Implications for the formation of Oort cloud-like structures and interstellar comets in dense environments

Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria

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Received: 1 April 2025
Accepted: 19 December 2025

Abstract

Most stars form in dense stellar environments, where frequent close encounters can strongly perturb and reshape the early architecture of planetary systems. The Solar System, with its rich population of distant comets, provides a natural laboratory to study these processes. We performed detailed numerical simulations using the LonelyPlanets framework that combines NBODY6++GPU and REBOUND to explore the evolution of debris disks around Solar System analogues embedded in stellar clusters. Two initial configurations are considered, the Extended model and the Compact model, each containing four giant planets and either an extended or compact debris disk. We find that compact disks primarily form Kuiper belt and scattered disk-like populations through planet–disk interactions, while extended disks are more strongly shaped by stellar encounters, producing Oort cloud-like structures and interstellar comets with ejection velocities of 1–3 km s⁻¹. Stellar perturbations are most effective for encounter inclinations between 0° and 30°, giving rise to distinct dynamical populations, like Sednoids, and inner Oort cloud analogues, and a characteristic tail in semimajor axis-eccentricity space. In coplanar encounters, the disk remains largely flattened, whereas polar flybys redistribute angular momentum vertically, producing nearly isotropic outer populations that resemble an emerging Oort cloud. Our results suggest that cometary reservoirs and interstellar objects are natural byproducts of planet–disk interactions and stellar flybys in dense clusters, linking the architecture of outer planetary systems to their birth environments.