The Effect of Atmospheric Chemistry on the Optical Geometric Albedos of Hot Jupiters

TL;DR

This study compares observed geometric albedos of hot Jupiters from multiple space telescopes with theoretical models, revealing key absorbers like sodium and water influence albedo, while TiO and VO are inconsistent with observations.

Contribution

It provides a comprehensive analysis of hot Jupiter albedos using hierarchical Bayesian models and confronts observations with first-principles atmospheric models.

Findings

No statistical difference in albedo distributions across telescopes.

Sodium and water are primary absorbers affecting albedo.

TiO and VO absorption lead to low albedos inconsistent with data.

Abstract

We investigate the geometric albedos of hot Jupiters by comparing observational data from space telescopes TESS, Kepler, CoRoT, and CHEOPS against theoretical models. The study aims to understand the distribution of observed geometric albedos across different bandpasses and how these observations align with or deviate from model predictions. We have curated a comprehensive sample of observed geometric albedos, using either existing Spitzer secondary eclipse measurements or a scaling law between the equilibrium and dayside temperature to remove any contaminating thermal planetary emission. We then utilised hierarchical Bayesian modelling to identify trends with planetary properties such as equilibrium temperature, gravity, and stellar metallicity. On a population level, we found no statistical difference in the distributions of geometric albedos measured by TESS compared to those by Kepler, CoRoT and CHEOPS. We confront the geometric albedo sample with a simple, but first principles, model that includes Rayleigh scattering by molecular hydrogen and absorption by sodium, water and titanium oxide and vanadium oxide. We find that the abundance of sodium and water are the key absorbers that influence the geometric albedos of hot Jupiters, whilst the addition of titanium oxide and vanadium oxide (in the absence of condensation) results in vanishing geometric albedos that are inconsistent with the observed distributions.