Short answers, pulled from the story.
Mimas was discovered by the astronomer William Herschel on the 17th of September 1789 using his 40-foot reflecting telescope, which had a 48-inch aperture. Herschel recorded detecting the seventh satellite of Saturn when it was at its greatest preceding elongation.
Herschel Crater measures 139 kilometres across, nearly one-third of Mimas's mean diameter of 396.4 kilometres. Its walls stand approximately 5 kilometres high, parts of its floor are 10 kilometres deep, and its central peak rises 6 kilometres above the crater floor.
Evidence strongly supports the existence of a liquid ocean beneath Mimas's icy surface. On the 7th of February 2024, researchers at the Paris Observatory announced that Mimas's orbital precession is slower than a solid body would produce, pointing to an internal ocean located 20 to 30 kilometres below the surface. Scientists estimate the ocean is younger than 25 million years old, and possibly only 2 to 3 million years old.
Mimas's giant Herschel Crater, with its concave shape, resembles the superlaser dish of the Death Star from the 1977 film Star Wars. The resemblance is coincidental: the film was made nearly three years before any spacecraft resolved the crater in enough detail to observe it.
Particles in the Huygens Gap at the inner edge of the Cassini Division orbit Saturn twice for every single orbit Mimas completes, a 2:1 orbital resonance. The repeated gravitational pulls from Mimas, always in the same direction, push those particles out of the gap and clear the region between Saturn's A Ring and B Ring.
Mimas has a mean diameter of 396.4 kilometres and a density of 1.15 grams per cubic centimetre, indicating it is composed mostly of water ice with only a small amount of rock. Its surface area is slightly less than the land area of Spain or California, making it the smallest astronomical body known to be roughly rounded by its own gravity.