Astro Seminar by Jayesh Goyal: What are we learning about Transiting Exoplanet Atmospheres from JWST and HST?

James Webb Space Telescope has led to unprecedented observations of Exoplanet atmospheres in the last few years. In this talk I will start by discussing some of the important results of the Transiting Exoplanets JWST ERS and TST GTO programs, that I am involved in. I will then discuss about SANSAR (Suite of Adaptable plaNetary atmoSphere model And Retrieval), an adaptable planetary atmosphere modelling suite that we are developing to interpret planetary atmosphere observations. I will present the first published results from this model, placing most robust constraints on the atmosphere of HD 209458b, the first exoplanet on which atmosphere was detected, using combined HST and JWST transmission spectra observations. I will discuss the need for measurements in the optical using HST to robustly constrain the exoplanet atmospheric abundances, metallicity and C/O ratio, even if we have infrared measurements with JWST, demonstrated for HD 209458b. I will also discuss how stellar abundances and choice of opacities can lead to different constraints with self-consistent grid retrievals for HD 149026b emission spectra observations. Finally, I will briefly discuss how we are using SANSAR to prepare for Indian Venus mission Shukrayaan that will be launched in 2027 and ExoWorld mission, a 2m class dedicated mission to characterize exoplanet atmospheres and some ancillary science, that is being considered by the India Space Research Organization (ISRO).