Mimas, Saturn’s moon, harbors global ocean 20-30 km beneath surface, scientists confirm
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A study published in Nature in February 2024 confirms that Saturn’s moon Mimas contains a global ocean buried 20 to 30 kilometers beneath its cratered ice shell. The finding, based on Cassini spacecraft data, reveals the ocean likely formed 5 to 15 million years ago, making it geologically young. The ocean’s youth explains why its surface shows no fractures or plumes like Saturn’s active moon Enceladus.
Orbital Clues
NASA’s Cassini spacecraft tracked Mimas’s position and rotational wobble, known as libration, over a decade. These measurements could not be reconciled with a fully frozen moon. Valéry Lainey’s team at Observatoire de Paris modeled the slow drift of Mimas’s orbit and found that a global ocean 20–30 km beneath the ice best explained both the libration and orbital motion. The finding, published in Nature in February 2024, is based on geophysical modeling, not direct imaging.
A Young Ocean
The ocean likely formed only 5 to 15 million years ago, according to estimates from the Observatoire de Paris, while the ice shell thinned to within 30 km of the surface only 2–3 million years ago. This youth explains why Mimas lacks the fractured terrain seen on older ocean moons like Enceladus. A 2022 study of the massive Herschel crater concluded that if an ocean exists now, the ice must have been tens of kilometers thicker when the crater formed, consistent with a recent thinning.
What's Next
Astronomers plan further analysis of Cassini data to refine models of Mimas’s interior. It remains unclear whether tidal heating alone can sustain a liquid ocean on such a small moon.
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Mimas, Saturn’s moon, harbors global ocean 20-30 km beneath surface, scientists confirm
