Science!

A moon of Saturn that resembles the Death Star from Star Wars because of a massive impact crater on its surface has a hidden ocean buried miles beneath its battered crust, researchers say.

The unexpected discovery means Mimas, an ice ball 250 miles wide, becomes the latest member of an exclusive club, joining Saturn’s Titan and Enceladus and Jupiter’s Europa and Ganymede as moons known to harbour subterranean oceans.

“It’s quite a surprise,” said Valéry Lainey, an astronomer at the Observatoire de Paris in France. “If you look at the surface of Mimas, there’s nothing that betrays a subsurface ocean. It’s the most unlikely candidate by far.”


Peculiarities in Mimas’s orbit had led astronomers to entertain two possibilities: either it contained an elongated core shrouded in ice, or an internal ocean that allowed its outer shell to shift independently of the core.

By analysing thousands of images from Nasa’s Cassini mission to Saturn, Lainey and his colleagues reconstructed the precise spin and orbital motion of Mimas as it looped around the gas giant. Their calculations showed Mimas must possess a hidden subsurface ocean to move the way it does.

“There is no way to explain both the spin of Mimas and the orbit with a rigid interior,” Lainey said. “You definitely need to have global ocean on which the icy shelf can slip.”

Their calculations suggest an ocean 45 miles deep lurks beneath Mimas’s 15-mile-thick icy shell, with temperatures near the sea floor reaching tens of degrees celsius. The ocean would account for more than half of Mimas’s volume. Details are published in Nature.……

https://www.theguardian.com/science...oon-mimas-hidden-ocean?CMP=Share_iOSApp_Other