Sublimation rate of water ice as a function of the distance from the ice front to the cometary nucleus surface. The solid red curve represents the variation of the water-ice production rate with the distance from the ice front to the surface at the temperature of 208 K. The horizontal dashed black line indicates the water-ice production rate of Q_H2O ≈ 4.2 × 10²⁰ molecules m⁻² s⁻¹, while the vertical dashed black line denotes the depth of 0.646 m, corresponding to two seasonal thermal skin depths below the surface.