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Saturn’s moon Enceladus is erupting a plume of gas and ice grains from its south pole. Linked directly to the moon’s subsurface global ocean, plume material travels through cracks in the icy crust and is ejected into space. The subsurface ocean is believed to be in contact with the rocky core, with ongoing hydrothermal activity present. The Cassini spacecraft’s Ion and Neutral Mass Spectrometer (INMS) detected volatile, gas phase, organic species in the plume and the Cosmic Dust Analyzer (CDA) discovered high mass, complex organic material in a small fraction of ice grains. Here, we present a broader compositional analysis of CDA mass spectra from organic-bearing ice grains. Through analogue experiments we find spectral characteristics attributable to low mass organic compounds in the Enceladean ice grains: nitrogen-bearing, oxygen-bearing and aromatic. By comparison with INMS results we identify low mass amines (particularly (di)methylamine and/or ethylamine) and carbonyls (with acetic acid and/or acetaldehyde most suitable) as the best candidates for the Nand O-bearing compounds respectively. Inferred organic concentrations in individual ice particles vary but may reach tens of mmol levels. The low mass nitrogenand oxygen-bearing compounds are dissolved in the ocean, evaporating efficiently at its surface and entering the ice grains via vapour adsorption. The potentially partially water soluble, low mass aromatic compounds may alternatively enter ice grains via aerosolisation. These amines, carbonyls and aromatic compounds could be ideal precursors for mineral-catalysed Friedel-Crafts hydrothermal synthesis of biologically relevant organic compounds in the warm depths of Enceladus’ ocean.

Low-mass nitrogen-, oxygen-bearing, and aromatic compounds in Enceladean ice grains