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Mimas (mye'-mus) is a moon of Saturn that was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology (Greek Μίμας, Latin Mimās, rarely Mimans), and is also designated Saturn I.

Discovered by William Herschel
Discovered on September 17, 1789
Orbital characteristics
Semimajor axis 185,404 km
Eccentricity 0.0202 [1]
Orbital period 0.9424218 d [2]
Inclination 1.51° (to Saturn's equator)
Is a satellite of Saturn
Physical characteristics
Mean diameter 397.2 km (418.2×392.4×382.8 km)
Surface area ~1,990,000 km2
Volume ~32,900,000 km3
Mass 3.84×1019 kg
Mean density 1.17 g/cm3
Surface gravity ~0.077 m/s2
Escape velocity ~0.16 km/s
Rotation period synchronous
Axial tilt zero
Albedo 0.77
Surface temp.
min mean max
K ~64 K K
Atmosphere none


The name "Mimas" and the names of all seven satellites of Saturn then known were suggested by Herschel's son John Herschel in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope ([3])

According to Liddell and Scott's Greek-English Lexicon, the correct adjectival form for Mimas would be Mimantean (the genitive case is Mimantis, Greek Μῑμάντ-). In practice, however, anglicisms such as Mimasian and Mimian are very occasionally seen, and more commonly writers simply use the form 'of Mimas'.

Physical characteristics

Mimas' low density (1.17) indicates that it is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, the moon is not perfectly spherical; its longest axis is about 10% longer than the shortest. The somewhat ovoid shape of Mimas is especially noticeable in recent images from the Cassini probe.

Mimas, imaged by Cassini, looking notably egg-shaped

Mimas' most distinctive feature is a colossal impact crater 130 km across, named Herschel after the moon's discoverer. Herschel's diameter is almost a third of the moon's own diameter; its walls are approximately 5 km high, parts of its floor measure 10 km deep, and its central peak rises 6 km above the crater floor. If there were a crater of an equivalent scale on Earth it would be over 4,000 km in diameter, wider than Canada. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through the moon's body.

The surface is saturated with smaller impact craters, but no others are anywhere near the size of Herschel. Although Mimas is heavily cratered, the cratering is not uniform. Most of the surface is covered with craters greater than 40 km in diameter, but in the south polar region, craters greater than 20 km are generally lacking. This suggests that some process removed the larger craters from these areas.

Scientists officially recognise two types of geological features on Mimas: craters and chasmata (chasms). See also: List of geological features on Mimas.

Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn's two widest rings, A Ring and B Ring.

Mimas in Fiction and Film

Mimas bears a striking resemblance to the Death Star, a space station in the movie Star Wars

Comparisons have been made between Mimas' appearance and the appearance of the Death Star from the movie Star Wars (see picture). However, this is merely a coincidence, as Mimas was not photographed until three years after the release of the film.

In the novels of Rob Grant and Doug Naylor based on their sitcom Red Dwarf, Mimas is the site of a large, congested spaceport from which Dave Lister escapes as a stowaway and begins his journey on the Red Dwarf. Both the book and the series refer to the local delicacy "Mimean Bladderfish".

An episode of Star Trek: The Next Generation features Mimas as the site of an evacuation station to which four Starfleet cadets, including Wesley Crusher, transport after their vessels collide.

In the 1958 novel Lucky Starr and the Rings of Saturn (one of Isaac Asimov's famous Lucky Starr juvenile space opera series, which were originally published under the pseudonym of Paul French) the hero, knowing that Mimas is almost entirely made of ice, guides his ship on a collision course toward it, melts its surface with his weapons, and thus hides the ship underwater in order to escape from his enemies, the people from the Sirius System.

. | Janus, Epimetheus | Mimas | Methone | ...

Cassini Maps Saturn's Moon Mimas

Saturn's natural satellites

Pan | Daphnis | Atlas | Prometheus | S/2004 S 6 | S/2004 S 4 | S/2004 S 3 | Pandora | Epimetheus and Janus | Mimas | Methone | Pallene | Enceladus | Telesto, Tethys, and Calypso | Polydeuces, Dione, and Helene | Rhea | Titan | Hyperion | Iapetus | Kiviuq | Ijiraq | Phoebe | Paaliaq | Skathi | Albiorix | S/2004 S 11 | Erriapo | Siarnaq | S/2004 S 13 | Tarvos | Mundilfari | S/2004 S 17 | Narvi | S/2004 S 15 | S/2004 S 10 | Suttungr | S/2004 S 12 | S/2004 S 18 | S/2004 S 9 | S/2004 S 14 | S/2004 S 7 | Thrymr | S/2004 S 16 | Ymir | S/2004 S 8

see also: Rings of Saturn | Cassini-Huygens | Themis

see also: The Solar System

Astronomy Encyclopedia

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