Measurement and Implications of Surface Energies of Titan’s Haze Analogs “Tholins”

Abstract:

Titan, Saturn’s largest moon, has a substantial nitrogen-methane atmosphere. In its upper atmosphere, photochemistry leads to the formation of complex organic particles that form Titan’s thick haze layers. The haze particles could act as the cloud condensation nuclei (CCN) for various organic clouds [1]. The haze particles would also eventually sediment down to Titan’s surface, interacting with the surface hydrocarbon lakes [2], and they are believed to be the main dune-forming materials [3]. In order to better understand these physical and geological processes involving the haze particles, we investigate the surface energy, an intrinsic property governing the adhesion and wetting, of laboratory-made Titan’s haze analog, “tholin”. The surface energies of tholins have been previously measured with samples produced in the Planetary HAZE Research (PHAZER) experimental system to be around 60-70 mJ/m² [4]. The relatively high surface energy of tholin indicates that the haze particles are highly cohesive and easily wettable by hydrocarbon liquids/solids. Thus, they are good CCN for hydrocarbon clouds and would likely sink in the hydrocarbon lakes. In this study, we expand our sample size by including tholin samples made in other laboratories with different experimental conditions and setups. We use four separate tholin samples produced respectively through the PHAZER chamber at Johns Hopkins University [5], the Cosmic Simulation Chamber (COSmIC) at NASA Ames Research Center [6], and the photochemical aerosol chamber at University of Northern Iowa [7] (Table 1). Via the sessile drop contact angle method, we measure and compare the surface energies for these tholin samples in a dry nitrogen environment. We will discuss the effect of laboratory setup, energy sources, pressure, and temperature on the chemical makeups and the adhesive properties of tholins, and how these results would help us better constrain various physical processes on Titan.

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