Styx, Nix, and Hydra are thought to be in a 3-body orbital resonance with orbital periods in a ratio of 18:22:33; the respective ratio of orbits is 11:9:6. The ratios should be exact when orbital precession is taken into account. Hydra and Nix are in a simple 2:3 resonance. Styx and Nix are in an 11:9 resonance, while the resonance between Styx and Hydra has a ratio of 11:6. This means that in a recurring cycle there are 11 orbits of Styx for every 9 of Nix and 6 of Hydra. The ratios of synodic periods are then such that there are 5 Styx–Hydra conjunctions and 3 Nix–Hydra conjunctions for every 2 conjunctions of Styx and Nix. If formula_1 denotes the mean longitude and formula_2 the libration angle, then the resonance can be formulated as formula_3. As with the Laplace resonance of the Galilean satellites of Jupiter, triple conjunctions never occur. formula_2 librates about 180° with an amplitude of at least 10°.