Abstract:
Titan has a plethora of hydrocarbons and nitriles in the atmosphere and on the surface that interact with each other. For example, acetylene (C2H2) is a primary photochemical product in the atmosphere. Pyridine (C5H5N), a simple nitrogen heterocycle and a step towards nucleobases, has not been directly detected at Titan, however, pyridine could be produced when HCN is present. Interestingly, when acetylene and pyridine interact under specific temperatures and molar ratios, a co-crystal can form. Co-crystals are stable structures held together by weaker intermolecular interactions like hydrogen bonding. These “cryominerals” can be a good indicator of geologic processes and the chemical composition of Titan’s surface, which is important for future Titan missions. Here, we show experimental results on the pyridine:acetylene co-crystal under Titan conditions, which adds to the body of knowledge on this expanding field of Titan cryominerals.
We produce the co-crystal sample in a cryostage at Titan surface conditions (~90 K), and analyze the sample via micro-Raman spectroscopy and X-ray powder Diffraction (XRD). Within minutes, the co-crystal forms at 150 K, and is stable from 80-190 K. Distinct, new Raman bands and band shifts are clear evidence of the co-crystal. Additionally, the co-crystal is stable and detectable after being exposed to liquid ethane, indicating stability during an ethane rain event on Titan. XRD results indicate thermal expansion along the b and c crystallographic axes, which is likely due to relatively weaker interactions along those axes compared to the a axis. These results indicate that the co-crystal may readily form at Titan (either in the atmosphere or on the surface) and may be stable over long timescales.
About the speaker:
Ellen Czaplinski is a first-year NASA Postdoctoral Fellow at the Jet Propulsion Laboratory, working with Dr. Robert Hodyss. Her research interests include: experimental laboratory studies of Titan surface chemistry, habitability of Titan’s surface liquids, improving autonomous capabilities of ocean worlds missions, and robotic exploration of the lunar south pole. Ellen received her Ph.D. in Space and Planetary Sciences from the University of Arkansas in 2021, and a B.S. in Planetary Science from Purdue University in 2016. She enjoys rock climbing, hiking, strategic board games, and spending time with her dog, Stella.
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