Moons of Saturn

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An annotated picture of Saturn's many moons captured by the Cassini spacecraft. Shown in the image are Dione, Enceladus, Epimetheus, Prometheus, Mimas, Rhea, Janus, Tethys and Titan. Saturn - September 9 2007 - Annotated (50316920862).jpg
An annotated picture of Saturn's many moons captured by the Cassini spacecraft. Shown in the image are Dione, Enceladus, Epimetheus, Prometheus, Mimas, Rhea, Janus, Tethys and Titan.

The moons of Saturn are numerous and diverse, ranging from tiny moonlets only tens of meters across to the enormous Titan, which is larger than the planet Mercury. There are 146 moons with confirmed orbits, the most of any planet in the solar system. [1] [lower-alpha 1] This number does not include the many thousands of moonlets embedded within Saturn's dense rings, nor hundreds of possible kilometer-sized distant moons that were seen through telescopes but not recaptured. [3] [4] [5] Seven Saturnian moons are large enough to have collapsed into a relaxed, ellipsoidal shape, though only one or two of those, Titan and possiblyRhea, are currently in hydrostatic equilibrium. Three moons are particularly notable. Titan is the second-largest moon in the Solar System (after Jupiter's Ganymede), with a nitrogen-rich Earth-like atmosphere and a landscape featuring river networks and hydrocarbon lakes. [6] Enceladus emits jets of ice from its south-polar region and is covered in a deep layer of snow. [7] Iapetus has contrasting black and white hemispheres as well as an extensive ridge of equatorial mountains among the tallest in the solar system.

Contents

Of the known moons, 24 are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane, [8] with the exception of Iapetus which has a prograde but highly inclined orbit, [9] [10] an unusual characteristic for a regular moon. They include the seven major satellites, four small moons that exist in a trojan orbit with larger moons, and five that act as shepherd moons, of which two are mutually co-orbital. Two tiny moons orbit inside of Saturn's B and G rings. The relatively large Hyperion is locked in an orbital resonance with Titan. The remaining regular moons orbit near the outer edges of the dense A Ring and the narrow F 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 122, with mean diameters ranging from 2 to 213 km (1 to 132 mi), are irregular satellites, whose orbits are much farther from Saturn, have high orbital inclinations and eccentricities, and are mixed between prograde and retrograde. These moons are probably captured minor planets, or fragments from the collisional breakup of such bodies after they were captured, creating collisional families. Saturn is expected to have around 150 irregular satellites larger than 2.8 km (1.7 mi) in diameter, plus many hundreds more that are even smaller. The irregular satellites are classified by their orbital characteristics into the prograde Inuit and Gallic groups and the large retrograde Norse group, and their names are chosen from the corresponding mythologies (with the Gallic group corresponding to Celtic mythology). The sole exception is Phoebe, the ninth moon of Saturn and largest irregular one, discovered at the end of the 19th century; it is part of the Norse group but named for a Greek Titaness.

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. [11] Thus an absolute number of Saturnian moons cannot be given, because there is no consensus on a 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. [4]

There are 83 designated moons that are still unnamed (as of May 2023); all but one (the designated B-ring moonlet S/2009 S 1) are irregular. (There are many other undesignated ring moonlets.) If named, most of the irregulars will receive names from Gallic, Norse and Inuit mythology based on the orbital group of which they are a member. [12] [13]

Discovery

Saturn (overexposed) and the moons Iapetus, Titan, Dione, Hyperion, and Rhea viewed through a 12.5-inch telescope Iapetus-2010Mar04.jpg
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 [14] on a refracting telescope of his own design. [15] Tethys, Dione, Rhea and Iapetus (the "Sidera Lodoicea") were discovered between 1671 and 1684 by Giovanni Domenico Cassini. [16] Mimas and Enceladus were discovered in 1789 by William Herschel. [16] Hyperion was discovered in 1848 by W. C. Bond, G. P. Bond [17] and William Lassell. [18]

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. [19] In 1966 the tenth satellite of Saturn was discovered by Audouin Dollfus, when the rings were observed edge-on near an equinox. [20] 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. [20] 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. [21] 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). [21]

Observations by spacecraft

Five moons in a Cassini image: Rhea bisected in the far-right foreground, Mimas behind it, bright Enceladus above and beyond the rings, Pandora eclipsed by the F Ring, and Janus off to the left PIA12797-Saturn&FiveMoons-20110729-FullColor-20180730.jpg
Five moons in a Cassini image: Rhea bisected in the far-right 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 uncrewed 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. [21] In addition, Epimetheus was confirmed as distinct from Janus. In 1990, Pan was discovered in archival Voyager images. [21]

The Cassini mission, [22] which arrived at Saturn in July 2004, initially discovered three small inner moons: Methone and Pallene between Mimas and Enceladus, and the second trojan moon of Dione – Polydeuces. It also observed three suspected but unconfirmed moons in the F Ring. [23] 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, had been visually confirmed at the time. [24] In 2007 Anthe was announced. [25] 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. [26] In March 2009, Aegaeon, a moonlet within the G Ring, was announced. [27] In July of the same year, S/2009 S 1, the first moonlet within the B Ring, was observed. [28] In April 2014, the possible beginning of a new moon, within the A Ring, was reported. [29] (related image)

Outer moons

Quadruple Saturn-moon transit captured by the Hubble Space Telescope Quadruple Saturn moon transit.jpg
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 20th century, Phoebe stood alone among Saturn's known moons with its highly irregular orbit. Then in 2000, three dozen additional irregular moons were discovered using ground-based telescopes. [30] 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. [31] They are probably fragments of larger bodies captured by Saturn's gravitational pull. [30] [31] In 2005, astronomers using the Mauna Kea Observatory announced the discovery of twelve more small outer moons, [32] [33] in 2006, astronomers using the Subaru 8.2 m telescope reported the discovery of nine more irregular moons, [34] in April 2007, Tarqeq (S/2007 S 1) was announced and in May of the same year S/2007 S 2 and S/2007 S 3 were reported. [35] In 2019, twenty new irregular satellites of Saturn were reported, resulting in Saturn overtaking Jupiter as the planet with the most known moons for the first time since 2000. [13] [3]

In 2019, researchers Edward Ashton, Brett Gladman, and Matthew Beaudoin conducted a survey of Saturn's Hill sphere using the 3.6-meter Canada–France–Hawaii Telescope and discovered about 80 new Saturnian irregular moons. [5] [36] Follow-up observations of these new moons took place over 2019–2021, eventually leading to S/2019 S 1 being announced in November 2021 and an additional 62 moons being announced from 3–16 May 2023. [37] [2] These discoveries brought Saturn's total number of confirmed moons up to 145, making it the first planet known to have over 100 moons. [37] [38] [39] Yet another moon, S/2006 S 20, was announced on 23 May 2023, bringing Saturn's total count moons to 146. [2] All of these new moons are small and faint, with diameters over 3 km (2 mi) and apparent magnitudes of 25–27. [5] The researchers found that the Saturnian irregular moon population is more abundant at smaller sizes, suggesting that they are likely fragments from a collision that occurred a few hundred million years ago. The researchers extrapolated that the true population of Saturnian irregular moons larger than 2.8 km (1.7 mi) in diameter amounts to 150±30, which is approximately three times as many Jovian irregular moons down to the same size. If this size distribution applies to even smaller diameters, Saturn would therefore intrinsically have more irregular moons than Jupiter. [5]

Discovery of outer planet moons

   Moons of Jupiter
   Moons of Saturn
   Moons of Uranus

Naming

The modern names for Saturnian moons were suggested by John Herschel in 1847. [16] He proposed to name them after mythological figures associated with the Roman god of agriculture and harvest, Saturn (equated to the Greek Cronus). [16] In particular, the then known seven satellites were named after Titans, Titanesses and Giants—brothers and sisters of Cronus. [19] The idea was similar to Simon Marius' mythological naming scheme for the moons of Jupiter. [40]

