Moons of Saturn

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 with respect 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] Seven Saturnian moons are large enough to be ellipsoidal in shape, though only two of those, 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 (after Jupiter's Ganymede) 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 is seemingly similar in chemical makeup to comets,[5] emits jets of gas and dust and may harbor liquid water under its south pole region.[6]

Twenty-four of Saturn's moons are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane.[7] They include the seven major satellites, four small moons that exist in a trojan orbit with larger moons, two mutually co-orbital moons and two moons that 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, 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 around Saturn.[8] Thus a precise number of Saturnian moons cannot be given, because 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.[9]

Discovery and naming

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

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[10] on a refracting telescope of his own design.[11] Tethys, Dione, Rhea and Iapetus (the "Sidera Lodoicea") were discovered between 1671 and 1684 by Giovanni Domenico Cassini.[12] Mimas and Enceladus were discovered in 1789 by William Herschel.[12] Hyperion was discovered in 1848 by W.C. Bond, G.P. Bond[13] and William Lassell.[14]

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.[15] In 1966 the tenth satellite of Saturn was discovered by Audouin Dollfus, when the rings were observed edge-on near an equinox.[16] 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.[16] 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.[17] 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).[17]

Observations by spacecraft

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.[17] In addition, Epimetheus was confirmed as distinct from Janus. In 1990, Pan was discovered in archival Voyager images.[17]

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.[18] 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).[19] In 2007 Anthe was announced.[20] 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.[21] In March 2009, Aegaeon, a moonlet within the G Ring, was announced.[22] In July of the same year, S/2009 S 1, the first moonlet within the B Ring, was observed.[3] In April 2014, the possible beginning of a new moon, within the A Ring, was reported.[23] (related image)

Outer moons

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.[24] 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.[25] They are probably fragments of larger bodies captured by Saturn's gravitational pull.[24][25] In 2005, astronomers using the Mauna Kea Observatory announced the discovery of twelve more small outer moons.[26][27] In 2006, astronomers using the Subaru 8.2 m telescope reported the discovery of further nine irregular moons.[28] 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.[29]

Naming

Main article: Naming of moons

The modern names for Saturnian moons were suggested by John Herschel in 1847.[12] He proposed to name them after mythological figures associated with the Roman god of agriculture and harvest, Saturn (equated to the Greek Cronus).[12] In particular, the then known seven satellites were named after Titans, Titanesses and Giants—brothers and sisters of Cronus.[15] In 1848 Lassell proposed that the eighth satellite of Saturn was named Hyperion after another Titan.[14] 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.[30] All the irregular moons (except Phoebe) are named after Inuit and Gallic gods and after Norse ice giants.[31]

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

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

Saturn's satellite 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% of the mass, and the remaining 55 small moons, together with the rings, comprise only 0.04%.[lower-alpha 1]

Saturn's major satellites, compared to the Moon
Name
 Diameter
(km)[32]		 Mass
(kg)[33]		 Orbital radius
(km)[34]		 Orbital period
(days)[34]
Mimas 396
(12% Moon) 		0.4×1020
(0.05% Moon) 		185,539
(48% Moon) 		0.9
(3% Moon)
Enceladus 504
(14% Moon) 		1.1×1020
(0.2% Moon) 		237,948
(62% Moon) 		1.4
(5% Moon)
Tethys 1,062
(30% Moon) 		6.2×1020
(0.8% Moon) 		294,619
(77% Moon) 		1.9
(7% Moon)
Dione 1,123
(32% Moon) 		11×1020
(1.5% Moon) 		377,396
(98% Moon) 		2.7
(10% Moon)
Rhea 1,527
(44% Moon) 		23×1020
(3% Moon) 		527,108
(137% Moon) 		4.5
(20% Moon)
Titan 5,150
(148% Moon)
(75% Mars) 		1,350×1020
(180% Moon) 		1,221,870
(318% Moon) 		16
(60% Moon)
Iapetus 1,470
(42% Moon) 		18×1020
(2.5% Moon) 		3,560,820
(926% Moon) 		79
(290% Moon)

Orbital groups

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.[35] 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.[36] 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.[31]

Ring moonlets

Main article: Rings of Saturn
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.[37]

Possible beginning of a new moon of Saturn imaged on 15 April 15 2014

In 2006, four tiny moonlets were found in Cassini images of the A Ring.[38] 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.[38] 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.[39] The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly.[9] 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.[9] This region is relatively free from the disturbances caused by resonances with larger satellites,[9] 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.[39] 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.[9]

