Mimas joins an elite club of solar system moons harboring subsurface oceans with potential habitability.
An odd little moon that orbits closely to Saturn just revealed its biggest mystery: a hidden ocean that lies beneath its heavily cratered surface.
Mimas is less than 123 miles (198 kilometers) wide, too small to be perfectly round, and its icy shell is covered with deep scarring from objects slamming into it. Its most prominent impact crater, Herschel, stretches across a third of its face, giving it the nickname Death Star in homage to the Empire’s gigantic space station in Star Wars. The moon is so unassuming that scientists believed it was the least likely place to look for a subsurface ocean, and yet an analysis of Mimas’ orbital motion revealed an ocean 12 to 18 miles (20 to 30 kilometers) beneath its icy shell.
The discovery is detailed in a study published on Wednesday in the journal Nature. Using data from the Cassini space probe, which orbited Saturn from 2004 to 2017, the scientists behind the new study observed the subtle changes in Mimas’ orbit. Based on its motion and spin as it looped around Saturn, the data suggests that Mimas harbors a recently formed ocean that is still evolving.
