Number of models for the corresponding H₂ outgassing flux as a function of fO₂ (left) and H₂O concentration (right) at a surface temperature of 1573 K. Red and green horizontal lines show a comparison of different mantle conditions with modern Earth and Mars H₂ outgassing flux. Bulk redox states of Mercury (M. Y. Zolotov et al. 2013), Earth (D. C. Catling & J. F. Kasting 2017), and Mars (A. E. Doyle et al. 2020) are marked by dashed lines. Solid red lines mark Earth-like outgassing (R. Hu et al. 2023).