Habitable zone evolution for planets with an initial interior water content of 500 ppm. Left column: HZ boundaries in terms of stellar irradiation (S₀), around an M, K, G, and F dwarf (from top to bottom). Right column: HZ boundaries in orbital distance (au), which includes the stellar luminosity evolution. For illustration we indicate the orbital distance evolution of S_eff = 1S₀ with a grey solid line, which is the radiation the Earth receives from the Sun today, and the orbital distances of Venus, Earth, and Mars in panel f with vertical grey dashed lines. The stellar age corresponding to the interior evolution times is indicated on the secondary y-axis where applicable.