Exploring in the laboratory the impact of low energy oxygen ions on Titan's aerosols

International audienceThe Saturn system has been explored for 13 years (2004-2017) by the Cassini-Huygens mission that revealed the extraordinary chemical diversity of Titan and Enceladus. In particular, O$^+$ ions (1 - 100 keV), originating from Enceladus' geysers, precipitate in Titan's upper atmosphere where molecules reaching mass-on-charge (m/z) of several thousand atomic mass units have been detected. These aerosol embryos have been attributed to polycyclic aromatic (nitrogen bearing) hydrocarbons (PANHs) that most likely result from the ionization and dissociation of the major atmospheric compounds, N$_2$ and CH$_4$ by solar photons [Hörst, 2017]. It is to be expected that the small fraction of energetic O$^+$ ions, implanting themselves in organic aerosols, would modify their optical properties and chemical composition. If complex oxygenated molecules are formed, the aerosols, by sedimenting towards the surface, can then provide it with prebiotic material, adding a dimension with strong exobiological implications to the carbon / nitrogen / hydrogen chemistry endogenous to Titan [Hörst et al., 2012]. The objective of this project is thus to study the impact of oxygen ions from 1 to 100 keV on Titan aerosol analogues (tholins) and model materials by characterizing their effect on the chemical, structural and optical properties of the targets