oblong body is illuminated from the left. The terminator is near the right limb. The body is elongated in the top-bottom direction. The surface is punctured by numerous impact craters, which make it look like a sponge or cheese.270±8
(360 × 266 × 205)
5620±501481010+21.276610.568°0.123006in 4:3 resonance with Titan1848W. Bond
G. Bond
W. Lassell
23VIIIIapetusIapetusaɪˈæpɨtəsA walnut shaped body illuminated from the bottom-left. The terminator runs from the top to right along the top-right limb. An equatorial ridge runs from the left to right and is convex in the direction of the bottom-left. Above and below it there are dark areas. Above the upper dark area and below the lower one there are bright poles. There numerous craters. Three among them are very large: one sits on the limb at the right another is in the center above the ridge. The third is below the ridge near the left limb.1468.6±5.6
(1491 × 1491 × 1424)
1805635±3753560820+79.321515.47°0.028613 1671G. Cassini
24XXIVKiviuqKiviuqˈkɪviək≈ 16≈ 2.7911294800+448.1649.087°0.3288Inuit group2000B. Gladman, J. Kavelaars, et al.
25XXIIIjiraqIjiraqˈiː.ɨrɒk≈ 12≈ 1.1811355316+451.7750.212°0.3161Inuit group2000B. Gladman, J. Kavelaars, et al.
26IXPhoebe ♣†PhoebeˈfiːbiːAn approximately spherical heavily cratered body is illuminated from the bottom-right. The terminator runs near the left and top limbs. There is huge crater at the top, which affects the shape, and another slightly smaller at the bottom.213.0±1.4
(219 × 217 × 204)
8292±1012869700−545.09173.047°0.156242Norse group1899W. Pickering
27XXPaaliaqPaaliaqˈpɑːliɒk≈ 22≈ 7.2515103400+692.9846.151°0.3631Inuit group2000B. Gladman, J. Kavelaars, et al.
28XXVIISkathiSkathiˈskɒði≈ 8≈ 0.3515672500−732.52149.084°0.246Norse (Skathi) Group2000B. Gladman, J. Kavelaars, et al.
29XXVIAlbiorixAlbiorixˌælbiˈɒrɪks≈ 32≈ 22.316266700+774.5838.042°0.477Gallic group2000M. Holman
30 S/2007AS/2007 S 2≈ 6≈ 0.1516560000−792.96176.68°0.2418Norse group2007S. Sheppard, D. Jewitt, J. Kleyna, B. Marsden
31XXXVIIBebhionnBebhionnbɛˈviːn, ˈvɪvi.ɒn≈ 6≈ 0.1517153520+838.7740.484°0.333Gallic group2004S. Sheppard, D. Jewitt, J. Kleyna
32XXVIIIErriapusErriapusˌɛriˈæpəs≈ 10≈ 0.6817236900+844.8938.109°0.4724Gallic group2000B. Gladman, J. Kavelaars, et al.
33XLVIISkollSkollˈskɒl, ˈskɜːl≈ 6≈ 0.1517473800−862.37155.624°0.418Norse (Skathi) group2006S. Sheppard, D. Jewitt, J. Kleyna
34XXIXSiarnaqSiarnaqˈsiːɑrnək≈ 40≈ 43.517776600+884.8845.798°0.24961Inuit group2000B. Gladman, J. Kavelaars, et al.
35LIITarqeqTarqeqˈtɑrkeɪk≈ 7≈ 0.2317910600+894.8649.904°0.1081Inuit group2007S. Sheppard, D. Jewitt, J. Kleyna
36 S/2004BS/2004 S 13≈ 6≈ 0.1518056300−905.85167.379°0.261Norse group2004S. Sheppard, D. Jewitt, J. Kleyna
37LIGreipGreipˈɡreɪp≈ 6≈ 0.1518065700−906.56172.666°0.3735Norse group2006S. Sheppard, D. Jewitt, J. Kleyna
