They discover an ocean under the surface of Saturn's moon Mimas

Nuevas evidencias de un oceano bajo la gelida superficie de Mimas

In 1789, astronomer William Herschel discovered two satellites of Saturn: Enceladus and the one that would later be named one of the giants of Greek mythology: Mimas. The data collected by the Cassini probe on these icy moons made it possible to discover that Enceladus hides an ocean with thermal springs, whose products are expelled by giant plumes of ice and gas into space.

pampers 1

Pampers, however, which reminds some of the death star from Star Wars, presents a surface full of craters that does not reveal that there is that large body of water frigid below, but that is precisely what a team of French researchers has discovered by reviewing data taken by the Cassini spacecraft before its spectacular disintegration in 2017 in the atmosphere of Saturn.

Although some previous study already suggested it, according to the new article, published this week by the magazine Nature, he subsurface ocean of Mimas is relatively recent and is still evolving.

Cassini data reveals that Saturn's moon Mimas has a relatively recent subsurface ocean

Under a frozen layer of 20-30 km

The simulations indicate that it appeared ago between 25 and 2 million years, and which is under an icy layer about 20 to 30 km deep. The ocean-ice interface reached this depth relatively recently, less than 2 or 3 million years, so it would not have had time to leave its mark on the lunar surface yet.

To reach these results, the researchers looked at the orbit data of this satellite. “We used tens of thousands of images of Saturn's 19 moons to completely constrain the orbital dynamics of the entire system,” the lead author, explains to SINC. Valery Lainey, from the Paris Observatory, “and later, we were able to constrain the orbital motion of Mimas so precisely that we were able to detect a slight change in the drift of the orientation of this orbit in space.”

Previous research had suggested two possibilities to explain what the interior of Mimas is like: a solid body with a rocky core elongated, or with a global ocean beneath its surface

The analyzes by Lainey and his colleagues settle the debate in favor of the second option, after revealing the changes in the rotation movement and orbit of the small moon affected by its inland ocean.

Applying the solid-body model would require the rocky core to be elongated, almost pancake-shaped, which is inconsistent with orbital observations. Instead, measurements of Mimas's position indicate that the evolution of its orbit is better explained if such a subsurface ocean exists.

Oceans where to look for signs of life

Lainey remembers that there are already four moons with a global ocean: “EuropeGanymede [both from Jupiter], Titan and Enceladus [of Saturn], and now Mimas joins us, plus some other candidates, such as Callisto, Dione and Triton.” These ocean worlds are good candidates for searching for signs of life beyond Earth in our solar system.


There were four moons with a global ocean: Europa, Ganymede, Titan and Enceladus, and now Mimas is added, plus some other candidates, such as Callisto, Dione and Triton

Valery Lainey (Paris Observatory)
Mimas (center) joins the 'club' of moons with a global ocean: Enceladus and Titan (left) and Europa and Ganymede (right). / Frédéric Durillon, Animea Studio/Observatoire de Paris – PSL, IMCCE

The researcher clarifies that the technique they have used requires very precise data on the movement of objects, and perhaps cannot be applied to other satellites: “It works better for objects close to your planet. In practice, it will probably not be possible to apply this method to many other moons, until data from future space missions are available.

Similar processes on other icy worlds

In any case, these results imply that recent processes at Mimas may have been common in the early stages of formation of others. frozen worlds, according to the authors, who anticipate that new studies on this satellite of Saturn could teach us more about its formation.

In a parallel assessment, also published in Nature, American astronomers Matija Ćuk and Alyssa Rose Rhoden conclude: “The findings of Lainey and his colleagues will motivate a comprehensive examination of medium-sized icy moons throughout the solar system, and force a rethinking of what an oceanic moon is.”


V. Lainey et al. “A recently formed ocean inside Saturn's moon Mimas”. Nature

Source: Enrique Sacristán/SINC
Octavio Alonso