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Astronomers have uncovered additional evidence that Mimas, one of Saturn’s smallest moons, hides a global ocean beneath its icy surface. Creating stronger evidence for the existence of water, which is essential 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 had previously thought Mimas was just a large chunk of ice before NASA’s Cassini mission studied Saturn and some of its 146 moons while orbiting the ringed planet between 2004 and 2017.
Discovered as a small dot near Saturn by British astronomer William Herschel in 1789, Mimas was first imaged from space by the Voyager probes in 1980. Craters cover the surface of Mimas, but the largest are 80 miles (about 130 kilometers) in diameter, causing craters. The moon will resemble the Death Star in the “Star Wars” movies.
The data collected during Cassini’s flybys close to Mimas attracted the attention of astronomers. The Moon takes just over 22 hours to orbit Saturn and is only 115,000 miles (186,000 kilometers) away from the planet. Cassini data showed that Mimas’ spin and orbital motion experienced changes triggered by the moon’s interior.
A team of European researchers determined in 2014 that the moon’s rotation and motion are caused by a solid, elongated and rocky core, or subsurface ocean.
Continuing the previous study, Paris Observatory astronomer Dr. Valéry Lainey and colleagues analyzed orbital motion data to see which scenario was most likely. The findings were published Wednesday in the journal Nature.
The team determined that if Mimas has a pancake-shaped rocky core, the moon’s rotation and orbital motion do not match Cassini observations. Instead, the evolution of Mimas’ orbit over time suggests that an interior ocean is shaping its motion, Lainey said.
“This discovery adds Mimas to an exclusive club of moons with interior oceans, including Enceladus and Europa, but with a unique difference: its ocean is quite young, estimated to be only 5 (million) to 15 million years old,” said one of the study’s authors. ” said. Dr. is an honorary research fellow in the astronomy unit at the School of Physical and Chemical Sciences at Queen Mary University of London. Nick Cooper made a statement.
Old surface, young ocean
The research team determined the origin and age of the Mimas ocean by examining how the moon, which is approximately 249 miles (400 kilometers) in diameter, responded to the gravitational forces exerted on it by Saturn.
“The internal warming must be due to Saturn’s tides on Mimas,” Lainey said. “These tidal effects caused friction inside the satellite and provided heat.”
The team suspects the ocean lies beneath the moon’s ice shell at a depth of about 12.4 miles to 18.6 miles (20 kilometers to 30 kilometers). Astronomically speaking, since the ocean is so young, there would be no signs of external activity on the surface that would imply the existence of a subsurface ocean.
Craters on Mimas behave like wrinkles, suggesting it has an ancient surface. But Saturn’s Enceladus appears younger because active geysers contribute to resurfacing, or deposition of new, fresh material on the 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.
A closer look at ocean worlds
This discovery could change the way astronomers think about moons in our solar system.
“If Mimas hides a global ocean, that means liquid water could be found almost everywhere,” Lainey said. “We already have serious candidates for the global oceans (of the moons) Callisto, Dione and Triton.”
In 2017, NASA reported that ocean worlds may be the places most likely to find life beyond Earth, and that missions such as the European Space Agency’s Juice and NASA’s Europa Clipper and Dragonfly spacecraft are investigating the potential habitability of Jupiter’s moons Europa, Ganymede, and Callisto. He announced that he would investigate. Saturn’s moon Titan.
“The presence of a recently formed liquid water ocean makes Mimas a prime candidate for researchers investigating the origin of life,” Cooper said.
The study’s authors said it may be time to observe other seemingly quiet moons throughout the solar system that could hide conditions that could support life.
“Lainey and colleagues’ findings will motivate a comprehensive examination of medium-sized icy moons in the Solar System,” wrote Dr. In an article accompanying the study by Matija Ćuk and Alyssa Rose Rhoden. Ćuk is a research scientist at the SETI Institute in California, and Rhoden is a principal scientist in the Planetary Science Directorate of the Southwest Research Institute in Colorado.
Neither author was involved in the study, but Rhoden wrote research about the potential for a “hidden” ocean at Mimas.
“Fundamentally, the difference between our 2022 paper and this new paper is that we find an ocean that cannot be ignored by the geology of Mimas, whereas they are actually detecting signatures of the ocean orbiting Mimas,” Rhoden said. “This is the strongest evidence we have so far that Mimas actually has an ocean today.”
Rhoden and his research group have continued their study of Mimas since the 2022 report, and they agree with the new study’s conclusion about the relatively young age of the lunar ocean.
“Mimas definitely shows that moons with old surfaces can hide young oceans, which is pretty exciting,” Rhoden said. “I think we can speculate that moons formed oceans much more recently than we thought.”
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