Similar moonlets may reside in the F Ring.[9] 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.[40]

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.[22] 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.[41]

In April 2014, NASA scientists reported the possible beginning of a new moon, within the A Ring, of the planet Saturn.[23] (related image)

Ring shepherds

Main article: Rings of Saturn

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).[18][22] 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.[35]

Co-orbitals

Janus and Epimetheus are called co-orbital moons.[17] They are of roughly equal size, with Janus being slightly larger than Epimetheus.[35] 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.[42]

Inner large moons

The innermost large moons of Saturn orbit within its tenuous E Ring, along with three smaller moons of the Alkyonides 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
Saturn's rings and Tethys, Hyperion and Prometheus (July 14, 2014).

Alkyonides

Cassini image of Methone's leading side taken on 20 May 2012

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.[49] Of these three moons, only Methone has been photographed at close range, showing it to be egg-shaped with very few or no craters.[50]

Trojan moons

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).[18] Helene is by far the largest trojan moon,[43] while Polydeuces is the smallest and has the most chaotic orbit.[42] These moons are coated with dusty material that has smoothened out their surfaces.[51]

Outer large moons

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

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.[24] 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.[25] The irregulars generally have featureless visible and near infrared spectra dominated by water absorption bands.[24] They are neutral or moderately red in color—similar to C-type, P-type, or D-type asteroids,[31] though they are much less red than Kuiper belt objects.[24][lower-alpha 3]

Inuit group

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.[25][31] The moons are Ijiraq, Kiviuq, Paaliaq, Siarnaq, and Tarqeq.[31] The largest among them is Siarnaq with an estimated size of about 40 km.

Gallic group

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.[25][31] They are Albiorix, Bebhionn, Erriapus, and Tarvos.[31] 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

The Norse (or Phoebe) group consists of 29 retrograde outer moons.[25][31] 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.[31] 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.[31]

