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Chemistry driven by Lightning and Aurorae in Exoplanet and Brown Dwarf Atmospheres

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Lightning and aurorae have been observed on Earth, on the gas and ice giants within our solar system. Optical aurorae were recently detected on the late-type M dwarf LSRJ1835 +3259. Lightning has for a long time been proposed as an energy source driving prebiotic chemistry on the Earth during its first billion years. It turns out that the Earth at this time probably had an oxidizing atmosphere, and lightning does not efficiently drive prebiotic chemistry in an oxidizing atmosphere. Massive super-Earths, on the other hand, are capable of retaining their early hydrogen-rich atmosphere, and recent studies suggest that several exoplanets may have atmospheres with more total elemental carbon than oxygen, making them potentially ideal laboratories for prebiotic chemistry. In addition to lightning, UV Photons and cosmic rays can provide sufficient energy to overcome the barriers to forming prebiotic species, and also open up new pathways for forming these species via ion-neutral reactions.

In this talk, I present a comprehensive ion-neutral chemical kinetics network, treating H, C, N and O, accurate between 300 K and 30000 K. This network treats cosmic ray ionization and photochemistry. I apply this network to two shock models: (1) a simulated lightning shock in a model super-Earth atmosphere, and (2) a shock within a simulated Miller-Urey style experiment. I find in the case of the lightning shock model that a significant amount of molecular oxygen and methane can be simultaneously produced by lighting in the model super-Earth atmosphere; lightning therefore may be able to produce false biosignatures in certain exoplanet environments. In the case of the laboratory shock model, I find that more glycine is produced the more reducing the atmosphere becomes, but only up to a point. Surprisingly, when the redox ratio dips under a value of 0.1, virtually no glycine is formed. I will conclude with a brief discussion of the optical aurora on LSRJ1835 +3259.

This talk is part of the Exoplanet Meetings series.

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