A small Saturnian moon has been confirmed to host an underground ocean—and it could have enormous ramifications for the search for life off-Earth.
It’s an incredible discovery because only geologically active worlds are thought to have any chance of hosting oceans. The smallest and innermost of Saturn’s major moons, taking just 22 hours to orbit the ringed planet, Mimas was judged to be geologically inert—as shown by its crater-covered surface, which suggests that it doesn’t change.
One of its giant craters, Herschel, dominates its surface and makes it look like the Death Star from the movie Star Wars.
However, there are signs of activity on Mimas. Craters at its south pole appear to be smaller than those elsewhere, suggesting that melting or resurfacing has occurred there recently.
The paper suggests that the ocean on Mimas lies beneath an icy shell approximately 20–30 km deep and that it formed about 25 million years ago.
Published in the journal Nature this week, a new paper reveals the discovery of a global ocean of liquid water on Mimas that formed just five to 15 million years ago.
“This discovery adds Mimas to an exclusive club of moons with internal oceans, including Enceladus and Europa, but with a unique difference: its ocean is remarkably young,” said Dr Nick Cooper, a co-author of the study and Honorary Research Fellow in the Astronomy Unit of the School of Physical and Chemical Sciences at Queen Mary University of London.
The ocean was detected after scientists studied the moon’s tidal interactions with Saturn, which revealed an irregularity in its orbit that could only be caused by a subterranean ocean. They used data from NASA’s Cassini mission, which orbited Saturn and studied its moons for 13 years until 2015.
At less than 123 miles (198 kilometers) in radius, Mimas is a small world, but this discovery could have a big impact. If small, inactive moons can host hidden oceans—creating potentially life-essential conditions—then there’s almost nowhere in the solar system that scientists shouldn’t consider the possibility of life existing. It’s thought that interactions between an underground ocean and the rocky core of a moon could generate enough chemical energy to sustain organisms.
“The existence of a recently formed liquid water ocean makes Mimas a prime candidate for study, for researchers investigating the origin of life,” said Cooper.
The ocean on Mimas may be the most unexpected, but it is not the first to be found on moons in the solar system. Planetary oceanographers have previously detected subsurface oceans on two of Saturn’s other moons, Enceladus and Titan, and Europa, Ganymede and Callisto, orbiting Jupiter.
The discovery of an ocean on Mimas—just where it wasn’t expected—means that small icy moons throughout the solar system are about to get a thorough examination.
Wishing you clear skies and wide eyes.