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| Discovery | |
|---|---|
| Discovered by | William Herschel |
| Discovered on | September 17, 1789 |
| Orbital characteristics | |
| Semimajor axis | 185,520 km |
| Eccentricity | 0.0202 |
| Orbital period | 22 h 37 min 5 s |
| Inclination | 1.53 ° |
| Is a satellite of | Saturn |
| Physical characteristics | |
| Mean diameter | 397.2 km |
| Mass | 3.84×1019 kg |
| Mean density | 1.17 g/cm3 |
| Surface gravityThis article covers the physics of gravitation. See also gravity (disambiguation). Gravitation is the tendency of masses to move toward each other. The first mathematical formulation of the theory of gravitation was made by Sir Isaac Newton and proved ast | 0.077 m/s2In physics, acceleration (symbol: a is defined as the rate of change (or time derivative) of velocity. It is thus a vector quantity with dimension length/ time˛. In SI units, this is metre/second˛. To accelerate an object is to change its velocity over a |
| Rotation periodprograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 one sidereal day). | 22 h 37 min 5 s ( synchronousIn astronomy, synchronous rotation is a planetological term describing a body orbiting another, where the orbiting body takes as long to rotate on its axis as it does to make one orbit; and therefore always keeps the same hemisphere pointed at the body it) |
| Axial tiltAxial tilt is an astronomical term regarding the inclination angle of a planet's rotation axis in relation to its orbital plane. It is also called obliquity . A planet whose rotation axis were perpendicular to the orbital plane would have an axial tilt of | 0.005 ° |
| AlbedoNote: This article discusses the physical or planetological property of albedo. For other usage, see Albedo (disambiguation). The albedo is a measure of reflectivity of a surface or body. It is the ratio of electromagnetic radiation reflected to the amoun | 0.77 |
| Atmosphere | none |
Mimas ("MY muss") 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. It is also designated Saturn I.
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 [1].
Mimas' low density (1.17) indicates that it is composed mostly of water ice with only a small amount of rock.
Mimas' most distinctive feature is a colossal impact crater 130 km across, named Herschel after the moon's discoverer. Herschel covers almost 1/3 of the diameter of the entire moon; 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 4000 km in diameter, wider than Canada. The impact that made this crater must have nearly disrupted Mimas entirely; fractures can be seen on the opposite side of Mimas that may be due to the shock waves from the impact travelling through the moon's body.
The surface is saturated with other 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 feature on Mimas: craters and chasmata (chasms). See also: List of geological features on Mimas
The Cassini-Huygens orbiter is due to perform a flyby of Mimas on August 1, 2005.
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