Enceladus, hypothesis: methane compatible with the activity of microorganisms

A study shows that the data collected by Cassini on the methane present on Saturn’s moon are compatible with microbial activity, but caution is a must.

The surface of Enceladus. Photo: NASA / JPL-Caltech / Space Science Institute

Enceladus, one of Saturn’s moons, could host microorganisms? This is the question that astronomers have been asking for several years, especially since the data of the probe Nasa Cassini they indicated the presence on the satellite of an liquid ocean, placed between the shell of ice external and internal rock. Not only that: on the surface of Enceladus there are enormous ones plumes of water, similar to geysers. The probe analyzes tell us that a good percentage of methane. Behind this production, there is a unknown process, but that could be it compatible with the microbial life. This is what a study published in Nature Astronomy by scientists from the University of Arizona and Paris Sciences & Lettres University.

Where does all this methane come from?

Despite his activities be finished for almost four years, the Cassini probe has continued to amaze us. The mission Cassini-Huygens, created in collaboration between Nasa, l’European space agency (Esa) and theItalian space agency (Asi), from October 1997 to September 2017 (when the spacecraft ended its 10 honored years of service by plunging into Saturn’s atmosphere), aimed at studio of this planet and yours system of rings and satellites, particularly Titan, the largest satellite. But also Enceladus, another of the many moons of the planet, over the years has reserved very interesting data: Cassini’s observations have suggested that this moon had a Ocean internal liquid. In addition, on the surface of the satellite the NASA probe has detected enormous plumes of oceanic material, which erupt and are ejected into space. But what are they made of?

This is what the scientists wondered, finding singular results: passing through the plumes and sampling theirs chemical composition, the Cassini spacecraft detected a relatively high concentration of molecular hydrogen, methane and carbon dioxide. In particular, the amount of methane found in the plumes was unexpected. These molecules, on Earth, are associated with hydrothermal vents at the bottom of the oceans, which are home to whole ecosystems of microorganisms called methanogens. In fact, on Earth, methane is also produced byhydrothermal activity generated between the waters of the oceans and deep layers of the earth’s crust, but the process is very slow: most of the methane is in fact attributable to microorganisms. And about Enceladus? “We wanted to know: Could Earth-like microbes producing methane explain the surprisingly large amount of methane detected by Cassini?“, Says Regis Ferriere, one of the two main authors of the study.

I study

However, the search for these microorganisms on Enceladus’s ocean floor would require demanding and costly space missions, which are not currently planned. Scientists then built gods mathematical models, which combine the geochemistry With the’microbial ecology, to calculate the chance that different processes could explain Cassini’s data. Among these, also the generation of methane by microbes. According to the study, and give of the probe would be consistent with either microbial activity altogether similar to what we see in hydrothermal vents on Earth, both at anunknown microbial activity which behaves differently from what happens on our planet. The mere production of methane without the intervention of living organisms would not be sufficient to explain the high concentration of methane found by the NASA probe.

This is certainly not proof that there is life on Enceladus, but it opens up interesting future developments for investigations on Saturn’s moon: Cassini’s measurements could also indicate unknown sources of methane, habitable by microorganisms. “Of course, we are not concluding that there is life in the ocean of Enceladus“, Concludes Ferriere:”Rather, we wanted to understand how likely it was that the hydrothermal vents of Enceladus could be habitable by Earth-like microorganisms. Most likely, Cassini’s data tell us. And biological methanogenesis (the process of production of methane by microorganisms, ed) appears to be compatible with the data. In other words, we cannot discard the hypothesis of life as highly unlikely.

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