Mimas is one of Saturn’s moons. It was discovered in 1789 by the German-born British astronomer William Herschel.

Diameter: 3.92 x 105 m
Mass: 3.79 x 1019 kg
Composition: Water-ice and some rock
Orbit: 1.85 x 105 m from Saturn

Mimas is the seventh largest of Saturn’s moon, the 20th-largest moon in the Solar System and the smallest shape to have its body rounded by gravitational forces. Saturn has 62 moons with confirmed orbits, 53 of which have names. 24 of these are regular satellites that orbit Saturn with only small inclinations to the planet’s equatorial plane. 37 of the remaining 38 are irregular satellites that orbit at high inclinations and a much greater distance from Saturn. These are probably minor planets that were captured by Saturn or debris from their break-up during the process. The final irregular satellite is unclear.

Saturn, the Roman god of agriculture and harvest, had a number of brothers and sisters, whose names were used for the plant’s known moons. When more moons were discovered, additional names of characters from Greek or Roman mythology or figures from other cultures had to be used. The irregular satellites are named after characters from Inuit, Gallic and Norse mythology. Mimas is named after one of the Gigantes, the giant sons of Gaia, who was the mother of all the heavenly gods. Mimas was slain by Hercules, the son of Jupiter. The name was first suggested 1847 by William Herschel’s son John.

The composition of Mimas is mainly water-ice with small amounts of rock. There is no known past or present geological activity such as volcanism. Its most dominant surface feature is the 130 km wide Herschel crater – named after the moon’s discoverer – that is one third of Mimas’ diameter. The walls of the crater are 5 km high and its floor reaches depths of 10 km. Shock waves from the impact that caused this crater created lineaments, ridges, grooves and other fractures. There are other, smaller impact craters and crater chains (catenae), but none of them has the dimensions of Herschel.

Mimas is responsible for clearing material in the Cassini Division, the gap between Saturn’s two widest rings, the A ring and the B ring. It is in resonance with two other Saturn moons, Dione and Enceladus, who speed up in their orbits as they approach each other and slow down when they move away. The Mimas orbital period around Saturn is 0.92 Earth days. This coincides with the rotation of the moon on its own axis.

Spacecraft missions Voyager 1 and 2 took the first photographs of Mimas. The Cassini mission to Saturn provided detailed images. It photographed Mimas from a distance of 9,500 km with a resolution of 5km. The images revealed surprisingly hot regions on the surface of the moon that resembled a “Pac-man” computer image eating a dot.

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