Explaining the Diversity of Cold Exoworlds with JWST

Substellar atmospheres exhibit a variety of chemical species and physical and chemical processes that determine their appearances. As substellar atmospheres cool, their chemistry becomes more complex. The JWST Cycle 1 program GO 2124 observed a sample of 12 of the coldest known extrasolar atmospheres of objects at the T/Y transition. With unprecedented precision using NIRSpec G395H spectra and MIRI long wavelength photometry, we present a detailed spectral sequence of the coldest brown dwarfs focusing on the diversity present in ultracool atmospheres. Particularly, we present: 1) prominent molecules and their state of chemical equilibrium/disequilibrium 2) the most complete SED of an extrasolar world and its retrieval and forward modeling analysis, 3) the detection and modeling of methane in emission in a substellar atmosphere indicative of auroral activity, 4) far/mid-infrared color-magnitude diagrams, and 4) progress on the retrieval and self-consistent modeling for the whole sample. Because of similarities between T/Y transition dwarfs and giant exoplanets, the observations and results presented here also allow us to constrain the aspects that may influence the appearance of exoplanets.