In fact, if the impact had been much greater, it would have disrupted the entire satellite . The large crater has been named Herschel after the 1789 discoverer of Mimas, Sir William Herschel . Mimas' low mass produces a surface gravity just strong enough to create a spherical body but weak enough to allow such relatively large surface features. Mimas is made of mostly water ice with a smattering of rock - so it is accurately described as a big dirty snowball. Voyager 1 flew by in 1980 and took the above picture .
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