page_title: Mimas (moon)
section_title: Physical characteristics
hierarchical_section_title: Mimas (moon) / Physical characteristics
caption_attribution_description: The most detailed images ever taken of Saturn's moon Mimas show it to be one of the most heavily cratered Saturnian moons, with little if any evidence for internal activity. Mimas has been so heavily cratered that new impacts can only overprint or even completely obliterate other older craters. Mimas is 397 kilometers or (247 miles) across. The moon displays an unexpected array of crater shapes. The highest crater walls tower 6 kilometers (4 miles) above the floors and show signs of material sliding down slope. Indeed, many of the large craters -- more than 15 kilometers (10 miles) in diameter -- appear to be filled in with rough-surfaced material, likely the result of landslides triggered by subsequent impacts elsewhere on Mimas' surface. Some of these deposits have craters superimposed on them, demonstrating that the landslides themselves may be quite old. Grooves, some of which are over a kilometer deep, cut across the surface for more than 100 kilometers (63 miles). These are some of the only indications that there might have once been internal activity under this ancient, battered surface. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org. The NASA image has been cropped.
context_page_description: 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 396 kilometres, 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.
context_section_description: 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 130 km (81 mi) across, named Herschel after the discoverer of Mimas. Herschel's diameter is almost a third of Mimas's own diameter; its walls are approximately 5 km (3 mi) high, parts of its floor measure 10 km (6 mi) deep, and its central peak rises 6 km (4 mi) above the crater floor. If there were a crater of an equivalent scale on Earth (in relative size) it would be over 4,000 km (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 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 40 km (25 mi) in diameter, but in the south polar region, there are generally no craters larger than 20 km (12 mi) in diameter.
  Three types of geological features are officially recognized on Mimas: craters, chasmata (chasms) and catenae (crater chains).
caption: Cassini view of Mimas's trailing hemisphere, showing craters up to 6 km deep and 1-km-deep chasmata (grooves). The large crater near center is Morgan; Arthur is close to the lower right limb. Pelion Chasma is faintly visible as a horizontal trough left of Arthur and below Morgan.
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