Evolution of aerosols in Titan’s ionospheric plasma: An experimental simulation

Observatio ns by the space mission Cassini have revealed the formation of complex organic molecules in Titan ’s ionosphere. To better understand this complex chemistry, several experiments were conducted to reproduce analogs of Titan ’s aerosols in laboratories, named ‘tholins’. These tholins appear to be polymeric and nitrogenous molecules . Aerosols stay many years in Titan ’s upper atmosphere, a dusty plasma where molecules are continuously bombarded by charged molecules. Consequently, they are likely to evolve during their stay. Here we address this question by experimental simulation: we analyze the effect of harsh plasma environment on tholins alread y formed. o separate the processes of formation and evolution, aerosols samples used are first formed with the experiment PAMPRE at LATMOS [ T Gautier Icarus 2016 ]. T hen tholins are prepared in the shape of thin pellets and positi oned at the center of a plasma reactor, where they are exposed during several hours in a DC N 2 - H 2 glow discharge, partially representative of Titan’s ionosphere. Methane is purposefully removed from this second phase to prevent the formation of new aerosol s. Morphological changes. Pellets become rougher during the exposure. Surface structure is observed through a Scanning Electron Microscope before and after an exposure of four hours. It shows that plasma sputteri ng attacks the surface and removes some material. Chemical modifications. We perform in situ infrared transmission spectroscopy during the exposure. Characteristic absorption bands of tholins are distorted, witnessing changes in the samples chemical struc ture. Especially, we suspect C - H bond environment to be complexed. Nitrile functions are also modified.