Top left panel: result of four N-body simulations leading to capture in the 2:1 MMR. In all cases m₁ = 20m_⊕. Color lines indicate different mass ratios: m₂/m₁ = 2 (orange), m₂/m₁ = 1.8 (purple), m₂/m₁ = 1.7 (blue), and m₂/m₁ = 1.6 (green). Remaining panels: different dynamical characteristics of the orbital evolution within the resonance of the run with m₂/m₁ = 1.6. The black continuous lines in the bottom panels represent the analytical predictions given by expressions (3).