N-body simulations to track the long-term fate of impact–induced debris

Impact events represent the most energetic processes during late-stage terrestrial planet accretion and generate large amounts of debris that can be redistributed throughout the inner Solar System. The long-term dynamical fate of this impact-generated material plays a key role in regulating planetary growth, cross-planet mass exchange, and material loss from the system. However, most N-body accretion models still rely on simplified collision prescriptions that neglect the detailed structure and dynamics of impact remnants.

In this study, we investigate the long-term evolution and final fate of impact-induced debris by coupling high-resolution Smoothed Particle Hydrodynamics (SPH) simulations with GPU-accelerated N-body integrations. We perform a systematic suite of SPH simulations spanning a broad parameter space in impactor mass, impact velocity, and impact angle. Gravitationally bound clumps (GBCs) formed in the impact aftermath are identified using an energy-based clustering algorithm and mapped self-consistently into N-body initial conditions, which are then evolved for 15 Myr using the GENGA integrator in a realistic inner Solar System configuration.

Our simulations reveal a two-stage debris clearance process. More than 80% of the ultimately accreted mass is reaccreted within the first 10⁵ years after impact, followed by a prolonged phase of dynamical depletion dominated by planetary perturbations. Earth is the primary sink of impact debris, reaccreting on average ∼40% of the total fragment mass, while Venus acts as a significant secondary reservoir, capturing ∼18-27%. In contrast, Mercury and Mars contribute only marginally to debris accretion. Approximately 25-30% of the debris is ultimately ejected from the Solar System, primarily through gravitational scattering by Jupiter.

Statistical analysis demonstrates that impact angle and velocity are the dominant parameters controlling debris fate, with high-velocity and grazing impacts strongly enhancing mass loss via ejection. Initial orbital phase also modulates debris survival and reaccretion efficiency. These results provide quantitative constraints on post-impact mass redistribution and highlight the importance of explicitly resolving impact remnants when modeling late-stage terrestrial planet formation.