Tables

Confirmed moons

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


Order Label
[lower-alpha 4]		 Name Pronunciation (key) Image Diameter (km)[lower-alpha 5] Mass
(×1015 kg) [lower-alpha 6]		 Semi-major axis (km) [lower-alpha 7] Orbital period (d)[lower-alpha 7][lower-alpha 8] Inclination [lower-alpha 7][lower-alpha 9] Eccentricity Position Discovery
year[30]		 Discoverer
[30]
1 S/2009 S/2009 S 1 — ≈ 0.3 < 0.0001 ≈ 117000 ≈ 0.47≈ 0° ≈ 0 outer B Ring 2009 Cassini–Huygens[3]
(moonlets) — A noisy image showing a few bright dots marked by circles 0.04 to 0.4 (Earhart) < 0.0001 ≈ 130000 ≈ 0.55≈ 0°≈ 0 Three 1000 km bands within A Ring 2006 Cassini–Huygens
2 XVIII Pan Pan ˈpæn A 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±0.75 133584 +0.57505 0.001° 0.000035 in Encke Division 1990 M. Showalter
3 XXXV Daphnis Daphnis ˈdæfnɨs Two 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±0.012 136505 +0.59408 ≈ 0° ≈ 0 in Keeler Gap 2005 Cassini–Huygens
4 XV Atlas Atlas ˈætləs An 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±0.045 137670 +0.60169 0.003° 0.0012 outer A Ring shepherd 1980 Voyager 2
5 XVI Prometheus Prometheus proʊˈmiːθiːəs An 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±1.5 139380 +0.61299 0.008° 0.0022 inner F Ring shepherd 1980 Voyager 2
6 XVII Pandora Pandora pænˈdɔərə An 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±1.9 141720 +0.62850 0.050° 0.0042 outer F Ring Shepherd 1980 Voyager 2
7a XI Epimetheus Epimetheus ˌɛpɨˈmiːθiːəs A 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±0.6 151422 +0.69433 0.335° 0.0098 co-orbital with Janus 1977 J. Fountain, and S. Larson
7b X Janus Janus ˈdʒeɪnəs An 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±0.6 151472 +0.69466 0.165° 0.0068 co-orbital with Epimetheus 1966 A. Dollfus
9 LIII Aegaeon Aegaeon iːˈdʒiːən There 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 ≈ 0.0001 167500 +0.80812 0.001° 0.0002 G Ring moonlet 2008 Cassini–Huygens
10 I Mimas †Mimas ˈmaɪməs A 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±31 185404 +0.942422 1.566° 0.0202   1789 W. Herschel
11 XXXII Methone Methone mɨˈθoʊniː From May 2012 flyby 3.2±1.2 ≈ 0.02 194440 +1.00957 0.007° 0.0001 Alkyonides 2004 Cassini–Huygens
14 XLIX Anthe Anthe ˈænθiː ≈ 1 ≈ 0.007 197700 +1.03650 0.1° 0.001 Alkyonides 2007 Cassini–Huygens
13 XXXIII Pallene Pallene pəˈliːniː A dot in the glare of Saturn 5.0±1.2
(6 × 6 × 4) 		≈ 0.05 212280 +1.15375 0.181° 0.0040 Alkyonides 2004 Cassini–Huygens
14 II Enceladus †Enceladus ɛnˈsɛlədəs A 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±101 237950 +1.370218 0.010° 0.0047 Generates the E ring 1789 W. Herschel
15 III Tethys †Tethys ˈtiːθɨs / ˈtɛθɨs A 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±132 294619 +1.887802 0.168° 0.0001   1684 G. Cassini
15a XIII Telesto Telesto tɨˈlɛstoʊ 24.8±0.8
(33 × 24 × 20)		 ≈ 9.41 294619 +1.887802 1.158° 0.000 leading Tethys trojan 1980 B. Smith, H. Reitsema, S. Larson, and J. Fountain
15b XIV Calypso Calypso kəˈlɪpsoʊ An oblong reddish body is seen in this low resolution image. 21.4±1.4
