Mimas (moon)
Mimas, also designated Saturn I, is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology.
With a diameter of, it is the smallest astronomical body that is known to still be rounded in shape because of self-gravitation. However, Mimas is not actually in hydrostatic equilibrium for its current rotation.
Discovery
Mimas was discovered by the astronomer William Herschel on 17 September 1789. He recorded his discovery as follows: "The great light of my forty-foot telescope was so useful that on the 17th of September, 1789, I remarked the seventh satellite, then situated at its greatest western elongation."The 40-foot telescope was a metal mirror reflecting telescope built by Herschel, with a aperture. The 40 feet refers to the length of the focus, not the aperture diameter as more common with modern telescopes.
Name
Mimas is named after one of the Giants in Greek mythology, Mimas. 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. He named them after Titans specifically because Saturn was the leader of the Titans and ruler of the world for some time. Mimas was a son of the Greek goddess Gaia.The customary English pronunciation of the name is, though some people attempt a more 'authentic' pronunciation,.
The Greek and Latin root of the name is Mimant-, and so the English adjectival form is Mimantean or Mimantian, either spelling pronounced ~.
Physical characteristics
The surface area of Mimas is slightly less than the land area of Spain. The low density of Mimas, 1.15 g/cm3, indicates that it is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, Mimas is noticeably prolate; its longest axis is about 10% longer than the shortest. The ellipsoidal shape of Mimas is especially noticeable in some recent images from the Cassini probe.Mimas's most distinctive feature is a giant impact crater across, named Herschel after the discoverer of Mimas. Herschel's diameter is almost a third of Mimas's own diameter; its walls are approximately high, parts of its floor measure deep, and its central peak rises above the crater floor. If there were a crater of an equivalent scale on Earth it would be over in diameter, wider than Australia. 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 Mimas's core.
The Mimantean 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 larger than in diameter, but in the south polar region, there are generally no craters larger than in diameter.
Three types of geological features are officially recognized on Mimas: craters, chasmata and catenae.
Orbital resonances
A number of features in Saturn's rings are related to resonances with Mimas. Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn's two widest rings, the A Ring and B Ring. Particles in the Huygens Gap at the inner edge of the Cassini division are in a 2:1 orbital 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. The boundary between the C and B rings is in a 3:1 resonance with Mimas. Recently, the G Ring was found to be in a 7:6 co-rotation eccentricity resonance with Mimas; the ring's inner edge is about inside Mimas's orbit.Mimas is also in a 2:1 mean-motion resonance with the larger moon Tethys, and in a 2:3 resonance with the outer F Ring shepherd moonlet, Pandora
Anomalous libration
In 2014, researchers noted that the librational motion of Mimas has a component that cannot be explained by its orbit alone, and concluded that it was due to either an interior that is not in hydrostatic equilibrium or an internal ocean. However, in 2017 it was concluded that the presence of an ocean in Mimas' interior would have led to surface tidal stresses comparable to or greater than those on tectonically active Europa. Thus, the lack of evidence for surface cracking or other tectonic activity on Mimas argues against the presence of such an ocean; as the formation of a core would have also produced an ocean and thus the nonexistent tidal stresses, that possibility is also unlikely. The presence of an asymmetric mass anomaly associated with the crater Herschel may be a more likely explanation for the libration.Exploration
Pioneer 11 flew by Saturn in 1979, and its closest approach to Mimas was 104,263 km on September 1, 1979. Voyager 1 flew by in 1980, and Voyager 2 in 1981.Mimas was imaged several times by the Cassini orbiter, which entered into orbit around Saturn in 2004. A close flyby occurred on February 13, 2010, when Cassini passed by Mimas at.
In popular culture
When seen from certain angles, Mimas resembles the Death Star, a fictional space station and superweapon known from the 1977 film Star Wars. Herschel resembles the concave disc of the Death Star's "superlaser". This is coincidental, as the film was made nearly three years before Mimas was resolved well enough to see the crater.In 2010, NASA revealed a temperature map of Mimas, using images obtained by Cassini. The warmest regions, which are along one edge of Mimas, create a shape similar to the video game character Pac-Man, with Herschel Crater assuming the role of an "edible dot" or "power pellet" known from Pac-Man gameplay.