High-inclination Centaur reservoirs beyond Neptune

Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, CS 34229, 06304 Nice, France

^★ Corresponding author: namouni@oca.eu

Received: 8 August 2025
Accepted: 30 October 2025

Abstract

Context. Numerical simulations of the 4.5 Gyr past evolution of high-inclination Centaurs show that they originated from orbits beyond Neptune that were perpendicular to the Solar System’s invariable plane in a region called the polar corridor. The existence of the polar corridor is explained by the Tisserand inclination pathways followed by Neptune-crossing objects in the three-body problem. Recently, a study of Centaur injection in the three-body problem has shown that Neptune-crossing trans-Neptunian objects (TNOs) in the polar corridor with semimajor axes in the range [40:160] au have dynamical times that exceed the Solar System’s age, suggesting the possible presence of long-lived reservoirs that produce high-inclination Centaurs.

Aims. We aim to numerically demonstrate the existence of such reservoirs in the Solar System by simulating the TNOs’ time-forward evolution under the gravitational perturbations of the giant planets, the Galactic tide, and passing stars. We also aim to assess the efficiency of Centaur injection as a function of the initial inclination and determine if high-inclination Centaurs can be produced by low-inclination reservoirs.

Methods. The motion of the giant planets, TNOs, and passing stars was simulated using the IAS15 N-body numerical integrator of the REBOUND package. The Galactic tide was included using the REBOUNDx package. Two TNO orbit types were considered in the semimajor axis range [40:140] au: cold TNOs with circular orbits and hot TNOs with a perihelion range of [32:50] au. The TNO Tisserand parameters, T, with respect to Neptune were taken in the range [−2:2.8] which corresponds to inclinations far from Neptune in the range [8^°:135^°], in order to examine Centaur injection at low and high initial inclinations.

Results. We find that TNO reservoirs in the semimajor axis range [50:140] au are long-lived and their populations peak at T = 0.5 and T = −1.5. Saturn is found to induce secondary structures in the polar corridor by holding the perihelia of a fraction of high-inclination reservoir material. We find that the Centaur inclination at minimum semimajor axis depends linearly on the Tisserand parameter regardless of the initial semimajor axis. Its amplitude shows that low-inclination reservoirs such as the early protoplanetary disk are unlikely to produce high-inclination Centaurs, in contrast to reservoirs in the polar corridor.

Conclusions. We have identified the likely location of the closest reservoirs to Neptune populated by TNOs captured in the early Solar System that produce high-inclination Centaurs. The Legacy Survey of Space and Time of the Vera Rubin Observatory will be able to constrain the reservoirs’ extent and population size.