As Saturn devoured his children, his family could not be assembled around him, so that the choice lay among his brothers and sister, the Titans and Titanesses. The name Iapetus seemed indicated by the obscurity and remoteness of the exterior satellite, Titan by the superior size of the Huyghenian, while the three female appellations [Rhea, Dione, and Tethys] class together the three intermediate Cassinian satellites. The minute interior ones seemed appropriately characterized by a return to male appellations [Enceladus and Mimas] chosen from a younger and inferior (though still superhuman) brood. ["Results of the Astronomical Observations made...at the Cape of Good Hope," p. 415]

In 1848, Lassell proposed that the eighth satellite of Saturn be named Hyperion after another Titan. [18] [40] 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. [41] All the irregular moons (except Phoebe, discovered about a century before the others) are named after Inuit and Gallic gods and after Norse ice giants. [42]

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, three more asteroids would share the names of Saturnian moons but for spelling differences made permanent by the International Astronomical Union (IAU): Calypso and asteroid 53 Kalypso; Helene and asteroid 101 Helena; and Gunnlod and asteroid 657 Gunlöd.

Physical characteristics

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 small moons, together with the rings, comprise only 0.04%. [lower-alpha 2]

The relative masses of Saturn's moons. Values are ×1021 kg. With Titan in the comparison (left), Mimas and Enceladus are invisible at this scale. Even excluding Titan (right), Phoebe, Hyperion, the smaller moons and the rings are invisible.
Saturn's major satellites, compared with the Moon
Name
Diameter
(km) [43] 		Mass
(kg) [44] 		Orbital radius
(km) [45] 		Orbital period
(days) [45]
Mimas 396
(0.12 D☾)		4×1019
(0.0005 M☾)		185,539
(0.48 a☾)		0.9
(0.03 T☾)
Enceladus 504
(0.14 D☾)		1.1×1020
(0.002 M☾)		237,948
(0.62 a☾)		1.4
(0.05 T☾)
Tethys 1,062
(0.30 D☾)		6.2×1020
(0.008 M☾)		294,619
(0.77 a☾)		1.9
(0.07 T☾)
Dione 1,123
(0.32 D☾)		1.1×1021
(0.015 M☾)		377,396
(0.98 a☾)		2.7
(0.10 T☾)
Rhea 1,527
(0.44 D☾)		2.3×1021
(0.03 M☾)		527,108
(1.37 a☾)		4.5
(0.20 T☾)
Titan 5,149
(1.48 D☾)
(0.75 D ♂ )		1.35×1023
(1.80 M☾)
(0.21 M ♂ )		1,221,870
(3.18 a☾)		16
(0.60 T☾)
Iapetus 1,470
(0.42 D☾)		1.8×1021
(0.025 M☾)		3,560,820
(9.26 a☾)		79
(2.90 T☾)

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. [46] 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. [3] 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. [42]

Inner moons

Ring moonlets

PIA18352-SaturnRings&Moons-Enceladus&Rhea-20150924.jpg
Saturn's F Ring along with the moons, Enceladus and Rhea
Aegaeon (2008 S1).jpg
Sequence of Cassini images of Aegaeon embedded within the bright arc of Saturn's G Ring

During late July 2009, a moonlet, S/2009 S 1, was discovered in the B Ring, 480 km from the outer edge of the ring, by the shadow it cast. [28] 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. [47]

In 2006, four tiny moonlets were found in Cassini images of the A Ring. [48] 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. [48] 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. [49] The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly. [4]

Possible beginning of a new moon of Saturn imaged on 15 April 2014 PIA18078-PossibleBeginning-NewMoonOfPlanetSaturn-20130415.jpg
Possible beginning of a new moon of Saturn imaged on 15 April 2014

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. [4] This region is relatively free from the disturbances caused by resonances with larger satellites, [4] 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. [49] 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. [4] In April 2014, NASA scientists reported the possible consolidation of a new moon within the A Ring, implying that Saturn's present moons may have formed in a similar process in the past when Saturn's ring system was much more massive. [29]

Similar moonlets may reside in the F Ring. [4] 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. [50]

One recently discovered moon, Aegaeon, resides within the bright arc of G Ring and is trapped in the 7:6 mean-motion resonance with Mimas. [27] 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. [51]

Ring shepherds

Shepherd moon Daphnis in the Keeler gap PIA08319 Daphnis in Keeler Gap.jpg
Shepherd moon Daphnis in the Keeler gap
From top to bottom, Atlas, Daphnis and Pan (enhanced color). They bear distinct equatorial ridges that appear to have formed from material accreted from Saturn's rings. PIA21449-SaturnMoons-Atlas-Daphnis-Pan-20170628color.jpg
From top to bottom, Atlas, Daphnis and Pan (enhanced color). They bear distinct equatorial ridges that appear to have formed from material accreted from Saturn's rings.

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), Prometheus (F Ring), Janus (A Ring), and Epimetheus (A Ring). [23] [27] These moons 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. [46]

Janus and Epimetheus are co-orbital moons. [21] They are of similar size, with Janus being somewhat larger than Epimetheus. [46] They have orbits with less than a 100-kilometer difference in semi-major axis, close enough that they would collide if they attempted to pass each other. Instead of colliding, their gravitational interaction causes them to swap orbits every four years. [52]

Other inner moons

Other inner moons that are neither ring shepherds nor ring moonlets include Atlas and Pandora.

Inner large

South pole map of tiger stripes on Enceladus Enceladus south pole SE15.png
South pole map of tiger stripes on Enceladus
Saturn's rings and moons
PIA18357-SaturnMoons-TethysEnceladusMimas-CassiniHuygens-20151203.jpg
Saturn's moons from bottom to top: Mimas, Enceladus, and Tethys
PIA18355-SaturnMoon-Tethys-20151123.jpg
Tethys and the rings of Saturn
Dione and Saturn.jpg
Color view of Dione in front of Saturn

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

Alkyonides

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 have very faint ring arcs along their orbits, whereas Pallene has a faint complete ring. [60] Of these three moons, only Methone has been photographed at close range, showing it to be egg-shaped with very few or no craters. [61]

Trojan

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). [23] Helene is by far the largest trojan moon, [53] while Polydeuces is the smallest and has the most chaotic orbit. [52] These moons are coated with dusty material that has smoothed out their surfaces. [62]

Outer large

Saturn's outer large moons
PIA08148 (Rhea-Splat).jpg
Inktomi or "The Splat", a relatively young crater with prominent butterfly-shaped ejecta on Rhea's leading hemisphere
Ringside with Titan and Dione.jpg
Titan in front of Dione and the rings of Saturn
PIA17193-SaturnMoon-Hyperion-20150531.jpg
Cassini image of Hyperion
Iapetus equatorial ridge.jpg
Equatorial ridge on Iapetus

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

Irregular

Diagram illustrating the orbits of the irregular satellites of Saturn (with Titan and Iapetus included for comparison). The inclination and semi-major axis are represented on the Y and X-axis, respectively. The satellites with inclinations below 90deg are prograde, those above 90deg are retrograde. The X-axis is labeled in terms of Saturn's Hill radius. The prograde Inuit and Gallic groups and the retrograde Norse group are identified. Saturn irregular moon orbits a vs. i.png
Diagram illustrating the orbits of the irregular satellites of Saturn (with Titan and Iapetus included for comparison). The inclination and semi-major axis are represented on the Y and X-axis, respectively. The satellites with inclinations below 90° are prograde, those above 90° are retrograde. The X-axis is labeled in terms of Saturn's Hill radius. The prograde Inuit and Gallic groups and the retrograde Norse group are identified.
Orbits and positions of Saturn's 122 irregular moons as of 25 February 2023. Prograde orbits are colored blue while retrograde orbits are colored red. Saturn's outermost regular moons, Titan, Hyperion, and Iapetus, are also shown with turquoise orbits. Saturn irregular moon orbits top-side 2023.png
Orbits and positions of Saturn's 122 irregular moons as of 25 February 2023. Prograde orbits are colored blue while retrograde orbits are colored red. Saturn's outermost regular moons, Titan, Hyperion, and Iapetus, are also shown with turquoise orbits.

