The mystery of Mimas: the youngest ocean in the Solar System found on Saturn's moon (4 photos)

Subsurface oceans on the moons of gas giants are not uncommon in our Solar System. Along with Jupiter's Europa and Ganymede, Saturn's Enceladus and Dione, and possibly Neptune's Triton, we can now add another candidate: Saturn's moon Mimas.





The most detailed image of Mimas to date

An unexpected discovery

Mimas is a small moon of Saturn, only 396 kilometers in diameter, reminiscent of the Death Star from the Star Wars film series due to the massive 140-kilometer-wide Herschel crater. The surface of the Saturnian moon, pockmarked with numerous impact features, gave scientists no hint of the existence of a liquid ocean beneath its icy crust.



Herschel Crater and its central peak, casting a huge shadow, were captured in the frame.

However, data from the Cassini mission revealed strange irregularities in the orbit of this small moon. These anomalies could be caused by two factors:

The presence of a rocky core of a very unusual shape;

The presence of a liquid subsurface ocean.

Computer modeling conducted by an international team of researchers points to the second possibility as the most likely. The first hypothesis turned out to be incorrect—to cause the observed orbital anomalies, Mimas's core would have to be pancake-shaped, which is physically extremely unlikely.

The Youngest Ocean in the Solar System

"Mimas is a small moon, and its heavily cratered surface offered no hint of a hidden ocean beneath," explains Dr. Nick Cooper, co-author of the study from Queen Mary University of London. "Our discovery adds Mimas to the exclusive club of moons with subsurface oceans, but with a distinct distinction: its ocean is remarkably young, no more than 25 million years old."

Depending on the model used, Mimas's subsurface ocean could be anywhere from 2 million to 25 million years old. For comparison, the subsurface ocean of Jupiter's Europa is about 4.5 billion years old—roughly the same age as the Solar System itself.

If the models are correct, Mimas's ocean is reliably isolated from the harsh environment of space by an ice shell 20 to 30 kilometers thick.





Mimas passing in front of Saturn's rings

Prospects for the search for life

"The existence of a relatively recently formed ocean makes Mimas a prime candidate for study by scientists investigating the origins of life," Dr. Cooper emphasizes.

Mimas's subsurface ocean could offer scientists a unique opportunity to study how quickly conditions suitable for the emergence of life can form. If even prebiotic compounds are discovered in such a young ocean, it could completely change our understanding of the rate of evolutionary processes.

The Legacy of the Legendary Cassini Mission

This discovery was made possible thanks to data from the Cassini spacecraft, an international collaboration between NASA, the European Space Agency, and the Italian Space Agency. The probe spent 13 years in the Saturn system, studying the planet, its rings, and numerous moons in detail. The data collected during this time continues to lead to significant discoveries.



Mimas with Saturn's northern hemisphere in the background

The Cassini mission concluded on September 15, 2017, when the spacecraft was deliberately diverted into Saturn's atmosphere, where it burned up to avoid chemical contamination of potentially habitable moons that could create false biomarkers for future studies.

"This was a remarkable team effort: colleagues from five different institutions and three different countries came together under the leadership of Dr. Valerie Laney to uncover yet another interesting and unexpected feature of the Saturnian system," concluded Dr. Cooper.