Dynamic mineral clouds on HD 189733b

Abstract

Context. As the 3D spatial properties of exoplanet atmospheres are being observed in increasing detail by current and new generations of telescopes, the modelling of the 3D scattering effects of cloud forming atmospheres with inhomogeneous opacity structures becomes increasingly important to interpret observational data. Aims. We model the scattering and emission properties of a simulated cloud forming, inhomogeneous opacity, hot Jupiter atmosphere of HD 189733b. We compare our results to available Hubble Space Telescope (HST) and Spitzer data and quantify the effects of 3D multiple scattering on observable properties of the atmosphere. We discuss potential observational properties of HD 189733b for the upcoming Transiting Exoplanet Survey Satellite (TESS) and CHaracterising ExOPlanet Satellite (CHEOPS) missions. Methods. We developed a Monte Carlo radiative transfer code and applied it to post-process output of our 3D radiative-hydrodynamic, cloud formation simulation of HD 189733b. We employed three variance reduction techniques, i.e. next event estimation, survival biasing, and composite emission biasing, to improve signal to noise of the output. For cloud particle scattering events, we constructed a log-normal area distribution from the 3D cloud formation radiative-hydrodynamic results, which is stochastically sampled in order to model the Rayleigh and Mie scattering behaviour of a mixture of grain sizes. Results. Stellar photon packets incident on the eastern dayside hemisphere show predominantly Rayleigh, single-scattering behaviour, while multiple scattering occurs on the western hemisphere. Combined scattered and thermal emitted light predictions are consistent with published HST and Spitzer secondary transit observations. Our model predictions are also consistent with geometric albedo constraints from optical wavelength ground-based polarimetry and HST B band measurements. We predict an apparent geometric albedo for HD 189733b of 0.205 and 0.229, in the TESS and CHEOPS photometric bands respectively. Conclusions. Modelling the 3D geometric scattering effects of clouds on observables of exoplanet atmospheres provides an important contribution to the attempt to determine the cloud properties of these objects. Comparisons between TESS and CHEOPS photometry may provide qualitative information on the cloud properties of nearby hot Jupiter exoplanets.

Aerosols in Exoplanet Atmospheres

“…manuscript submitted to JGR: Planets formation on gas abundances. Several studies have more fully coupled DRIFT to GCMs (G. Lee et al, 2016;G. K. H. Lee et al, 2017;Lines, Mayne, et al, 2018;Lines, Manners, et al, 2018), such that both particle advection, cloud microphysics, and cloud radiative feedback are considered simultaneously.…”

Exoplanet Reflected-light Spectroscopy with PICASO

“…Chebyshev-Gauss angles easily translate to planetary latitude and longitude, making it possible to explore the effect of 3D general circulation models on albedo spectra, as in e.g. Webber et al (2015) and Lee et al (2017).…”

“…With the detection and analysis of reflected light from optical phase curves (Demory et al 2013;Esteves et al 2015;Niraula et al 2018) and optical photometry (Evans et al 2013;Barstow et al 2014;Garcia Munoz & Isaak 2015;Webber et al 2015;Lee et al 2017), and the onset of reflected light direct imaging missions on the horizon, such has WFIRST and ELTs, Spergel et al (2013), there has been an increasing demand for an accessible, versatile reflected light code.…”

Outstanding Challenges of Exoplanet Atmospheric Retrievals

“…Helling et al 2008;Ackerman and Marley 2001) and including cloud in GCMs (e.g. Lee et al 2017;Mendonça et al 2018) are available; the ideal would be a parameterised model that can recover key cloud properties from this range of available cloud models, whilst also accurately retrieving other atmospheric properties.…”