New research has presented evidence for a key building block of life on Saturn’s moon Enceladus’ subsurface ocean. Modelling indicates that the ocean on Enceladus is relatively rich in dissolved phosphorus, which is an essential ingredient for life.
A research article documenting the study has been published in Proceedings of the National Academy of Sciences (PNAS).
“Enceladus is one of the prime targets in humanity’s search for life in our solar system. In the years since NASA’s Cassini spacecraft visited the Saturn system, we have been repeatedly blown away by the discoveries made possible by the collected data,” said Christopher Glein, co-author of the paper, in a press statement. Glein is an expert in extraterrestrial oceanography.
NASA’s Cassini spacecraft discovered the subsurface liquid water on Enceladus and analysed samples of plumes of ice grains and water vapour that erupted into space from cracks in the icy surface of the planet.
“What we have learned is that the plume contains almost all the basic requirements of life as we know it. While the bioessential element phosphorus has yet to be identified directly, our team discovered evidence for its availability in the ocean beneath the moon’s icy crust,” added Glein.
Worlds with oceans beneath a layer of ice are not rare in our solar system. Icy satellites of giant planets, like Europa, Titan and Enceladus, fall into this category. Even Pluto has a similar icy subsurface ocean. In order for oceans to exist on the surface like on Earth, they must be within a narrow range of distance from their star to maintain a temperature where water neither freezes nor boils off. But interior ocean worlds can exist at a much wider range of distances.
“The quest for extraterrestrial habitability in the solar system has shifted focus, as we now look for the building blocks for life, including organic molecules, ammonia, sulfur-bearing compounds as well as the chemical energy needed to support life. Phosphorus presents an interesting case because previous work suggested that it might be scarce in the ocean of Enceladus, which would dim the prospects for life,” explained Glein.
Phosphorus in the form of phosphates is essential for the creation of various important organic components, from RNA and DNA to energy-carrying molecules and cell membranes to bones and teeth.
Based on data about the ocean system on Enceladus from Cassini, the research team members created thermodynamic and kinetic models that simulate the geochemistry of phosphorus. They found that phosphate minerals would be unusually soluble there. According to Klein, the underlying geochemistry makes the presence of dissolved phosphorus inevitable.