Date of Graduation

7-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Space & Planetary Sciences (PhD)

Degree Level

Graduate

Department

Space & Planetary Sciences

Advisor/Mentor

Chevrier, Vincent F.

Committee Member

Roe, Larry A.

Second Committee Member

Allison, Neil T.

Third Committee Member

Oliver, William F. III

Fourth Committee Member

Soderblom, Jason

Keywords

Cassini VIMS; Experimental; Hydrocarbon liquids; Liquid-atmosphere interactions; Nitrogen dissolution and exsolution; Titan

Abstract

Saturn’s moon, Titan, has surface conditions (89–94 K, 1.5-bar atmosphere) that permit lakes of methane, ethane, and dissolved atmospheric nitrogen. The effects of atmospheric nitrogen on methane-ethane liquid properties is poorly understood, leading to uncertainty in Titan modeling. I address this question by experimentally investigating the physical properties of methane-ethane liquids under a 1.5-bar nitrogen atmosphere in a simulated Titan environmental chamber.

Chapter 1 addresses nitrogen dissolution kinetics in Titan’s liquid hydrocarbons. I found an exponential increase in nitrogen quantity and diffusion coefficients with increasing methane mol%. I find that Titan’s liquids are likely not saturated in nitrogen, with dissolution alone. This would result in strong disequilibria between liquid layers, creating lake dynamics (i.e. overturn).

Chapter 2 systematically investigates the conditions necessary for bubble formation under Titan surface conditions. I found that liquid methane and ethane, along with temperature and concentration perturbations, are necessary for bubble formation. Bubbles are likely prevalent in Titan’s lakes and influence the formation of geologic features (i.e. deltas).

Chapter 3 investigates methane-ethane freezing points in equilibrium with a 1.5-bar nitrogen atmosphere. I found that liquid ethane-alkane compositions of ~75–100 mol% will freeze above 89 K, and a peritectic point is observed. Brightening events on Titan’s surface may indeed be ethane-rich hydrocarbon ice, while bright features in the seas are likely not floating or suspended ice.

Chapter 4 couples Cassini Visual and Infrared Mapping Spectrometer (VIMS) observations with laboratory Fourier Transform Infrared Spectroscopy (FTIR) to find that Cassini VIMS is sensitive to ethane-alkane quantities of 5–75 mol%. Titan’s lakes are likely within this compositional range.

The results of this dissertation indicate that dissolved atmospheric nitrogen plays a significant role in Titan’s liquid hydrocarbons. Small perturbations of temperature and concentration will cause explosive bubble exsolution events, and nitrogen increases the likelihood of methane-ethane freezing on Titan’s surface. Nitrogen will also cause changes in methane’s density, leading to lake dynamics, such as overturn, stratification, and bubble formation. By comparing Cassini VIMS and RADAR measurements of Titan’s liquid bodies, we can discern if the liquids are indeed stratified or well mixed.

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