(30 × 23 × 14)		 ≈ 6.3 294619 +1.887802 1.473° 0.000 trailing Tethys trojan 1980 D. Pascu, P. Seidelmann, W. Baum, and D. Currie
18 IV Dione †Dione daɪˈoʊniː A 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±168 377396 +2.736915 0.002° 0.0022   1684 G. Cassini
18a XII Helene Helene ˈhɛlɨniː An irregularly shaped body illuminated from the left. Its surface is covered by numerous impact craters. 35.2±0.8
(43 × 38 × 26) 		≈ 24.46 377396 +2.736915 0.212° 0.0022 leading Dione trojan 1980 P. Laques and J. Lecacheux
18b XXXIV Polydeuces Polydeuces ˌpɒliˈdjuːsiːz A small oblong body is barely resolved in this image. 2.6±0.8
(3 × 2 × 1) 		≈ 0.03 377396 +2.736915 0.177° 0.0192 trailing Dione trojan 2004 Cassini–Huygens
21 V Rhea †Rhea ˈriːə A 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±353 527108 +4.518212 0.327° 0.001258   1672 G. Cassini
22 VI Titan ♠Titan ˈtaɪtən An 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. 5151 134520000±20000 1221930 +15.94542 0.3485° 0.0288   1655 C. Huygens
23 VII Hyperion †Hyperion haɪˈpɪəriən An 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±50 1481010 +21.27661 0.568° 0.123006 in 4:3 resonance with Titan 1848 W. Bond
G. Bond
W. Lassell
24 VIII Iapetus †Iapetus aɪˈæpɨtəs A 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±375 3560820 +79.3215 15.47° 0.028613   1671 G. Cassini
25 XXIV Kiviuq ‡Kiviuq ˈkɪviək ≈ 16 ≈ 2.79 11294800 +448.16 49.087° 0.3288 Inuit group 2000 B. Gladman, J. Kavelaars, et al.
26 XXII Ijiraq ‡Ijiraq ˈiː.ɨrɒk ≈ 12 ≈ 1.18 11355316 +451.77 50.212° 0.3161 Inuit group 2000 B. Gladman, J. Kavelaars, et al.
27 IX Phoebe ♣†Phoebe ˈfiːbiː An 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±10 12869700 −545.09 173.047° 0.156242 Norse group 1899 W. Pickering
28 XX Paaliaq ‡Paaliaq ˈpɑːliɒk ≈ 22 ≈ 7.25 15103400 +692.98 46.151° 0.3631 Inuit group 2000 B. Gladman, J. Kavelaars, et al.
29 XXVII Skathi ♣Skathi ˈskɒði ≈ 8 ≈ 0.35 15672500 −732.52 149.084° 0.246 Norse (Skathi) Group 2000 B. Gladman, J. Kavelaars, et al.
30 XXVI Albiorix ♦Albiorix ˌælbiˈɒrɪks ≈ 32 ≈ 22.3 16266700 +774.58 38.042° 0.477 Gallic group 2000 M. Holman
31   S/2007A ♣S/2007 S 2 — ≈ 6 ≈ 0.15 16560000 −792.96 176.68° 0.2418 Norse group 2007 S. Sheppard, D. Jewitt, J. Kleyna, B. Marsden
32 XXXVII Bebhionn ♦Bebhionn bɛˈviːn, ˈvɪvi.ɒn ≈ 6 ≈ 0.15 17153520 +838.77 40.484° 0.333 Gallic group 2004 S. Sheppard, D. Jewitt, J. Kleyna
33 XXVIII Erriapus ♦Erriapus ˌɛriˈæpəs ≈ 10 ≈ 0.68 17236900 +844.89 38.109° 0.4724 Gallic group 2000 B. Gladman, J. Kavelaars, et al.
34 XLVII Skoll ♣Skoll ˈskɒl, ˈskɜːl ≈ 6 ≈ 0.15 17473800 −862.37 155.624° 0.418 Norse (Skathi) group 2006 S. Sheppard, D. Jewitt, J. Kleyna
35 XXIX Siarnaq ‡Siarnaq ˈsiːɑrnək ≈ 40 ≈ 43.5 17776600 +884.88 45.798° 0.24961 Inuit group 2000 B. Gladman, J. Kavelaars, et al.
36 LII Tarqeq ‡Tarqeq ˈtɑrkeɪk ≈ 7 ≈ 0.23 17910600 +894.86 49.904° 0.1081 Inuit group 2007 S. Sheppard, D. Jewitt, J. Kleyna
37   S/2004B ♣S/2004 S 13 — ≈ 6 ≈ 0.15 18056300 −905.85 167.379° 0.261 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna
38 LI Greip ♣Greip ˈɡreɪp ≈ 6 ≈ 0.15 18065700 −906.56 172.666° 0.3735 Norse group 2006 S. Sheppard, D. Jewitt, J. Kleyna
