Fig. 3.

Evolution of the Sun's bolometric luminosity relative to its present value (upper panel) and the equilibrium temperature of Mars (lower panel). The solid line corresponds to an evolution track of Tognelli et al. (2011) and the dotted line to Baraffe et al. (1998), both for a star of solar mass and metallicity. The present-day values in both panels are indicated by diamonds. For the evolution of the $T_{\mathrm{eq}}$, a constant albedo was assumed.