Analogue Experiments for the Identification of Bacterial Biosignatures in Ice Grains from Enceladus and Europa Using Mass Spectrometry

Active ocean worlds, such as Saturn’s icy moon Enceladus and possibly Jupiter’s moon Europa, eject water ice grains into space [1,2], making their subsurface oceans accessible for analysis during spacecraft flybys [3]. Impact Ionization mass spectrometers can sample the emitted ice grains and provide insights into the oceans’ compositions. Enceladus’ ocean is salty [4], sustains water-rock hydrothermal interactions [5], and contains organic material, including complex macromolecules [6] and low mass volatile compounds, potentially acting as amino acid precursors [7].

These discoveries were supported by Laser Induced Liquid Beam Ion Desorption (LILBID) experiments, a technique known to accurately reproduce impact ionization mass spectra of ice grains recorded in space [8]. This analogue technique has shown that potential biosignatures, such as amino acids, fatty acids and peptides, could be detected by future space instruments down to ppm or ppb levels [9,10]. Here we report our next steps — investigating whether DNA and lipids, indicators for terrestrial life, could also be identified.

We therefore conducted LILBID experiments on DNA and lipid extracts from two bacteria, S. alaskensis and E. coli, to simulate their characteristic spectral features in cationic and anionic impact ionization mass spectra. Microbial fragments, such as fatty acids derived from the bacteria’s membrane lipids, were clearly identifiable. In the DNA mass spectra, purine bases (adenine and guanine) and phosphate deoxyribose compounds were detected. The mass spectra have been added to a growing database of LILBID spectra, designed to aid in the planning and data analysis of future missions to icy ocean worlds.

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[4] Postberg et al. (2009) Nature 459.7250: 1098-1101

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[6] Postberg et al. (2018) Nature 558:564–568

[7] Khawaja et al. (2019) Mon Not R Astron Soc 489:5231–5243

[8] Klenner et al. (2019) Rapid Commun Mass Spectrom 33.22: 1751-1760

[9] Klenner et al. (2020a) Astrobiology 20:179-189

[10] Klenner et al. (2020b) Astrobiology 20:1168-1184