Astronomers have found the best evidence of a vast young ocean beneath the icy exterior of Saturn’s Death Star-like minimoon.
The French team analyzed changes in Mimas’ orbit and rotation and reported Wednesday that a hidden ocean 20 to 30 km beneath the frozen crust is more likely than an elongated rocky core. The scientists based their conclusions on observations from NASA’s Cassini spacecraft, which observed Saturn and its more than 140 moons for more than a decade before plunging into the ringed planet’s atmosphere and burning up in 2017.
This cratered moon with a diameter of only 400 km does not have the faults and geysers – typical signs of subterranean activity – like Enceladus (Saturn) and Europa (Jupiter).
“Mimas was probably the most unlikely place to find a global ocean — and liquid water in general,” study co-author Valéry Lainey of the Paris Observatory said in an email. So it is 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, due to the Moon’s small size, it accounts for only 1.2% to 1.4% of Earth’s oceans. Despite its small size, Mimas has the second largest impact crater of any moon in the Solar System, leading to comparisons to the fictional space station the Death Star 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 subsurface ocean is 5 to 15 million years old, too young to mark the surface of the Moon, and its global temperature would be around freezing. But at the bottom of the ocean, the temperature of the water could be much higher.
Nick Cooper of Queen Mary University of London, co-author of the study, said the existence of a “remarkably young” ocean of liquid water made Mimas a prime candidate for studying the origins of life.
Discovered in 1789 by the English astronomer William Herschel, Mimas is named after a giant from Greek mythology.