38XLIVHyrrokkinHyrrokkinhɪˈrɒkɨn≈ 8≈ 0.3518168300−914.29153.272°0.3604Norse (Skathi) group2006S. Sheppard, D. Jewitt, J. Kleyna
39LJarnsaxaJarnsaxajɑrnˈsæksə≈ 6≈ 0.1518556900−943.78162.861°0.1918Norse group2006S. Sheppard, D. Jewitt, J. Kleyna
40XXITarvosTarvosˈtɑrvɵs≈ 15≈ 2.318562800+944.2334.679°0.5305Gallic group2000B. Gladman, J. Kavelaars, et al.
41XXVMundilfariMundilfariˌmʊndəlˈvɛri≈ 7≈ 0.2318725800−956.70169.378°0.198Norse group2000B. Gladman, J. Kavelaars, et al.
42 S/2006S/2006 S 1≈ 6≈ 0.1518930200−972.41154.232°0.1303Norse (Skathi) group2006S. Sheppard, D.C. Jewitt, J. Kleyna
43 S/2004CS/2004 S 17≈ 4≈ 0.0519099200−985.45166.881°0.226Norse group2004S. Sheppard, D. Jewitt, J. Kleyna
44XXXVIIIBergelmirBergelmirbɛərˈjɛlmɪər≈ 6≈ 0.1519104000−985.83157.384°0.152Norse (Skathi) group2004S. Sheppard, D. Jewitt, J. Kleyna
45XXXINarviNarviˈnɑrvi≈ 7≈ 0.2319395200−1008.45137.292°0.320Norse (Narvi) group2003S. Sheppard, D. Jewitt, J. Kleyna
46XXIIISuttungrSuttungrˈsʊtʊŋɡər≈ 7≈ 0.2319579000−1022.82174.321°0.131Norse group2000B. Gladman, J. Kavelaars, et al.
47XLIIIHatiHatiˈhɑːti≈ 6≈ 0.1519709300−1033.05163.131°0.291Norse group2004S. Sheppard, D. Jewitt, J. Kleyna
48 S/2004AS/2004 S 12≈ 5≈ 0.0919905900−1048.54164.042°0.396Norse group2004S. Sheppard, D. Jewitt, J. Kleyna
49XLFarbautiFarbautifɑrˈbaʊti≈ 5≈ 0.0919984800−1054.78158.361°0.209Norse (Skathi) group2004S. Sheppard, D. Jewitt, J. Kleyna
50XXXThrymrThrymrˈθrɪmər≈ 7≈ 0.2320278100−1078.09174.524°0.453Norse group2000B. Gladman, J. Kavelaars, et al.
51XXXVIAegirAegirˈaɪ.ɪər≈ 6≈ 0.1520482900−1094.46167.425°0.237Norse group2004S. Sheppard, D. Jewitt, J. Kleyna
52 S/2007BS/2007 S 3≈ 5≈ 0.0920518500≈ −1100177.22°0.130Norse group2007S. Sheppard, D. Jewitt, J. Kleyna
53XXXIXBestlaBestlaˈbɛstlə≈ 7≈ 0.2320570000−1101.45147.395°0.77Norse (Narvi) group2004S. Sheppard, D. Jewitt, J. Kleyna
54 S/2007CS/2004 S 7≈ 6≈ 0.1520576700−1101.99165.596°0.5299Norse group2004S. Sheppard, D. Jewitt, J. Kleyna
55 S/2006S/2006 S 3≈ 6≈ 0.1521076300−1142.37150.817°0.4710Norse (Skathi) group2006S. Sheppard, D. Jewitt, J. Kleyna
56XLIFenrirFenrirˈfɛnrɪər≈ 4≈ 0.0521930644−1212.53162.832°0.131Norse group2004S. Sheppard, D. Jewitt, J. Kleyna
57XLVIIISurturSurturˈsɜrtər≈ 6≈ 0.1522288916−1242.36166.918°0.3680Norse group2006S. Sheppard, D. Jewitt, J. Kleyna
58XLVKariKariˈkɑri≈ 7≈ 0.2322321200−1245.06148.384°0.3405Norse (Skathi) group2006S. Sheppard, D. Jewitt, J. Kleyna
59XIXYmirYmirˈɪmɪər≈ 18≈ 3.9722429673−1254.15172.143°0.3349Norse group2000B. Gladman, J. Kavelaars, et al.
60XLVILogeLogeˈlɔɪ.eɪ≈ 6≈ 0.1522984322−1300.95166.539°0.1390Norse group2006S. Sheppard, D. Jewitt, J. Kleyna
61XLIIFornjotFornjotˈfɔrnjɒt≈ 6≈ 0.1524504879−1432.16167.886°0.186Norse group2004S. Sheppard, D. Jewitt, J. Kleyna

