Ultra-hot Jupiters Through the Eye of JWST – Suman Saha

Ultra-hot Jupiters (UHJs) are among the most extreme planetary populations, with day-side temperatures exceeding ~2200K. While much has been debated about the formation of these extreme worlds, the precise measurement of key physical and chemical properties, essential for constraining these speculations, has long remained lacking. However, with the advent of JWST, such precise estimations have become a reality for the first time.

In this talk, I will present some of my very recent results from the analyses of JWST observations of two very interesting UHJs, beginning with the reduction of the raw data using two independent pipelines, followed by fitting the spectroscopic lightcurves to obtain the transmission and emission spectra, and comprehensive atmospheric retrieval analyses using both free and equilibrium chemistry models. I will show how both transmission and emission spectroscopic observations using the near-infrared bands of JWST have enabled us to determine their precise atmospheric compositions, thereby accurately estimating their atmospheric metallicity and C/O ratios.

For both UHJs, we have found highly metallic atmospheres, indicating extreme levels of photoevaporation. We have also found precisely constrained super-solar metallicities exceeding ~0.9, which might have resulted from selective photoevaporations in the upper atmosphere. Alternatively, these planets might have migrated inward during the early stages of their formation, accreting a significant amount of inner protoplanetary dust or even engulfing inner planets/planetesimals. Thus, our findings serve as benchmarks for testing sophisticated planet formation and evolution models in the future.