Fig. 3

Orbital-evolution scenario. 1: Protoplanet formed in the outer area migrates to the disk’s inner edge, which is within \(r_{\mathrm{crit}}\). 2: Planet moves to an orbit where positive and negative torques balance-out. This balancing point moves outward as the protoplanetary disk dissipates. 3: Planet remains near the unstable boundary after disk dissipation