The moon Mimas features a large crater that resembles the Death Star from the Star Wars franchise, but that’s not what catches our attention. Now, data from NASA’s Cassini mission has shown convincing evidence of a curious libration, or wobble in the moon’s rotation , which could point to the possibility of an internal liquid ocean.
Worlds with subsurface oceans are common in our solar system
Although to contain an ocean on the surface, the worlds must be at a fairly close distance from their star to maintain temperatures that precisely allow the ocean to remain liquid, if we talk about subterranean oceans, this changes the perspective, since it allows that the required distance of the body from its star be much more flexible. Hence it is possible that there are many habitable worlds with subsurface oceans throughout the galaxy.
“Because the surface of Mimas is cratered, we thought it was just a frozen block of ice,” says Alyssa Rhoden, a researcher at the Southwest Research Institute. “Inner water ocean worlds, such as Enceladus and Europa, tend to fracture and show other signs of geological activity” .
According to experts, “it turns out that the surface of Mimas was playing tricks on us, and our new understanding has greatly expanded the definition of a potentially habitable world in our Solar System and beyond.”
Mimas, which was discovered in 1789 by William Herschel, has a more eccentric (elliptical) orbit than Enceladus, which means it should experience stronger tides; however, its activity is much less than that of Enceladus. Hence, scientists initially thought it was completely frozen.
But the trace of a physical ‘wobble’ remained. If it was 100% solid, it wouldn’t wobble like this. Thus, the moon’s libration suggests that it has a distinct core or liquid ocean.
Using models of tidal heating, the team developed numerical methods to create the most plausible explanation for a 22-32 km thick steady-state ice layer on top of a liquid ocean.
“Although our results support a present-day ocean within Mimas, it is challenging to reconcile the moon’s geologic and orbital characteristics with our current understanding of its thermal orbital evolution,” Rhoden said.
It is clear that this moon is presented as a more than convincing objective in which to continue the investigations.
Referencia: Alyssa Rose Rhoden & Matthew E. Walker. 2022. The case for an ocean-bearing Mimas from tidal heating analysis. Icarus 376: 114872; doi: 10.1016/j.icarus.2021.114872
