Discriminating Aromatic Parent Compounds and their Derivative Isomers in Ice Grains from Enceladus and Europa using a Laboratory Analogue for Spaceborne Mass Spectrometers

The Cassini-Huygens space mission discovered a plume at Enceladus that ejects gases and frozen ice grains originating from an ocean of liquid water below its icy shell. In these ice grains, a range of interesting organic molecules were discovered by Cassini’s Cosmic Dust Analyzer (CDA) mass spectrometer. Organic molecules are important in the search for life beyond Earth as they form the basis of all known Earth life, and active biology elsewhere would likely have a discernible effect on the local inventory of organic species. One class of organic, with a ring structure of carbon atoms, called aromatics, were discovered in the plume. We investigate the spectral appearance of one example of aromatic compound, benzoic acid, as well as two similar compounds with additional chemical groups attached to the aromatic ring. The two similar compounds have the same mass and general structure, but slightly different arrangements of the additional groups, known as isomers. We find that it is simple to distinguish mass spectral features between benzoic acid and its related compounds, but more difficult to explain the differences between the isomers. This work will assist the analysis of mass spectrometry data from future habitability-investigating space missions to ocean-bearing icy moons.