Particle dynamics in TOI-178 planetary system

The TOI-178 system hosts six planets with five of them locked in a 2:4:6:9:12 Laplace resonance chain. We perform N-body simulations to investigate the dynamics of test particles in this system. We observe that co-orbital regions around each planet are approximately 30% wider than predicted by classical theory for planets in the resonance chain, while TOI-178b, which lies outside the chain, shows a 52% enhancement. The region between TOI-178e and TOI-178f reveals Kirkwood gap-like structures created by mean-motion resonances with TOI-178f (4:3, 5:4, 6:5) and TOI-178g (5:3), where particle clearing occurs on 500-year timescales. An extended integration of the innermost region (0.015–0.025 au) shows periodic inclination oscillations with period 196 years, coincident with TOI-178b’s own oscillation period, with maximum amplitude occurring near the 3:2 resonance location. These structures are consistent with the system’s resonant architecture and provide a baseline characterization that enables future comparative studies of similar phenomena in other multi-planet systems with resonant configurations.