Date of Graduation

5-2023

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

Heyes, Colin D.

Third Committee Member

Kral, Timothy A.

Keywords

Astrobiology; Habitability; Hydrocarbons; Solubility; Tholins; Titan

Abstract

Titan’s production of organics in its atmosphere and the liquid hydrocarbon lakes present on its surface make it a prime target for astrobiologists. Many previous studies on laboratory analogs of these organics, called "tholins", have found amino acids, nitriles, and other building blocks necessary for life. The potential solubility of tholins in the lakes of Titan presents an opportunity to create physical and chemical changes within the organics. While the lakes of Titan are primarily comprised of nonpolar compounds (methane and ethane), many predict that very small amounts of polar hydrocarbons are also present. To better understand these processes, researchers create “tholins” to utilize in these studies. Since the production of tholins is also a randomized process, variations in the structure are to be expected in tholin production. Studies have been developed to better understand variability in the compounds and how best to simulate conditions being investigated. Chapter 1 investigates the effects of varying production times on tholin molecular structure. While the process of tholin production is randomized, general structural trends resulting from the effects of certain variables can be observed. Through these experiments, we seek to characterize the effects of different production time scales on the structure and composition of tholins. Matrix-Assisted Laser Desorption Ionization (MALDI) was utilized to observe large variations and spectral shifts on 1-hour, 4-hour, 6-hour, and 12-hour production times of tholins. Resulting spectra do not show large changes in the molecular weights of tholins produced at different timescales. The resulting organics produced however might be different, with more aromatics and ring structures being present as production time increases. Therefore, the tholins produced at longer production times might not be dissimilar to tholin produced at shorter timescales. Chapters 2, 3, and 4 investigate tholins in the lakes on Titan. To better understand the impact these liquid polar compounds within the lakes might have on tholins, we utilize a mixture of both polar and nonpolar solvents. Acetonitrile, hexane, and a mixture solvent of hexane saturated with acetonitrile act as analogs to the Titan lake environment. Dynamic Light Scattering (DLS) was used in Chapter 2 to observe the physical characteristics (such as hydrodynamic diameter and dispersity indices) of the tholin particles within each solution. Measurements showed that the presence of acetonitrile did increase particle diameter and polydispersity values. Additionally, Fourier Transform infrared spectroscopy (FTIR) and MALDI were utilized in Chapter 3 and 4 for spectroscopic analysis of organics with and without oxygen-containing species, respectively. Results from both of these studies showed no chemical changes in the samples containing mixtures of solvents. These projects can provide insight into the environment of Titan and further our knowledge of its potential habitability.

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