Saturn's moons and rings

A small Solar System: Saturn's moons

Saturn has the most moons of any planet in the Solar System; currently 62 known moons (as of the first half 2011). Of these, 53 have been named. Of the 62 known moons, 29 have been discovered since 2004.

It is really no surprise that people talk about the Saturn system as being an analogy of the Solar System. This is a world of unique complexity, made up of a central body and its satellites, not to mention the famous ring surrounding the planet at its equator. Saturn is also being orbited by a man-made satellite, the space probe Cassini, which will remain in orbit around the planet until at least 2017. The orbiter will perform repeated fly-bys of the planet's moons at various distances and at different orbital inclinations, gathering scientific data from every conceivable angle.

Like the gas giant Jupiter, the largest planet in the Solar System, the moons of Saturn vary enormously in their composition and the age of their surfaces. With the exception of Titan, however, Saturn's moons are much smaller than Jupiter's four large moons: Ganymede (the largest satellite in the Solar System), Callisto, Io and Europa, known collectively as the 'Galilean' moons after the astronomer who discovered them.

Like the Galilean moons, the moons of Saturn (except Io) are composed primarily of ice, mixed with varying proportions of rock and, in some cases, organic substances (carbon compounds). As well as photographically documenting the surface geology using the camera system on board the Cassini spacecraft, another principal objective of the Cassini-Huygens mission is to study the chemical and mineralogical composition of the planet's moons using the spectrometers onboard the Cassini probe (and in the case of Titan, the Huygens lander).

Titan's upper atmosphere in ultraviolet

Titan, the second largest moon in the Solar System (its diameter of 5150 kilometres makes it even larger than Mercury and Pluto), has one unique feature: its dense atmosphere of nitrogen and methane. This is one of the features that rank Titan amongst the most important targets of exploration in the outer Solar System.

The European atmospheric and lander probe Huygens was taken on a six-year journey to Saturn by Cassini with the express aim of exploring the mysterious moon. The Huygens probe touched down on Titan's icy-cold (-180º) surface of frozen methane on 14 January 2005 after a three-hour parachute descent, during which it took important measurements and pictures.

The first of Saturn's satellites were discovered in the 17th century by the Italian-French astronomer Giovanni Cassini (1625-1712) and his Dutch contemporary Christiaan Huygens (1629-1695). However, it was the two US Pioneer probes, and later Voyager I and II, that provided us in 1980 with the first close-up pictures of these unknown worlds, providing the stimulus for the most ambitious project ever launched in the exploration of the outer Solar System: the US-European probe Cassini-Huygens.

Classifying Saturn's moons is no easy task, but categorising them by size puts Titan at the top of the list by a considerable amount. There are four much smaller moons, with diameters ranging from 1060 to 1530 kilometres: Rhea, Iapetus, Dione and Tethys. Then there are three moons whose diameters range from almost 200 to 500 kilometres: Enceladus, Mimas and Hyperion. These moons are also known as the 'main' satellites.

Saturn's moon Enceladus above the planet's rings

Janus, Phoebe, Epimetheus, Prometheus and Pandora, the largest of the smaller satellites, are not at all spherical in shape, and each has a diameter of between 10 and 100 kilometres. Then there are a dozen satellites barely more than 10 kilometres in diameter, starting with Siarnaq, which measures 40 kilometres. Finally, there are numerous irregularly shaped satellites, with sizes of less than 10 kilometers.

A dozen of these minuscule moons were discovered using what was then the largest reflecting telescope in the world, on Mauna Kea in Hawaii. Eleven of these bodies orbit Saturn in the opposite direction to the planet's own direction of rotation, supporting the idea that they were not formed together with the planet in their current location in the Solar System, but originated in the 'comet reservoir' of the Kuiper Belt between the orbital paths of Uranus, Neptune and Pluto before being captured by Saturn's gravitational force. Analyses performed by the VIMS spectrometer on board Cassini suggest that the 200 kilometre diameter moon Phoebe may be of similar origin. The hypothesis that many of these small, irregular bodies do not originate within the Saturn system but in other regions of the Solar System is also supported by the fact that these moons often have orbital inclinations that deviate markedly from the plane of the equator.

