Transmission spectral properties of clouds for hot Jupiter exoplanets

TL;DR

This paper investigates how clouds in hot Jupiter exoplanet atmospheres affect transmission spectra, highlighting infrared vibrational features that can help identify cloud composition and formation processes, especially with JWST observations.

Contribution

It provides a framework for interpreting transmission spectra by analyzing cloud condensate species, grain sizes, and vibrational features across optical to infrared wavelengths.

Findings

Infrared vibrational features are prominent for small sub-micron cloud particles.

Different condensate species produce distinguishable vibrational modes.

Infrared features can help differentiate cloud formation scenarios.

Abstract

Clouds have an important role in the atmospheres of planetary bodies. It is expected that, like all the planetary bodies in our solar system, exoplanet atmospheres will also have substantial cloud coverage, and evidence is mounting for clouds in a number of hot Jupiters. In order to better characterise planetary atmospheres we need to consider the effects these clouds will have on the observed broadband transmission spectra. Here we examine the expected cloud condensate species for hot Jupiter exoplanets and the effects of various grain sizes and distributions on the resultant transmission spectra from the optical to infrared, which can be used as a broad framework when interpreting exoplanet spectra. We note that significant infrared absorption features appear in the computed transmission spectrum, the result of vibrational modes between the key species in each condensate, which can potentially be very constraining. While it may be hard to differentiate between individual condensates in the broad transmission spectra, it may be possible to discern different vibrational bonds, which can distinguish between cloud formation scenarios such as condensate clouds or photochemically generated species. Vibrational mode features are shown to be prominent when the clouds are composed of small sub-micron sized particles and can be associated with an accompanying optical scattering slope. These infrared features have potential implications for future exoplanetary atmosphere studies conducted with JWST, where such vibrational modes distinguishing condensate species can be probed at longer wavelengths.