Time snapshots of the flattened surface density of the disc in the nominal simulation, N4. The empty circles give the positions of Jupiter (red), Saturn (blue), Uranus (green), and Neptune (white). Panel a shows the entry of Uranus in the 2:1 MMR with Saturn. Panel b shows the moment when Neptune has just been locked in the 3:2 resonance with Uranus. In panel c, the four planets enter into their final resonant configurations (2:1, 3:2, 4:3). Finally, panel d shows the stable system at the beginning of the mock disc dispersal phase (see Sec. 2.4 for more details). These moments are snapshots in the evolution of the planetary orbits that can be found in Fig. 2.