Saturn's 'Death Star' moon has a hidden ocean under its surface, scientists say

Scientists have discovered a recently formed "force" under one of Saturn's most storied moons.

Saturn's Mimas moon resembles the Empire's Death Star station in the "Star Wars" franchise due to its gray, icy shell and large impact crater on its surface -- but its famous likeness is not what has researchers talking.

French astronomer Valéry Lainey and a team of researchers from Observatoire de Paris announced the discovery of Mimas' newly formed ocean, a finding that could change the way scientists define ocean moons as well as the conditions for habitability.

The research was published in Nature on Wednesday.

The 250-mile-wide celestial body joins Saturn's other moons, Titan and Enceladus, and Jupiter's Europa and Ganymede moons in the growing list of moons known to have subterranean oceans.

Mimas' neighboring moon, Enceladus, has icy fracturing across its surface and has been observed spouting geysers of water, which indicted the existence of a below-surface body of water, according to NASA.

Mimas' thick, icy exterior, however, has never indicated the existence of an ocean. Researchers suggest this is because Mimas' ocean dwells 12 to 18 miles (20 to 30 kilometers) below the moon's 15-mile-thick frozen shell.

"Mimas would be the most unlikely place to look for the presence of a global ocean," researchers wrote. However, after a "detailed analysis of Mimas' orbital motion" they found that the moon's ocean is "likely to be less than 25 million years old and still evolving."

The researchers from Observatoire de Paris based their findings off observations made by NASA's Cassini spacecraft, which analyzed Saturn's 140-plus moons for over a decade before 2017, when it crashed into the ringed planet.

"The major finding here is the discovery of habitability conditions on a solar system object which we would never, never expect to have liquid water," Valery Lainey told Space.com. "It's really astonishing."

Fellow researchers have hailed the findings on Mimas' hidden ocean as "inspiring," though note the previous hypothesis surrounding Mimas' unique orbit.

"The idea that relatively small, icy moons can harbor young oceans is inspiring," SETI Institute's Matija Ćuk and Southwest Research Institute's Alyssa Rose Rhoden remarked in an editorial published in Nature News & Views Wednesday.

The researchers note that previous understanding of Mimas' orbit came from what was believed to be a "very elongated core," however, the internal ocean hypothesis is "just as plausible."

"This could be explained either by the moon having a very elongated rocky core, which would enhance the difference between its moments of inertia, or an internal ocean, which would allow its outer shell to oscillate independently of its core," Ćuk and Rhoden wrote.

Though colloquially referred to as the Death Star moon after "Star Wars" fame, Mimas was discovered in 1789 by astronomer William Herschel. The name Mimas hails from a giant in Greek mythology.