Investigating the formation and growth of Titan's atmospheric aerosols using an experimental approach

Abstract

Titan has a climate system with similarities to Earth, including the presence of a thick atmosphere made up of several atmospheric layers. As on Earth, Titan's climate is influenced by several factors: the gaseous species making up the atmosphere, the energy deposited on the satellite, and solid organic aerosols. Indeed, numerous observations have revealed the presence of solid particles in the form of an opaque orange haze in Titan's atmosphere, influencing radiation balance and atmospheric dynamics, for example. However, the influence of these suspended solid particles seems to evolve according to the atmospheric altitude where they are located, certainly testifying to the presence of organic solids with different physico-chemical properties. At present, it is suspected that several populations/classes of atmospheric aerosols may form following different chemical pathways, and that aerosols undergo growth processes that modify their properties. In this experimental study, we present new observations on the evolution of morphological and chemical properties observed on Titan aerosol analogues, produced from a mixture of 20 % CH₄ and 80 % N₂ injected into a dusty RF plasma experiment. Using SEM (morphological) and FTICR-LDI-MS (chemical composition) analyses, we observe that properties evolve according to certain formation and growth mechanisms, which differentiate over time. The evolution of the neutral gaseous chemical composition analyzed in-situ by QMS in parallel shows correlations with the evolution of solid properties, testifying to the selective involvement of certain neutral products in the formation and growth mechanisms of solid aerosols. By linking the analyses of the gas phase and organic solids, we propose the calculation of an uptake coefficient between six neutral gaseous products (C₂H₂, HCN, C₂H₆, C₂H₃N, HC₃N, C₂N₂) and the surface of the Titan aerosol analogues produced in this study.