Hydrocarbon chemistry in the atmosphere of a Warmer Exo-Titan

Creators: Adams, Danica¹; Luo, Yangcheng¹; Yung, Yuk L.^{1, 2}

1. California Institute of Technology
2. Jet Propulsion Lab

Abstract

Hosting a ∼1.5 bar N₂ atmosphere and reducing atmospheric composition, Titan has the energy sources needed to drive disequilibrium chemistry and hosts an aerosol layer which shields the surface from incident UV radiation. This world draws parallels to an early Earth-like world (although ∼200 K cooler), and the atmospheric chemistry may be capable of forming relevant prebiotic species. Exo-Titan worlds at close-in orbits host photochemistry relevant to habitability with rich hydrocarbon chemistry. We investigate the effect of stellar type of the host star, equilibrium temperature, incident radiation, and vertical transport efficiency on the production of higher-order hydrocarbons. We find a greater incident radiation (a closer orbit) increases the rate of methane photolysis as well as photolysis of hydrocarbons. A larger H₂ abundance and warmer temperature increases the rate of the back reaction H₂ + CH₃ → CH₄ + H, and the temperature dependence is so great that CH₃ recycles back into CH₄ instead of forming C₂H₆. A larger H₂ abundance and warmer temperature also encourages interesting cycling between C₂H₂, C₂H₃, and C₂H₄ via reactions with atomic H.

Copyright and License

© 2022 Adams, Luo and Yung. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

Acknowledgement

We thank Karen Willacy, Mark Swain, and Randy Gladstone for providing helpful discussions which greatly helped this work.

Funding

DA was supported by NASA’s FINESST program under Proposal Number 80NSSC19K1548. YL was supported in party by funding from NASA’s Astrobiology Institute’s proposal “Habitability of Hydrocarbon Worlds: Titan and Beyond” (PI: R.M. Lopes of JPL).

Contributions

DA and YL developed the research concept and contributed to drafting and editing the manuscript. DA performed the model simulations.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Data Availability

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

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