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Astronomers have found further evidence that one of Saturn’s smallest moons, Mimas, is hiding a global ocean beneath its icy surface. Building a stronger case for the presence of water – essential to life as we know it – could help scientists better understand where they can search for habitable depths in the vastness of deep space.
Scientists previously thought Mimas was just a big 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 in 1789 by the English astronomer William Herschel as a tiny dot near Saturn, Mimas was first imaged from space by the Voyager probes in 1980. Craters cover the surface of Mimas, but the largest is 80 miles (about 130 kilometers) across and causes. the moon to resemble the Death Star from the “Star Wars” movies.
Data collected during Cassini flybys of Mimas intrigued astronomers… The moon takes a little more than 22 hours to orbit Saturn and is only about 115,000 miles (186,000 kilometers) from the planet. Cassini data showed that the interior of the moon caused changes in Mimas’ rotation and orbital motion.
A team of European researchers determined in 2014 that the rotation and movement of the moon was caused by a rigid, elongated and rocky core or subsurface ocean.
To follow up on the previous study, the astronomer Observatoire de Paris Dr. Valéry Lainey and his colleagues analyzed the orbital motion data to see what the most likely scenario was. The results were published on Wednesday in the journal Nature.
The team determined that the moon’s spin and orbital motion did not match Cassini’s observations if Mimas had a pancake-shaped rocky core. Instead, the evolution of Mimas’ orbit over time suggested that its motion is shaped by an internal ocean, Lainey said.
“This discovery adds Mimas to an exclusive club of moons with internal oceans, including Enceladus and Europa, but with a unique difference: its ocean is extremely young, estimated to be only 5 (million) to 15 million years old age,” said the study’s coauthor. Nick Cooper, honorary research fellow in the astronomy unit of the School of Physical and Chemical Sciences at Queen Mary University of London, in a statement.
Old surface, young ocean
The research team determined the origin and age of the Mimas ocean by studying how the moon, about 249 miles (400 kilometers) in diameter, responded to the gravitational forces exerted on it by Saturn.
“Internal heating must come from the tides raised by Saturn on Mimas,” Lainey said. “These tidal effects have induced friction within the satellite, providing heat.”
The team suspects that the ocean is about 12.4 miles to 18.6 miles (20 kilometers to 30 kilometers) deep beneath the moon’s ice shell. With the ocean so young, from an astronomical point of view, there would be no outward signs of surface activity to suggest the existence of a subterranean ocean.
The craters across Mimas act like telltale wrinkles, suggesting an ancient surface. But Saturn’s Enceladus appears younger because active geysers have helped resurface, or deposit new, fresh material on the surface of that moon.
The ocean is still developing, so Mimas could provide unique insight into the processes behind how the subsurface oceans formed on other icy moons, the researchers said.
A closer look at sea life
The discovery could change the way astronomers think about moons throughout our solar system.
“If Mimas hides a global ocean, this means liquid water could be almost anywhere,” Lainey said. “We already have serious candidates for global oceans (on moons like Callisto, Dione and Triton.”
In 2017, NASA announced that the world’s oceans may be the most likely places to find life beyond Earth, and missions such as the European Space Agency’s Juice and NASA’s Europa Clipper and Dragonfly spacecraft will investigate the possible habitability of Jupiter’s moons Europa, Ganymede and Callisto and Saturn’s moon Titan.
“Because of a recently formed liquid water ocean, Mimas is a prime candidate for study, for researchers investigating the origins of life,” Cooper said.
Maybe it’s time to look at other moons that seem quiet around the solar system that may be hiding conditions that could support life, the authors of the study said.
“The results of Lainey and colleagues will encourage a thorough examination of intermediate-sized icy moons throughout the Solar System,” wrote Dr. Matija Ćuk and Alyssa Rose Rhoden in an article accompanying the study. Ćuk is a research scientist at the SETI Institute in California, and Rhoden is a principal scientist at the Planetary Science Directorate of the Southwest Research Institute in Colorado.
Neither author was involved in the study, but Rhoden has written research about the potential for a “stealth” ocean on Mimas.
“Basically, the difference between our 2022 paper and this new paper is that we found that the geology of Mimas could not rule out an ocean, but they are detecting the signature of the ocean within the orbit of Mimas,” Rhoden said . “It’s the strongest evidence we have, so far, that Mimas actually has an ocean today.”
Since the 2022 report, Rhoden and her research group have been continuing their study of Mimas, and agree with the new study’s conclusion about the relatively young age of the moon’s ocean.
“Mimas definitely shows that moons with old surfaces can be hiding young oceans, which is pretty exciting,” Rhoden said. “I think we can speculate about the moons that the oceans developed much later than we often think.”
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