Research into Saturn’s moon Mimas suggests the presence of a subsurface ocean, potentially reshaping our understanding of this celestial body. Recent studies mapping the moon’s icy crust reveal not only the possible age of the ocean but also indicate areas where the crust is thinnest. These regions are prime targets for future spacecraft missions aimed at confirming the existence of this hidden ocean.
At a recent gathering of the Europlanet Science Congress-Division for Planetary Sciences, planetary scientist Alyssa Rhoden from the Southwest Research Institute (SwRI) in Boulder, Colorado, discussed the findings. Unlike other oceanic moons in the solar system, such as Enceladus and Europa, which feature extensive surface cracks indicative of ice melting, Mimas displays a more solid exterior. The moon’s craters appear stable, suggesting a surface composition more akin to rock than ice.
Last year, scientists reported data from NASA’s Cassini spacecraft that supports the theory of a relatively young ocean beneath Mimas’ icy shell. This hypothesis has gained traction over the past decade as new data emerged from Cassini’s ongoing analysis. Initial observations hinted at an ocean, but skepticism prevailed until recent findings provided clearer evidence. Current models indicate that this ocean may lie beneath 12 to 19 miles (20 to 30 kilometers) of ice.
Rhoden and her team applied models from Europa’s thermal characteristics to Mimas, aiming to understand the moon’s ice shell and heat flow. Their research indicates that if melting occurs, it happens rapidly. The origins of this melting are closely tied to Mimas’ orbital dynamics. Although the formation of moons in the Saturn system remains a topic of investigation, it is believed that any ocean present during Mimas’ formation would have frozen long ago. The possible ocean today is likely a recent phenomenon, resulting from changes in the moon’s orbit.
As Mimas orbits Saturn, gravitational interactions create heat that can melt ice into water. A shift in its orbit towards a more eccentric path increased the gravitational tug, generating the necessary heat. If Mimas’ orbit eventually stabilizes into a more circular shape, the tidal forces will diminish, likely leading to the refreezing of any newly formed ocean.
Rhoden’s research includes simulations of how Mimas’ eccentric orbit might have evolved, suggesting a significant orbital change occurred within the last 10 to 15 million years—an exceptionally brief period in astronomical terms. This timeframe aligns with existing estimates regarding the age of the ocean.
The study of Mimas is further bolstered by the examination of its largest crater, Herschel, which spans approximately 80 miles (130 kilometers). The features of this crater provide insight into the moon’s subsurface conditions. Research indicates that Herschel could not have formed when the ice was entirely rigid and likely developed as the moon approached a melting threshold.
Planetary scientist Adeene Denton, also from SwRI, noted the importance of understanding Mimas’ historical melting processes. “Mimas needs to be right on the tipping point,” she explained, emphasizing that while it can remain near that threshold for millions of years, it must stay close to it for the ocean to exist.
Denton’s research extends the possible timeline for Herschel’s formation from one million to ten million years, significantly enhancing our understanding of Mimas’ geological history. Her work, along with Rhoden’s thermal studies and ongoing surface investigations, is contributing to a more coherent narrative regarding Mimas as a potential ocean world.
Future missions aimed at exploring Mimas could utilize its thermal characteristics to search for the subsurface ocean. While challenging, Rhoden indicated that such a mission could be feasible with the right technology. “It would be hard, but may be doable,” she concluded.
As scientists continue to unravel the mysteries of Saturn’s moons, the prospect of a hidden ocean on Mimas adds to the intrigue of the solar system’s icy bodies. With further research and exploration planned, Mimas may soon reveal its secrets, transforming our understanding of ocean worlds beyond Earth.
