Dynamical maps on the a–e plane (left panel) and a–I plane (right panel) of the moon’s initial conditions calculated for the PC binary and a small moon of Styx’s mass with initial Styx orbital elements from JPL in Table 1. The current positions of the moons are shown by red crosses. The locations of the main MMRs are indicated, and the grey line in the right panel indicates the current inclination of Charon. The colour scale varies with Δe and Δi, increasing from blue (regular motion) to red (chaotic motion), as shown in the colour bars on the top of the figure.