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. [30] 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. [31] The irregulars generally have featureless visible and near infrared spectra dominated by water absorption bands. [30] They are neutral or moderately red in color—similar to C-type, P-type, or D-type asteroids, [42] though they are much less red than Kuiper belt objects. [30] [lower-alpha 4]

Inuit

The Inuit group includes twelve prograde outer moons that are similar enough in their distances from the planet (190–300 radii of Saturn), their orbital inclinations (45–50°) and their colors that they can be considered a group. [31] [42] The Inuit group is further split into three distinct subgroups at different semi-major axes, and are named after their respective largest members. Ordered by increasing semi-major axis, these subgroups are the Kiviuq group, the Paaliaq group, and the Siarnaq group. [1] The Kiviuq group includes five members: Kiviuq, Ijiraq, S/2005 S 4, S/2019 S 1, and S/2020 S 1. The Siarnaq group includes six members: Siarnaq, Tarqeq, S/2004 S 31, S/2019 S 14, S/2020 S 3, and S/2020 S 5. [84] In contrast to the Kiviuq and Siarnaq subgroups, the Paaliaq subgroup does not contain any other known members besides Paaliaq itself. [1] Of the entire Inuit group, Siarnaq is the largest member with an estimated size of about 40 km. [85]

Gallic

The Gallic group includes seven prograde outer moons that are similar enough in their distance from the planet (200–300 radii of Saturn), their orbital inclination (35–40°) and their color that they can be considered a group. [31] [42] They are Albiorix, Bebhionn, Erriapus, Tarvos, [42] Saturn LX, [86] S/2007 S 8, and S/2020 S 4. [84] The largest of these moons is Albiorix with an estimated size of about 32 km. [85]

Norse

All 100retrograde outer moons of Saturn are broadly classified into the Norse group. [31] [42] They are Aegir, Angrboda, Alvaldi, Beli, Bergelmir, Bestla, Eggther, Farbauti, Fenrir, Fornjot, Geirrod, Gerd, Greip, Gridr, Gunnlod, Hati, Hyrrokkin, Jarnsaxa, Kari, Loge, Mundilfari, Narvi, Phoebe, Skathi, Skoll, Skrymir, Surtur, Suttungr, Thiazzi, Thrymr, Ymir, [42] and 69 unnamed satellites. After Phoebe, Ymir is the largest of the known retrograde irregular moons, with an estimated diameter of only 18 km. [1]

  • Phoebe, at 213±1.4 km in diameter, is by far the largest of Saturn's irregular satellites. [30] It has a retrograde orbit and rotates on its axis every 9.3 hours. [87] Phoebe was the first moon of Saturn to be studied in detail by Cassini, in June 2004; during this encounter Cassini was able to map nearly 90% of the moon's surface. Phoebe has a nearly spherical shape and a relatively high density of about 1.6 g/cm3. [30] Cassini images revealed a dark surface scarred by numerous impacts—there are about 130 craters with diameters exceeding 10 km. Such impacts may have ejected fragments of Phoebe into orbit around Saturn—two of these may be S/2006 S 20 and S/2006 S 9, whose orbits are similar to Phoebe. [1] [88] [89] Spectroscopic measurement showed that the surface is made of water ice, carbon dioxide, phyllosilicates, organics and possibly iron-bearing minerals. [30] Phoebe is believed to be a captured centaur that originated in the Kuiper belt. [30] It also serves as a source of material for the largest known ring of Saturn, which darkens the leading hemisphere of Iapetus (see above). [81]

Outlier prograde satellites

Three prograde moons of Saturn do not definitively belong to either the Inuit or Gallic groups. [1] S/2004 S 24 and S/2006 S 12 have similar orbital inclinations as the Gallic group, but have much more distant orbits with semi-major axes of ~400 Saturn radii and ~340 Saturn radii, respectively. [84] [13] [1] Whether S/2019 S 6 is in the Gallic group or Inuit group is disputed. [lower-alpha 5]

List

Orbital diagram of the orbital inclination and orbital distances for Saturn's rings and moon system at various scales. Notable moons, moon groups, and rings are individually labeled. Open the image for full resolution. Saturnmoonsdiagram.png
Orbital diagram of the orbital inclination and orbital distances for Saturn's rings and moon system at various scales. Notable moons, moon groups, and rings are individually labeled. Open the image for full resolution.

Confirmed

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 and marked with a blue background, while the irregular moons are listed in red, orange, green, and gray background. The orbits and mean distances of the irregular moons are strongly variable over short timescales due to frequent planetary and solar perturbations, so the orbital elements of irregular moons listed here are averaged over a 5,000-year numerical integration by the Jet Propulsion Laboratory. These may sometimes strongly differ from the osculating orbital elements provided by other sources. [84] [86] Their orbital elements are all based on a reference epoch of 1 January 2000. [84]

