Read at www.theguardian.com
Mimas, a moon of Saturn known for its resemblance to the Death Star from Star Wars, has a hidden ocean buried beneath its crust, according to researchers. The discovery means Mimas joins other moons in Saturn and Jupiter that are known to have subterranean oceans. The unexpected finding was made by analyzing Mimas's spin and orbital motion, which led researchers to conclude that it must possess a hidden subsurface ocean to move the way it does. The ocean is estimated to be 45 miles deep and accounts for more than half of Mimas's volume.
It's quite a surprise, said Valery 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.
The discovery of a hidden ocean on Mimas suggests that the moon's surface remains heavily battered due to impacts, with the Herschel crater being one such impact. The age of the subsurface ocean is estimated to be around 25 million years, formed through powerful tidal forces exerted by Saturn that warmed Mimas's core and melted the overlying ice. The details of the discovery are published in the journal Nature.
By astronomical standards, Mimas's ocean appears to be relatively young, forming in the past 25 million years when powerful tidal forces exerted by Saturn deformed Mimas's core, warming it like a massaged squash ball. The heated core then melted overlying ice, creating an ocean inside the Saturnian moon.