AUTHOR=Adams Danica , Luo Yangcheng , Yung Yuk L. 

TITLE=Hydrocarbon chemistry in the atmosphere of a Warmer Exo-Titan

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2022.823227

DOI=10.3389/fspas.2022.823227

ISSN=2296-987X

ABSTRACT=<p>Hosting a ∼1.5 bar N<sub>2</sub> 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 H<sub>2</sub> abundance and warmer temperature increases the rate of the back reaction H<sub>2</sub> + CH<sub>3</sub> → CH<sub>4</sub> + H, and the temperature dependence is so great that CH<sub>3</sub> recycles back into CH<sub>4</sub> instead of forming C<sub>2</sub>H<sub>6</sub>. A larger H<sub>2</sub> abundance and warmer temperature also encourages interesting cycling between C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>3</sub>, and C<sub>2</sub>H<sub>4</sub><italic>via</italic> reactions with atomic H.</p>