Mimas

Mimas 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, and is also designated Saturn I.

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. Mimas' surface gravity is .008g or eight/one-thousands of that for Earth.

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. 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.

''Note: In Turtledove's introduction to the story in the Departures Short Story Collection, he indicates he named the features based on a preliminary map submitted by the Voyager science team to the International Astronomical Union. These names were based on the Arthurian legends and the largest crater was named after King Arthur. The Union elected to name this crater after Herschel (see above). Turtledove decided Les Mortes d'Herschel made for a less dramatic title and so left it well enough alone.''