A Multiple Scattering Polarized Radiative Transfer Model: Application to HD 189733b

Abstract

We present a multiple scattering vector radiative transfer model which produces disk integrated, full phase polarized light curves for reflected light from an exoplanetary atmosphere. We validate our model against results from published analytical and computational models and discuss a small number of cases relevant to the existing and possible near-future observations of the exoplanet HD 189733b. HD 189733b is arguably the most well observed exoplanet to date and the only exoplanet to be observed in polarized light, yet it is debated if the planet's atmosphere is cloudy or clear. We model reflected light from clear atmospheres with Rayleigh scattering, and cloudy or hazy atmospheres with Mie and fractal aggregate particles. We show that clear and cloudy atmospheres have large differences in polarized light as compared to simple flux measurements, though existing observations are insufficient to make this distinction. Futhermore, we show that atmospheres that are spatially inhomogeneous, such as being partially covered by clouds or hazes, exhibit larger contrasts in polarized light when compared to clear atmospheres. This effect can potentially be used to identify patchy clouds in exoplanets. Given a set of full phase polarimetric measurements, this model can constrain the geometric albedo, properties of scattering particles in the atmosphere and the longitude of the ascending node of the orbit. The model is used to interpret new polarimetric observations of HD 189733b in a companion paper.

13 pages, 13 figures. Accepted for publication in ApJ

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Cited by in corpus (9)

• Aerosols in Exoplanet Atmospheres
• Aggregate Hazes in Exoplanet Atmospheres
• Polarized Radiative Transfer in Planetary Atmospheres and the Polarization of Exoplanets
• Reflected Light Curves, Spherical and Bond Albedos of Jupiter- and Saturn-like Exoplanets
• Dynamic mineral clouds on HD 189733b II. Monte Carlo radiative transfer for 3D cloudy exoplanet atmospheres: combining scattering and emission spectra
• Polarization of hot Jupiter systems: a likely detection of stellar activity and a possible detection of planetary polarization
• The rotation of alpha Oph investigated using polarimetry
• Computation of the transmitted and polarized scattered fluxes by the exoplanet HD 189733b in X-rays
• Generic Models for Disk-Resolved and Disk-Integrated Phase Dependent Linear Polarization of Light Reflected from Exoplanets