Key
 
Small regular moons		♠
Major moons		♦
Inuit group		♣
Gallic group		‡
Norse group		§
Outlier prograde irregular moons
Label
[lower-alpha 6] 		NamePronunciationImage Abs.
magn. [lower-alpha 7] 		Diameter
(km) [lower-alpha 8] 		Mass
(×1015 kg) [lower-alpha 9] 		Semi-major
axis
(km) [lower-alpha 10] 		Orbital period (d) [lower-alpha 10] [lower-alpha 11] Inclination
(°) [lower-alpha 10] [lower-alpha 12] 		Eccentricity [lower-alpha 10] Position Discovery
year [95] 		Year announcedDiscoverer [41] [95]
S/2009 S 1 —
PIA11665 moonlet in B Ring cropped.jpg
—0.3≈ 0.0000071 116900 0.47150≈ 0.0≈ 0.000outer B Ring20092009 Cassini [28]
(moonlets)—
First moonlets PIA07792 (closeup).jpg
—0.04–0.4< 0.000017≈ 130000≈ 0.55≈ 0.0≈ 0.000Three 1,000 km bands within A Ring [4] 2006— Cassini
XVIII Pan /ˈpæn/
Pan by Cassini, March 2017.jpg
9.227.4
(34.6 × 28.2 × 21.0)		4.30133600+0.575050.00.000in Encke Division19901990 Showalter
XXXV Daphnis /ˈdæfnəs/
Daphnis (Saturn's Moon).jpg
—7.8
(9.8 × 8.4 × 5.6)		0.068136500+0.594080.00.000in Keeler Gap20052005 Cassini
XV Atlas /ˈætləs/
Atlas color PIA21449.png
8.529.8
(40.8 × 35.4 × 18.6)		5.490137700+0.604600.00.00119801980 Voyager 1
XVI Prometheus /proʊˈmiːθiəs/
Prometheus 12-26-09a.jpg
6.785.6
(137 × 81 × 56)		159.72139400+0.615880.00.002F Ring shepherd19801980 Voyager 1
XVII Pandora /pænˈdɔːrə/
PIA21055 - Pandora Up Close (cropped).jpg
6.580.0
(103 × 79 × 63)		135.7141700+0.631370.00.00419801980 Voyager 1
XI Epimetheus /ɛpəˈmiːθiəs/
PIA09813 Epimetheus S. polar region.jpg
5.5117.2
(130 × 116 × 107)		525.607151400+0.697010.30.020co-orbital with Janus19661967Fountain & Larson
X Janus /ˈdʒeɪnəs/ PIA12714 Janus crop.jpg 4.5178.0
(203 × 186 × 149)		1893.88151500+0.697350.20.007co-orbital with Epimetheus19661967 Dollfus
LIII Aegaeon /iːˈdʒiːɒn/
N1643264379 1.jpg
—0.66
(1.4 × 0.5 × 0.4)		0.0000782167500+0.808120.00.000G Ring moonlet20082009 Cassini
I ♠ Mimas /ˈmaɪməs/
Mimas Cassini.jpg
3.2396.4
(416 × 393 × 381)		37509.4186000+0.942421.60.020 17891789 Herschel
XXXII Methone /məˈθoʊniː/
Methone PIA14633.jpg
—2.90
(3.88 × 2.58 × 2.42)		0.00392194700+1.009550.00.002Alkyonides20042004 Cassini
XLIX Anthe /ˈænθiː/
Anthe crop.jpg
—1.8≈ 0.0015198100+1.038900.00.002Alkyonides20072007 Cassini
XXXIII Pallene /pəˈliːniː/
Pallene Cassini color-crop 20101016.png
—4.46
(5.76 × 4.16 × 3.68)		≈ 0.023212300+1.156060.20.004Alkyonides20042004 Cassini
II ♠ Enceladus /ɛnˈsɛlədəs/
PIA17202 - Approaching Enceladus.jpg
2.1504.2
(513 × 503 × 497)		108031.8238400+1.370220.00.005Generates the E ring17891789 Herschel
III ♠ Tethys /ˈtiːθəs/
Tethys.jpg.fromcassini.jpg
0.71062.2
(1077 × 1057 × 1053)		617495.9295000+1.887801.10.001 16841684 Cassini
XIII Telesto /təˈlɛstoʊ/
Telesto cassini closeup.jpg
8.724.6
(33.2 × 23.4 × 19.2)		≈ 3.9295000+1.887801.20.001leading Tethys trojan (L4)19801980 Smith et al.
XIV Calypso /kəˈlɪpsoʊ/
Calypso N1644755236 1.jpg
9.219.0
(29.4 × 18.6 × 12.8)		≈ 1.8295000+1.887801.50.001trailing Tethys trojan (L5)19801980Pascu et al.
XII Helene /ˈhɛləniː/
PIA12758 Helene crop.jpg
8.236.2
(45.2 × 39.2 × 26.6)		7.1377600+2.736920.20.007leading Dione trojan (L4)19801980Laques & Lecacheux
XXXIV Polydeuces /pɒliˈdjuːsiːz/
Polydeuces.jpg
—3.06
(3.50 × 3.10 × 2.62)		≈ 0.0075377600+2.736920.20.019trailing Dione trojan (L5)20042004 Cassini
IV ♠ Dione /daɪˈoʊniː/
Dione in natural light (cropped).jpg
0.81122.8
(1128 × 1123 × 1119)		1095486.8377700+2.736920.00.002 16841684 Cassini
V ♠ Rhea /ˈreɪə/
Rhea true color.jpg
0.11527.6
(1530 × 1526 × 1525)		2306485.4527200+4.517500.30.001 16721673 Cassini
VI ♠ Titan /ˈtaɪtən/
Titan in true color.jpg
–1.35149.46
(5149 × 5149 × 5150)		134518035.41221900+15.94540.30.029 16551656 Huygens
VII Hyperion /haɪˈpɪəriən/
Hyperion true.jpg
4.8270.0
(360 × 266 × 205)		5551.01481500+21.27670.60.105in 4:3 resonance with Titan18481848 Bond & Lassell
VIII ♠ Iapetus /aɪˈæpətəs/
Iapetus.jpg
1.21468.6
(1491 × 1491 × 1424)		1805659.13561700+79.33107.60.028 16711673 Cassini
♦ S/2019 S 1 —
2019 S 1 CFHT 2019-07-01 5x205s stack annotated.png
15.3≈ 6≈ 0.1111245400+445.5149.50.384 Inuit group (Kiviuq)20192021Ashton et al.
XXIV ♦Kiviuq /ˈkɪviək/
Kiviuq-CFHT.gif
12.7≈ 19≈ 3.611307300+449.1348.90.182Inuit group (Kiviuq)20002000Gladman et al.
♦S/2005 S 4—15.7≈ 5≈ 0.06511324500+450.2248.00.315Inuit group (Kiviuq)20052023Sheppard et al.
♦ S/2020 S 1 —15.9≈ 4≈ 0.03411338700+451.1048.20.337Inuit group (Kiviuq)20202023Ashton et al.
XXII ♦Ijiraq /ˈiːɪrɒk/
Ijiraq-discovery-CFHT.gif
13.3≈ 15≈ 1.811344600+451.4649.20.353Inuit group (Kiviuq)20002000Gladman et al.
IX ‡Phoebe /ˈfiːbi/
Phoebe cassini full.jpg
6.7213.0
(219 × 217 × 204)		8312.312929400−550.30175.20.164 Norse group (Phoebe)18981899 Pickering
‡ S/2006 S 20 —15.7≈ 5≈ 0.06513193800−567.27173.10.206Norse group (Phoebe)20062023Sheppard et al.
‡ S/2006 S 9 —16.5≈ 3≈ 0.01414406600−647.89173.00.248Norse group (Phoebe)20062023Sheppard et al.
XX ♦Paaliaq /ˈpɑːliɒk/
Paaliaq-CFHT.gif
11.7≈ 30≈ 1414997300+687.0847.10.384Inuit group (Paaliaq)20002000Gladman et al.
XXVII ‡Skathi /ˈskɑːði/
Skathi-discovery-CFHT.gif
14.4≈ 9≈ 0.3815575100−728.10149.70.265Norse group20002000Gladman et al.
‡ S/2007 S 5 —16.2≈ 4≈ 0.03415835700−746.88158.40.104Norse group20072023Sheppard et al.
‡S/2007 S 7—16.2≈ 4≈ 0.03415931700−754.29169.20.217Norse group20072023Sheppard et al.
