Level curves of the Hamiltonian function for a circularorbit. The parameters are a∕r_M = 1.1 and ε = 40°. The separatrix is shown by a thicker black curve. The coloured dots represent the three kinds of equilibrium points (‘Laplace states’), labelled as in the text. A dark colour is used for points P₁ and P₃ lying at δ_Q = 0 and for P₂ lying at δ_Q = π∕2. A light colour is used for the symmetric equilibrium point that corresponds to the same Laplace state with reversed orbital motion. Figure 2a shows the same phase portrait plotted on the sphere.