How does thermal scattering shape the infrared spectra of cloudy exoplanets? A theoretical framework and consequences for atmospheric retrievals in the JWST era
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP)
Authors:
Jake Taylor, Vivien Parmentier, Michael R Line, Graham KH Lee, Patrick GJ Irwin, Suzanne Aigrain
Abstract:
Observational studies of exoplanets are suggestive of an ubiquitous presence
of clouds. The current modelling techniques used in emission to account for the
clouds tend to require prior knowledge of the cloud condensing species and
often do not consider the scattering effects of the cloud. We explore the
effects that thermal scattering has on the emission spectra by modelling a
suite of hot Jupiter atmospheres with varying cloud single-scattering albedos
(SSAs) and temperature profiles. We examine cases ranging from simple
isothermal conditions to more complex structures and physically driven cloud
modelling. We show that scattering from nightside clouds would lead to
brightness temperatures that are cooler than the real atmospheric temperature,
if scattering is unaccounted for. We show that scattering can produce spectral
signatures in the emission spectrum even for isothermal atmospheres. We
identify the retrieval degeneracies and biases that arise in the context of
simulated JWST spectra when the scattering from the clouds dominates the
spectral shape. Finally, we propose a novel method of fitting the SSA spectrum
of the cloud in emission retrievals, using a technique that does not require
any prior knowledge of the cloud chemical or physical properties.
