Investigating the chemical pathways to prebiotic compounds in exoplanet atmospheres

On geological timescales, Earth’s atmosphere has evolved from a reducing chemical composition to today’s oxidising composition. Life is thought to have originated in the early reduced environment, with a key role for basic prebiotic compounds such as hydrogen cyanide (HCN) and formaldehyde (H2CO). Rocky exoplanets are found in diverse stellar and planetary environments, inevitably presenting diverse atmospheric compositions. We use VULCAN, a 1D photochemical kinetics code, to test the formation mechanisms of prebiotic compounds like HCN and H2CO on exoplanets orbiting around M-dwarf host stars. We explore the sensitivity of the atmospheric chemistry of these compounds, within broader chemical networks, to prior knowledge of the corresponding chemical reactions and rate coefficients. For each sensitivity experiment, we identify the key pathways that form prebiotic compounds from the background atmospheric species. By inserting these key pathways of one chemical network into another, we attempt to reconcile the inter-network differences. Our work paves the way for implementing the key prebiotic pathways in a 3D climate-chemistry model, which we will briefly outline. Finally, since any observation of an exoplanet will represent only a snapshot of its long-term evolution, we argue that understanding different evolutionary epochs is crucial in the search for biosignatures on rocky exoplanets.