ARCiS framework for exoplanet atmospheres

Abstract

Context. Understanding of clouds is instrumental in interpreting current and future spectroscopic observations of exoplanets. modeling clouds consistently is complex, since it involves many facets of chemistry, nucleation theory, condensation physics, coagulation, and particle transport. Aims. We aim to develop a simple physical model for cloud formation and transport, efficient and versatile enough that it can be used, in modular fashion for parameter optimization searches of exoplanet atmosphere spectra. In this work we present the cloud model and investigate the dependence of key parameters as the cloud diffusivity K and the nuclei injection rateΣn on the planet's observational characteristics.Methods. The transport equations are formulated in 1D, accounting for sedimentation and diffusion. The grain size is obtained through a moment method. For simplicity, only one cloud species is considered and the nucleation rate is parametrized. From the resulting physical profiles we simulate transmission spectra covering the visual to mid-IR wavelength range. Results. We apply our models toward KCl clouds in the atmosphere of GJ1214 b and toward MgSiO3 clouds of a canonical hot-Jupiter. We find that larger K increases the thickness of the cloud, pushing the τ = 1 surface to a lower pressure layer higher in the atmosphere. A larger nucleation rate also increases the cloud thickness while it suppresses the grain size. Coagulation is most important at highΣn and low K. We find that the investigated combinations of K andΣn greatly affect the transmission spectra in terms of the slope at near-IR wavelength (a proxy for grain size), the molecular features seen at ∼µm (which disappear for thick clouds, high in the atmosphere), and the 10 µm silicate feature, which becomes prominent for small grains high in the atmosphere. Conclusions. Clouds have a major impact on the atmospheric characteristics of hot-Jupiters, and models as those presented here are necessary to reveal the underlying properties of exoplanet atmospheres. The result of our hybrid approach -aimed to provide a good balance between physical consistency and computational efficiency -is ideal toward interpreting (future) spectroscopic observations of exoplanets.

Detectable Molecular Features above Hydrocarbon Haze via Transmission Spectroscopy with JWST: Case Studies of GJ 1214b-, GJ 436b-, HD 97658b-, and Kepler-51b-like Planets

“…Besides hydrocarbon haze, the existence of other aerosols can mute spectral features in transmission: condensation clouds such as KCl, ZnS, K 2 SO 4 , ZnO, and graphite clouds in the temperature range of interest in this study ( 1000 K) (Miller-Ricci Kempton et al 2012;Morley et al 2013;Mbarek & Kempton 2016;Ohno & Okuzumi 2018;Gao & Benneke 2018;Ormel & Min 2019) and photochemical haze made of sulfur species (Hu et al 2013;Zahnle et al 2016;Gao et al 2017).…”

Aluminium oxide in the atmosphere of hot Jupiter WASP-43b

“…Full details on the ARCiS code are presented in a separate paper (Min et al 2020). The most important information can be found in Ormel & Min (2019). The code consists of a forward modelling part based on correlated-k molecular opacities and cloud opacities using Mie and distribution of hollow spheres (DHS; see Min et al 2005) computations.…”

“…The code consists of a forward modelling part based on correlated-k molecular opacities and cloud opacities using Mie and distribution of hollow spheres (DHS; see Min et al 2005) computations. With ARCiS it is possible to compute cloud formation (Ormel & Min 2019) and chemistry (Woitke et al 2018) from physical and chemical principles. The code has been benchmarked against petitCODE (Mollière et al 2015) in Ormel & Min (2019).…”

“…With ARCiS it is possible to compute cloud formation (Ormel & Min 2019) and chemistry (Woitke et al 2018) from physical and chemical principles. The code has been benchmarked against petitCODE (Mollière et al 2015) in Ormel & Min (2019). For the retrieval part the MULTINEST algorithm is employed.…”

Theoretical Transmission Spectra of Exoplanet Atmospheres with Hydrocarbon Haze: Effect of Creation, Growth, and Settling of Haze Particles. II. Dependence on UV Irradiation Intensity, Metallicity, C/O Ratio, Eddy Diffusion Coefficient, and Temperature

“…We have demonstrated that the efficient eddy diffusion yields a steep Rayleigh-scattering slope in the optical and more prominent molecular-absorption features (see § 3.5). Such a dependence is opposite to that for the case of condensation clouds (Gao & Benneke 2018;Ormel & Min 2019). This is because haze particles are formed at high altitudes and transported downward, while condensation clouds are formed at relatively low altitudes and transported upward.…”