Modelling reflected polarized light from close-in giant exoplanet WASP-96b using PolHEx (Polarization of hot exoplanets)

We present the Polarization of Hot Exoplanets (PolHEx) code for modelling the total flux (F) and degree of linear Polarization (P) of light spectra reflected by close-in, tidally locked exoplanets. We use the output from a global climate model (GCM) combined with a kinetic cloud model of hot Jupiter WASP-96b as a base to investigate effects of atmospheric longitudinal-latitudinal inhomogeneities on these spectra. We model F and P-spectra as functions of wavelength and planet orbital phase for various model atmospheres. We find different materials and sizes of cloud particles to impact the reflected flux F, and particularly the linear Polarization state P. A range of materials are used to form inhomogeneous mixed-material cloud particles (Al₂O₃, Fe₂O₃, Fe₂SiO₄, FeO, Fe, Mg₂SiO₄, MgO, MgSiO₃, SiO₂, SiO, TiO₂), with Fe₂O₃, Fe, and FeO the most strongly absorbing species. The cloud particles near the relatively cool morning terminator are expected to have smaller average sizes and a narrower size distribution than those near the warmer evening terminator, which leads to different reflected spectra at the respective orbital phases. We also find differences in the spectra of F and P as functions of orbital phase for irregularly or spherically shaped cloud particles. This work highlights the importance of including Polarization in models and future observations of the reflection spectra of exoplanets.