Time evolution of the planets’ orbital properties. From top to bottom: the planets’ semi-major axes, the orbital period ratio of the outer planet to the inner one, and the eccentricity of the inner and outer planets. In the top panel, the solid lines represent the inner planet and the dashed lines the outer planet. The two planets are initially located close to a 2:1 resonance. The horizontal dashed line, r = 0.22, corresponds to the inner damping radius. The vertical dark and light grey lines represent the time when the planets are in resonance. In our fiducial model, the dark grey line corresponds to t = 4840 yr and the light grey line to t = 11 660 yr.