Scientists say that Saturn’s “Death Star” moon hides an inner ocean

Scientists say that Saturn’s “Death Star” moon hides an inner ocean

Frédéric Dorion/Anime Studio/Paris Observatory – PSL, IMCCE

Artist’s illustration depicting Mimas in orbit around Saturn. The small moon resembles the Death Star in the “Star Wars” movies, thanks to a huge crater.

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Astronomers have discovered further evidence that one of Saturn’s smallest moons, Mimas, hides a global ocean beneath its icy surface. Building a stronger case for the existence of water — which is essential for life as we know it — could help scientists gain a better understanding of where to look for habitable worlds in the vast expanse of deep space.

Scientists previously thought Mimas was just a large chunk of ice before NASA’s Cassini mission studied Saturn and some of its 146 moons by orbiting the ringed planet between 2004 and 2017.

Discovered by English astronomer William Herschel in 1789 as a small dot near Saturn, Mimas was first imaged from space by Voyager’s probes in 1980. Craters cover Mimas’ surface, but the largest are 80 miles (about 130 kilometers) across and cause the moon to resemble the Death Star from Star Wars movies.

Data collected during Cassini The flyby of Mimas aroused the interest of astronomers. The Moon takes just over 22 hours to orbit Saturn, and is only about 115,000 miles (186,000 kilometers) from the planet. Cassini data showed that Mimas’ rotation and orbital motion experienced changes caused by the moon’s interior.

A team of European researchers determined in 2014 that either a solid, elongated, rocky core or a subsurface ocean was what caused the moon’s rotation and movement.

To follow up on the previous study, astronomer at the Paris Observatory Dr. Valéry Ligny and his colleagues analyzed orbital motion data to find out the most likely scenario. The results were published on Wednesday in the journal Nature.

The team determined that the Moon’s rotation and orbital motion did not match Cassini observations if Mimas had a rocky, pancake-shaped core. Instead, the evolution of Mimas’ orbit over time suggests that the inner ocean shaped its motion, Lainey said.

“This discovery adds Mimas to an exclusive club of moons with inner oceans, including Enceladus and Europa, but with a unique difference: its ocean is remarkably young, and its age is estimated at only 5 million to 15 million years,” said the study’s co-author. Dr. Nick Cooper, Honorary Research Fellow in the Astronomy Unit in the School of Physical and Chemical Sciences at Queen Mary University of London, said in a statement.

The research team determined the origin and age of the Mimas Ocean by studying how the moon, which has a diameter of about 249 miles (400 kilometers), responds to the gravitational forces exerted by Saturn on it.

“The internal heating must come from the tides that Saturn stirs up on Mimas,” Lainey said. “These tidal effects caused friction within the satellite, which provided heat.”

The team suspects the ocean depth is about 12.4 miles to 18.6 miles (20 kilometers to 30 kilometers) beneath the moon’s icy crust. Because the ocean is so young, astronomically speaking, there would be no outward signs of surface activity to indicate a subsurface ocean.

Craters on Mimas’ surface act like visible wrinkles, indicating that its surface is ancient. But Saturn’s Enceladus appears younger because active geysers have contributed to the reappearance or deposition of new material on that moon’s surface.

The ocean is still evolving, so Mimas may offer a unique window into the processes behind how subsurface oceans form on other icy moons, the researchers said.

This discovery could change the way astronomers think about moons across our solar system.

“If Mimas hides a global ocean, that means liquid water could exist almost anywhere,” Lainey said. “We already have serious candidates for global oceans (on moons like) Callisto, Dione, and Triton.”

In 2017, NASA announced that ocean worlds may be the most likely places to find extraterrestrial life, and missions such as ESA’s Juice and NASA’s Europa Clipper and Dragonfly spacecraft will investigate the potential habitability of Jupiter’s moons Europa, Ganymede, Callisto, and Jupiter. Saturn’s moon Titan.

Frédéric Dorion/Anime Studio/Paris Observatory – PSL, IMCCE

Ocean worlds like Enceladus and Europa (top left, top right), Titan and Callisto (bottom left, bottom right) and now Mimas (center), may be the best worlds to search for extraterrestrial life.

“The presence of a recently formed liquid water ocean makes Mimas a prime candidate for study for researchers searching for the origin of life,” Cooper said.

The study’s authors said it may be time to observe other seemingly quiet moons across the solar system, which could hide conditions that could support life.

“The findings of Linney and colleagues will stimulate a comprehensive examination of medium-sized icy moons throughout the solar system,” the doctors wrote. Mattia Cook and Alyssa Rose Rhoden in an article accompanying the study. Cook is a research scientist at the SETI Institute in California, and Roden is a principal scientist in the Planetary Sciences Directorate at the Southwest Research Institute in Colorado.

None of the authors were involved in the study, but Roden did author a paper on the possibility of a “hidden” ocean at Mimas.

“Basically, the difference between our 2022 paper and this new paper is that we find that the ocean cannot be ruled out by the geology of Mimas, whereas they are actually detecting the signature of the ocean within the orbit of Mimas,” Roden said. “It is the strongest evidence we have, to date, that Mimas actually has an ocean today.”

Since the 2022 report, Roden and her research team have continued their study of Mimas, and they agree with the new study’s conclusion about the relatively young age of the moon’s ocean.

“Mimas certainly proves that moons with old surfaces can hide young oceans, which is very exciting,” Roden said. “I think we can speculate that the moons have developed oceans much more recently than we often assume.”

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