The potential habitability of the icy moons of Jupiter and Saturn, in particular Europa and Enceladus, has been hotly debated in recent years. The recent Cassini mission to Enceladus carried the Ion and Neutral Mass Spectrometer (INMS), and the forthcoming Europa Clipper mission will also carry a mass spectrometer, MASPEX, enabling molecular detection of material in the plumes of the icy moons. The most likely candidates for life on icy moons are simple organisms similar to earthly extremophiles that can withstand extreme conditions of temperature, salinity and acidity.
Different strains of extremophile Archaea and Bacteria were analyzed in pure form with flash pyrolysis-GC-MS. Flash pyrolysis offers a good analogue of the impact fragmentation that occurs as the spacecraft flies through a plume. In our experiments pyrolysis is coupled with gas chromatography-mass spectrometry (GC-MS). This separates the pyrolysis products, enabling identification of individual molecules. This GC stage is missing on the spacecraft instruments but simulated INMS or MASPEX spectra can be reconstructed from the chromatograms.
Our results show that pyrolysis-GC-MS analysis of intact archaea and bacteria produces distinctive fingerprints of biotic substances. Decomposition products from protein, amino acid, carbohydrate and lipid species were detected from all the strains analyzed. We have also identified the ion series that represent specific compound types which are related to different components of the organisms. These ion series greatly help with the interpretation of complex mass spectra when no separation technique is present, i.e. in INMS and MASPEX. Although only a relatively small number of strains have been analyzed in this study, there is diversity among the results obtained with differing ratios of carbohydrate and protein products detected. However, all the strains also share common features, such as the presence of indole and phenols. The mass spectra obtained from Archaea and Bacteria are clearly different from those of abiotic materials such as meteorites. This shows that mass spectrometry is a powerful technique for distinguishing between non-biological and biological materials.