‡ S/2007 S 2 —15.6≈ 5≈ 0.06515939100−754.90174.10.232Norse group20072007Sheppard et al.
‡ S/2004 S 37 —15.9≈ 4≈ 0.03415940400−754.48158.20.447Norse group20042019Sheppard et al.
‡S/2004 S 47—16.3≈ 4≈ 0.03416050600−762.49160.90.291Norse group20042023Sheppard et al.
‡S/2004 S 40—16.3≈ 4≈ 0.03416075600−764.60169.20.297Norse group20042023Sheppard et al.
XXVI ♣Albiorix /ˌælbiˈɒrɪks/
Albiorix WISE-W4.jpg
11.228.6≈ 1216329100+783.4938.90.470 Gallic group 20002000 Holman
‡ S/2019 S 2 —16.5≈ 3≈ 0.01416559900−799.82173.30.279Norse group20192023Ashton et al.
XXXVII ♣Bebhionn /ˈbeɪvɪn/
Bebhionn-cassini.png
15.0≈ 7≈ 0.1817028900+834.9437.40.482Gallic group20042005Sheppard et al.
♣S/2007 S 8—16.0≈ 4≈ 0.03417049000+836.9036.20.490Gallic group20072023Sheppard et al.
LX ♣ S/2004 S 29 —15.8≈ 5≈ 0.06517063900+837.7838.60.485Gallic group20042019Sheppard et al.
‡S/2019 S 3—16.2≈ 4≈ 0.03417077200−837.74166.90.249Norse group20192023Ashton et al.
‡ S/2020 S 7 —16.8≈ 3≈ 0.01417400000−861.70161.50.500Norse group20202023Ashton et al.
♦ S/2004 S 31 —15.6≈ 5≈ 0.06517497300+866.1048.10.159Inuit group (Siarnaq)20042019Sheppard et al.
XXVIII ♣Erriapus /ɛriˈæpəs/
Erriapus-discovery-CFHT.gif
13.7≈ 12≈ 0.9517507200+871.1038.70.462Gallic group20002000Gladman et al.
XLVII ‡Skoll /ˈskɒl/
Skoll-Cassini.png
15.4≈ 6≈ 0.1117625700−878.44158.40.470Norse group20062006Sheppard et al.
LII ♦Tarqeq /ˈtɑːrkeɪk/
Tarqeq-cassini.png
14.8≈ 7≈ 0.1817748200+884.9849.70.119Inuit group (Siarnaq)20072007Sheppard et al.
♦ S/2019 S 14 —16.3≈ 4≈ 0.03417853000+893.1446.20.172Inuit group (Siarnaq)20192023Ashton et al.
‡S/2020 S 2—16.9≈ 3≈ 0.01417869300−897.60170.70.152Norse group20202023Ashton et al.
XXIX ♦Siarnaq /ˈsiːɑːrnək/
Siarnaq-discovery-CFHT.gif
10.639.3≈ 3217880800+895.8748.20.311Inuit group (Siarnaq)20002000Gladman et al.
‡S/2019 S 4—16.5≈ 3≈ 0.01417956700−904.26170.10.409Norse group20192023Ashton et al.
♦ S/2020 S 3 —16.4≈ 3≈ 0.01418054700+907.9946.10.144Inuit group (Siarnaq)20202023Ashton et al.
‡S/2004 S 41—16.3≈ 4≈ 0.03418095000−914.61165.70.300Norse group20042023Sheppard et al.
XXI ♣Tarvos /ˈtɑːrvəs/
Tarvos discovery.gif
13.1≈ 16≈ 2.118215100+926.3738.60.528Gallic group20002000Gladman et al.
♣S/2020 S 4—17.0≈ 3≈ 0.01418235500+926.9240.10.495Gallic group20202023Ashton et al.
‡S/2004 S 42—16.1≈ 4≈ 0.03418240800−925.91165.70.158Norse group20042023Sheppard et al.
XLIV ‡Hyrrokkin /hɪˈrɒkən/
Hyrrokkin-cassini.png
14.3≈ 9≈ 0.3818342600−931.89150.30.331Norse group20042005Sheppard et al.
LI ‡Greip /ˈɡreɪp/
Greip-cassini.png
15.3≈ 6≈ 0.1118380400−936.98173.40.317Norse group20062006Sheppard et al.
♦ S/2020 S 5 —16.6≈ 3≈ 0.01418391300+933.8848.20.220Inuit group (Siarnaq)20202023Ashton et al.
‡ S/2004 S 13 —16.3≈ 4≈ 0.03418453300−942.57169.00.265Norse group20042005Sheppard et al.
‡S/2007 S 6—16.4≈ 3≈ 0.01418544900−949.50166.50.169Norse group20072023Sheppard et al.
XXV ‡Mundilfari /mʊndəlˈværi/
Mundilfari-discovery-CFHT.gif
14.6≈ 8≈ 0.2718590300−952.95168.40.210Norse group20002000Gladman et al.
‡ S/2006 S 1 —15.6≈ 5≈ 0.06518745000−964.14156.00.105Norse group20062006Sheppard et al.
‡ S/2004 S 43 —16.3≈ 4≈ 0.03418935000−980.08171.10.432Norse group20042023Sheppard et al.
‡S/2006 S 10—16.4≈ 3≈ 0.01418979900−983.14161.60.151Norse group20062023Sheppard et al.
‡S/2019 S 5—16.6≈ 3≈ 0.01419076900−990.38158.80.215Norse group20192023Ashton et al.
LIV ‡Gridr /ˈɡriːðər/ 15.8≈ 5≈ 0.06519250700−1004.75163.90.187Norse group20042019Sheppard et al.
XXXVIII ‡Bergelmir /bɛərˈjɛlmɪər/
Bergelmir.png
15.2≈ 6≈ 0.1119269100−1005.58158.70.144Norse group20042005Sheppard et al.
L ‡Jarnsaxa /jɑːrnˈsæksə/ 15.6≈ 5≈ 0.06519279700−1006.92163.00.219Norse group20062006Sheppard et al.
XXXI ‡Narvi /ˈnɑːrvi/
Narvi.jpg
14.5≈ 8≈ 0.2719286500−1003.84143.70.449Norse group20032003Sheppard et al.
XXIII ‡Suttungr /ˈsʊtʊŋɡər/
Suttungr-discovery-CFHT.gif
14.6≈ 8≈ 0.2719391700−1016.71175.00.116Norse group20002000Gladman et al.
‡ S/2007 S 3 —15.7≈ 5≈ 0.06519513700−1026.35175.60.162Norse group20072007Sheppard et al.
‡S/2004 S 44—15.8≈ 5≈ 0.06519515400−1026.16167.70.129Norse group20042023Sheppard et al.
§ S/2006 S 12 —16.2≈ 4≈ 0.03419569800+1035.0538.60.542Gallic group? [lower-alpha 13] 20062023Sheppard et al.
‡S/2004 S 45—16.0≈ 4≈ 0.03419693600−1038.70154.00.551Norse group20042023Sheppard et al.
XLIII ‡Hati /ˈhɑːti/
Hati-cassini.png
15.4≈ 6≈ 0.1119697100−1040.29164.10.375Norse group20042005Sheppard et al.
‡ S/2004 S 17 —16.0≈ 4≈ 0.03419699300−1040.86167.90.162Norse group20042005Sheppard et al.
‡S/2006 S 11—16.5≈ 3≈ 0.01419711900−1042.28174.10.144Norse group20042023Sheppard et al.
‡ S/2004 S 12 —15.9≈ 4≈ 0.03419801200−1048.57164.70.337Norse group20042005Sheppard et al.
LIX ‡Eggther /ˈɛɡθɛər/ 15.4≈ 6≈ 0.1119844700−1052.33165.00.157Norse group20042019Sheppard et al.
‡S/2006 S 13—16.1≈ 4≈ 0.03419953800−1060.63162.00.313Norse group20062023Sheppard et al.
§ S/2019 S 6 —16.1≈ 4≈ 0.03420048600+1066.4041.30.259Inuit/Gallic group [lower-alpha 5] 20192023Ashton et al.
‡S/2007 S 9—16.1≈ 4≈ 0.03420174600−1078.07159.30.360Norse group20072023Sheppard et al.
‡S/2019 S 7—16.3≈ 4≈ 0.03420181300−1080.29174.20.232Norse group20192023Ashton et al.
‡S/2019 S 8—16.3≈ 4≈ 0.03420284400−1088.68172.80.311Norse group20192023Ashton et al.
XL ‡Farbauti /fɑːrˈbaʊti/ 15.8≈ 5≈ 0.06520292500−1087.29157.70.248Norse group20042005Sheppard et al.
