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Research focused on Enceladus, one of Saturn’s natural moons, has gradually ranked it among the best candidates for potentially harboring life, its surface and its icy oceans containing key elements. However, the last piece of the puzzle – phosphorus – was not directly detected in the Enceladus dust samples taken by Cassini as part of the initial analysis. But an international study recently confirmed its presence (and in large quantities), adding to the list of six essential elements for all life forms and placing the satellite among the favorite for habitability (within the solar system).
On our planet, every form of life is made up of six main elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur. Without these key elements, life on Earth would not have appeared. Other parameters must also be present, including liquid water. Over the past 25 years, astrophysicists have focused on icy stars, some of which have oceanic layers beneath their surface. This parameter would even be quite common in our solar system: Europa, Titan, Enceladus and also some planetary bodies located beyond the orbit of Pluto.
Earth maintains its liquid oceans thanks to its ideal distance from the Sun. But in the case of planetary bodies like Enceladus, the Sun is unfortunately too far away to warm the surface and preserve a liquid ocean. Beneath the thick icy surface, however, Enceladus’ oceans are kept liquid by its hot and active core. This feature, which would not be so rare in the universe, greatly increases the number of potentially habitable planets in our galaxy.
Because the presence of liquid water is not as rare as previously thought, ” the search for extraterrestrial habitability in the solar system has shifted as we now look for the building blocks of life, including organic molecules, ammonia, sulfur compounds, as well as the chemical energy needed to sustain life. “, indicates va communicated Christopher Glein, co-author of a new study published in PNAS and a PhD researcher at the Southwest Research Institute.
Phosphorus in particular is a very active area of research because scientists previously thought it would be rare in Enceladus’ oceans. However, phosphorus molecules are essential metabolic and structural components for all life forms, being present in DNA synthesis, in the structure of cell membranes and even in the marine microbiome.
In 2015, when the Cassini spacecraft flew by about 30 miles (49 km) from the surface of Enceladus, its mass spectrometer was able to analyze samples of dust ejected from the geysers on its surface that feed the E ring of Saturn, its mother planet. The spectrometer then detected various compounds such as organic and inorganic carbon, molecular hydrogen, various nitrogenous and oxygenated and aromatic compounds, ammonia, etc.
However, phosphorus could not yet be detected because initial analyzes could only be performed in the middle spectra. The new study then reanalyzed samples taken by the probe and compared the results to (high-resolution) results previously obtained by other researchers. ” While the bio-essential element phosphorus has not yet been directly identified, our team has discovered evidence of its availability in the ocean beneath the satellite’s icy crust. says Glen.
Higher concentration of phosphorus than on Earth
Indirect detection of phosphorus in dust samples from Enceladus was carried out by scientists from the Chinese Academy of Sciences, Division of Space Science and Engineering, Southwest Research Institute, CSIRO (Australia), the University of Berlin and the University of Washington. Specifically, the team performed experiments based on thermodynamic and kinetic models to simulate the geochemistry of the satellite’s oceans. The aim of this simulation is to determine whether the conditions of the satellite allow phosphorus to be present, and also to assess whether it can be present in large quantities in the form of orthophosphate.
Scientists then discovered that the basic geochemistry of Enceladus made the presence of phosphorus inevitable, in amounts similar to or greater than in our oceans. Additionally, out of 1,000 dust particles from the Cassini samples, 9 contained traces of phosphorus. This could indicate that the concentration of this element in Enceladus’ oceans would be 100 to 1000 times higher than in Earth’s oceans.
However, phosphorus has not yet been detected in molecules containing organic carbon. But scientists hope that further research will reveal them. ” For astrobiology, this means we can be more confident than ever that Enceladus’ ocean is habitable. concludes Glen.