Dynamical maps around the L₄ point of Uranus on the (a₀, i₀) plane. The colour indicating the regularity of orbits represents the base-10 logarithm of SN of cosσ. Orbits escape from the 1:1 MMR with Uranus during the integration time are not included in these maps. The libration centres for different i₀ are depicted by the dark line. Left panel: result for 4.25 × 10⁶ yr; right panel: result for 3.4 × 10⁷ yr, which is eight times the former.