Investigations reveal more evidence that Mimas is a stealth ocean world

When scientists at the Southwest Institute discovered surprising evidence that Saturn’s smallest innermost moon can generate just the right amount of heat to support its liquid interior ocean, colleagues wondered what its interior was like. Numerical simulations of the Moon’s Herschel impact basin, the most prominent feature of the cratered surface, provide insight into the structure of the basin and the tectonics of Mimas. The lack determined to be compatible with a thinning ice shell and a geologically young sea.

“At the end of NASA’s Cassini mission to Saturn, the spacecraft identified an interesting oscillation in Mimas’ rotation, which often indicates a geologically active object that could support an inland sea. ,” said Alyssa Rhoden, Ph.D., SwRI. Expert in the geophysics of icy satellites, especially those containing oceans, and the evolution of giant planetary satellite systems. She is her second author of New. Geophysical Research Letter Subject paper.

“Mimas looked like an unlikely candidate. Its icy, cratered surface is marked by one giant impact crater that creates a smaller one. Moon It looks like the Death Star from Star Wars. If Mimas has an ocean, it represents a new class of small ‘stealth’ ocean worlds with surfaces that do not betray the presence of the ocean. ”

Rhoden worked with Purdue graduate student Adeene Denton to better understand how cratered moons like Mimas can have internal oceans. Denton used iSALE-2D simulation software to model the formation of the Herschel collision basin. Models have shown that Mimas’ ice shell must be at least 34 miles (55 km) thick at the time of the Herschel-forming impact.

In contrast, Mimas’ observations and models of its internal heating limit the current ice shell thickness to less than 19 miles (30 km) if there is currently an ocean. These results suggest that the present-day ocean within Mimas must have warmed and expanded since the basin formed. It is also possible that Mimas was completely frozen both during the Herschel collision and now. However, Denton found that including the inland sea in the impact model helped generate the shape of the basin.

Denton, now a postdoctoral researcher at the University of Arizona, said, “We found that if Herschel formed with an ice shell of its current thickness, it would not have been able to annihilate the ice shell at the impact site.” If Mimas has an ocean, the ice shell It has thinned out since Herschel’s formation. This could also explain the absence of fractures on Mimas. Become. ”

“While our results support a modern ocean within Mimas, it is difficult to reconcile the moon’s orbit and geological features with our current understanding of thermal orbital evolution,” Roden said. “Evaluating the status of Mimas as an oceanic moon will benchmark models of its formation and evolution, which are similar to those of Saturn’s rings and medium-sized moons, and potentially habitable moons.” It helps us better understand the spread. ocean Moons, especially Uranus. Mimas is an attractive target that requires continued investigation. ”