An Arctic analogue for the future exploration of possible biosignatures on Enceladus

Abstract

Methane-rich emissions to the seafloor along the Arctic mid-oceanic ridge hold strong astrobiological significance, as they may represent analogues of putative hydrothermal vent environments on Enceladus. Although such environments on Enceladus would be ideal to sample in future astrobiological missions, this may not be possible due to technological and logistical limitations. As such, searching for biosignatures in the more readily sampled cryovolcanic plumes or Enceladus’ icy shell is preferable. In this regard, the Arctic Ocean, where the geologically active seafloor is covered by thousands of metres of salty water and sealed by an ice cap, is a unique terrestrial analogue of Enceladus. In the present study, we have sought to determine whether any geochemical biosignatures associated with methane cycling (e.g., elevated methane concentrations, carbon isotopic fractionation) can be detected in Arctic ice and seawater samples using mass spectrometric techniques similar to those likely to be included in the payloads of planned missions to Enceladus. Our results have shown that, although no unequivocal evidence of methane could be detected in our Arctic samples, the carbon isotopic composition of carbon dioxide gas and the oxygen isotopic composition of water vapour emitted from the Arctic samples could indeed be measured. Furthermore, an excess of molecular hydrogen with abundances comparable to the composition of Enceladus’ southern pole plume was possibly observed in one of the Arctic ice samples. These results have implications for detectable indirect geochemical evidence of putative ecosystems of hydrogenotrophic methanogenic life on the seafloor of Enceladus and justify future efforts at method development and refinement using apparatus similar to that likely to be included in the payloads of future missions.