Microphysics of Water Clouds in the Atmospheres of Y Dwarfs and Temperate Giant Planets

Abstract

Water clouds are expected to form on Y dwarfs and giant planets with equilibrium temperatures near or below that of Earth, drastically altering their atmospheric compositions and their albedos and thermal emission spectra. Here we use the 1D Community Aerosol and Radiation Model for Atmospheres (CARMA) to investigate the microphysics of water clouds on cool substellar worlds to constrain their typical particle sizes and vertical extent, taking into consideration nucleation and condensation, which have not been considered in detail for water clouds in H/He atmospheres. We compute a small grid of Y dwarf and temperate giant exoplanet atmosphere models with water clouds forming through homogeneous nucleation and heterogeneous nucleation on cloud condensation nuclei composed of meteoritic dust, organic photochemical hazes, and upwelled potassium chloride cloud particles. We present comparisons with the Ackerman & Marley parameterization of cloud physics to extract the optimal sedimentation efficiency parameter (f${}_{sed}$) using Virga. We find that no Virga model replicates the CARMA water clouds exactly and that a transition in f${}_{sed}$ occurs from the base of the cloud to the cloud top. Furthermore, we generate simulated thermal emission and geometric albedo spectra and find large, wavelength-dependent differences between the CARMA and Virga models, with different gas absorption bands reacting differently to the different cloud distributions and particularly large differences in the M band. Therefore, constraining the vertically-dependent properties of water clouds will be essential to estimating the gas abundances in these atmospheres.

10 pages, 8 figures, published to ApJ

References in corpus (26)

• The NumPy array: a structure for efficient numerical computation
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets
• The 0.8-14.5 micron Spectra of Mid-L to Mid-T Dwarfs: Diagnostics of Effective Temperature, Grain Sedimentation, Gas Transport, and Surface Gravity
• Water Vapor and Clouds on the Habitable-Zone Sub-Neptune Exoplanet K2-18b
• Water vapour in the atmosphere of the habitable-zone eight Earth-mass planet K2-18 b
• Water Clouds in Y Dwarfs and Exoplanets
• Exoplanet Reflected Light Spectroscopy with PICASO
• A Giant Planet Candidate Transiting a White Dwarf
• Characterizing 51 Eri b from 1-5 $\mu$m: a partly-cloudy exoplanet
• The Featureless Transmission Spectra of Two Super-Puff Planets
• Dust Ablation on the Giant Planets: Consequences for Stratospheric Photochemistry
• Near-infrared photometry of Y dwarfs: low ammonia abundance and the onset of water clouds
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• A Uniform Retrieval Analysis of Ultracool Dwarfs. III. Properties of Y-Dwarfs
• Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b
• Clouds will likely prevent the detection of water vapor in JWST transmission spectra of terrestrial exoplanets
• Formation and dynamics of water clouds on temperate sub-Neptunes: The example of K2-18b
• Haze Evolution in Temperate Exoplanet Atmospheres Through Surface Energy Measurements
• A Low-order Model of Water Vapor, Clouds, and Thermal Emission for Tidally Locked Terrestrial Planets
• Indications of Water Clouds in the Coldest Known Brown Dwarf
• Spitzer Detection of the Transiting Jupiter-analog Exoplanet Kepler-167e
• Information in the Reflected Light Spectra of Widely Separated Giant Exoplanets
• Cloud Parameterizations and their Effect on Retrievals of Exoplanet Reflection Spectroscopy
• Using HARPS-N to characterise the long-period planets in the PH-2 and Kepler-103 systems
• Impacts of Water Latent Heat on the Thermal Structure of Ultra-Cool Objects: Brown Dwarfs and Free-Floating Planets

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• Three-dimensional dynamical evolution of cloud particle microphysics in sub-stellar atmospheres I. Description and exploring Y-dwarf atmospheric variability
• PICASO 4.0: Clouds and Photochemistry in Climate Models of Brown Dwarfs and Exoplanets
• Microphysical Prescriptions for Parameterized Water Cloud Formation on Ultra-cool Substellar Objects
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