Poster 15: Exploring the Composition of Titan's Lakes through Laboratory Experiments

Previous studies have shown that the lakes of Titan are composed of methane and/or ethane, but the relative proportions are mostly unclear. Understanding the past and current stability of these lakes requires characterizing the interactions of liquid methane and ethane. Mixtures of these hydrocarbons are not fully understood, and a phase diagram has not yet been established. Our current cryogenic laboratory setup reaches temperatures down to 30 K, allowing us to map the full liquidus line (freezing points) of the methane-ethane system as a function of composition and temperature. While pure methane and ethane both freeze around 91 K, our results show that when mixed, the freezing point is depressed down to ∼72 K for a mixture of ∼64% methane and ∼36% ethane. Any mixing of these two species together will depress the freezing point of the lake below Titan's surface temperature, preventing them from freezing. Also, when ethane ice forms, it freezes on the bottom of the liquid, while methane ice freezes at the top of the liquid, implying ethane ice is denser than the solution, while methane ice is less dense; this holds for all concentrations. Concurrently with the phase diagram determination, we have acquired transmission spectra of these mixtures to understand how the spectral features change with concentration and temperature. These results will help interpret future observational data, and guide current theoretical models.