How to identify cell material in a single ice grain emitted from Enceladus or Europa

Icy moons like Enceladus, and perhaps Europa, appear to express material sourced from their subsurface oceans into space via plumes of ice grains and gas. Cassini’s Cosmic Dust Analyzer (CDA) revealed that Enceladus’ ocean is salty, hydrothermally active, and contains organic compounds. Only 1-3 % of Enceladus’ plume grains contain organic material in high concentrations, highlighting the importance of compositional analyses of individual grains compared to a bulk sample. Currently this is only possible via impact ionization mass spectrometry, as employed by CDA or Europa Clipper’s SUrface Dust Analyzer. Here we report experiments simulating the impact ionization mass spectra of ice grains containing one bacterial cell, or fractions thereof, as encountered by a spacecraft at flyby speeds of 4-6 km/s. Mass spectral signals characteristic of the bacteria are shown to be clearly identifiable by future impact ionization mass spectrometers, even if an ice grain contains much less than one cell.