For many years, Enceladus has attracted the attention of scientists for its potential to harbor extraterrestrial life. New data reinforces the idea that the hidden ocean of this moon of Saturn would be well suited to the development of life.
In search of extraterrestrial life, scientists are particularly interested in finding new Earth-sized exoplanets located in the habitable zone of their star. But our best chance of finding living organisms may well be much closer to us, inside our solar system itself.
A liquid ocean under an ice crust
For several decades already, certain moons of JupiterJupiter and Saturn indeed attract the attention of scientists and exobiologists because of the presence of an important crustcrust of water ice on their surface. EnceladusEnceladussmall moonmoon of Saturn, only 500 kilometers in diameter, has thus been the subject of very particular attention since the passage of the Cassini probe in 2004. If the surface of this moon orbiting around the gas giantgas giant within the outermost ring appears totally frozen, many observations suggest the presence of water liquidliquid under this thick crust of ice. Many geysersgeysers bursting the surface have indeed been observed, suggesting that this internal liquid ocean would be animated by currents of convectionconvection due to the presence of important sources of heatheat.
Liquid water and geological activity producing intense and continuous heat, that’s all it takes to raise the hopes of scientists on the potential presence of living organisms under the icy surface of Enceladus. These two criteria allowing the habitability of the small moon have just been supplemented by a third. Through modelingmodelingresearchers have found that the hidden ocean of Enceladus is relatively rich in phosphorusphosphorusa chemical elementchemical element essential to the development of life. On Earth, phosphorus, in the form of phosphate, is indeed a basic ingredient for the constructionconstruction of the’DNADNA and of theRNARNAbut also enters into the composition of many energetic molecules, cell membranescell membranes, bones and teeth. It is also an essential component in the development of simpler organisms, such as the planktonplankton.
Liquid water, heat and organic molecules: the ingredients of life come together
During its passage near Enceladus in 2004, the Cassini probe was able to sample and analyze the grains of ice and the steam emitted by the geysers bursting the frozen surface. The data collected had then stunned the scientific community by the extraordinary potential of this moon of Saturn. The samples indeed contained all the basic elements necessary for life, but the presence of phosphorus could not be confirmed. The new hypothesis that the liquid ocean does indeed contain a large quantity of it therefore only reinforces these previous results.
To reach this conclusion, the researchers carried out modeling thermodynamicsthermodynamics and kinetics simulating the geochemical cycle of phosphorus based on the data reported by the Cassini probe. The results, published in the journal PNASthus show how the mineralsminerals forming the core solidsolid of Enceladus dissolve in contact with water alkalinealkaline (containing NaHCO3 and/or Na2CO3). According to their model, the presence of phosphorus in the ocean of Enceladus is therefore inevitable and even reaches quantities equivalent to, or even greater than, what is observed in sea water on Earth.
The clues supporting the habitability of the ocean of this moon of Saturn therefore continue to accumulate. For scientists, the next step can only be the sending of a new probe intended to validate or not this hypothesis.