Experimental Study of Ethylene Evaporites under Titan Conditions

Abstract

Titan has an abundance of lakes and seas, as confirmed by Cassini. Major components of these liquid bodies include methane ($CH_4$) and ethane ($C_2H_6$); however, evidence indicates that minor components such as ethylene ($C_2H_4$) may also exist in the lakes. As the lake levels drop, 5 $\mu m$-bright deposits, resembling evaporite deposits on earth, are left behind. Here, we provide saturation values, evaporation rates, and constraints on ethylene evaporite formation by using a Titan simulation chamber capable of reproducing Titan surface conditions (89-94 K, 1.5 bar $N_2$). Experimental samples were analyzed using Fourier transform infrared spectroscopy, mass, and temperature readings. Ethylene evaporites form more quickly in a methane solvent than in an ethane solvent or in a mixture of methane/ethane. We measured an average evaporation rate of $(2.8 \pm 0.3) \times 10^{-4} kg \; m^{-2} \; s^{-1}$ for methane and an average upper limit evaporation rate of less than $5.5 \times 10^{-6} kg \; m^{-2} \; s^{-1}$ for ethane. Additionally, we observed red shifts in ethylene absorption bands at 1.630 and 2.121 $\mu m$ and the persistence of a methane band at 1.666 $\mu m$.