The Open-source <tt>Photochem</tt> Code: A General Chemical and Climate Model for Interpreting (Exo)Planet Observations
Nicholas F. Wogan, Natasha E. Batalha, Kevin Zahnle, Joshua Krissansen‐Totton, David C. Catling, Eric Wolf, Tyler D. Robinson, Victoria Meadows, Giada Arney, Shawn Domagal‐Goldman
Abstract
Abstract With the launch of the James Webb Space Telescope, we are firmly in the era of exoplanet atmosphere characterization. Understanding exoplanet spectra requires atmospheric simulations that span the diversity of planetary atmospheres. Here we present Photochem, a more general chemical and climate model developed for this purpose. We benchmark the open-source, 1D code against the observed compositions and climates of Venus, Earth, Mars, Jupiter, and Titan with a single set of kinetics, thermodynamics and opacities. We also model the chemistry of the hot Jupiter exoplanet WASP-39b. All simulations are open-source and reproducible. To first order, Photochem broadly reproduces the gas-phase chemistry and pressure−temperature profiles of all six planets. The largest model−data discrepancies are found in Venus’s sulfur chemistry, motivating future experimental work on sulfur kinetics and spacecraft missions to Venus. We also find that clouds and hazes are important for the energy balance of Venus, Earth, Mars, and Titan and that accurately predicting aerosols with Photochem is challenging. Finally, we benchmark Photochem against the popular VULCAN and HELIOS photochemistry and climate models, finding excellent agreement for the same inputs; we also find that Photochem simulates atmospheres from 2× to ∼10 2 × more efficiently. These results show that Photochem provides a comparatively general description of atmospheric chemistry and physics that can be leveraged to study solar system worlds or interpret telescope observations of exoplanets.