POSEIDON: A Multidimensional Atmospheric Retrieval Code for Exoplanet Spectra

Abstract: Spectroscopic observations of exoplanet atmospheres can reveal the chemical composition, temperature, cloud properties, and (potentially) the habitability of these distant worlds. The inference of such properties is generally enabled by Bayesian atmospheric retrieval algorithms. However, until recently, many retrieval codes have not been publicly available. Here, we describe the open source release of the POSEIDON exoplanet radiative transfer and retrieval code. POSEIDON is a Python package for the 1D, 2D, or 3D modelling and analysis of exoplanet spectra, which is frequently used to interpret Hubble and JWST observations of exoplanet atmospheres. We provide extensive tutorials on both forward modelling and retrievals in POSEIDON's online documentation, which we hope will serve as a helpful resource for the exoplanet atmosphere community.