Astronomers discover a global subsurface ocean in Saturn’s moon Mimas

A team of astronomers led by Dr. Valéry Lainey of the Observatoire de Paris has discovered a global ocean of liquid water under the icy surface of Saturn’s small moon, Mimas, by analyzing the data from NASA’s Cassini spacecraft.

NASA's Cassini spacecraft captured Saturn's moon Mimas during its closest-ever flyby on February 13, 2010
NASA’s Cassini spacecraft captured Saturn’s moon Mimas during its closest-ever flyby on February 13, 2010. The largest crater of Mimas, named Herschel, is seen here, which is about 130 kilometers wide and 10 kilometers deep. (Image credit: NASA/JPL/SSI)

This research has been published in the scientific journal “Nature” on February 7, 2024.

The result of the research indicates that the subsurface ocean is very young, less than 25 million years old, and it’s located 20 to 30 kilometers below the surface of Mimas.

A co-author of the study, Dr Nick Cooper, wrote:

“Mimas is a small moon, only about 400 kilometers in diameter, and its heavily cratered surface gave no hint of the hidden ocean beneath. This discovery adds Mimas to an exclusive club of moons with internal oceans, including Enceladus and Europa, but with a unique difference: its ocean is remarkably young, estimated to be only 5 to 15 million years old.” 

Till now, Mimas is the smallest moon in our solar system, where astronomers have found an internal ocean. Previously, subsurface oceans were found beneath the icy surface of Jupiter’s moons Ganymede and Europa and Saturn’s moons Titan and Enceladus.

How have researchers discovered the subsurface ocean in Mimas?

Mimas is tidally locked with Saturn due to its close orbit, so the same side of Mimas always faces Saturn. As a result, we see the synchronous rotation of Mimas, meaning it takes the same amount of time to rotate around its own axis as it takes to complete an orbit around Saturn. It’s very similar to our moon, which always shows the same side to us.

In 2014, the same research team found that Mimas wobbles in its orbit around Saturn in addition to its synchronous rotation while comparing the computer-simulated results with the Cassini spacecraft data. They concluded that either Mimas has a subsurface global ocean or a very large and elongated core.

Further studies in 2024 showed that Mimas not only wobbles in its orbit around Saturn but also rapidly shifts its orbit around Saturn, and researchers confirmed that this result can only be explained by the presence of a global ocean hidden beneath the entire surface of Mimas.

This result indicates that even a small, seemingly inactive moons can harbor hidden oceans capable of supporting life-essential conditions.

“The existence of a recently formed liquid water ocean makes Mimas a prime candidate for study, for researchers investigating the origin of life,” explains Dr Cooper. 

Bottom line: The growing number of moons that contain global subsurface oceans increases the probability of extraterrestrial life in our solar system and we need robotic exploration to confirm it.

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Ashim

Ashim Chandra Sarkar founded Space & Telescope in 2022. He holds a M.Sc. in physics and has five years of research experience in optical astronomy. His passion for astronomy inspired him to open this website. He is responsible for the editorial vision of spaceandtelescope.com.

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