Location of the inner and outer evections (full lines) for the masses and eccentricities of the Dione–Helene system. The stable branches (related to the libration centers) are shown in blue, and the unstable branch (related to the saddle point of the outer evection) is plotted in red. The full dots indicate the current position of the prograde satellites of Saturn, and the vertical dashed line indicates the outermost limit of the irregular satellites. The letters specify the locations of Dione (D), Tethys (T), and Rhea (R), respectively. For the outer evection, the stable branch at ψ ₁ = 180° and e₁ ≲ 0.14 is related to a kinematic libration (Fig. 4b).