One of Saturn’s smallest moons has a secret ocean

(CNN) — Astronomers have found further evidence that one of Saturn’s smallest moons, Mimas, hides a global ocean beneath its icy surface. Developing a stronger case for the presence of water necessary for life as we know it could help scientists better understand where to look for habitable worlds in the vast expanses of deep space.

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

Discovered in 1789 by English astronomer William Herschel as a small dot near Saturn, Mimas was first photographed from space by the Voyager probes in 1980. looks like the Death Star from the Star Wars movie saga.

Data collected during Cassini’s flybys of Mimas have intrigued astronomers. The moon orbits Saturn in just over 22 hours and is only 186,000 kilometers from the planet. Cassini data showed that Mimas’s rotation and orbital motion were altered by the Moon’s interior.

Ocean worlds such as 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 life beyond Earth. Frédéric Durillon / Animea Studio / Paris Observatory – PSL, IMCCE

In 2014, a team of European researchers determined that the Moon’s rotation and motion is caused by a solid, elongated, rocky core or underground ocean.

Following up on previous research, astronomer Dr Valerie Laney and colleagues at the Paris Observatory analyzed orbital data to see which scenario was most likely. The results were published this Wednesday in the journal Nature.

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

“This discovery adds Mimas to the exclusive club of satellites with internal oceans, including Enceladus and Europa, but with a unique difference: its ocean is remarkably young, estimated to be only 5 (million) to 15 million years old,” the study said. in a statement co-author Dr Nick Cooper, honorary researcher in the Department of Astronomy, School of Physical and Chemical Sciences, Queen Mary University of London.

Old surface, young ocean

The research team determined the origin and age of the Mimas Ocean by studying how the Moon, which is about 400 kilometers in diameter, responded to the gravitational forces that Saturn exerted on it.

“The internal heating must come from tides caused by Saturn at Mimas,” Laney said. “These tidal effects caused friction inside the satellite, generating heat.”

The team suspects the ocean lies 20 to 30 kilometers below the Moon’s icy surface. Because the ocean is so young, astronomically speaking, there would be no outward signs of surface activity that would imply the presence of a subsurface ocean.

Mimas’s craters act like tell-tale wrinkles, suggesting it has an ancient surface. But Saturn’s Enceladus appears younger because active geysers have contributed to the resurgence, or deposition, of fresh, new material on the moon’s surface.

With the ocean still developing, Mimas may offer a unique window into the formation of subsurface oceans on other icy moons, the researchers say.

A Closer Look at Ocean Worlds

This discovery could change the way astronomers view the moons in our solar system.

“If Mimas hides a global ocean, that means liquid water could be just about anywhere,” Laney said. “We already have strong candidates for the role of the world’s oceans (on moons such as Callisto, Dione and Triton).

In 2017, NASA announced that ocean worlds may be the most likely places to search for life beyond Earth, and missions such as the European Space Agency’s Juice and NASA’s Europa Clipper and Dragonfly spacecraft will explore the potential habitability of Jupiter’s moons Europa, Ganymede and Callisto , as well as Saturn’s moon Titan.

Saturn Moon

The illustration shows Mimas in orbit around Saturn. The small moon looks like the Death Star from the Star Wars movies thanks to its huge crater. (Photo: Frédéric Durillon/Animea Studio/Paris Observatory – PSL, IMCCE)

“The existence of a recently formed liquid water ocean makes Mimas an ideal candidate for study by researchers investigating the origins of life,” Cooper said.

It may be time to look at other seemingly quiet moons in the solar system that may harbor conditions that could support life, the study authors say.

“Laney and colleagues’ results will stimulate a comprehensive study of medium-sized icy moons throughout the solar system,” the doctors wrote. Matija Czuk and Alyssa Rose Rhoden in an article accompanying the study. Chuk is a research scientist at the SETI Institute in California, and Roden is a senior scientist in the Office of Planetary Sciences at the Southwest Research Institute in Colorado.

Neither author was involved in the study, but Rodin is the author of a study on the possibility of a “hidden” ocean at Mimas.

“Essentially, the difference between our 2022 paper and this new paper is that we found that the geology of Mimas cannot rule out the presence of an ocean, although in fact they detect ocean signatures in the orbit of Mimas,” Roden said. “This is the strongest evidence yet that there is indeed an ocean on Mimas today.”

Since the publication of the 2022 report, Rodin and his research team have continued to study Mimas and agree with the new study’s conclusion that the lunar ocean is relatively young.

“Mimas certainly demonstrates that moons with old surfaces can hide young oceans, and that’s very exciting,” Roden said. “I think we can speculate about whether oceans appeared on the moons much later than we often think.”

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