Query : 2020A&A...639A.107S

2020A&A...639A.107S - Astronomy and Astrophysics, volume 639A, 107-107 (2020/7-1)

Mineral snowflakes on exoplanets and brown dwarfs. Effects of micro-porosity, size distributions, and particle shape.


Abstract (from CDS):

Context. Exoplanet atmosphere characterisation has become an important tool in understanding exoplanet formation, evolution, and it also is a window into potential habitability. However, clouds remain a key challenge for characterisation: upcoming space telescopes (e.g. the James Webb Space Telescope, JWST, and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey) and ground-based high-resolution spectrographs (e.g. the next-generation CRyogenic high-resolution InfraRed Echelle Spectrograph) will produce data requiring detailed understanding of cloud formation and cloud effects for a variety of exoplanets and brown dwarfs.
Aims. We aim to understand how the micro-porosity of cloud particles affects the cloud structure, particle size, and material composition on exoplanets and brown dwarfs. We further examine the spectroscopic effects of micro-porous particles, the particle size distribution, and non-spherical cloud particles.
Methods. We expanded our kinetic non-equilibrium cloud formation model to study the effect of micro-porosity on the cloud structure using prescribed 1D (Tgas-pgas) profiles from the DRIFT-PHOENIX model atmosphere grid. We applied the effective medium theory and the Mie theory to model the spectroscopic properties of cloud particles with micro-porosity and a derived particle size distribution. In addition, we used a statistical distribution of hollow spheres to represent the effects of non-spherical cloud particles.
Results. Highly micro-porous cloud particles (90% vacuum) have a larger surface area, enabling efficient bulk growth higher in the atmosphere than for compact particles. Increases in single scattering albedo and cross-sectional area for these mineral snowflakes cause the cloud deck to become optically thin only at a wavelength of ∼100µm instead of at the ∼20µm for compact cloud particles. A significant enhancement in albedo is also seen when cloud particles occur with a locally changing Gaussian size distribution. Non-spherical particles increase the opacity of silicate spectral features, which further increases the wavelength at which the clouds become optically thin.
Conclusions. Retrievals of cloud properties, particularly particle size and mass of clouds, are biased by the assumption of compact spherical particles. The JWST mid-infrared instrument will be sensitive to signatures of micro-porous and non-spherical cloud particles based on the wavelength at which clouds are optically thin. Details of spectral features are also dependent on particle shape, and greater care must be taken in modelling clouds as observational data improves.

Abstract Copyright: © ESO 2020

Journal keyword(s): planets and satellites: gaseous planets - planets and satellites: atmospheres - planets and satellites: composition - brown dwarfs - opacity

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 HD 10069b Pl 01 37 25.0335097438 -45 40 40.376513381           ~ 349 1
2 CD-38 3220b Pl 07 10 24.0606039387 -39 05 50.570553937           ~ 271 0
3 WASP-43b Pl 10 19 38.0089444408 -09 48 22.603103969           ~ 328 1
4 K2-18b Pl 11 30 14.5176249117 +07 35 18.257210626           ~ 136 0
5 BD+47 2846b Pl 19 28 59.3538131541 +47 58 10.216250846           ~ 360 1
6 HD 209458b Pl 22 03 10.7729598762 +18 53 03.548248479           ~ 1799 1

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