Enceladus, one of Saturn's moons, is one of the most promising places in the Solar System to host life beyond Earth. And as of this Wednesday it is even more so: this icy world is covered by a global ocean under an ice sheet in which scientists have just discovered phosphorus, one of the ingredients they consider critical for it to be habitable.

As detailed in research published in the journal Nature, this is the first time that phosphorus has been found in oceans outside the Earth, a discovery that, in addition to advancing the understanding of these oceanic worlds of the Solar System, supports that Enceladus may meet the necessary conditions to host some type of life.

The discovery has been made using data from the Cassini probe, whose mission concluded in 2017 by diving into Saturn's atmosphere to self-destruct. Scientists are still analyzing the abundant data he collected during the 13 years he spent exploring the ringed planet and its moons Titan and Enceladus, in which he has found elements that make them candidates for life in the Solar System.

Specifically, the discovery of phosphorus was possible thanks to the analysis of ice particles ejected from the moon's underground ocean through cracks from which a kind of geysers escaped. Previous models had suggested the presence of phosphorus, but it was unclear whether this element was found in large quantities.

"Previous Cassini measurements had already shown that Enceladus' subsurface ocean has moderate salinity, adequate pH, a wide variety of organic compounds, and likely hydrothermal systems on the ocean floor as an energy source. However, phosphorus had not yet been detected, although in general, it is considered a critical ingredient for life. Life on Earth cannot exist without phosphorus (it is in DNA or cell membranes, for example)," Frank Postberg, professor of Planetary Sciences at the Institute of Geological Sciences of the Free University of Berlin and leader of the research, explains to EL MUNDO. "Our finding of phosphorus in the form of soluble phosphates, readily available in the ocean, can be interpreted as the missing piece for the ocean of this moon Saturn to be habitable. However, that does not necessarily mean that it is inhabited, "he points out.

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Where do the geysers on the moon Enceladus come from?


Where do the geysers on the moon Enceladus come from?

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J. Miguel Mas Hesse, scientist and former director of the Center for Astrobiology (CAB / CSIC-INTA), agrees that the effective detection of nutrients such as phosphates "is very relevant" and would support that water from this moon is a good 'primordial soup' for the development of life. "The fact that they have found phosphates in the water ejected from Enceladus is very interesting news in order to determine the possibility that life has arisen there. Phosphorus is a building block for life (among other things it forms the band in which the bases of DNA are anchored), and finding it in abundance indicates that, at least, the precise nutrients for life are found there," he says.

This discovery, he adds, "seems to indicate that the chemistry in the oceans of icy moons, at least in the case of Enceladus, would be sufficiently complete and complex to host biological processes."

As the Spanish scientist lists, without connection to this study, the icy moons of Jupiter and Saturn constitute a first priority environment for astrobiology for several reasons: they have a large amount of water; the bottom of its oceans is rocky; because of their proximity to Jupiter and Saturn, which causes tidal forces to warm the interior, so they have an energy source comparable perhaps to hydrothermal vents in the Earth's oceans; and by the icy crust of the surface, which protects them from the high levels of radiation in the vicinity of Jupiter and Saturn.

"Since they formed from the same molecular cloud from which the rest of the Solar System formed, they must have a chemical composition with all the elements necessary for life. They are very promising environments to have developed living beings, "says Mas Hesse, who recalls that "Arthur C. Clarke, the author of 2001, A Space Odyssey, already suggested in the continuation, 2010, published in 1982, that there could be life below the surface of Europa. "

However, like his colleague Postberg, Mas Hesse stresses that although "there is no doubt that the biochemistry of these frozen oceans must be very rich, more than enough for them to have formed life, as denoted by other chemical elements that they have been able to identify, at the moment there is no evidence that this has been the case."

Large amounts of phosphorus

The Postberg-led team analyzed data collected by Cassini's Cosmic Dust Analyzer (CDA) to determine the major components of Enceladus' oceans. These measurements not only detected phosphorus but, together with laboratory data, suggest that phosphorus could be available in concentrations at least 100 times higher than in Earth's oceans.

Enceladus, one of Saturn's moonsNASA

Frank Postberg assures that they are completely sure of the presence of this element. "Our detection occurred in situ near Enceladus with a spacecraft and we analyzed ice grains that undoubtedly originate in the subsurface of Enceladus," he explains when asked if this result could be questioned by other authors, as happened in 2020 after the announcement of the discovery of phosphine gas in the clouds of Venus. "In contrast to the supposed weak phosphine signal, the phosphate signal in the Cassini data is extremely strong and unambiguous, coming from sodium phosphate and sodium hydrogen phosphate which are soluble in water (from the ocean)."

In addition, scientists believe that high phosphate levels could be observed more widely on other icy ocean worlds with similar environmental parameters.

In an article analyzing this study also published in Nature, Mikhail Yu. Zolotov, a researcher at Arizona State University, notes that "the presence of phosphorus components in water is crucial for biological production on Earth." That there are phosphates in Enceladus' ocean, he adds, confirms that its water is alkaline.

After this exciting discovery, Frank Postberg anticipates that he will continue analyzing the Cassini data: "The observations made by the James Webb telescope of Enceladus, recently published, have not given us new knowledge," says the scientist, who believes that "to find out if Enceladus is not only habitable but inhabited, we have to send – and we should send – another spacecraft. "

As Mas Hesse reviews, NASA and the European Space Agency (ESA) are working on a mission called Joint Europa Mission, which will land a small probe on the surface of Europa, Jupiter's moon, with the aim of making chemical analysis of the brown dust that covers it, in search of remains of biological activity. "But we will still have to wait many years for something like this to be done. The mission that will be able to carry it out, Joint Europa Mission, is still in the study phase. And when it launches, it will take about eight years to get there. Meanwhile, the Juice spacecraft is on its way to Jupiter and Europa, and another NASA mission, Europa Clipper, will depart in 2024 or 2025 to continue detailed study of Europa's surface."

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