Dynamical maps of max(Δe) for the 2:1 (left) and 3:2 MMR (right) for fictitious two-planet systems with m₁ = 0.05m_Jup and m₂ = 0.10m_Jup orbiting a central star with mass m₀ = 1m_⊙. The orbit of the outer planet was initially circular with a₂ = 1 AU, and all angular variables where chosen equal to zero. Total integration time was 10³ yr. The green lines indicate the location of the zero-amplitude ACR-type librational solutions, estimated from the simple analytical model (see Eq. (14)). The white dots in the left panel are the result of three N-body simulations of resonance trapping in the 2:1 resonance. The broad black curve in the right plot corresponds to the Marchal-Bozis stability limit. See text for details.