Exploring Exoplanet Cloud Assumptions in \textit{JWST} Transmission Spectra

TL;DR

This study assesses how JWST transmission spectra can constrain exoplanet cloud and atmospheric properties, highlighting the importance of specific wavelength ranges and the challenges posed by degeneracies in cloud parameter retrievals.

Contribution

It systematically evaluates the ability to retrieve cloud and atmospheric parameters for hot-Jupiters and warm-Neptunes using various JWST modes and cloud models, revealing key observational requirements.

Findings

NIRCam is critical for atmospheric property inference.

NIRISS and MIRI are necessary for constraining cloud parameters.

Higher SNR improves parameter constraints but does not resolve degeneracies.

Abstract

Clouds are ubiquitous in extrasolar planet atmospheres and are critical to our understanding of planetary climate and chemistry. They also represent one of the greater challenges to overcome when trying to interpret transit transmission spectra of exoplanet atmospheres as their presence can inhibit precise constraints on atmospheric composition and thermal properties. In this work we take a phenomenological approach towards understanding 1) our ability to constrain bulk cloud properties, and 2) the impact of clouds on constraining various atmospheric properties as obtained through transmission spectroscopy with the \textit{James Webb Space Telescope (JWST)}. We do this by exploring retrievals of atmospheric and cloud properties for a generic "hot-Jupiter" as a function of signal-to-noise ratio (SNR), \textit{JWST} observing modes and four different cloud parameterizations. We find that most key atmospheric and cloud inferences can be well constrained in the wavelength range ($\lambda = $ 0.6 - 11 $\mu$m), with NIRCam ($\lambda =$ 2.5 - 5 $\mu$m) being critical in inferring atmospheric properties and NIRISS + MIRI ($\lambda =$ 0.6 - 2.5, 5 - 11 $\mu$m) being necessary for good constraints on cloud parameters. However, constraining the cloud abundance and therefore the total cloud mass requires an observable cloud base in the transit geometry. While higher SNR observations can place tighter constraints on major parameters such as temperature, metallicity and cloud sedimentation, they are unable to eliminate strong degeneracies among cloud parameters. Our investigation of a generic "warm-Neptune" with photochemical haze parameterization also shows promising results in constraining atmospheric and haze properties in the cooler temperature regime.