Clouds : empirically determining substellar cloud compositions in the era of JWST

For decades, the long standing question of the cloud condensation sequence for substellar atmospheres, has been unknown. Theory predicts that an objects temperature controls which clouds form in a substellar atmosphere. However the specific species, condensation sequence, particle sizes, locations and crystalline structures are still debated. Particularly, the Ackerman & Marley (2001) cloud model presents a mismatch between theoretical model spectra and data from the SPITZER space telescope for both photometric and spectroscopic observations. Here we create a new cloudy model grid for brown dwarf and exoplanet atmospheres that includes the effects of particle size, composition and crystalline structure. We show that the optical constants of particular minerals when varying particle size, location and crystalline structure can change the spectral features across ∼1-20μm. We then compare our new cloudy models to SPITZER/IRAC photometric data and SPITZER/IRS spectroscopic data that better match the space observations. Using the informed data analysis of 5 brown dwarfs known for tentative evidence of the silicate feature across 8-10μm, we then create model thermal emission spectra based our new cloudy models. These models can be used to compare to newly released JWST spectra for the Cycle 1 data release. We predict that by monitoring both variable and non- variable gas-giant atmospheres with the newly launched MIRI on JWST, we can determine the cloud condensation sequence and establish weather as the cause for brown dwarf variability, removing previous ambiguity.