39 XLIV Hyrrokkin ♣Hyrrokkin hɪˈrɒkɨn ≈ 8 ≈ 0.35 18168300 −914.29 153.272° 0.3604 Norse (Skathi) group 2006 S. Sheppard, D. Jewitt, J. Kleyna
40 L Jarnsaxa ♣Jarnsaxa jɑrnˈsæksə ≈ 6 ≈ 0.15 18556900 −943.78 162.861° 0.1918 Norse group 2006 S. Sheppard, D. Jewitt, J. Kleyna
41 XXI Tarvos ♦Tarvos ˈtɑrvɵs ≈ 15 ≈ 2.3 18562800 +944.23 34.679° 0.5305 Gallic group 2000 B. Gladman, J. Kavelaars, et al.
42 XXV Mundilfari ♣Mundilfari ˌmʊndəlˈvɛri ≈ 7 ≈ 0.23 18725800 −956.70 169.378° 0.198 Norse group 2000 B. Gladman, J. Kavelaars, et al.
43   S/2006 ♣S/2006 S 1 — ≈ 6 ≈ 0.15 18930200 −972.41 154.232° 0.1303 Norse (Skathi) group 2006 S. Sheppard, D.C. Jewitt, J. Kleyna
44   S/2004C ♣S/2004 S 17 — ≈ 4 ≈ 0.05 19099200 −985.45 166.881° 0.226 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna
45 XXXVIII Bergelmir ♣Bergelmir bɛərˈjɛlmɪər ≈ 6 ≈ 0.15 19104000 −985.83 157.384° 0.152 Norse (Skathi) group 2004 S. Sheppard, D. Jewitt, J. Kleyna
46 XXXI Narvi ♣Narvi ˈnɑrvi ≈ 7 ≈ 0.23 19395200 −1008.45 137.292° 0.320 Norse (Narvi) group 2003 S. Sheppard, D. Jewitt, J. Kleyna
47 XXIII Suttungr ♣Suttungr ˈsʊtʊŋɡər ≈ 7 ≈ 0.23 19579000 −1022.82 174.321° 0.131 Norse group 2000 B. Gladman, J. Kavelaars, et al.
48 XLIII Hati ♣Hati ˈhɑːti ≈ 6 ≈ 0.15 19709300 −1033.05 163.131° 0.291 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna
49   S/2004A ♣S/2004 S 12 — ≈ 5 ≈ 0.09 19905900 −1048.54 164.042° 0.396 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna
50 XL Farbauti ♣Farbauti fɑrˈbaʊti ≈ 5 ≈ 0.09 19984800 −1054.78 158.361° 0.209 Norse (Skathi) group 2004 S. Sheppard, D. Jewitt, J. Kleyna
51 XXX Thrymr ♣Thrymr ˈθrɪmər ≈ 7 ≈ 0.23 20278100 −1078.09 174.524° 0.453 Norse group 2000 B. Gladman, J. Kavelaars, et al.
52 XXXVI Aegir ♣Aegir ˈaɪ.ɪər ≈ 6 ≈ 0.15 20482900 −1094.46 167.425° 0.237 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna
53   S/2007B ♣S/2007 S 3 — ≈ 5 ≈ 0.09 20518500 ≈ −1100 177.22° 0.130 Norse group 2007 S. Sheppard, D. Jewitt, J. Kleyna
54 XXXIX Bestla ♣Bestla ˈbɛstlə ≈ 7 ≈ 0.23 20570000 −1101.45 147.395° 0.5145 Norse (Narvi) group 2004 S. Sheppard, D. Jewitt, J. Kleyna
55   S/2007C ♣S/2004 S 7 — ≈ 6 ≈ 0.15 20576700 −1101.99 165.596° 0.5299 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna
56   S/2006 ♣S/2006 S 3 — ≈ 6 ≈ 0.15 21076300 −1142.37 150.817° 0.4710 Norse (Skathi) group 2006 S. Sheppard, D. Jewitt, J. Kleyna
57 XLI Fenrir ♣Fenrir ˈfɛnrɪər ≈ 4 ≈ 0.05 21930644 −1212.53 162.832° 0.131 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna
58 XLVIII Surtur ♣Surtur ˈsɜrtər ≈ 6 ≈ 0.15 22288916 −1242.36 166.918° 0.3680 Norse group 2006 S. Sheppard, D. Jewitt, J. Kleyna
59XLV Kari ♣Kari ˈkɑri ≈ 7 ≈ 0.23 22321200 −1245.06 148.384° 0.3405 Norse (Skathi) group 2006 S. Sheppard, D. Jewitt, J. Kleyna
60 XIX Ymir ♣Ymir ˈɪmɪər ≈ 18 ≈ 3.97 22429673 −1254.15 172.143° 0.3349 Norse group 2000 B. Gladman, J. Kavelaars, et al.
61 XLVI Loge ♣Loge ˈlɔɪ.eɪ ≈ 6 ≈ 0.15 22984322 −1300.95 166.539° 0.1390 Norse group 2006 S. Sheppard, D. Jewitt, J. Kleyna
62 XLII Fornjot ♣Fornjot ˈfɔrnjɒt ≈ 6 ≈ 0.15 24504879 −1432.16 167.886° 0.186 Norse group 2004 S. Sheppard, D. Jewitt, J. Kleyna

