Light Scattering Measurements of KCl Particles as an Exoplanet Cloud Analog

Abstract

Salt clouds are predicted to be common on warm exoplanets, but their optical properties are uncertain. The Exoplanet Cloud Ensemble Scattering System (ExCESS), a new apparatus to measure the scattering intensity and degree of linear polarization (DOLP) for an ensemble of particles, is introduced here and used to study the light scattering properties of KCl cloud analogs. ExCESS illuminates particles with a polarized laser beam (532 nm) and uses a photomultiplier tube detector to sweep the plane of illumination. Scattering measurements for KCl particles were collected for three size distributions representative of modeled clouds for the warm exoplanet GJ 1214b. Our measurements show that Lorenz-Mie calculations, commonly used to estimate the light scattering properties of assumedly spherical cloud particles, offer an inaccurate depiction of cubic and cuboid shaped KCl particles. All of our measurements indicate that Lorenz-Mie scattering overestimates the backscattering intensity of our cloud analogs and incorrectly predicts the scattering at mid-phase angles (~90 degrees) and preferential polarization state of KCl scattered light. Our results align with the general scattering properties of non-spherical particles and underscore the importance of further understanding the effects that such particles will have on radiative transfer models of exoplanet atmospheres and reflected light observations of exoplanets by the upcoming Nancy Grace Roman Space Telescope and Habitable Worlds Observatory.

arXiv commentPublished in the Planetary Science Journal

References in corpus (43)

• A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
• Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b
• Neglected Clouds in T and Y Dwarf Atmospheres
• The Flat Transmission Spectrum of the Super-Earth GJ1214b from Wide Field Camera 3 on the Hubble Space Telescope
• A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b
• Photometric Light Curves and Polarization of Close-in Extrasolar Giant Planets
• Transitions in the cloud composition of hot Jupiters
• Inference of Inhomogeneous Clouds in an Exoplanet Atmosphere
• Thermal Emission and Albedo Spectra of Super Earths with Flat Transmission Spectra
• Quantitatively Assessing the Role of Clouds in the Transmission Spectrum of GJ 1214b
• HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance
• Probing dust grain evolution in IM Lupi's circumstellar disc. Multi-wavelength observations and modelling of the dust disc
• The Atmospheric Chemistry of GJ 1214b: Photochemistry and Clouds
• Spectropolarimetric signatures of Earth-like extrasolar planets
• A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curve
• Observations of Exoplanet Atmospheres
• A comprehensive study of Kepler phase curves and secondary eclipses -- temperatures and albedos of confirmed Kepler giant planets
• SO2, silicate clouds, but no CH4 detected in a warm Neptune
• 3D modeling of GJ1214b's atmosphere: formation of inhomogeneous high clouds and observational implications
• Aerosols in Exoplanet Atmospheres
• Spitzer Phase Curves of KELT-1b and the Signatures of Nightside Clouds in Thermal Phase Observations
• Spitzer Transits of the Super-Earth GJ1214b and Implications for Its Atmosphere
• Light scattering by fractal dust aggregates: I. Angular dependence of scattering
• Microphysics of KCl and ZnS Clouds on GJ 1214b
• Uniformly hot nightside temperatures on short-period gas giants
• The Hazy and Metal-Rich Atmosphere of GJ 1214 b Constrained by Near and Mid-Infrared Transmission Spectroscopy
• VLT/FORS2 comparative transmission spectroscopy II: confirmation of a cloud-deck and Rayleigh scattering in WASP-31b, but no potassium?
• Microphysical Modeling of Mineral Clouds in GJ1214 b and GJ436 b: Predicting Upper Limits on the Cloud-Top Height
• The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) Technology Demonstration
• Optical Linear Polarimetry of Ultra Cool Dwarfs
• Experimental phase function and degree of linear polarization of cometary dust analogs
• Clouds of Fluffy Aggregates: How They Form in Exoplanetary Atmospheres and Influence Transmission Spectra
• Probing exoplanet clouds with optical phase curves
• A Universal Cloud Composition on the Nightsides of Hot Jupiters
• Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach
• Linear polarization of rapidly rotating ultracool dwarfs
• Aerosols are not Spherical Cows: Using Discrete Dipole Approximation to Model the Properties of Fractal Particles
• The Impact of Phase Equilibrium Cloud Models on GCM Simulations of GJ~1214b
• A comparative study of WASP-67b and HAT-P-38b from WFC3 data
• The polarization of the planet-hosting WASP-18 system
• Colors of an Earth-like exoplanet -- Temporal flux and polarization signals of the Earth
• Interpretation through experimental simulations of phase functions revealed by Rosetta in 67P dust coma
• Polarized Signatures of a Habitable World: Comparing Models of an Exoplanet Earth with Visible and Near-infrared Earthshine Spectra

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