Top panel: surface coverage (H₂O nm⁻²) as a function of temperature (K) (left panel) and water vapor density (cm⁻³) (right panel). Each data point is the average ±σ of the coverage values at equilibrium (see Fig. 4). Left panel: dashed lines are used here to link each point and emphasize the step-like decrease in the surface coverage with temperature. Bottom panel: simulated [1 0 0] forsterite surface grids at 6  ×  10⁸ cm⁻³ and T  =  [300 − 700] K (from left to right panels). The color scale indicates the adsorption energy of the occupied sites in the range between 13 000 K (blue) and 25 000 K (yellow).