Families, S_i (i = 1…9), of planar symmetric periodic orbits in the 1:2:3 resonant chain close to the dynamical vicinity of Kepler-51 (top panels) and until their termination points (bottom panels) presented on the (e₁ cos θ₁, e₂ cos θ₂) and (e₂ cos θ₂, e₃ cos θ₃) planes. The angles for the different configurations of the families are shown in Table 3. Kepler-51 is identified in the top panels by the cyan “+” symbol, while the errors provided by Masuda (2014) are delineated by magenta dashed lines.