Known moons of Saturn (as of 12/2005)

Name of
moon

Astronomical designation

Diameter (km)

Distance_to_ Saturn centre (km)

Discoverer

Titan51501 221 9001655
Christiaan Huygens
Rhea1528527 1001672
Giovanni Cassini
Iapetus14363 560 8001671
Giovanni Cassini
Dione1118377 4001684
Giovanni Cassini
Tethys1060294 700 1684
Giovanni Cassini
Enceladus499238 100 1789
Wm Herschel
Mimas397185 600 1789
Wm Herschel
Hyperion2661 464 100 1848
W. & G. Bond; W. Lassell
JanusS/1980 S 1178151 500 1980
Audouin Dollfus
Phoebe12012 944 300 1898
W. H. Pickering
D. L. Stewart
EpipmetheusS/1980 S 3119151 400 1980
R. Walker
PrometheusS/1980 S 27100139 400 1980
S. Collins
PandoraS/1980 S 2684141 7001980
S. Collins
SiarnaqS/2000 S 34018 160 0002000
Gladman & Kavelaars
Atlas S/1980 S 28 32137 700 1980
Richard Terrile
Helene S/1980 S 6 32377 400 1980
P. Lacques & J. Lecacheux
Albiorix S/2000 S 11 3216 404 000 2000
Matthew Holman
Telesto S/1980 S 13 24 294 700 1980
B. Smith et al
Paaliaq S/2000 S 2 22 15 199 000 2000
Brett Gladman
Pan S/1980 S 13 20 133 600 1981
Mark Showalter
Calypso S/1980 S 25 19 294 700 1980
D. Pascu et al
Ymir S/2000 S 1 18 23 096 000 2000
Brett Gladman
Kiviuq S/2000 S 5 16 11 365 000 2000
Brett Gladman
Tarvos S/2000 S 4 15 18 247 000 2000
Kavelaars & Gladman
Ijiraq S/2000 S 6 12 11 440 000 2000
Kavelaars & Gladman
Erriapo S/2000 S 10 10 17 616 000 2000
Kavelaars & Gladman
Skathi (Skadi) S/2000 S 8 815 647 000 2000
Kavelaars & Gladman
Daphnis S/2005 S 1 7136 500 2005
Cassini ISS Team
Mundilfari S/2000 S 9 718 709 000 2000
Gladman & Kavelaars
Narvi S/2003 S 1 718 719 000 2003
Sheppard et al
Suttungr S/2000 S 12 719 463 000 2000
Gladman & Kavelaars
S/2004 S 18 719 650 000 2004
David Jewitt et al
Thrymr S/2000 S 7 720 382 000 2000
Gladman & Kavelaars
S/2004 S 11 616 950 000 2004
S. S. Shepard
S/2004 S 13 618 450 000 2004
David Jewitt et al
S/2004 S 15 618 750 000 2004
David Jewitt et al
S/2004 S 10 619 350 000 2004
David Jewitt et al
S/2004 S 7 619 800 000 2004
David Jewitt et al
S/2004 S 14 619 950 000 2004
David Jewitt et al
S/2004 S 8 622 200 000 2004
David Jewitt et al
S/2004 S 12 519 650 000 2004
David Jewitt et al
S/2004 S 9 519 800 000 2004
David Jewitt et al
Pallene S/2004 S 2 4211 000 2004
Charnóz & Porco
Polydeuces S/2004 S 5 4377 400 2004
Carolyn Porco
S/2004 S 17 418 600 000 2004
David Jewitt et al
S/2004 S 16 422 200 000 2004
David Jewitt et al
Methone S/2004 S 1 3194 000 2004
Charnóz & Porco

Saturn's rings

Ring

Distance

Width

D66 970 km 7540 km
C74 510 km 17 490 km
B92 000 km 25 580 km
A122 170 km 14 610 km
F140 180 km 50 km
G170 180 km500 to several thousand km
E181 000 km 302 000 km

Distance is from Saturn's centre to closest edge of ring

Last modified: 18/07/2011 15:23:18

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Contacts

Elke Heinemann
Deutsches Zentrum für Luft- und Raumfahrt (DLR) - German Aerospace Center

Tel.: +49 2203 601-2867

Fax: +49 2203 601-3249
Ulrich Köhler
Deutsches Zentrum für Luft- und Raumfahrt (DLR) - German Aerospace Center

Tel.: +49 30 67055-215

Fax: +49 30 67055-402

The 21 largest satellites of Saturn

Die 21 größten Saturn%2dTrabanten

In the upper half of the illustration, the 21 largest Saturn satellites are represented full-scale with respect to each other and in relation to the parent planet (beige circular segment under the moons) and to the rings (in the background). The lower half shows the positions of several of the moons up to a distance of approximately seven Saturn radii from the planet's centre, which can be seen as an outline hemisphere having a radius of 71,500 kilometres at the left (shown in correct full scale).

Titan's upper atmosphere in ultraviolet

Titans obere Atmosphäre in Ultraviolett

Titan's upper atmosphere in ultraviolet. Several dust layers are easily recognizable.

Links

  • DLR Institute of Planetary Research / Cassini
    (http://solarsystem.dlr.de/PG/cassini/)
  • ESA Cassini-Huygens Special
    (http://www.esa.int/SPECIALS/Cassini-Huygens/index.html)
  • NASA Cassini-Huygens Special
    (http://saturn.jpl.nasa.gov/home/index.cfm)