2024-02-18 08:48:35
Astronomers have compared it, also due to its outward resemblance, to the Death Star from Star Wars, but it turns out that it could be more hospitable than previously thought. Saturn’s small moon Mimas likely contains a liquid ocean beneath its icy surface, ideal for life, according to a study published this Wednesday.
Mimas thus joined the family of rare moons in the Solar System that harbor liquid water under their icy mantle: Europa and Ganymede (around Jupiter), Enceladus and Titan (around Saturn).
“If there is a place in the universe where we did not expect to find conditions favorable to life, it is Mimas,” Valéry Lainey, lead author of the study published in the journal Nature, explained at a press conference.
The moon of the ringed planet, which was discovered in 1789 by astronomer William Herschel, “was not at all at the top of the interest of scientists”, explained this astronomer from the Paris Observatory. The star, only 400 kilometers in diameter, was nicknamed the “death moon” because it appeared to be very cold, motionless, and therefore uninhabitable. The reason is clear, its surface is littered with craters, including one huge one that makes it look like the Death Star, the station of the Galactic Empire in the Star Wars film saga.
This moon’s icy shell appeared to be frozen, with no evidence of internal geological activity to alter it – unlike its larger brother Enceladus, whose smooth surface is regularly reshaped by the activity of an internal ocean and geysers, the source of the heat needed to sustain water in liquid state.
However, scientists suspected that “something was going on inside” Mimas, Lainey said. So they investigated the rotation of the satellite around itself and its small oscillations, so-called librations, which can change depending on the internal structure of the star. Their original work, published in 2014, found no evidence for the existence of a liquid ocean. Most scientists were more inclined to the stone core hypothesis.
“We could have left it alone, but we were frustrated,” recalled Valéry Lainey. His team then acquired several dozen images taken by NASA’s Cassini probe (2004-2017) to expand their research to the entire Saturn system and its 19 moons.
These data made it possible to analyze the orbital motion of Mimas around Saturn and the way it affects its librations. And to detect minute deviations of these librations in the order of several hundred meters, which reveal the presence of a liquid ocean under the entire surface.
“That is the only possible conclusion,” wrote Matija Cuk of the American SETI Project for the Search for Extraterrestrial Intelligence (California) and Alyssa Rose Rhoden of the Colorado Research Institute in a commentary attached to the study.
The ocean moves under ice 20 to 30 kilometers thick, which is comparable to the ice on Enceladus, the study describes. It is thought to have formed under the influence of the gravity of Saturn’s other moons: “tidal phenomena” that shake the star and generate heat that prevents the ocean from freezing.
Calculations suggest that the sea formed only recently, between five and 15 million years ago, which would explain why no geological traces have yet been detected on the surface. “The Moon meets all the conditions for habitability: liquid water maintained by a heat source, in contact with rock, so that the chemical exchanges necessary for life can develop,” summarized one of the authors of the study, Nicolas Rambaux.
Could Mimas harbor primitive life forms such as bacteria? “This question will be addressed by future space missions in the coming decades,” Lainey predicts. “One thing’s for sure, if you’re looking for the latest hints of possible habitability in the solar system, Mimas is a place to really look,” concluded the astronomer.