Astronomers have found evidence of a young ocean on Saturn’s moon

Astronomers have found the clearest evidence of a vast, young ocean beneath the icy surface of Saturn’s mini-moon, the Death Star.

A team led by French astronomers analyzed changes in Mimas’s orbit and rotation and reported Wednesday that it is more likely to be an ocean hidden 20 to 30 kilometers (12 to 18 miles) beneath an icy crust than an elongated, rocky core. The scientists based their findings on observations from NASA’s Cassini spacecraft, which observed Saturn and its more than 140 moons for more than a decade before passing through the ringed planet’s atmosphere in 2017 and burning up.

The moon, just 400 kilometers (250 miles) in diameter, is devoid of the rifts and geysers – typical signs of underground activity – of Saturn’s Enceladus and Jupiter’s Europa.

“Mimas was perhaps the most unexpected place to look for the global ocean and liquid water more broadly,” co-author Valerie Laney of the Paris Observatory said in an email. “So it looks like a potentially habitable world. But no one knows how long it will take for life to appear.”

The results were published in the journal Nature.

According to Laney, the ocean is thought to fill half the volume of Mimas. However, given the Moon’s small size, it barely accounts for 1.2% to 1.4% of Earth’s oceans. Despite its small size, Mimas has the second largest impact crater of any moon in the solar system, leading it to be compared to the fictional Death Star space station from the Star Wars saga.

“The idea that relatively small, icy moons could harbor young oceans is exciting,” Matija Czuk of the SETI Institute and Alyssa Rose Rhoden of the Southwest Research Institute wrote in an editorial accompanying the paper. They were not part of the study.

This internal ocean, believed to be between 5 and 15 million years old, is too young to mark the Moon’s surface and its overall temperature may approach freezing, Laney said. But on the seabed, he says, temperatures can be much higher.

Co-author Nick Cooper of Queen Mary University of London said the existence of an “extremely young” liquid water ocean makes Mimas a prime candidate for studying the origins of life.

Mimas, discovered in 1789 by English astronomer William Herschel, is named after a giant from Greek mythology.

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