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Saturn’s moon Mimas harbors an ocean beneath its scarred surface

Mimas is less than 198 kilometers in diameter, which means it is not perfectly spherical. Its icy shell is dotted with deep scars from numerous collisions with space objects. The most prominent crater, Herschel, cuts across a third of the moon’s surface, giving Mimas the nickname “Death Star” after the enormous space station from Star Wars. Scientists considered Mimas the least likely candidate for the presence of a subsurface ocean, but analysis of its orbital motion showed the presence of an ocean at a depth of 20-30 kilometers under the icy crust.

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The discovery is described in a study published in the journal Nature. Using data from the Cassini probe, which orbited Saturn from 2004 to 2017, scientists recorded subtle changes in Mimas’s orbit. Based on its motion and rotation as it orbits Saturn, these data point to the existence of a recently formed ocean that is still evolving.

The ocean is believed to be approximately 5-15 million years old. For comparison, the internal ocean of the moon Enceladus formed about a billion years ago, and the ocean of Europa has existed for almost 4 billion years.

Mimas thus joins Enceladus, Europa, Saturn’s moon Titan and Jupiter’s moon Ganymede on the list of icy “ocean worlds” in the solar system. However, deeper research may reveal other similar objects. The icy satellites are heated by tidal forces, causing the ice to melt from the inside and freeze on the outside, forming a covering layer. These satellites are prime candidates for the search for life in our system as we know it.

As model calculations show, this ocean reached its current depth relatively recently – less than 2-3 million years ago. This period may not have been long enough for the emergence of life, offering a rare opportunity to study the habitability conditions of the early solar system.

Meanwhile, the JUICE mission heads to Jupiter’s icy moons to search for signs of habitability. Alas, we will still have to wait before sending new missions to Saturn and its moons.

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