Aura-3D: A Three-dimensional Atmospheric Retrieval Framework for Exoplanet Transmission Spectra

TL;DR

AURA-3D is a novel three-dimensional atmospheric retrieval framework for exoplanet transmission spectra, enabling more accurate characterization of atmospheric structures and compositions, especially considering day-night temperature variations, with applications to JWST data.

Contribution

This work introduces AURA-3D, the first 3D atmospheric retrieval framework that models azimuthally-averaged temperature structures and can incorporate inhomogeneous chemistry and clouds.

Findings

Accurately estimates day-night temperature variations in hot Jupiters.

Traditional 1D retrievals can bias chemical abundance estimates.

AURA-3D improves retrieval accuracy using 3D models with JWST-quality data.

Abstract

Atmospheric retrievals of exoplanet transmission spectra allow constraints on the composition and structure of the day-night terminator region. Such retrievals in the past have typically assumed one-dimensional temperature structures which were adequate to explain extant observations. However, the increasing data quality expected from exoplanet spectroscopy with JWST motivates considerations of multidimensional atmospheric retrievals. We present AURA-3D, a three-dimensional atmospheric retrieval framework for exoplanet transmission spectra. AURA-3D includes a forward model that enables rapid computation of transmission spectra in 3D geometry for a given atmospheric structure and can, therefore, be used for atmospheric retrievals as well as for computing spectra from General Circulation Models (GCMs). In order to efficiently explore the space of possible 3D temperature structures in retrievals, we develop a parametric 3D pressure-temperature profile which can accurately represent azimuthally-averaged temperature structures of a range of hot Jupiter GCMs. We apply our retrieval framework to simulated JWST observations of hot Jupiter transmission spectra, obtaining accurate estimates of the day-night temperature variation across the terminator as well as the abundances of chemical species. We demonstrate an example of a model hot Jupiter transmission spectrum for which a traditional 1D retrieval of JWST-quality data returns biased abundance estimates, whereas a retrieval including a day-night temperature gradient can accurately retrieve the true abundances. Our forward model also has the capability to include inhomogeneous chemistry as well as variable clouds/hazes. This new retrieval framework opens the field to detailed multidimensional atmospheric characterisation using transmission spectra of exoplanets in the JWST era.