An underground ocean discovered on Saturn’s moon Mimas | The science

Mars is the planet that aliens identify with, but there are other nearby worlds in the solar system where life is possible. Covered by tens or hundreds of kilometers of rock and ice, the underground oceans of some of the moons of Jupiter or Saturn remain warm enough to contain liquid water and have chemical conditions in which some Earth-based microorganisms can survive. When the probe Voyager 2 While passing Jupiter’s moon Europa in 1979, he noticed grooves and cracks in the frozen surface, raising suspicions about what was hidden inside. After decades of observations, it is believed that, in addition to Europa, there are at least seas inside Ganymede, the largest moon of the Solar System, on Saturn’s moon Enceladus, from where plumes emerge into space, or on Titan, which has its surface covered with methane lakes. Today an article that was published in the magazine Naturesuggests that Saturn’s moon Mimas also has an underground sea.

The existence of a sea under the Moon can usually be inferred from changes in its surface, such as the rifts of Europa, caused by changes in the volume of water as it freezes or melts. But in Mimas, a world that has long seemed geologically dead, they are not. However, the authors of the work published in Nature, led by Valery Laney of the Paris Observatory, found it through a detailed analysis of its motion around Saturn. This small moon, with a diameter of only 400 kilometers, will have a liquid ocean under a layer of ice 20 or 30 kilometers thick. Modeling suggests that the sea appeared recently, between 25 million and two million years ago, not enough time to cause visible effects on its surface.

Olga Prieto, head of the Department of Planetology and Habitability at the Astrobiology Center in Madrid, believes that the most interesting thing about this work “is that it shows that in worlds where there is no external manifestation of their existence, oceans can exist.” “This makes it possible that underground seas in the solar system are the norm rather than the exception. Besides the moons of Jupiter or Saturn, other bodies such as Vesta, in the asteroid belt, several moons of Uranus and even the dwarf planet Pluto may have under their surface with a large amount of water.

In some celestial bodies, the decay of radioactive elements may explain the heat needed to form liquid water at such a distance from the Sun. the same mechanism that causes tides on Earth, but much more intense and causing internal temperatures to rise. This phenomenon raises the possibility that intersections with the orbits of other objects could create conditions for ice melting, and raises questions about the stability of the habitats that would make life on these worlds possible.

Astrobiologist Alfonso Davila of NASA’s Ames Research Center explains that while some of these moons may now support life, it is unclear whether life could have arisen in these environments the way it did on Earth. “We don’t know the conditions under which life began here. There are models that place this origin at the surface, with an important role for ultraviolet radiation and light, with episodes of flooding and drying important for organic chemistry and geochemical evolution, and there are oceanic models that talk about hydrothermal pipes. where conditions for life have been created. In addition, some of the oldest organisms are thermophiles and love high temperatures,” explains Davila. However, if life could not originate in the ocean, moons such as Europa or Enceladus would be habitable but barren. “There is no such environment on Earth because life colonizes all habitable places, so it would be interesting to study this place,” he says.

Despite the proximity of these water worlds and their abundance, a paper published today suggests Nature, many of them are as inaccessible as planets orbiting stars light years away. With current technology, drilling through tens of kilometers of ice seems like science fiction, but according to Prieto, there are already crazy ideas that space agencies are listening to as possible long-term plans. For example, the Exobiology Extant Life Surveyor is a robotic worm that can crawl through the cracks through which Enceladus’ plumes emerge and crawl to reach its ocean tens of kilometers deep.

It seems even more difficult to reach the newly discovered Mimas Sea, hidden by a surface that seems to belong to an inert world. Davila believes that if one could once reach its interior, it would be impossible to find life there. “Models tell us that life on Earth arose relatively quickly in geological terms, but it may have taken 200 or 300 million years,” he says. At Mimas, where the ocean is only 25 million years old, there was no time for life to develop, but one can find an environment in which simple molecules begin to combine to form molecules such as DNA, which later made life possible. “There we could study that very interesting point in the stages before the origin of life that we won’t have on Earth because the geological record was destroyed,” Davila says. At the moment, the Mimas Ocean is a new surprise that changes ideas about our cosmic neighborhood.

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