Stable resonant capture of a two-planet system with convergent migration. The planet and disk parameters are m_i=1 M_⊕, m_o=10 M_⊕, τ_m=2 × 10⁵ yr and τ_m/τ_e = 1200. The planets get trapped in a 2:1 MMR at t≃10⁴ yr exciting the inner planet’s eccentricity to 0.02. The resonant angle φ_i shifts from 0 to 2τ/3 as the system transitions into the resonant state. It gradually decreases as convergent migration strengthens the resonant interaction, causing the libration center to drift slowly. In phase space, the trajectory converges toward the resonant equilibrium and co-evolves with it. We refer to this resonant capture at a stationary equilibrium as a stable trap. See https://github.com/llh-astro/resonance/raw/main/gif/stable_trap.gif