XXX ‡Thrymr /ˈθrɪmər/
Thrymr-discovery-CFHT.gif
14.3≈ 9≈ 0.3820326500−1091.84174.80.467Norse group20002000Gladman et al.
XXXIX ‡Bestla /ˈbɛstlə/
Bestla-cassini.png
14.6≈ 8≈ 0.2720337900−1087.46136.30.461Norse group20042005Sheppard et al.
‡S/2019 S 9—16.3≈ 4≈ 0.03420359000−1093.11159.50.433Norse group20192023Ashton et al.
‡ S/2004 S 46 —16.4≈ 3≈ 0.01420513000−1107.58177.20.249Norse group20042023Sheppard et al.
LV ‡Angrboda /ˈɑːŋɡərboʊðə/ 16.2≈ 4≈ 0.03420591000−1114.05177.40.216Norse group20042019Sheppard et al.
‡ S/2019 S 11 —16.2≈ 4≈ 0.03420663700−1115.00144.60.513Norse group20192023Ashton et al.
XXXVI ‡Aegir /ˈaɪ.ɪər/ 15.5≈ 5≈ 0.06520664600−1119.33166.90.255Norse group20042005Sheppard et al.
LXI ‡Beli /ˈbiːli/ 16.1≈ 4≈ 0.03420703800−1121.76158.90.087Norse group20042019Sheppard et al.
‡S/2019 S 10—16.7≈ 3≈ 0.01420713400−1123.04163.90.249Norse group20192023Ashton et al.
‡S/2019 S 12—16.3≈ 4≈ 0.03420904500−1138.85167.10.476Norse group20192023Ashton et al.
LVII ‡Gerd /ˈjɛərð/ 15.9≈ 4≈ 0.03420947500−1142.97174.40.517Norse group20042019Sheppard et al.
‡ S/2019 S 13 —16.7≈ 3≈ 0.01420965800−1144.92177.30.318Norse group20192023Ashton et al.
‡ S/2006 S 14 —16.5≈ 3≈ 0.01421062100−1152.68166.70.060Norse group20062023Sheppard et al.
LXII ‡Gunnlod /ˈɡʊnlɒð/ 15.6≈ 5≈ 0.06521141900−1157.98160.40.251Norse group20042019Sheppard et al.
‡S/2019 S 15—16.6≈ 3≈ 0.01421189700−1161.54157.70.257Norse group20192023Ashton et al.
‡S/2020 S 6—16.6≈ 3≈ 0.01421265300−1168.86166.90.481Norse group20202023Ashton et al.
‡ S/2004 S 7 —15.6≈ 5≈ 0.06521328200−1173.93164.90.511Norse group20042005Sheppard et al.
‡ S/2006 S 3 —15.6≈ 5≈ 0.06521353000−1174.76156.10.432Norse group20062006Sheppard et al.
‡ S/2005 S 5 —16.4≈ 3≈ 0.01421366200−1177.82169.50.588Norse group20052023Sheppard et al.
LVI ‡Skrymir /ˈskrɪmɪər/ 15.6≈ 5≈ 0.06521448000−1185.15175.60.437Norse group20042019Sheppard et al.
‡S/2006 S 16—16.5≈ 3≈ 0.01421720700−1207.52164.10.204Norse group20062023Sheppard et al.
‡S/2006 S 15—16.2≈ 4≈ 0.03421799400−1213.96161.10.117Norse group20062023Sheppard et al.
‡ S/2004 S 28 —15.8≈ 5≈ 0.06521865900−1220.68167.90.159Norse group20042019Sheppard et al.
‡S/2020 S 8—16.4≈ 3≈ 0.01421966700−1228.12161.80.252Norse group20202023Ashton et al.
LXV ‡Alvaldi /ɔːlˈvɔːldi/ 15.6≈ 5≈ 0.06521995600−1232.19177.40.238Norse group20042019Sheppard et al.
XLV ‡Kari /ˈkɑːri/
Kari-cassini.png
14.5≈ 8≈ 0.2722029700−1231.01153.00.482Norse group20062006Sheppard et al.
‡S/2004 S 48—16.0≈ 4≈ 0.03422136700−1242.40161.90.374Norse group20042023Sheppard et al.
LXVI ‡Geirrod /ˈjeɪrɒd/ 15.9≈ 4≈ 0.03422259500−1251.14154.40.539Norse group20042019Sheppard et al.
XLI ‡Fenrir /ˈfɛnrɪər/ 15.9≈ 4≈ 0.03422331800−1260.25164.30.136Norse group20042005Sheppard et al.
‡S/2004 S 50—16.4≈ 3≈ 0.01422346000−1260.44164.00.450Norse group20042023Sheppard et al.
‡S/2006 S 17—16.0≈ 4≈ 0.03422384900−1264.58168.70.425Norse group20062023Sheppard et al.
‡S/2004 S 49—16.0≈ 4≈ 0.03422399700−1264.25159.70.453Norse group20042023Sheppard et al.
‡S/2019 S 17—15.9≈ 4≈ 0.03422724100−1291.39155.50.546Norse group20192023Ashton et al.
XLVIII ‡Surtur /ˈsɜːrtər/ 15.8≈ 5≈ 0.06522753800−1296.49168.30.449Norse group20062006Sheppard et al.
‡ S/2006 S 18 —16.1≈ 4≈ 0.03422760700−1298.40169.50.131Norse group20062023Sheppard et al.
XLVI ‡Loge /ˈlɔɪ.eɪ/
Loge N00177425.jpg
15.4≈ 6≈ 0.1122918300−1311.83166.90.192Norse group20062006Sheppard et al.
XIX ‡Ymir /ˈiːmɪər/
Ymir-CFHT.gif
12.4≈ 22≈ 5.622957100−1315.16173.10.337Norse group20002000Gladman et al.
‡ S/2019 S 19 —16.5≈ 3≈ 0.01423047200−1318.05151.80.458Norse group20192023Ashton et al.
‡ S/2004 S 21 —16.2≈ 4≈ 0.03423123500−1325.43153.20.394Norse group20042019Sheppard et al.
‡S/2019 S 18—16.6≈ 3≈ 0.01423140700−1327.06154.60.509Norse group20192023Ashton et al.
‡ S/2004 S 39 —16.1≈ 4≈ 0.03423195400−1336.17165.90.101Norse group20042019Sheppard et al.
‡S/2019 S 16—16.7≈ 3≈ 0.01423266700−1341.17162.00.250Norse group20192023Ashton et al.
‡S/2004 S 53—16.2≈ 4≈ 0.03423279800−1342.44162.60.240Norse group20042023Sheppard et al.
§ S/2004 S 24 —16.0≈ 4≈ 0.03423338900+1341.3337.40.071Gallic group? [lower-alpha 13] 20042019Sheppard et al.
‡ S/2004 S 36 —16.1≈ 4≈ 0.03423430300−1352.93153.30.625Norse group20042019Sheppard et al.
LXIII ‡Thiazzi /θiˈætsi/ 15.9≈ 4≈ 0.03423577500−1366.68158.80.511Norse group20042019Sheppard et al.
‡S/2019 S 20—16.7≈ 3≈ 0.01423678600−1375.45156.10.354Norse group20192023Ashton et al.
‡ S/2006 S 19 —16.1≈ 4≈ 0.03423801100−1389.33175.50.467Norse group20062023Sheppard et al.
LXIV ‡ S/2004 S 34 —16.2≈ 4≈ 0.03424145500−1420.77168.30.279Norse group20042019Sheppard et al.
XLII ‡Fornjot /ˈfɔːrnjɒt/
Fornjot-cassini.png
15.1≈ 6≈ 0.1124937300−1494.03169.50.214Norse group20042005Sheppard et al.
‡S/2004 S 51—16.1≈ 4≈ 0.03425208200−1519.43171.20.201Norse group20042023Sheppard et al.
‡S/2020 S 10—16.9≈ 3≈ 0.01425314800−1527.22165.60.295Norse group20202023Ashton et al.
‡ S/2020 S 9 —16.0≈ 4≈ 0.03425434100−1534.97161.40.531Norse group20202023Ashton et al.
LVIII ‡ S/2004 S 26 —15.7≈ 5≈ 0.06526097100−1603.95172.90.148Norse group20042019Sheppard et al.
‡ S/2019 S 21 —16.2≈ 4≈ 0.03426439000−1636.32171.90.155Norse group20192023Ashton et al.
‡S/2004 S 52—16.5≈ 3≈ 0.01426448100−1633.98165.30.292Norse group20042023Sheppard et al.

