Mimas (moon) - Physical Characteristics

Physical Characteristics

For more details on this topic, see List of geological features on Mimas.

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, the moon is not perfectly spherical; its longest axis is about 10% longer than the shortest. The ellipsoid shape of Mimas is especially noticeable in recent images from the Cassini probe.

Mimas's most distinctive feature is a giant impact crater 130 kilometres (81 mi) 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 kilometres (3.1 mi) high, parts of its floor measure 10 kilometres (6.2 mi) deep, and its central peak rises 6 kilometres (3.7 mi) above the crater floor. If there were a crater of an equivalent scale on Earth it would be over 4,000 kilometres (2,500 mi) 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 the moon's body.

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 greater than 40 kilometres (25 mi) in diameter, but in the south polar region, craters greater than 20 kilometres (12 mi) are generally lacking.

Three types of geological features are officially recognized on Mimas: craters, chasmata (chasms) and catenae (crater chains).