Mimas

Mimas is the innermost large moon of Saturn, orbiting at a mean distance of 115,000 mi (185,000 km). It whirls rapidly around the ringed planet, completing each orbit in only 0.94 Earth days. Mimas was discovered by William Herschel in 1789.

Mimas is small - 243 mi (392) km in diameter - and has a low density, indicating that it probably consists mostly of water ice. Its surface is icy and heavily cratered. There is an enormous crater, named Herschel, on one side, which is nearly one-third the diameter of Mimas itself. Herschel is the result of an impact that nearly split Mimas apart. Traces of fracture marks can be seen on the opposite side of the small moon.