Unconfirmed

These F Ring moonlets listed in the following table (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. [23]

NameImageDiameter (km)Semi-major
axis (km) [52] 		Orbital
period (d) [52] 		PositionDiscovery yearStatus
S/2004 S 3 and S 4 [lower-alpha 14] S2004 S 3 - PIA06115.png ≈ 3–5≈ 140300≈ +0.619uncertain objects around the F Ring2004Were undetected in thorough imaging of the region in November 2004, making their existence improbable
S/2004 S 6 S2004 S6.jpg ≈ 3–5≈ 140130+0.618012004Consistently detected into 2005, may be surrounded by fine dust and have a very small physical core

Spurious

Two moons were claimed to be discovered by different astronomers but never seen again. Both moons were said to orbit between Titan and Hyperion. [96]

Hypothetical

In 2022, scientists of the Massachusetts Institute of Technology proposed the hypothetical former moon Chrysalis, using data from the Cassini–Huygens mission. Chrysalis would have orbited between Titan and Iapetus, but its orbit would have gradually become more eccentric until it was torn apart by Saturn. 99% of its mass would have been absorbed by Saturn, while the remaining 1% would have formed Saturn's rings. [97] [98]

Temporary

Much like Jupiter, asteroids and comets will infrequently make close approaches to Saturn, even more infrequently becoming captured into orbit of the planet. The comet P/2020 F1 (Leonard) is calculated to have made a close approach of 978000±65000 km (608000±40000 mi) to Saturn on 8 May 1936, closer than the orbit of Titan to the planet, with an orbital eccentricity of only 1.098±0.007. The comet may have been orbiting Saturn prior to this as a temporary satellite, but difficulty modelling the non-gravitational forces makes whether or not it was indeed a temporary satellite uncertain. [99]

Other comets and asteroids may have temporarily orbited Saturn at some point, but none are presently known to have.

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, [100] or that two large moons fused to form Titan, with the collision scattering icy debris that formed the mid-sized moons. [101] On 23 June 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. [71] Studies based on Enceladus's tidal-based geologic activity and the lack of evidence of extensive past resonances in Tethys, Dione, and Rhea's orbits suggest that the moons up to and including Rhea may be only 100 million years old. [102]

See also

Notes

  1. ↑ 62 moons were announced 3–16 May, 2023: S/2020 S 1, S/2006 S 9, S/2007 S 5, S/2004 S 40, S/2019 S 2, S/2019 S 3, S/2020 S 2, S/2020 S 3, S/2019 S 4, S/2004 S 41, S/2020 S 4, S/2020 S 5, S/2007 S 6, S/2004 S 42, S/2006 S 10, S/2019 S 5, S/2004 S 43, S/2004 S 44, S/2004 S 45, S/2006 S 11, S/2006 S 12, S/2019 S 6, S/2006 S 13, S/2019 S 7, S/2019 S 8, S/2019 S 9, S/2004 S 46, S/2019 S 10, S/2004 S 47, S/2019 S 11, S/2006 S 14, S/2019 S 12, S/2020 S 6, S/2019 S 13, S/2005 S 4, S/2007 S 7, S/2007 S 8, S/2020 S 7, S/2019 S 14, S/2019 S 15, S/2005 S 5, S/2006 S 15, S/2006 S 16, S/2006 S 17, S/2004 S 48, S/2020 S 8, S/2004 S 49, S/2004 S 50, S/2006 S 18, S/2019 S 16, S/2019 S 17, S/2019 S 18, S/2019 S 19, S/2019 S 20, S/2006 S 19, S/2004 S 51, S/2020 S 9, S/2004 S 52, S/2007 S 9, S/2004 S 53, S/2020 S 10, and S/2019 S 21 which were published in MPECs 2023-J21 to 2023-K05. One more moon, S/2006 S 20, was announced on 23 May 2023, which brings the final count to 146. [2] [1]
  2. ↑ The mass of the rings is about the mass of Mimas, [11] 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.
  3. ↑ Inktomi was once known as "The Splat". [67]
  4. ↑ The photometric color may be used as a proxy for the chemical composition of satellites' surfaces.
  5. 1 2 JPL's mean orbital elements suggest an inclination that is similar to those of the Gallic group; however other sources say it belongs to the Inuit group.
  6. ↑ A confirmed moon is given a permanent designation by the IAU consisting of a name and a Roman numeral. [41] The eight moons that were known before 1850 are numbered in order of their distance from Saturn; the rest are numbered in the order by which they received their permanent designations. Many small moons have not yet received a permanent designation.
  7. ↑ Absolute magnitudes of regular satellites are calculated from their mean diameters and geometric albedos given in NASA's Saturnian Satellite Fact Sheet. [45] Absolute magnitude estimates for some small inner moons are not available as they do not have measured geometric albedos. Absolute magnitudes of irregular satellites were taken from the Minor Planet Center's Natural Satellites Ephemeris Service. [90] Calculations were made with NASA/JPL's Asteroid Size Estimator. [91]
  8. ↑ The diameters and dimensions of the small inner moons, from Pan to Helene, are taken from Thomas et al., 2020, Table 1. [92] Diameters and dimensions of Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus, and Phoebe are from Thomas 2010, Table 1. [43] Diameters of Siarnaq and Albiorix are from Grav et al., 2015, Table 3. [85] The approximate sizes of all other irregular satellites are calculated from their absolute magnitudes with an assumed geometric albedo of 0.04, [91] which is the average value for that population. [85]
  9. ↑ Masses of the large round moons, including Hyperion, Phoebe, and Helene, were taken from Jacobson et al., 2022, Table 5. [93] Masses of Atlas, Prometheus, Pandora, Epimetheus, and Janus were taken from Lainey et al., 2023, Table 1. [94] Masses of Pan, Daphnis, Aegaeon, Methone, and Pallene were taken from Thomas et al., 2020, Table 2. [92] Masses of other regular satellites were calculated by multiplying their volumes with an assumed density of 500 kg/m3 (0.5 g/cm3), while masses of irregular satellites were calculated with an assumed density of 1000 kg/m3 (1.0 g/cm3).
  10. 1 2 3 4 Time-averaged orbital elements of all satellites were taken from JPL Solar System Dynamics. [84]
  11. ↑ Negative orbital periods indicate a retrograde orbit around Saturn (opposite to the planet's rotation). Orbital periods of irregular satellites may not directly correlate with their semi-major axes due to perturbations.
  12. ↑ Orbital inclinations of regular satellites and Phoebe are with respect to the Laplace plane. Orbital inclinations of irregular satellites are with respect to the ecliptic. [84]
  13. 1 2 May be part of the Gallic group because it has a similar inclination; however, it has a more distant semi-major axis. [1]
  14. ↑ S/2004 S 4 was most likely a transient clump—it has not been recovered since the first sighting. [23]

Related Research Articles

<span class="mw-page-title-main">Saturn</span> Sixth planet from the Sun

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine-and-a-half times that of Earth. It has only one-eighth the average density of Earth, but is over 95 times more massive. Even though Saturn is nearly the size of Jupiter, Saturn has less than one-third of Jupiter's mass. Saturn orbits the Sun at a distance of 9.59 AU (1,434 million km) with an orbital period of 29.45 years.

<span class="mw-page-title-main">Natural satellite</span> Astronomical body that orbits a planet

A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body. Natural satellites are colloquially referred to as moons, a derivation from the Moon of Earth.

