A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres

TL;DR

This paper introduces a comprehensive ion-neutral chemical network, Stand2015, for planetary atmospheres, capable of modeling prebiotic chemistry and organic molecule formation across a wide temperature range, with applications to exoplanets and early Earth.

Contribution

The paper presents a new, detailed chemical network for planetary atmospheres that accurately models complex organic chemistry, including glycine formation, across diverse environments.

Findings

Successfully tested against atmospheric models of HD209458b, Jupiter, and Earth.

Glycine production increases with ammonia and methane presence.

Production of glycine is inhibited in strongly reducing gases.

Abstract

There are many open questions about prebiotic chemistry in both planetary and exoplanetary environments. The increasing number of known exoplanets and other ultra-cool, substellar objects has propelled the desire to detect life and prebiotic chemistry outside the solar system. We present an ion-neutral chemical network constructed from scratch, Stand2015, that treats hydrogen, nitrogen, carbon and oxygen chemistry accurately within a temperature range between 100 K and 30000 K. Formation pathways for glycine and other organic molecules are included. The network is complete up to H6C2N2O3. Stand2015 is successfully tested against atmospheric chemistry models for HD209458b, Jupiter and the present-day Earth using a simple 1D photochemistry/diffusion code. Our results for the early Earth agree with those of Kasting (1993) for CO2, H2, CO and O2, but do not agree for water and atomic oxygen. We use the network to simulate an experiment where varied chemical initial conditions are irradiated by UV light. The result from our simulation is that more glycine is produced when more ammonia and methane is present. Very little glycine is produced in the absence of any molecular nitrogen and oxygen. This suggests that production of glycine is inhibited if a gas is too strongly reducing. Possible applications and limitations of the chemical kinetics network are also discussed.