Saturn's 'Death Star' Moon May Hide an Ocean

Relatively young ocean thought to fill half of Mimas' volume
By Newser Editors and Wire Services
Posted Feb 8, 2024 6:25 PM CST
Saturn's 'Death Star' Moon May Hide an Ocean
This Feb. 13, 2010 image provided by NASA shows Saturn's moon Mimas and it's large Herschel Crater, captured by the Cassini spacecraft.   (NASA/JPL-Caltech/Space Science Institute via AP)

Astronomers have found the best evidence yet of a vast, young ocean beneath the icy exterior of Saturn's Death Star lookalike mini moon. The French-led team analyzed changes in Mimas' orbit and rotation and reported that a hidden ocean 12 to 18 miles beneath the frozen crust was more likely than an elongated rocky core, per the AP. The scientists based their findings, published in the journal Nature, on observations by NASA's Cassini spacecraft, which observed Saturn and its more than 140 moons for more than a decade before diving through the ringed planet's atmosphere in 2017 and burning up.

Barely 250 miles in diameter, the heavily cratered moon lacks the fractures and geysers—typical signs of subsurface activity—of Saturn's Enceladus and Jupiter's Europa. "Mimas was probably the most unlikely place to look for a global ocean—and liquid water more generally," co-author Valery Lainey of the Paris Observatory said in an email. It now "looks like a potential habitable world. But nobody knows how much time is needed for life to arise." Believed between 5 million and 15 million years old, too young to mark the moon's surface, this subterranean ocean would have an overall temperature right around freezing, according to Lainey. But at the seafloor, he said the water temperature could be much warmer.

The ocean is believed to fill half of Mimas' volume. Yet it represents only 1.2% to 1.4% of Earth's oceans given the moon's petite size. Despite being so small, Mimas boasts the second largest impact crater of any moon in the solar system—the reason it's compared to the fictional Death Star space station in Star Wars. "The idea that relatively small, icy moons can harbor young oceans is inspiring," SETI Institute's Matija Cuk and Southwest Research Institute's Alyssa Rose Rhoden wrote in an accompanying editorial. Co-author Nick Cooper of Queen Mary University of London said the existence of a "remarkably young" ocean of liquid water makes Mimas a prime candidate for studying the origin of life. (More space stories.)

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