Astronomers have found the best evidence yet of a vast, young ocean beneath the icy exterior of Saturn’s Death Star-like mini-moon.
The French-led team analyzed changes in Mimas’ orbit and rotation and reported Wednesday that a hidden ocean 20 to 30 km beneath the frozen crust was more likely than an elongated rocky core. The scientists based their conclusions on observations from NASA’s Cassini probe, which observed Saturn and its more than 140 moons for more than a decade before plunging into the ringed planet’s atmosphere in 2017 and burning up. .
With a diameter of just 400 km, this heavily cratered moon does not have the fractures and geysers – typical signs of subterranean activity – of Enceladus (Saturn) and Europa (Jupiter).
“Mimas was probably the most unlikely place to look for a global ocean ― and liquid water more generally,” Valéry Lainey of the Paris Observatory, co-author of the study, said in an email. It is therefore a potentially habitable world. But no one knows how long it takes for life to appear. »
The results were published in the journal Nature.
The ocean would fill half the volume of Mimas, according to Ms. Lainey. However, it only represents 1.2% to 1.4% of Earth’s oceans, given the small size of the moon. Despite its small size, Mimas has the second largest impact crater of any moon in the solar system, leading to comparisons to the fictional Death Star space station in Star Wars.
“The idea that relatively small, icy moons could support young oceans is inspiring,” Matija Cuk of the SETI Institute and Alyssa Rose Rhoden of the Southwest Research Institute wrote in an editorial. accompanying the study. They did not participate in the study.
According to Ms. Lainey, this subterranean ocean is between 5 and 15 million years old, which is too young to mark the surface of the moon, and its global temperature would be around the freezing point. But at the ocean floor, the water temperature could be much higher.
Nick Cooper of Queen Mary University of London, co-author of the study, said the existence of a “remarkably young” liquid water ocean made Mimas a prime candidate for studying the origin of life.
Discovered in 1789 by the English astronomer William Herschel, Mimas is named after a giant from Greek mythology.