Unconfirmed moons

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.[18]

Name Image Diameter (km) Semi-major
axis (km)[42]		 Orbital
period (d)[42]		 Position Discovery year
S/2004 S 6 A 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 +0.61801 uncertain objects around the F Ring 2004
S/2004 S 3/S 4[lower-alpha 10] ≈ 3–5 ≈ 140300 ≈ +0.619 2004

Hypothetical moons

Two moons were claimed to be discovered by different astronomers but never seen again. Both moons were said to orbit between Titan and Hyperion.[74]

Formation

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,[75] or that two large moons fused to form Titan, with the collision scattering icy debris that formed the mid-sized moons.[76] On June 23, 2014, NASA claimed to have strong evidence that nitrogen in the atmosphere of Titan came from materials in the Oort cloud, associated with comets, and not from the materials that formed Saturn in earlier times.[59]

Notes

  1. ↑ The mass of the rings is about the mass of Mimas,[8] whereas 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".[56]
  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.[30] 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.[32] Diameters and dimensions of Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus are from Thomas 2010, Table 1.[32] The approximate sizes of other satellites are from the website of Scott Sheppard.[36]
  6. ↑ Masses of the large moons were taken from Jacobson, 2006.[33] Masses of Pan, Daphnis, Atlas, Prometheus, Pandora, Epimetheus, Janus, Hyperion and Phoebe were taken from Thomas, 2010, Table 3.[32] Masses of other small moons were calculated assuming a density of 1.3 g/cm3.
  7. ↑ 7.0 7.1 7.2 The orbital parameters were taken from Spitale, et al. 2006,[42] IAU-MPC Natural Satellites Ephemeris Service,[73] and NASA/NSSDC.[34]
  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 S 4 was most likely a transient clump—it has not been recovered since the first sighting.[18]

