Work

pyrat bay 2.0: an upgraded framework for exoplanet atmosphere modelling in the JWST era

Year: 2026

Type: article

Abstract: ABSTRACT This article presents a major update to the open-source pyrat bay modelling framework (version 2.0), tailored for the characterization of exoplanet atmospheres with the observational capabilities of current facilities, such as the James Webb Space Telescope (JWST), and future missions. The upgraded framework introduces a standalone chemistry package, chemcat, enabling the modelling of exoplanet atmospheres via thermochemical-equilibrium calculations with custom compositions, self-consistent radiative-equilibrium thermal profiles, and equilibrium-chemistry retrievals. Other key implementations include nested sampling via multinest, isotopic-ratio fitting, transit light source modelling , and free-chemistry parametrization allowing vertical variations in volume mixing ratios. We validated the thermochemical- and radiative-equilibrium modules via comparisons with the ggchem, fastchem, and helios codes. We present an application of the new modelling framework by conducting an atmospheric characterization study using simulated transmission spectra of high signal-to-noise observations for a gas-giant exoplanet. We found that vertical abundance variations in planetary atmospheres can be accurately recovered using data of JWST quality. In such cases, retrievals that neglect these variations may result in biased abundance constraints, e.g. when employing the commonly used free-chemistry approach assuming constant abundance profiles. The results highlight the potential of JWST to study the multi-dimensional nature of exoplanetary atmospheres and their underlying physical processes.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stag1526

Authors: Patricio E Cubillos, Jasmina Blecic, Denis Shulyak, Luca Fossati