Polarimetric investigation of selected cloud compositions in exoplanetary atmospheres

Abstract

We investigated the impact of selected cloud condensates in exoplanetary atmospheres on the polarization of scattered stellar radiation. We considered a selection of 25 cloud condensates that are expected to be present in extrasolar planetary atmospheres. Using the three-dimensional Monte Carlo radiative transfer code POLARIS and assuming Mie scattering theory, we calculated and studied the net polarization of scattered radiation as a function of planetary phase angle at optical to near-infrared wavelengths. In addition to the well-known characteristics in the state of polarization, such as the rainbow determined by the real part of the refractive index, the behavior of the underlying imaginary part of the refractive index causes an increase or decrease in the degree of polarization and a change of sign in the polarization at a characteristic wavelength. In contrast to Al${}_2$O${}_3$ and MgFeSiO${}_4$, clouds composed of SiO, MnS, Na${}_2$S, or ZnS produce a rapidly decreasing degree of polarization with increasing wavelength in the context of an exoplanetary atmosphere. Furthermore, the sign of the polarization changes at a wavelength of about 0.5 $\mu$m to 0.6 $\mu$m, depending on the specific cloud condensate. The resulting net polarization is mainly positive for cloud compositions with large imaginary parts of the refractive index, such as Fe, FeS, and FeO. In addition, for Fe and FeS clouds, the maximum degree of polarization at long wavelengths is shifted to larger phase angles than for FeO. We found that most of these cloud condensates are distinguishable from each other due to their unique wavelength-dependent complex refractive index. In particular, an increase or decrease of the net polarization as a function of wavelength and a change of sign in the polarization at specific wavelengths are important features for characterizing cloud compositions in exoplanetary atmospheres.

arXiv commentAccepted for publication in Astronomy & Astrophysics, 12 pages, 6 figures

References in corpus (40)

• Astropy: A Community Python Package for Astronomy
• A Non-Gray Theory of Extrasolar Giant Planets and Brown Dwarfs
• Detection of an Extrasolar Planet Atmosphere
• The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
• Precipitating Condensation Clouds in Substellar Atmospheres
• Scattering by Interstellar Dust Grains: Optical and Ultraviolet
• SPHERE: the exoplanet imager for the Very Large Telescope
• Detection of atmospheric haze on an extrasolar planet: The 0.55 - 1.05 micron transmission spectrum of HD189733b with the Hubble Space Telescope
• Chemical Equilibrium Abundances in Brown Dwarf and Extrasolar Giant Planet Atmospheres
• ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD189733
• Materials Pushing the Application Limits of Wire Grid Polarizers further into the Deep Ultraviolet Spectral Range
• Neglected Clouds in T and Y Dwarf Atmospheres
• Photometric Light Curves and Polarization of Close-in Extrasolar Giant Planets
• Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars II. Sulfur and Phosphorus
• Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon
• Quantitatively Assessing the Role of Clouds in the Transmission Spectrum of GJ 1214b
• Dust in Brown Dwarfs and Extra-solar Planets I. Chemical composition and spectral appearance of quasi-static cloud layers
• Radiative transfer with POLARIS: I. Analysis of magnetic fields through synthetic dust continuum polarization measurements
• Spectropolarimetric signatures of Earth-like extrasolar planets
• Dynamic mineral clouds on HD 189733b I. 3D RHD with kinetic, non-equilibrium cloud formation
• Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS
• The high albedo of the hot Jupiter Kepler-7b
• Mie Scattering by Ensembles of Particles with Very Large Size Parameters
• Stellar Diameters and Temperatures VI. High angular resolution measurements of the transiting exoplanet host stars HD 189733 and HD 209458 and implications for models of cool dwarfs
• The optical transmission spectrum of the hot Jupiter HAT-P-32b: clouds explain the absence of broad spectral features?
• First detection of polarized scattered light from an exoplanetary atmosphere
• From parallel to perpendicular -- On the orientation of magnetic fields in molecular clouds
• Clouds in the atmospheres of extrasolar planets. I. Climatic effects of multi-layered clouds for Earth-like planets and implications for habitable zones
• A high-sensitivity polarimeter using a ferro-electric liquid crystal modulator
• Looking for the rainbow on exoplanets covered by liquid and icy water clouds
• Polarized scattered light from self-luminous exoplanets. Three-dimensional scattering radiative transfer with ARTES
• The polarisation of HD 189733
• The intrinsic and interstellar broadband linear polarization of nearby FGK dwarfs
• Polarized Radiative Transfer in Planetary Atmospheres and the Polarization of Exoplanets
• WARPFIELD Population Synthesis: The physics of (extra-)Galactic star formation and feedback driven cloud structure and emission from sub-to-kpc scales
• Pre-conditioned Backward Monte Carlo solutions to radiative transport in planetary atmospheres. Fundamentals: Sampling of propagation directions in polarising media
• Flux and polarization signals of spatially inhomogeneous gaseous exoplanets
• Using polarimetry to retrieve the cloud coverage of Earth-like exoplanets
• Polarization of hot Jupiter systems: a likely detection of stellar activity and a possible detection of planetary polarization
• Self-scattering on large, porous grains in protoplanetary disks with dust settling

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