The effect of the Solar motion on the flux of long-period comets

TL;DR

This study models how the Sun's motion through the Galaxy's tidal field affects the flux of long-period comets entering the Solar System over a billion years, revealing complex, quasi-periodic variations mainly driven by the Sun's radial movement.

Contribution

It provides a detailed simulation of the Galactic tidal effects on Oort cloud comets, emphasizing the importance of the Sun's radial motion in modulating cometary flux.

Findings

Cometary flux varies quasi-periodically with a 30% amplitude.

Radial motion of the Sun is the main driver of flux variations.

Galactic tidal influence should consider the Sun's orbit for accuracy.

Abstract

The long-term dynamics of Oort cloud comets are studied under the influence of both the radial and the vertical components of the Galactic tidal field. Sporadic dynamical perturbation processes are ignored, such as passing stars, since we aim to study the influence of just the axisymmetric Galactic tidal field on the cometary motion and how it changes in time. We use a model of the Galaxy with a disc, bulge and dark halo, and a local disc density, and disc scale length constrained to fit the best available observational constraints. By integrating a few million of cometary orbits over 1 Gyr, we calculate the time variable flux of Oort cloud comets that enter the inner Solar System, for the cases of a constant Galactic tidal field, and a realistically varying tidal field which is a function of the Sun's orbit. The applied method calculates the evolution of the comets by using first-order averaged mean elements. We find that the periodicity in the cometary flux is complicated and quasi-periodic. The amplitude of the variations in the flux are of order 30%. The radial motion of the Sun is the chief cause of this behaviour, and should be taken into account when the Galactic influence on the Oort cloud comets is studied.