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Mineral cloud and hydrocarbon haze particles for the JWST target WASP-43b

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WASP -43b is an extrasolar, giant gas planet that has been selected as a JWST target because it orbits a near-solar abundance K7V star at a distance of a ≈ 0.0153 au in 0.813 days. Its atmosphere can therefore be well characterised through transmission spectroscopy and thermal emission measurements. Applying a combined modelling approach of 3D GCMs, kinetic cloud and photochemically driven hydrocarbon haze formation, we provide insight into the details of the clouds that may form on WASP -43b, and their impact on the remaining gas phase.

Mineral condensation seeds form throughout the atmosphere of WASP -43b. This is in stark contrast to the ultra-hot Jupiters, like WASP -18b and HAT -P-7b. The dayside is not cloud free but is loaded with few but large mineral cloud particles in addition to hydrocarbon haze particles of comparable abundance. Photochemically driven hydrocarbon haze appears on the dayside, but does not contribute to the cloud formation on the nightside. The geometrical cloud extension differs across the globe due to the changing thermodynamic conditions. Day and night differ by 6000km in pressure scale height. As reported for other planets, the C/O is not constant throughout the atmosphere and varies between 0.74 and 0.3. The mean molecular weight is approximately constant in a H2-dominated WASP -43b atmosphere because of the moderate day/night-temperature differences compared to the super-hot Jupiters.

We therefore expect that WASP -43b is expected to be fully covered in clouds which are not homogeneously distributed throughout the atmosphere. The dayside and the terminator clouds will be a combination of mineral particles of locally varying size and composition, and of hydrocarbon hazes. The optical depth of hydrocarbon hazes is considerably lower than that of mineral cloud particles such that a wavelength-dependent radius measurement of WASP -43b would be determined by the mineral cloud particles but not by hazes.

This talk is part of the Exoplanet Meetings series.

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