Biological methane production under putative Enceladus-like conditions

The detection of silica-rich dust particles, as an indication for ongoing hydrothermal activity, and the presence of water and organic molecules in the plume of Enceladus, have made Saturn's icy moon a hot spot in the search for potential extraterrestrial life. Methanogenic archaea are among the organisms that could potentially thrive under the predicted conditions on Enceladus, considering that both molecular hydrogen (H₂) and methane (CH₄) have been detected in the plume. Here we show that a methanogenic archaeon, Methanothermococcus okinawensis, can produce CH₄ under physicochemical conditions extrapolated for Enceladus. Up to 72% carbon dioxide to CH₄ conversion is reached at 50 bar in the presence of potential inhibitors. Furthermore, kinetic and thermodynamic computations of low-temperature serpentinization indicate that there may be sufficient H₂ gas production to serve as a substrate for CH₄ production on Enceladus. We conclude that some of the CH₄ detected in the plume of Enceladus might, in principle, be produced by methanogens.