Injection of Oort Cloud Comets: The Fundamental Role of Stellar Perturbations

TL;DR

This study uses Monte Carlo simulations to analyze how stellar perturbations and Galactic tides inject comets from the Oort cloud into observable orbits, revealing a significant synergy between these influences that enhances comet injection rates.

Contribution

It provides the first detailed comparison of combined stellar and tidal effects on comet injection, highlighting the critical role of stellar perturbations and their synergy with Galactic tides.

Findings

Stellar perturbations significantly enhance comet injection rates.

Synergy between stellar and tidal effects increases injection beyond individual contributions.

Observable loss cone filling varies from less than 1% to nearly 100% depending on semi-major axis.

Abstract

We present Monte Carlo simulations of the dynamical evolution of the Oort cloud over the age of the Solar System, using an initial sample of one million test comets without any cloning. Our model includes perturbations due to the Galactic tide (radial and vertical) and passing stars. We present the first detailed analysis of the injection mechanism into observable orbits by comparing the complete model with separate models for tidal and stellar perturbations alone. We find that a fundamental role for injecting comets from the region outside the loss cone (perihelion distance q > 15 AU) into observable orbits (q < 5 AU) is played by stellar perturbations. These act in synergy with the tide such that the total injection rate is significantly larger than the sum of the two separate rates. This synergy is as important during comet showers as during quiescent periods and concerns comets with both small and large semi-major axes. We propose different dynamical mechanisms to explain the synergies in the inner and outer parts of the Oort Cloud. We find that the filling of the observable part of the loss cone under normal conditions in the present-day Solar System rises from <1 % for a < 20 000 AU to about 100 % for a >= 100 000 AU.