Phase portrait of the resonance 2:3 with the Earth for a small body with e = 0.6, i = 22°, ω = 322°, and Ω = 265°. The bottom panel shows the level curves of the Hamiltonian function in Eq. (1). The central semi-major axis of the resonance is a₀ = 1.31038 au (horizontal line). Coloured dots show the equilibrium points. The definition of the widths of resonance islands and sub-islands are represented by arrows. The top panel shows the behaviour of ɛW as a function of σ (i.e. this is a cut of the bottom panel along the horizontal line).