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The recent observations on WASP-39 b by JWST have revealed hints of highmetallicity within the atmosphere compared to its host star (Feinstein et al.2022; Ahrer et al. 2023; Alderson et al. 2023; Rustamkulov et al. 2023; Tsai etal. 2023). There are various theories on how these high metallic atmospheresemerge. In this study, we closely investigate the impact of extreme escape inthe form of hydrodynamic escape to see its impact on atmospheric metallicityand spectral features such as CH$_4$, CO$_2$, and SO$_2$. We perform a gridsimulation, with an adapted version of MESA that includes hydrodynamic escape(Kubyshkina et al. 2018; 2020), to fully evolve planets with similar masses andradii to the currently observed WASP-39 b estimates. By making use of(photo-)chemical kinetics and radiative transfer codes, we evaluate thetransmission spectra at various time intervals throughout the simulation. Ourresults indicate that the massive size of WASP-39 b limits the metalenhancement to a maximum of ~1.23 the initial metallicity. When incorporatingmetal drag, this enhancement factor is repressed to an even greater degree,resulting in an enrichment of at most ~0.4%. As a consequence, when assuming aninitial solar metallicity, metal-enriched spectral features like SO$_2$ arestill missing after ~9 Gyr into the simulation. This paper, thus, demonstratesthat hydrodynamic escape cannot be the primary process behind the highmetallicity observed in the atmosphere of WASP-39 b, suggesting instead that ametal-enhanced atmosphere was established during its formation.

Metallicity and Spectral Evolution of WASP-39 b: The Limited Role of Hydrodynamic Escape