Saturn's small moon Mimas, which astronomers liken to the Death Star from the “Star Wars” series, has an ocean beneath its icy surface, making it possible for some species to reach it, a recent study suggests.
Mimas is part of a family of rare moons in the Solar System that have liquid water beneath their icy layers. This family includes Jupiter's moons Europa and Ganymede and Saturn's moons Enceladus and Titan.
The lead author of the study published in the journal said:NatureValerie Linney, in a press conference: “If there's one place in the universe where we don't expect conditions favorable to life, it's Mimas.”
Discovered by astronomer William Herschel in 1789, the moon “has not been of much use since its appearance,” pointed out Linney, an astronomer at the Institute of Celestial Mechanics and Ephemeris Calculus at the Paris PSL Observatory.
The 400-kilometer-diameter star was nicknamed the “death moon” because it appeared cold, hard, and unfit for life. Its surface is riddled with craters, including a large one that gives the false impression that it resembles the Death Star from the “Star Wars” series.
Unlike Saturn's other moon Enceladus, the moon's icy crust was found frozen, its smooth surface constantly being reshaped by the activity of its internal ocean and its hot springs. The heat required to keep water liquid.
However, according to Leni, scientists sensed that something was going on inside Mimas. They studied the moon's rotation around itself and its tiny oscillations, which differ based on the internal structure of the star.
In their first study, published in 2014, scientists could not confirm the presence of a liquid ocean on the moon, and most scientists assumed it had a rocky core.
“We could have been satisfied with the result, but we were disappointed,” Leni said. The team used dozens of images taken by the US space agency's (NASA) Cassini probe to expand the study to include the entire Saturn system and its 19 moons.
Analysis of orbital motion of “MIMAS”.
These data allowed us to analyze the orbital motion of Mimas around Saturn and how it affects its oscillating motion, and to track small differences in this motion, known as libration, down to a few hundred meters, indicating the presence of a liquid ocean. its entire surface.
Matija Cook of the SETI Research Institute in California and Alyssa Rose Roden of the Southern Research Institute in Colorado said in an article accompanying the study: “This is the only possible conclusion.”
The ocean moves under an ice sheet 20 to 30 kilometers thick, a number similar to the thickness of the moon Enceladus' ocean.
The ocean may have formed under the influence of the gravitational pull of Saturn's other moons, “tidal effects” that shake the star and generate heat that prevents its surroundings from freezing.
Calculations indicate that the ocean was formed 5 to 15 million years ago, which explains why no geological signs have been seen on its surface until today.
Nicola Rambo, one of the study's authors, said the moon “combines all the conditions necessary for a form of life: water liquefied by a heat source, interacting with rocks and causing chemical exchanges” for a life form.
Could mimas harbor primitive life forms such as bacteria or archaea? “Future space missions in the coming decades will have to answer that,” Linney replies.
“One thing is certain: if scientists want to look for recent conditions favorable to life in the Solar System, they must turn to Mimas,” he added.