<span class="mw-page-title-main">Rhea (moon)</span> Moon of Saturn

Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System, with a surface area that is comparable to the area of Australia. It is the smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium. It was discovered in 1672 by Giovanni Domenico Cassini.

<span class="mw-page-title-main">Tethys (moon)</span> Moon of Saturn

Tethys, or Saturn III, is a fifth largest moon of Saturn about 1,060 km (660 mi) across. It was discovered by G. D. Cassini in 1684 and is named after the titan Tethys of Greek mythology.

<span class="mw-page-title-main">Iapetus (moon)</span> Moon of Saturn

Iapetus is a moon of Saturn. With an estimated diameter of 1,469 km, it is the third-largest moon of Saturn and the eleventh-largest in the Solar System. Named after the Titan Iapetus, the moon was discovered in 1671 by Giovanni Domenico Cassini.

<span class="mw-page-title-main">Pandora (moon)</span> Moon of Saturn

Pandora is an inner satellite of Saturn. It was discovered in 1980 from photos taken by the Voyager 1 probe and was provisionally designated S/1980 S 26. In late 1985, it was officially named after Pandora from Greek mythology. It is also designated as Saturn XVII.

<span class="mw-page-title-main">Hyperion (moon)</span> Moon of Saturn

Hyperion, also known as Saturn VII, is a moon of Saturn distinguished by its highly irregular shape, chaotic rotation, extremely low density and its unexplained sponge-like appearance. It was the first non-round moon to be discovered.

<span class="mw-page-title-main">Calypso (moon)</span> Trojan moon of Saturn

Calypso is a moon of Saturn. It was discovered in 1980, from ground-based observations, by Dan Pascu, P. Kenneth Seidelmann, William A. Baum, and Douglas G. Currie, and was provisionally designated S/1980 S 25. Several other apparitions of it were recorded in the following months: S/1980 S 29, S/1980 S 30, S/1980 S 32, and S/1981 S 2. In 1983 it was officially named after Calypso of Greek mythology. It is also designated Saturn XIV or Tethys C.

<span class="mw-page-title-main">Dione (moon)</span> Moon of Saturn

Dione, also designated Saturn IV, is the fourth-largest moon of Saturn. Its trailing hemisphere is marked by large ice cliffs called chasmata and is also darkened compared to the leading hemisphere. Based on its density, Dione’s interior is likely a combination of silicate rock and water ice in nearly equal parts by mass. The moon was discovered by Italian astronomer Giovanni Domenico Cassini in 1684 and is named after the Titaness Dione in Greek mythology.

<span class="mw-page-title-main">Enceladus</span> Natural satellite orbiting Saturn

Enceladus is the sixth-largest moon of Saturn. It is about 500 kilometers in diameter, about a tenth of that of Saturn's largest moon, Titan. It is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only −198 °C, far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.

<span class="mw-page-title-main">Mimas</span> Moon of Saturn

Mimas, also designated Saturn I, is a natural satellite of Saturn. With a mean diameter of 396.4 kilometres or 246.3 miles, Mimas is the smallest astronomical body known to be roughly rounded in shape due to its own gravity. Mimas's low density, 1.15 g/cm3, indicates that it is composed mostly of water ice with only a small amount of rock, and study of Mimas's motion confirmed that it has a liquid ocean beneath its surface ice. The surface of Mimas is heavily cratered and shows little signs of recent geological activity. A notable feature of Mimas' surface is Herschel, one of the largest craters relative to the size of the parent body in the Solar System. Herschel measures 139 kilometres across, about one-third of Mimas's mean diameter, and is believed to be formed from an extremely energetic impact event. The crater's name is derived from the discoverer of Mimas, William Herschel, in 1789. The moon's presence has created one of the largest 'gaps' in Saturn's ring, named the Cassini Division, due to orbital resonance destabilizing the particles' orbit there.

<span class="mw-page-title-main">Phoebe (moon)</span> Moon of Saturn

Phoebe is the most massive irregular satellite of Saturn with a mean diameter of 213 km (132 mi). It was discovered by William Henry Pickering on 18 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Station of the Carmen Alto Observatory near Arequipa, Peru, by DeLisle Stewart. It was the first satellite to be discovered photographically.

<span class="mw-page-title-main">Methone (moon)</span> Moon of Saturn

Methone is a small, egg-shaped moon of Saturn that orbits out past Saturn's ring system, between the orbits of Mimas and Enceladus. It was discovered in 2004, though it wasn't until 2012 that it was imaged in detail by the Cassini spacecraft.

<span class="mw-page-title-main">Rings of Saturn</span> Planar assemblage of icy particles orbiting Saturn

The rings of Saturn are the most extensive and complex ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometers to meters, that orbit around Saturn. The ring particles are made almost entirely of water ice, with a trace component of rocky material. There is still no consensus as to their mechanism of formation. Although theoretical models indicated that the rings were likely to have formed early in the Solar System's history, newer data from Cassini suggested they formed relatively late.

<span class="mw-page-title-main">Polydeuces (moon)</span> Trojan moon of Saturn

Polydeuces, also designated Saturn XXXIV, is a small trojan moon of Saturn occupying the trailing L5 Lagrange point of Dione. It was discovered by the Cassini Imaging Science Team in images taken by the Cassini space probe on 21 October 2004. With a mean diameter of about 3 km (1.9 mi), Polydeuces is thought to have a smooth surface coated with fine, icy particles accumulated from the cryovolcanic plumes of Enceladus. In its orbit around Saturn, Polydeuces periodically drifts away from Dione's Lagrange point due to gravitational perturbations by other nearby moons of Saturn. Of the four known trojan moons of Saturn, Polydeuces exhibits the largest displacement from its Lagrange point.

In astronomy, an inner moon or inner natural satellite is a natural satellite following a prograde, low-inclination orbit inwards of the large satellites of the parent planet. They are generally thought to have been formed in situ at the same time as the coalescence of the original planet. Neptune's moons are an exception, as they are likely reaggregates of the pieces of the original bodies, which were disrupted after the capture of the large moon Triton. Inner satellites are distinguished from other regular satellites by their proximity to the parent planet, their short orbital periods, their low mass, small size, and irregular shapes.

<span class="mw-page-title-main">S/2009 S 1</span> Small moonlet in Saturns B ring

S/2009 S 1 is a moonlet embedded in the outer part of Saturn's B Ring, orbiting 117,000 km (73,000 mi) away from the planet. The moonlet was discovered by the Cassini Imaging Team during the Saturnian equinox event on 26 July 2009, when the Cassini spacecraft imaged the moonlet casting a 36 km (22 mi)-long shadow onto the B Ring. With a diameter of 300 m (1,000 ft), it is most likely a long-lived solid body, which would count it as the smallest and innermost known moon of Saturn.

<span class="mw-page-title-main">Planetary-mass moon</span> Planetary-mass bodies that are also natural satellites

A planetary-mass moon is a planetary-mass object that is also a natural satellite. They are large and ellipsoidal in shape. Moons may be in hydrostatic equilibrium due to tidal or radiogenic heating, in some cases forming a subsurface ocean. Two moons in the Solar System are larger than the planet Mercury : Ganymede and Titan, and seven are larger and more massive than the dwarf planets Pluto and Eris.

<span class="mw-page-title-main">Solar eclipses on Saturn</span> When moons of Saturn pass before the Sun

Solar eclipses on Saturn occur when the natural satellites of Saturn pass in front of the Sun as seen from Saturn. These eclipses happen fairly often. For example, some of Saturn's moons can have a solar eclipse every day depending on the saturnian season.

The following outline is provided as an overview of and topical guide to Saturn:

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