Mimas, a small moon of Saturn, is heavily cratered and lacks the typical characteristics of an ocean-bearing moon, such as the active surface of Enceladus. However, measurements of Mimas, made by NASA’s Cassini mission, are best explained by an ocean under a relatively thick ice shell. In new research, a duo of planetary scientists tried to understand how this ice shell and ocean may have changed with time by modeling the formation of Mimas’ largest impact basin, Herschel.
Mimas is the innermost, and smallest (radius = 198.2 km, or 123 miles), regular moon of Saturn.
The moon’s surface is heavily cratered, and it is easily identified by the large Herschel impact basin.
Tectonic activity on Mimas is sparse, and there is no evidence of past or present volcanism.
“In the waning days of NASA’s Cassini mission to Saturn, the spacecraft identified a curious libration, or oscillation, in Mimas’ rotation, which often points to a geologically active body able to support an internal ocean,” said Dr. Alyssa Rhoden, a researcher at Southwest Research Institute.
“Mimas seemed like an unlikely candidate, with its icy, heavily cratered surface marked by one giant impact crater that makes the small moon look much 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 ocean’s existence.”
Dr. Rhoden and Purdue University graduate student Adeene Denton wanted to better understand how a heavily cratered moon like Mimas could possess an internal ocean.
They modeled the formation of the Hershel impact basin using iSALE-2D simulation software.
The models showed that Mimas’ ice shell had to be at least 55 km (34 miles) thick at the time of the Herschel-forming impact.
In contrast, observations of Mimas and models of its internal heating limit the present-day ice shell thickness to less than 30 km (19 miles) thick, if it currently harbors an…
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