Exonephology: Transmission spectra from a 3D simulated cloudy atmosphere of HD209458b

TL;DR

This paper presents high-resolution 3D simulated transmission spectra of HD209458b, revealing how extensive cloud decks flatten spectral features and identifying potential JWST-detectable cloud signatures, with implications for understanding hot-Jupiter atmospheres.

Contribution

It introduces the most comprehensive 3D radiative-hydrodynamics simulation of a cloudy hot-Jupiter atmosphere, analyzing cloud effects on transmission spectra and potential observability with JWST.

Findings

Cloud decks flatten spectral features, obscuring observed data signatures.

An 8-12 micron silicate absorption feature is a potential cloud marker.

Variations in cloud extent and composition significantly alter the spectrum.

Abstract

We present high resolution transmission spectra, calculated directly from a 3D radiative-hydrodynamics simulation that includes kinetic cloud formation, for HD209458b. We find that the high opacity of our vertically extensive cloud deck, composed of a large number density of sub-micron particles, flattens the transmission spectrum and obscures spectral features identified in observed data. We use the PandExo simulator to explore features of our HD209458b spectrum which may be detectable with the James Webb Space Telescope (JWST). We determine that an 8 - 12 micron absorption feature attributed to the mixed-composition, predominantly silicate cloud particles is a viable marker for the presence of cloud. Further calculations explore, and trends are identified with, variations in cloud opacity, composition heterogeneity and artificially scaled gravitational settling on the transmission spectrum. Principally, by varying the upper extent of our cloud decks, rainout is identified to be a key process for the dynamical atmospheres of hot-Jupiters and shown to dramatically alter the resulting spectrum. Our synthetic transmission spectra, obtained from the most complete, forward atmosphere simulations to--date, allow us to explore the model's ability to conform with observations. Such comparisons can provide insight into the physical processes either missing, or requiring improvement.