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EPS Seminar: Dr. Sarah Zeichner - Polycyclic aromatic hydrocarbons in samples of Ryugu formed in the interstellar medium

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Polycyclic aromatic hydrocarbons (PAHs) contain 20% of the carbon in the interstellar medium. They are potentially produced in circumstellar environments (at temperatures 1000 K), by reactions within cold (~10 K) interstellar clouds, or by processing of carbon-rich dust grains. We report isotopic properties of PAHs extracted from samples of the asteroid Ryugu and meteorite Murchison. The doubly-13C substituted compositions (D2×13C values) of the PAHs naphthalene, fluoranthene, and pyrene are 9 to 51‰ higher than values expected for a stochastic distribution of isotopes. The D2×13C values are higher than expected if the PAHs formed in a circumstellar environment, but consistent with formation in the interstellar medium. In contrast, the PAHs phenanthrene and anthracene in Ryugu samples have D2×13C values consistent with formation by higher-temperature reactions.


Dr. Sarah Zeichner is an organic geochemist interested in problems related to modern, ancient, and extraterrestrial carbon cycles. Her dissertation has worked across myriad subject areas, addressing questions ranging from “How did the Earth become muddy?” to “Where in the galaxy do aromatic organic molecules form?” She is currently a Resnick Postdoctoral Scholar at the California Institute of Technology, developing methods to use isotopic properties of molecules to understand the resilience of large organic molecules in modern surface environments. She received a Ph.D. in Geochemistry in 2023 from the California Institute of Technology and a B.S. in Geophysical Sciences from the University of Chicago in 2016. Between undergraduate and graduate school, she worked as a software developer for two years at McMaster-Carr, an industrial supply company based in Elmhurst, IL.


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