Death Star: Hidden ocean discovered on Saturn’s icy moon

Saturn’s moon, dubbed the Death Star, hides an ocean beneath its crust, scientists say. Their calculations show that beneath Mimas’s 15-mile-thick icy shell lies an internal body of water 45 miles deep.

Saturn’s moon, which resembles the Death Star from Star Wars due to the huge impact crater on its surface, has a hidden ocean buried miles beneath its shattered crust, researchers say.

According to The Guardian, the surprise discovery means Mimas, a 250-mile-wide icy ball, becomes “the latest member of an exclusive club,” joining Saturn’s Titan and Enceladus and Jupiter’s Europa and Ganymede, which are known to contain underground oceans.

“This is quite unexpected,” says Valerie Laney, an astronomer at the Paris Observatory in France. – If you look at the surface of Mimas, you will not see anything that would indicate the presence of a subsurface ocean. This is by far the most unlikely candidate.”

The peculiarities of Mimas’s orbit led astronomers to consider two possibilities: either it contained an elongated core covered in ice, or an internal ocean that allowed its outer shell to move independently of the core.

By analyzing thousands of images taken by NASA’s Cassini mission to Saturn, Valerie Laney and his colleagues reconstructed the precise rotation and orbital motion of Mimas as it circled the gas giant. Their calculations showed that Mimas must have a hidden subsurface ocean to move the way it does.

“It is impossible to explain Mimas’s rotation and orbit by rigid internal conditions,” Laney notes. “You definitely need a global ocean on which the ice shelf can slide.”

Their calculations show that beneath Mimas’s 15-mile-thick ice shell lies an ocean 45 miles deep, with temperatures near the seafloor reaching tens of degrees Celsius. The ocean accounts for more than half the volume of Mimas. Details published in Nature.

By astronomical standards, Mimas’ ocean appears to be relatively young, having formed over the past 25 million years as powerful tidal forces generated by Saturn warped Mimas’ core, heating it up like a massaged squash ball. The heated core then melted the ice on top, forming an ocean inside Saturn’s moon. The surface remains heavily damaged, with one giant impact creating Herschel Crater, named after astronomer William Herschel, who first discovered Mimas in 1789.

The discovery of global oceans on the moons of Saturn and Jupiter has sparked a flurry of interest from space agencies eager to explore their potential to host life. More than 100 geysers have been discovered on Enceladus, with steam escaping through cracks on the surface. If life ever developed on the tiny Moon, the plumes could carry extraterrestrial microbes into space, where they could be detected by visiting missions.

Laney notes that since Mimas contained water in contact with warm rock, he would not rule out life there. But if the hidden ocean is only tens of millions of years old, life may not have had a chance to emerge. “Whether it’s too early, no one knows,” he said. “I would say: why not?”

David Rothery, professor of planetary geosciences at the Open University, said that even if Mimas does have an underground ocean, there are easier places to look for life beyond Earth. “There is no indication of a connection between the interior ocean, where life could survive, and the surface or space where traces of life could be found and sampled, as we have done in the Enceladus plumes and hope to do on the surface or in the Europa plumes,” said Rothery. – If there was life inside Mimas, it would be hidden by more than 20 kilometers of solid ice. If the ocean existed for only 25 million years, that may not have been long enough for life to arise. Europa and Enceladus are much more promising candidates.”