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Mimas (moon)
From Wikipedia, the free encyclopedia
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| Discovery | |
|---|---|
| Discovered by: | William Herschel |
| Discovery date: | September 17, 1789[1] |
| Orbital characteristics | |
| Mean radius of orbit: | 185,520 km [2] |
| Eccentricity: | 0.0202[3] |
| Orbital period: | 0.9424218 d[3] |
| Inclination: | 1.51° (to Saturn's equator) |
| Satellite of: | Saturn |
| Physical characteristics | |
| Dimensions: | 414.8×394.4×381.4 km (0.0311 Earths)[4] |
| Mean radius: | 198.30 ± 0.30 km[5] |
| Surface area: | ~490,000 km² |
| Volume: | ~32,900,000 km3 |
| Mass: | 3.7493 ± 0.0031×1019 kg [5][6] (6.3×10-6 Earths) |
| Mean density: | 1.1479 ± 0.0053 g/cm3 [5] |
| Equatorial surface gravity: | 0.0636 m/s2 |
| Escape velocity: | 0.159 km/s |
| Rotation period: | synchronous |
| Axial tilt: | zero |
| Albedo: | 0.962 ± 0.004 (geometric)[7] |
| Temperature: | ~64 K |
| Apparent magnitude: | 12.9 [8] |
Mimas (pronounced /ˈmaɪməs/ mye'-məs, Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel.[9] It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I.
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— William Herschel, Philosophical Transactions of the Royal Society of London, Vol. 80 [10]
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Mimas is named after one of the Titans in Greek mythology. The names of all seven then-known satellites of Saturn, including Mimas, were suggested by William Herschel's son John in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope.[11][12] He named them after Titans specifically because Saturn (the Roman equivalent of Kronos in Greek mythology), was the leader of the Titans.
According to Liddell and Scott's Greek-English Lexicon, the adjectival form of Mimas would be Mimantean (the genitive case is Latin Mimantis, Greek Μῑμάντος). In practice, anglicisms such as Mimasian and Mimian are very occasionally seen, but more commonly writers simply use the phrase 'of Mimas'.
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' 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. Particles at the inner edge of the Cassini division are in a 2:1 resonance with Mimas. They orbit twice for each orbit of Mimas. The repeated pulls by Mimas on the Cassini division particles, always in the same direction in space, force them into new orbits outside the gap. Other resonances with Mimas are also responsible for other features in Saturn's rings: the boundary between the C and B ring is at the 3:1 resonance and the outer F ring shepherd, Pandora, is at the 3:2 resonance. More recently, a 7:6 corotation eccentricity resonance has been discovered with the G ring, whose inner edge is about 15000 km inside the orbit of Mimas.
Mimas has been imaged several times from moderate distances by the Cassini orbiter, the closest being at 63,000 km on 2005 August 01. There are no closer fly-bys planned.
 Mimas, imaged by Cassini, looking notably egg-shaped |
 Mimas, silhouetted against Saturn's northern latitudes |
- Mimas closely resembles the Death Star in the Star Wars film, which is also said to be several hundred kilometers in diameter. This is purely coincidental, as the first movie was made 3 years before the first close-up photographs of Mimas were taken.
- Mimas is featured in the book Red Dwarf: Infinity welcomes careful drivers as the moon Dave Lister lives on prior to his acceptance into the mining ship Red Dwarf.
- Mimas is the site of a Federation way station in the Star Trek universe.
- Cassini mission page - Mimas
- Mimas Profile by NASA's Solar System Exploration
- Journal of raw images from Cassini
- The Planetary Society: Mimas
- The Nine Planets - Mimas
- Views of the Solar System - Mimas
- ^ Imago Mundi - La Découverte des satellites de Saturne (French).
- ^ Harvey, Samantha (April 11, 2007). NASA: Solar System Exploration: Planets: Saturn: Moons: Mimas: Facts & Figures. NASA. Retrieved on 2007-10-10.
- ^ a b NASA Celestia
- ^ Thomas, P. C.; et al. (2006). Shapes of the Saturnian Icy Satellites. 37th Lunar and Planetary Science Conference. Retrieved on 2006-11-26.
- ^ a b c Jacobson, R. A.; Antreasian, P. G.; Bordi, J. J.; Criddle, K. E.; et al. (December 2006). "The Gravity Field of the Saturnian System from Satellite Observations and Spacecraft Tracking Data". The Astronomical Journal 132: 2520-2526.
- ^ Jacobson, R. A.; et al. (2005). "The GM values of Mimas and Tethys and the libration of Methone". Astronomical Journal 132: 711.
- ^ Verbiscer, A.; French, R.; Showalter, M.; and Helfenstein, P.; Enceladus: Cosmic Graffiti Artist Caught in the Act, Science, Vol. 315, No. 5813 (February 9, 2007), p. 815 (supporting online material, table S1)
- ^ Classic Satellites of the Solar System. Observatorio ARVAL. Retrieved on 2007-09-28.
- ^ Herschel, W. (1790). "Account of the Discovery of a Sixth and Seventh Satellite of the Planet Saturn; With Remarks on the Construction of Its Ring, Its Atmosphere, Its Rotation on an Axis, and Its Spheroidical Figure". Philosophical Transactions of the Royal Society of London 80: 1–20.
- ^ Herschel (1790), reported by Arago, M. (1871). "Herschel". Annual Report of the Board of Regents of the Smithsonian Institution: 198–223. Retrieved on 2006-11-26.
- ^ As reported by William Lassell, Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 3, pp. 42–43 1848 January 14)
- ^ Lassell, William (1848). "Satellites of Saturn: Observations of Mimas, the closest and most interior Satellite of Saturn". Monthly Notices of the Royal Astronomical Society 8: 42. Retrieved on 2006-11-26.
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| Generally listed in increasing distance from Saturn. Temporary names in italics. | |
| Ring shepherds | (moonlets) · Pan · Daphnis · Atlas · Prometheus · S/2004 S 6? · S/2004 S 4? · S/2004 S 3? · Pandora |
| Co-orbitals | Epimetheus · Janus |
| Inner large (and Trojan) |
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| Outer large | Rhea · Titan · Hyperion · Iapetus |
| Inuit group | Kiviuq · Ijiraq · Paaliaq · Siarnaq · Tarqeq |
| Norse group |
Phoebe · Skathi · S/2007 S 2 · Skoll · S/2004 S 13 · Greip · Hyrrokkin · Mundilfari · Jarnsaxa · S/2006 S 1 · S/2004 S 17 · Narvi · Bergelmir · Aegir · Suttungr · S/2004 S 12 · Bestla · Farbauti · Hati · S/2004 S 7 · Thrymr · S/2007 S 3 · S/2006 S 3 · Surtur · Kari · Fenrir · Ymir · Loge · Fornjot |
| Gallic group | Albiorix · Bebhionn · Erriapus · Tarvos |
| Rings of Saturn · Cassini-Huygens · Themis · Chiron | |
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|---|---|---|
| Planetary satellites | Terrestrial · Martian · Jovian · Saturnian · Uranian · Neptunian |  |
| Other satellite systems | Plutonian · Eridian · Asteroid satellites | |
| Largest satellites | Ganymede · Titan · Callisto · Io · Moon · Europa · Triton Titania · Rhea · Oberon · Iapetus · Charon · Umbriel · Ariel · Dione · Tethys · Enceladus · Miranda · Proteus · Mimas |
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| Inner satellites • Trojans • Irregulars • List • List by diameter • Timeline of discovery • Naming | ||