Evolution of the semi-major axis (top), eccentricity (middle), and period ratios of two embedded planets in the disk. The simulation was continued from the isothermal model shown in Fig. 8 (red line) that is shown in green here. At t ≈ 3500 yr, a second planet was added (blue line) at 2.0 au. At t ≈ 7000 yr, the planets entered a 3:2 mean-motion resonance and experienced a scattering event. At a later time (t ≈ 16 000), the original evolution with the two planets eventually became unstable. At around t ≈ 15 000, the disk mass was reduced by a factor of 10, and the simulation was continued (shown in purple for the outer planet and in light blue for the inner one).