References

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  2. ↑ Sheppard, Scott S. "The Giant Planet Satellite and Moon Page". Departament of Terrestrial Magnetism at Carniege Institution for science. Retrieved 2008-08-28.
  3. ↑ 3.0 3.1 3.2 3.3 Porco, C. and the Cassini Imaging Team (November 2, 2009). "S/2009 S1". IAU Circular 9091.
  4. ↑ http://www.space.com/15257-titan-saturn-largest-moon-facts-discovery-sdcmp.html
  5. ↑ Battersby, Stephen (March 26, 2008). "Saturn's moon Enceladus surprisingly comet-like". New Scientist. Retrieved April 16, 2015.
  6. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Enceladus
  7. ↑ http://abyss.uoregon.edu/~js/ast121/lectures/lec17.html
  8. ↑ 8.0 8.1 Esposito, L. W. (2002). "Planetary rings". Reports On Progress In Physics 65 (12): 1741–1783. Bibcode:2002RPPh...65.1741E. doi:10.1088/0034-4885/65/12/201.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Tiscareno, Matthew S.; Burns, J.A; Hedman, M.M; Porco, C.C (2008). "The population of propellers in Saturn's A Ring". Astronomical Journal 135 (3): 1083–1091. arXiv:0710.4547. Bibcode:2008AJ....135.1083T. doi:10.1088/0004-6256/135/3/1083.
  10. ↑ Nemiroff, Robert and Bonnell, Jerry (March 25, 2005). "Huygens Discovers Luna Saturni". Astronomy Picture of the Day. Retrieved March 4, 2010.
  11. ↑ Baalke, Ron. "Historical Background of Saturn's Rings (1655)". NASA/JPL. Retrieved March 4, 2010.
  12. ↑ 12.0 12.1 12.2 12.3 Van Helden, Albert (1994). "Naming the satellites of Jupiter and Saturn" (PDF). The Newsletter of the Historical Astronomy Division of the American Astronomical Society (32): 1–2.
  13. ↑ Bond, W.C (1848). "Discovery of a new satellite of Saturn". Monthly Notices of the Royal Astronomical Society 9: 1–2. Bibcode:1848MNRAS...9....1B.
  14. ↑ 14.0 14.1 Lassell, William (1848). "Discovery of new satellite of Saturn". Monthly Notices of the Royal Astronomical Society 8: 195–197. Bibcode:1848MNRAS...8..195L. doi:10.1093/mnras/8.9.195a.
  15. ↑ 15.0 15.1 Pickering, Edward C (1899). "A New Satellite of Saturn". Astrophysical Journal 9: 274–276. Bibcode:1899ApJ.....9..274P. doi:10.1086/140590.
  16. ↑ 16.0 16.1 Fountain, John W; Larson, Stephen M (1977). "A New Satellite of Saturn?". Science 197 (4306): 915–917. Bibcode:1977Sci...197..915F. doi:10.1126/science.197.4306.915. PMID 17730174.
  17. ↑ 17.0 17.1 17.2 17.3 17.4 Uralskaya, V.S (1998). "Discovery of new satellites of Saturn". Astronomical and Astrophysical Transactions 15: 249–253. Bibcode:1998A&AT...15..249U. doi:10.1080/10556799808201777.
  18. ↑ 18.0 18.1 18.2 18.3 18.4 Porco, C. C.; Baker, E.; Barbara, J. et al. (2005). "Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites" (PDF). Science 307 (5713): 1226–36. Bibcode:2005Sci...307.1226P. doi:10.1126/science.1108056. PMID 15731439.
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  20. ↑ Porco, C.; The Cassini Imaging Team (July 18, 2007). "S/2007 S4". IAU Circular 8857.
  21. ↑ 21.0 21.1 21.2 21.3 Jones, G.H.; Roussos, E.; Krupp, N. et al. (2008). "The Dust Halo of Saturn's Largest Icy Moon, Rhea". Science 319 (1): 1380–84. Bibcode:2008Sci...319.1380J. doi:10.1126/science.1151524. PMID 18323452.
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  25. ↑ 25.0 25.1 25.2 25.3 25.4 25.5 Gladman, Brett; Kavelaars, J. J.; Holman, Matthew et al. (2001). "Discovery of 12 satellites of Saturn exhibiting orbital clustering". Nature 412 (6843): 1631–166. doi:10.1038/35084032. PMID 11449267.
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  28. ↑ Sheppard, S. S.; Jewitt, D. C.; and Kleyna, J. (June 30, 2006). "Satellites of Saturn". IAU Circular No 8727. Retrieved January 2, 2010.
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  30. ↑ 30.0 30.1 30.2 30.3 "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21, 2006. Retrieved 2006-08-06.
  31. ↑ 31.0 31.1 31.2 31.3 31.4 31.5 31.6 31.7 31.8 31.9 Grav, Tommy; Bauer, James (2007). "A deeper look at the colors of the Saturnian irregular satellites". Icarus 191 (1): 267–285. arXiv:astro-ph/0611590. Bibcode:2007Icar..191..267G. doi:10.1016/j.icarus.2007.04.020.
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  33. ↑ 33.0 33.1 33.2 33.3 33.4 33.5 Jacobson, R. A.; Antreasian, P. G.; Bordi, J. J.; Criddle, K. E.; Ionasescu, R.; Jones, J. B.; Mackenzie, R. A.; Meek, M. C.; Parcher, D.; Pelletier, F. J.; Owen, Jr., W. M.; Roth, D. C.; Roundhill, I. M.; Stauch, J. R. (December 2006). "The Gravity Field of the Saturnian System from Satellite Observations and Spacecraft Tracking Data". The Astronomical Journal 132 (6): 2520–2526. Bibcode:2006AJ....132.2520J. doi:10.1086/508812.
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  39. ↑ 39.0 39.1 Sremčević, Miodrag; Schmidt, Jürgen; Salo, Heikki; Spahn, Frank; Albers, Nicole et al. (2007). "A belt of moonlets in Saturn's A ring". Nature 449 (7165): 1019–21. Bibcode:2007Natur.449.1019S. doi:10.1038/nature06224. PMID 17960236.
  40. ↑ Murray, Carl D.; Beurle, Kevin; Cooper, Nicholas J. et al. (2008). "The determination of the structure of Saturn's F ring by nearby moonlets". Nature 453 (7196): 739–744. Bibcode:2008Natur.453..739M. doi:10.1038/nature06999. PMID 18528389.
  41. ↑ Hedman, M. M.; J. A. Burns; M. S. Tiscareno; C. C. Porco; G. H. Jones; E. Roussos; N. Krupp; C. Paranicas; S. Kempf (2007). "The Source of Saturn's G Ring" (PDF). Science 317 (5838): 653–656. Bibcode:2007Sci...317..653H. doi:10.1126/science.1143964. PMID 17673659.
  42. ↑ 42.0 42.1 42.2 42.3 42.4 42.5 Spitale, J. N.; Jacobson, R. A.; Porco, C. C.; Owen, W. M., Jr. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations" (PDF). The Astronomical Journal 132 (2): 692–710. Bibcode:2006AJ....132..692S. doi:10.1086/505206.
  43. ↑ 43.0 43.1 43.2 43.3 43.4 43.5 Thomas, P.C; Burns, J.A.; Helfenstein, P. et al. (2007). "Shapes of the saturnian icy satellites and their significance" (PDF). Icarus 190 (2): 573–584. Bibcode:2007Icar..190..573T. doi:10.1016/j.icarus.2007.03.012.
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  46. ↑ Pontius, D.H.; Hill, T.W. (2006). "Enceladus: A significant plasma source for Saturn's magnetosphere" (PDF). Journal of Geophysical Research 111 (A9): A09214. Bibcode:2006JGRA..11109214P. doi:10.1029/2006JA011674.
  47. ↑ 47.0 47.1 Wagner, R. J.; Neukum, G.; Stephan, K.; Roatsch; Wolf; Porco (2009). "Stratigraphy of Tectonic Features on Saturn's Satellite Dione Derived from Cassini ISS Camera Data". Lunar and Planetary Science XL: 2142. Bibcode:2009LPI....40.2142W.
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  51. ↑ http://www.planetary.org/blogs/emily-lakdawalla/2009/2078.html
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