Open Source High-Resolution Exoplanet Atmosphere Retrievals with POSEIDON

TL;DR

This paper introduces POSEIDON, an open source, fast, and accessible high-resolution exoplanet atmosphere retrieval framework that enables reliable chemical and temperature analysis from ground-based spectra.

Contribution

The authors present a unified, open source high-resolution retrieval code for exoplanet atmospheres, validated on known planets, improving reproducibility and accessibility in the field.

Findings

Successfully reproduces previous atmospheric retrievals.

Demonstrates that user choices influence chemical abundance results.

Provides a fast, GPU-free, well-documented retrieval tool.

Abstract

High-resolution spectroscopy (R > 25,000) has opened new opportunities to characterize exoplanet atmospheres from the ground. By resolving individual lines in planetary emission and transmission spectra, one can sensitively probe the chemical inventory and temperature structure of exoplanets. However, a significant challenge to reliable and reproducible atmospheric inferences from high-resolution datasets has been the lack of open source codes for high-resolution retrievals. Here, we present a unified high-resolution retrieval framework, for both emission and transmission spectroscopy, made publicly available within the open source POSEIDON retrieval code. Our high-resolution retrieval framework is fast (typically < 12 hours), accessible (no GPUs required), and well-documented via Python notebooks. We validate our framework by reproducing previous emission retrievals of the hot Jupiter WASP-77Ab and transmission retrievals of the ultra-hot Jupiter WASP-121b. Our results are broadly consistent with those of published works when making the same data detrending assumptions, but we demonstrate that user choices can subtly propagate into retrieved chemical abundances.