PICASO: Modeling Exoplanetary Atmospheres Self-Consistently with Photochemistry and Vertical Mixing

JWST observations of exoplanetary atmospheres have already shown that processes causing disequilibrium chemistry, such as vertical mixing and photochemistry, are extremely important. Apart from being poorly understood, they are already identified as important pathways to probe the interiors and formation pathways of exoplanets. However, to effectively use these processes as probes of deep exoplanetary atmospheres and interiors in the JWST era, they need to be physically understood first, which requires more sophisticated atmospheric models than what is available today. We have developed PICASO 3.0, an open-sourced atmospheric model coupled with the 1D chemical network code VULCAN, which has allowed us to model the effects of vertical mixing, photochemistry, and molecular diffusion in exoplanetary atmospheres self-consistently. Using this state-of-the-art model, we have explored the impact of these processes on the thermal structure, transmission spectra, and emission spectra of H₂-He dominated atmospheres across a range of planet equilibrium temperatures and carbon-to-oxygen ratios. As this model is open-sourced and well-documented, it serves as an important resource for the whole community for modeling JWST observations of transiting exoplanets and brown dwarfs.