Unconfirmed moons[edit]

The following objects (observed by Cassini) have not been confirmed as solid bodies. It is not yet clear if these are real satellites or merely persistent clumps within the F Ring.[17]

NameImageDiameter (km)Semi-major
axis (km)[40]
Orbital
period (d)[40]
PositionDiscovery year
S/2004 S 6A bright narrow band runs from the top to bottom. To the right of it in the diffuse halo the is a bright small object.≈ 3–5≈ 140130+0.61801uncertain objects around the F Ring2004
S/2004 S 3/S 4[j]A segment of the ring with bright overexposed Saturn in the top-left corner. Near the right edge of the ring there is a bright dot.≈ 3−5≈ 140300≈ +0.6192004

Hypothetical moons[edit]

Two moons were claimed to be discovered by different astronomers but never seen again. Both moons were said to orbit between Titan and Hyperion.[69]

Formation[edit]

It is thought that the Saturnian system of Titan, mid-sized moons, and rings developed from a set-up closer to the Galilean moons of Jupiter, though the details are unclear. It has been proposed either that a second Titan-sized moon broke up, producing the rings and inner mid-sized moons,[70] or that two large moons fused to form Titan, with the collision scattering icy debris that formed the mid-sized moons.[71]

Notes[edit]

  1. ^ The mass of the rings is about the mass of Mimas,[7] while the combined mass of Janus, Hyperion and Phoebe—the most massive of the remaining moons—is about one-third of that. The total mass of the rings and small moons is around 5.5×1019 kg.
  2. ^ Inktomi was once known as "The Splat".[54]
  3. ^ The photometric color may be used as a proxy for the chemical composition of satellites' surfaces.
  4. ^ A confirmed moon is given a permanent designation by the IAU consisting of a name and a Roman numeral.[28] The nine moons that were known before 1900 (of which Phoebe is the only irregular) are numbered in order of their distance from Saturn; the rest are numbered in the order by which they received their permanent designations. Nine small moons of the Norse group and S/2009 S 1 have not yet received a permanent designation.
  5. ^ The diameters and dimensions of the inner moons from Pan through Janus, Methone, Pallene, Telepso, Calypso, Helene, Hyperion and Phoebe were taken from Thomas 2010, Table 3.[30] Diameters and dimensions of Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus are from Thomas 2010, Table 1.[30] The approximate sizes of other satellites are from the website of Scott Sheppard.[34]
  6. ^ Masses of the large moons were taken from Jacobson, 2006.[31] Masses of Pan, Daphnis, Atlas, Prometheus, Pandora, Epimetheus, Janus, Hyperion and Phoebe were taken from Thomas, 2010, Table 3.[30] Masses of other small moons were calculated assuming a density of 1.3 g/cm3.
  7. ^ a b c The orbital parameters were taken from Spitale, et al. 2006,[40] IAU-MPC Natural Satellites Ephemeris Service,[68] and NASA/NSSDC.[32]
  8. ^ Negative orbital periods indicate a retrograde orbit around Saturn (opposite to the planet's rotation).
  9. ^ To Saturn's equator for the regular satellites, and to the ecliptic for the irregular satellites
  10. ^ S/2004 S4 was most likely a transient clump—it has not been recovered since the first sighting.[17]

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