Exoplanetary Atmospheres in the Near I.R. Spectrum: Departures from a Homogeneously Distributed Gas Assumption

Radiative transfer models that are calibrated for exoplanet transit use both well-understood atmospheric mechanisms and measurements from our own solar system to set up the relative abundances of gases contributing to the observed total spectral modulation. This procedure helps to narrow down the possible composition of exoplanet atmospheres. However, existing retrieval codes depend on a uniform vertical mixing ratio (VMR), in order to cut computation costs. Departures from an atmosphere where gas is homogeneously distributed may reflect the effects of chemical quenching and photochemistry.

We explore if the uniform VMR assumption is a reasonable argument for the next generation of exoplanet data sets. Using a thermochemical equilibrium model built within Cerberus, an exoplanet radiative transfer code and a parameters retrieval package, we create forward models using non-uniform VMR profiles. We then fit these models against the spectral signature for WASP-12b from the HST data set, and against the predicted spectrum from JWST. Finally, we quantify the interactions between parameters by applying a Monte Carlo Markov Chain in order to demonstrate any significance.