May 31, 2021
On the day you arrived, the Earth was spinning at a thousand miles per hour, orbiting the Sun at sixty-seven thousand.
Mimas: Small Moon with a Big Crater
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APOD published May 31, 2021. Credit: NASA, JPL-Caltech, Space Science Institute, Cassini. A publication-date match, not a photo taken on your date. Independent of NASA.
Whatever hit Mimas nearly destroyed it. What remains is one of the largest impact craters on one of Saturn's smallest round moons. Analysis indicates that a slightly larger impact would have destroyed Mimas entirely. The huge crater, named Herschel after the 1789 discoverer of Mimas, Sir William Herschel, spans about 130 kilometers and is featured here. 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. The featured image was taken during the closest-ever flyby of the robot spacecraft Cassini past Mimas in 2010 while in orbit around Saturn. Interactive: Take a trek across Mimas
Image credit: NASA, JPL-Caltech, Space Science Institute, Cassini