Three-dimensional continuum radiative transfer of polarized radiation in exoplanetary atmospheres

Abstract

Polarimetry is about to become a powerful tool for determining the atmospheric properties of exoplanets. To provide the basis for the interpretation of observational results and for predictive studies to guide future observations, sophisticated analysis tools are required. Our goal is to develop a radiative transfer tool that contains all the relevant continuum polarization mechanisms for the comprehensive analysis of the polarized flux resulting from the scattering in the atmosphere of, on the surface of, and in the local planetary environment (e.g., planetary rings, exomoons) of extra-solar planets. Furthermore, our goal is to avoid common simplifications such as locally plane-parallel planetary atmospheres, the missing cross-talk between latitudinal and longitudinal regions, or the assumption of either a point-like star or plane-parallel illumination. As a platform for the newly developed numerical algorithms, we use the 3D Monte Carlo radiative transfer code POLARIS. The code is extended and optimized for the radiative transfer in exoplanetary atmospheres. We investigate the reflected flux and its degree of polarization for different phase angles for a homogeneous cloud-free atmosphere and an inhomogeneous cloudy atmosphere. To take advantage of the 3D radiative transfer and to demonstrate the potential of the code, the impact of an additional circumplanetary ring on the reflected polarized flux is studied. The presence of a circumplanetary ring consisting of small water-ice particles has a noticeable impact on the reflected polarized radiation. In particular, the reflected flux strongly increases at larger phase angles if the planetary orbit is seen edge-on because the considered particles tend to scatter forwards. In contrast, the degree of polarization decreases at these phase angles.

Accepted for publication in A&A, 12 pages, 10 figures

References in corpus (12)

• On the radiative equilibrium of irradiated planetary atmospheres
• On the Absorption and Redistribution of Energy in Irradiated Planets
• Predicting Photometric and Spectroscopic Signatures of Rings around Transiting Extrasolar Planets
• A high-sensitivity polarimeter using a ferro-electric liquid crystal modulator
• A grid of polarization models for Rayleigh scattering planetary atmospheres
• HIPPI-2: A Versatile High Precision Polarimeter
• Simultaneous Linear and Circular Optical Polarimetry of Asteroid (4) Vesta
• Using polarimetry to retrieve the cloud coverage of Earth-like exoplanets
• RefPlanets: Search for reflected light from extra-solar planets with SPHERE/ZIMPOL
• Self-scattering in protoplanetary disks with dust settling
• Scattered light may reveal the existence of ringed exoplanets
• Characterization of mid-infrared polarization due to scattering in protoplanetary disks

Cited by in corpus (4)

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• How much large dust could be present in hot exozodiacal dust systems?
• Scattered polarized radiation of extrasolar circumplanetary rings
• Impact of hot exozodiacal dust on the polarimetric analysis of close-in exoplanets