Mineral clouds in the atmosphere of the hot Jupiter HD189733b

Hot Jupiters are gas giant planets in short period, tidally locked orbits. Their properties offer a unique opportunity to study the composition of the gas and clouds in their atmospheres, which carry crucial information on their formation history. We propose to use JWST/MIRI in LRS mode for a detailed characterization of the aerosols in the atmosphere of HD189733b, one of the best studied, prototypical cloudy hot Jupiters. We will (1) establish the presence and composition of theoretically predicted mineral clouds, and (2) determine for the first time the chemical composition of the atmosphere by consistently including gas and clouds. This will constrain the formation history of HD189733b. Models for gas giant planet formation predict large variations in elemental abundances of the atmosphere resulting from accretion of pebbles and planetesimals. Cloud properties depend critically on this chemistry, and strongly impact the observable atmosphere. The MIRI instrument on board JWST offers for the first time access to the mid-infrared wavelength range for exoplanet studies, crucial for mineral cloud characterization. HD189733b has many advantages for the study of mineralogical clouds: 1) detailed studies have convincingly shown that clouds and/or hazes are present in the upper atmosphere, but their nature is not constrained, 2) from a theoretical perspective the temperature structure of the planet is ideal for hosting mineral clouds, 3) the exquisite observational properties of HD189733b and superb sensitivity of JWST allow us to even address day/night asymmetries in its atmosphere using a various parts of a single transit observation.