Spatially Resolved Modeling of Optical Albedos for a Sample of Six Hot Jupiters

TL;DR

This study uses 3D models to analyze optical albedos of six hot Jupiters, revealing diverse cloud properties and highlighting the need for improved understanding of atmospheric processes to explain observed albedo variations.

Contribution

The paper introduces 3D general circulation models with cloud and albedo maps for hot Jupiters, comparing different cloud models to observed albedos, and discusses limitations in current modeling approaches.

Findings

Observed albedos vary significantly among the six planets.

Certain planets are best modeled with cloud-free or compact cloud layers.

No single cloud model explains all observed albedos.

Abstract

Optical secondary eclipse measurements made by \emph{Kepler} reveal a diverse set of geometric albedos for hot Jupiters with equilibrium temperatures between $1550-1700$ K. The presence or absence of high altitude condensates, such as Mg$_2$SiO$_4$, Fe, Al$_2$O$_3$, and TiO$_2$, can significantly alter optical albedos, but these clouds are expected to be confined to localized regions in the atmospheres of these tidally locked planets. Here, we present 3D general circulation models and corresponding cloud and albedo maps for six hot Jupiters with measured optical albedos in this temperature range. We find that the observed optical albedos of K2-31b and K2-107b are best matched by either cloud free models or models with relatively compact cloud layers, while Kepler-8b and Kepler-17b's optical albedos can be matched by moderately extended ($f_{sed}$ = 0.1) parametric cloud models. HATS-11b has a high optical albedo, corresponding to models with bright Mg$_2$SiO$_4$ clouds extending to very low pressures ($f_{sed}$ = 0.03). We are unable to reproduce Kepler-7b's high albedo, as our models predict that the dayside will be dominated by dark Al$_2$O$_3$ clouds at most longitudes. We compare our parametric cloud model with a two-zone microphysical cloud model (\texttt{CARMA}). We find that even after accounting for the 3D thermal structure, no single cloud model can explain the full range of observed albedos within the sample. We conclude that a better knowledge of the vertical mixing profiles, cloud radiative feedback, cloud condensate properties, and atmospheric metallicities is needed in order to explain the unexpected diversity of albedos in this temperature range.