Mass evolution of close-in water-rich planets. The solid blue lines represent planets that retain their water envelopes for 10 Gyr. In contrast, the planet shown by the dashed red line loses its water envelope completely in 10 Gyr. We set L_p,0 = 1 × 10²⁴ erg s^-1, X_wt,0 = 75%, a = 0.1 AU, and ε = 0.1 for all the planets. In this model, we assume that the rocky core never evaporates.