Atmospheric Retrieval of the Hot Jupiter WASP-39b

This thesis focuses on the atmospheric analysis of WASP-39b. I used Bayesian techniques to infer the main atmospheric parameters of this exoplanet, using a real transmission spectrum obtained by the NIRSpec instrument on board of the James Webb Space Telescope. The thesis integrates principles of spectral line formation, radiative transfer, and various absorption mechanisms, employing the TauREx and TauREx-2D retrieval frameworks alongside FastChem and the MultiNest sampler. A series of models of varying complexity were developed, ranging from one-dimensional isothermal models to two-dimensional models, with a set of different temperaturepressure profiles. Model comparison is crucial to quantify the rationality of each physical assumption about the atmosphere and infer the most reasonable set of parameters to explaining the observed spectral features. The results suggest that one-dimensional models are adequate for this spectrum of WASP-39b, indicating no detectable day-night variations, with a difference of up to 20σ in favour of the 1D models. The models show evidence of a thermal inversion and a high mean molecular weight. The atmosphere is determined to be in chemical disequilibrium, as the tested free chemistry models have a greatly certain 20σ advantage to those with equilibrium chemistry. Likely detections of CO2, H2O, CO, H2S, SO2, Na, and K are consistent with existing studies, while the non-detections or weak detections of TiO, VO, and CH4 are also noted. Further investigation is required to clarify the potential dissociation of H2O and H2 in the atmosphere.