Rapid Aggregation and Dissolution of Organic Aerosols in Liquid Methane on Titan

Abstract

Complex organic aerosols in the upper atmosphere of Saturn's moon Titan reach the troposphere and surface, where a methane (CH4)-based hydrological cycle occur. Previous studies have assumed no interactions between organic aerosols and liquid CH4, although the dissolution of low-molecular-weight photochemical products in liquid CH4 has been considered. Here we report experimental results of soaking a laboratory analog (so-called tholin) of Titan's organic aerosols in liquid CH4 at 93–98 K for several hours and then evaporating the liquid, simulating wet–dry cycling on Titan. After wet–dry cycling, residual tholin particles form aggregates through cementation. Solid evaporitic deposits formed by evaporation of interacted liquid contain nitrogen-bearing aromatics, suggesting selective dissolution of aromatics. Our results suggest that organic aerosols or high-molecular-weight compounds adsorbed on them partly dissolve in liquid CH4 on Titan, even during short-term wetting events, promoting the growth of aerosols to dune particles via aggregation and providing aromatics to evaporites.