Outwardly, Saturn’s moon Mimas looks like a frozen solid mass of ice and rock. With the help of data from the Cassini mission, Alyssa Roden of the Southwest Research Institute in San Antonio and her team wanted to prove that, too. But in the end, the measurement results pointed in a completely different direction, As the Icarus working group wrote:: Like Saturn’s moons Titan and Enceladus, Mimas may have an inner ocean under the thick icy crust. It would therefore be another celestial body in our solar system that contains such an ocean.
“Because Mimas’ surface was so severely scratched, we thought it was just a frozen block of ice,” Roden says. “Moons with inner oceans, such as Enceladus and Europa, tend to be rugged and show other signs of geological activity. But Mimas’ surface has deceived us.” Thus it could represent a new class of ‘capped’ small ocean worlds with surfaces that do not reveal the presence of this Ocean.
Roden’s team developed a model to explain these differences: heat from orbital and rotational energy is accordingly transferred to the depths by tidal forces. This heating inside the Moon must be large enough to prevent the ocean from freezing. But it’s also small enough to maintain a thick ice crust. From their calculations, Rhoden and Co. concluded that this reservoir has a thickness of 24 to 31 kilometers.
The team also found that the heat flow from the surface was highly sensitive to the thickness of the ice crust, which can be verified by spacecraft. The Juno space probe is supposed to fly across the icy moon Europa and use its microwave radiometer to measure heat fluxes on this Jupiter moon. The data can then be used to infer how heat flow affects the cryosphere of oceanic worlds such as Mimas.
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