Abstract DGP2026-1

Rocky exoplanets around M dwarfs can form abiotic N2-O2 atmospheres

Lena Noack (1), Alexander Thamm (1), Caroline Brachmann (1,2), Philipp A. Baumeister (1), Hamish Innes (1), Kristina Kislyakova (2,3), Gwenaëlle Van Looveren (2), and Elsa Ducrot (3)

(1) Institute of Geological Sciences, Freie Universität Berlin, Germany, (2) Department of Astrophysics, University of Vienna, Austria (3) Université Paris-Saclay, CEA, CNRS, France.

The TRAPPIST-1 exoplanetary system has been investigated by many theoretical and observational studies in the recent years as a prime, near-by candidate system for comparative planetology. While close-in, hot rocky exoplanets are often termed exo-Venuses, recent observational campaigns suggest that TRAPPIST-1 b and -1 c may either not posses an atmosphere, or only a very thin atmosphere either full of hazes or not made of CO2.
In this work we aim at predicting possible atmospheric evolutionary pathways of the TRAPPIST-1 planetary atmospheres starting from compositional and evolutionary constraints of the star-planet system, and by modelling the evolution of the atmosphere including redox-dependent gas speciation, atmospheric chemical equilibrium, water condensation, solubility of volatiles in the melt, and atmospheric escape.

We consider that the innermost planets should be more reducing in their interior than the outer planets from our compositional model, and we show that this leads to different atmospheres than previously predicted, especially with N2-O2 rich atmospheres, that are consistent with the current JWST constraints.
Our results are not only relevant for the TRAPPIST-1 system but in general for close-in rocky exoplanets with reducing interiors around active stars and suggest that N2-O2 atmospheres may be common, but generated by abiotic processes.