Detailed alkali line opacities at high densities and their implications on the thermal structure of giant planets

Interior models of giant planets traditionally assume convection as the dominant heat transport mechanism in the molecular hydrogen envelope. However, several observations of Jupiter challenge this picture, including the atmospheric abundances of CO and water and the inferred depth of the zonal winds. One proposed solution to reconcile these observations is a stable layer near the kilobar level. In earlier work, we showed that, when radiative opacities are computed using the impact approximation, such a stable layer in Solar System giants can only be obtained with a strong alkali depletion. In this work, we present improved opacity calculations based on a unified line shape theory for the alkali (Na/K) resonance lines, which is needed to accurately determine their line widths and wing extents at high pressures. We find that the revised line profiles exhibit significantly stronger and more extended wings than those predicted by the impact approximation, together with density-dependent line shifts, increasing Rosseland mean opacities by up to an order of magnitude. Using our revised opacities, we reassess the conditions under which stable layers can form in Solar System giant planets and investigate whether stable stratification can persist throughout their evolution. Finally, we explore the impact of the revised opacities on warm and hot Jupiters.