Clouds and Hazes in Exoplanet Atmospheres

Abstract

Clouds and hazes are commonplace in the atmospheres of solar system planets and are likely ubiquitous in the atmospheres of extrasolar planets as well. Clouds affect every aspect of a planetary atmosphere, from the transport of radiation, to atmospheric chemistry, to dynamics and they influence - if not control - aspects such as surface temperature and habitability. In this review we aim to provide an introduction to the role and properties of clouds in exoplanetary atmospheres. We consider the role clouds play in influencing the spectra of planets as well as their habitability and detectability. We briefly summarize how clouds are treated in terrestrial climate models and consider the far simpler approaches that have been taken so far to model exoplanet clouds, the evidence for which we also review. Since clouds play a major role in the atmospheres of certain classes of brown dwarfs we briefly discuss brown dwarf cloud modeling as well. We also review how the scattering and extinction efficiencies of cloud particles may be approximated in certain limiting cases of small and large particles in order to facilitate physical understanding. Since clouds play such important roles in planetary atmospheres, cloud modeling may well prove to be the limiting factor in our ability to interpret future observations of extrasolar planets.

book chapter to appear in "Comparative Climatology of Terrestrial Planets" (S. Mackwell, M. Bullock, J. Harder, eds.; University of Arizona Press, 2013)

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• Spectra as Windows into Exoplanet Atmospheres
• Critical core mass for enriched envelopes: the role of H2O condensation
• On Signatures of Clouds in Exoplanetary Transit Spectra
• Clouds in Three-Dimensional Models of Hot Jupiters Over a Wide Range of Temperatures I: Thermal Structures and Broadband Phase Curve Predictions
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• Utilitarian Opacity Model for Aggregate Particles in Protoplanetary Nebulae and Exoplanet Atmospheres
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• Investigating the physical properties of transiting hot Jupiters with the 1.5-m Kuiper Telescope
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• Detection of Na, K and H${}_2$O in the hazy atmosphere of WASP-6b
• Neptune's Dynamic Atmosphere from Kepler K2 Observations: Implications for Brown Dwarf Light Curve Analyses
• Differentiating Modern and Prebiotic Earth Scenarios for TRAPPIST-1e: High-resolution Transmission Spectra and Predictions for JWST
• High-precision multi-wavelength eclipse photometry of the ultra-hot gas giant exoplanet WASP-103 b
• Clouds in the atmospheres of extrasolar planets. V. The impact of CO2 ice clouds on the outer boundary of the habitable zone
• Impact of stellar flares on the chemical composition and transmission spectra of gaseous exoplanets orbiting M dwarfs
• The phase curve and the geometric albedo of WASP-43b measured with CHEOPS, TESS and HST WFC3/UVIS
• Kepler Monitoring of an L Dwarf II. Clouds with Multiyear Lifetimes
• Using polarimetry to retrieve the cloud coverage of Earth-like exoplanets
• Near-UV transit photometry of HAT-P-32 b with the LBT: Silicate aerosols in the planetary atmosphere
• Simulating Reflected Light Exoplanet Spectra of the Promising Direct Imaging Target, $\upsilon$ Andromedae d, with a New, Fast Sampling Method Using the Planetary Spectrum Generator
• Probing the atmosphere of HD189733b with the Na I and K I lines
• Secondary eclipses of WASP-18b -- Near Infrared observations with the Anglo Australian Telescope, the Magellan Clay Telescope and the LCOGT network
• Exploring the Diversity of Jupiter-Class Planets (Discussion Meeting Contribution)
• Crossing the bottleneck of rain formation
• Theory and simulation of spectral line broadening by exoplanetary atmospheric haze
• Grain alignment and rotational disruption by radiative torques in exoplanet atmospheres