An ocean has been discovered beneath the surface of Saturn’s small moon Mimas

Although it bears the name of a giant from Greek mythology, Mimas is a fairly small satellite of Saturn with a radius of 200 kilometers. In our images of the star, we see a ball of highly cratered ice, whose pockmarked surface appears unchanged since the beginning of time. An apparently dead star, but looks can sometimes be deceiving. Because, beneath the frozen crust, in the dark depths of this Saturnian moon, a subterranean ocean appeared twenty-five million years ago due to a complex activity – that is, more recently, on the astronomical time scale, the solar system is more than 4.5 billion years old.

Published in a weekly magazine Nature, Wednesday February 7, The discovery is the fruit of long analysis work by an international team led by researchers from the Institute of Celestial Mechanics and Ephemeris Calculations (IMCCE), an institute of the Paris Observatory-PSL. More than an invention, language purists would speak of a performance, a complex performance in two stages separated by a decade.

Let’s go back ten years to refer to an article published by a journal Science In 2014, there was more or less the same team. At the time, these researchers wondered how to determine the internal structure of Mimas. To achieve this, “We’re Back to the Basics: Celestial Mechanics and Newton’s Laws”.

recalls Valerie Laney, an astronomer at the IMCCE and first author of the study Nature. The only clues available to scientists were photos taken by NASA’s Cassini space probe, which tirelessly explored the Saturn system between 2004 and 2017.

Satanic dynamics

This was enough to carefully study the rotation of Mimas and the small oscillations we detected there. To explain them, a 2014 article presented two hypotheses: either the satellite had a rocky core in the shape of a rugby ball, or its icy mantle had slipped over an internal ocean.

“We were frustrated not knowingMr. Lenny accepts. Most scientists were convinced that Mimas was cold, frozen, barren, that there was no liquid ocean. » But conviction does not perform. “We are looking for a solution to distinguish between the two scenarios”

, continues the IMCCE Astronomer. Deciding to no longer study the Moon’s rotation but the subtleties of its orbital motion, again thanks to Cassini data, in this case thousands of images.

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