Mass Spectrometric Fingerprints of Bacteria and Archaea for Life Detection on Icy Moons

The icy moons of the outer Solar System display evidence of subsurface liquid water and, therefore, potential habitability for life. Flybys of Saturn's moon Enceladus by the Cassini spacecraft have provided measurements of material from plumes that suggest hydrothermal activity and the presence of organic matter. Jupiter's moon Europa may have similar plumes and is the target for the forthcoming Europa Clipper mission that carries a high mass resolution and high sensitivity mass spectrometer, called the MAss Spectrometer for Planetary EXploration (MASPEX), with the capability for providing detailed characterization of any organic materials encountered. We have performed a series of experiments using pyrolysis-gas chromatography-mass spectrometry to characterize the mass spectrometric fingerprints of microbial life. A range of extremophile Archaea and Bacteria have been analyzed and the laboratory data converted to MASPEX-type signals. Molecular characteristics of protein, carbohydrate, and lipid structures were detected, and the characteristic fragmentation patterns corresponding to these different biological structures were identified. Protein pyrolysis fragments included phenols, nitrogen heterocycles, and cyclic dipeptides. Oxygen heterocycles, such as furans, were detected from carbohydrates. Our data reveal how mass spectrometry on Europa Clipper can aid in the identification of the presence of life, by looking for characteristic bacterial fingerprints that are similar to those from simple Earthly organisms.