Abstract : Titan is Saturn’s largest satellite. This object is unique in the solar system as it hosts a dense atmosphere  mainly made of molecular nitrogen N2 and methane CH4, with a surface pressure of 1.5 bar. The nitrogen-rich atmosphere and the presence of liquid areas at the surface make it one of the most interesting objects to understand the evolution of the primitive Earth before the emergence of life and to look for habitable worlds outside the solar system. The Cassini-Huygens Mission has been probing Titan since 2004. It has revealed an intense atmospheric photochemistry initiated by the photo-dissociation and ionization of N2 and CH4 . Photochemistry on Titan leads to the formation of solid organic aerosols responsible for a smog permanently surrounding the moon [2,3]. These aerosols are produced in large amounts and have a significant interest for astrobiology because they are among the most complex organic materials ever detected in extra-terrestrial bodies. In the upper atmosphere, the plasma spectrometer onboard Cassini detected signatures compatible with the presence of heavily charged molecules which are precursors for the solid core of the aerosols [4,5,6]. These observations hint at the key role of ion chemistry for organic growth. Further, it is now known that aerosols are initiated in the ionosphere, where gas and solid aerosols coexist in a fully coupled ionic and neutral chemistry. However, the processes coupling ion chemistry and aerosol production are mostly still unknown.
For the first time, we use an experimental approach, investigating the ion chemistry, responsible for the organic growth that we observe in Titan’s upper atmosphere. To do this, we use a plasma reactor simulating Titan’s heterogeneous ionosphere chemistry . Positive ions are investigated by in situ ion mass spec- trometry, alongside neutral products complementarily studied through infrared absorption spectroscopy and mass spectrometry.