Families of periodic orbits in 2/1 MMR of the ERTBP when m₂ = 0.001 presented as in Fig. 6 in four quadrants in correspondence with the four different symmetric configurations on the plane (e₁, e₂). Apart from the apsidal difference, Δϖ, being noted, the angles in brackets represent the pair of resonant angles (θ₁, θ₂). The dashed grey curve depicts the collision line between the planets.