The moon “Death Star” hides an ocean inside, according to scientists

Mimas, Saturn’s most star moon, yields evidence that it maintains a liquid ocean in its interior.

Simulations of the Herschel impact basin on Mimas, Saturn’s smallest and inner moon, provide more evidence that it is a world with a liquid ocean inside.

Both the striking structure of the basin, which resembles this moon to the ‘death star’ from Star Wars, and the absence of tectonics in Mimas are compatible with an increasingly thin layer of ice and a geologically young ocean.

“In the final days of NASA’s Cassini mission to Saturn, the spacecraft identified a curious libration, or wobble, in Mimas’s rotation, which often points to a geologically active body capable of hosting an internal ocean,” he said. In a statement, Dr. Alyssa Rhoden of SwRI (Southwest Research Institute), a specialist in the geophysics of icy satellites, particularly those that contain oceans, and in the evolution of giant planet satellite systems.

She is the second author of a new paper on the subject published in Geophysical Research Letters. “Mimas seemed an unlikely candidate, with its heavily cratered, icy surface scarred by a giant impact crater that makes the small moon look a lot like the Death Star from Star Wars. If Mimas has an ocean, it represents a new class of small “stealth” ocean worlds, with surfaces that do not give away the existence of the ocean.”

The study

Rhoden worked with Purdue graduate student Adeene Denton to better understand how a heavily cratered moon like Mimas could possess an internal ocean. Denton modeled the formation of the Hershel impact basin using the iSALE-2D simulation software.

Models showed that the Mimas ice sheet must have been at least 55 km thick at the time of the Herschel-forming impact. Instead, observations of Mimas and models of its internal warming limit the current thickness of the ice sheet to less than 30 km, if it currently hosts an ocean.

These results imply that a present-day ocean within Mimas must have been warming and expanding since the basin formed.

It is also possible that Mimas was completely frozen both at the time of Herschel’s impact and today. However, Denton found that including an inland ocean in the impact models helped produce the shape of the basin.

“We found that Herschel could not have formed in an ice sheet of its current thickness without destroying the ice sheet at the impact site,” explains Denton, who is now a postdoctoral researcher at the University of Arizona.

“If Mimas has an ocean today, the ice sheet has been thinning since the formation of Herschel, which could also explain the lack of fractures in Mimas.

If Mimas is an emerging ocean world, it places significant constraints on the formation, evolution, and habitability of all of Saturn’s midsize moons.”

“Although our results support the existence of a present-day ocean at Mimas, it is difficult to reconcile the moon’s orbital and geological characteristics with our current understanding of its thermal orbital evolution,” says Rhoden.

“Assessing the status of Mimas as an oceanic moon would serve as a reference for models of its formation and evolution. This would help us better understand Saturn’s rings and mid-size moons, as well as the prevalence of potentially habitable oceanic moons, especially Uranus. Mimas is an attractive target for further investigation.”