Mimas is a small, icy moon of Saturn. It was discovered in 1789 by William Herschel. Mimas has a diameter of 396 kilometers (246 miles), making it the smallest known body in the Solar System with an dynamic equilibrium ( hydrostatic balance ). Its surface is heavily cratered, and its most prominent feature is a large impact crater called Herschel (named after Mimas’ discoverer). Mimas is only 1/10th as massive as our own Moon. Despite its small size, Mimas has a relatively high density, indicating that it must have a very solid surface. The temperature on Mimas averages -179 degrees Celsius (-290 degrees Fahrenheit).
Mimas orbits Saturn at a distance of 185,520 kilometers (114,750 miles), taking 22 hours and 37 minutes to complete one orbit. It is tidally locked to Saturn, meaning that one side always faces the planet while the other faces away. This results in strong tidal forces exerted on Mimas by Saturn which cause “ripples” or “grooves” in its surface. These features are most visible near Herschel Crater.
The origin of Mimas is unknown. It may be a captured asteroid or comet, or it may have formed in situ from the same disk of material that formed Saturn’s other moons. Like all moons orbiting gas giants, it is thought to have accreted gradually from smaller bodies over time.