Bayesian analysis of Enceladus’s plume data to assess methanogenesis

With its global ocean and deep-sea hydrothermal systems, Saturn’s moon Enceladus is one of the hottest places for the search of extraterrestrial life in the solar system. A spectacular feature of Enceladus is the ejection in space of a plume of material from the ocean. From 2008 to 2015, the Cassini probe made measurements of the composition of the plume. As a multi-disciplinary team composed of chemists, astrophysicists and biologists associated with various institutions (ENS-Observatoire de Paris-Paris Sciences et Lettres university, University of Arizona, Muséum National d’Histoire Naturelle) and supported by the Origins and conditions for the emergence of life of PSL university, we show that currently known geochemical processes acting in Enceladus interior might match with conditions habitable to Earth-like hydrothermal vents inhabiting methane producing micro-organisms (“methanogens”). These processes alone are unable to explain the Cassini data, but including a population of micro-organisms in our model leads to predict methane levels in the plume compatible with the data. We conclude that a currently unknown methane producing process is at work in Enceladus’s interior, and that (biotic) methanogenesis could be a good explanation… provided that life emerging is not uncommon.