Finding the imprints of stellar encounters in long period comets

TL;DR

This study uses dynamical simulations to analyze how stellar encounters and the Galactic tide influence the injection of long-period comets from the Oort cloud, revealing the significant role of stellar encounters and suggesting a smaller Oort cloud population.

Contribution

It demonstrates that stellar encounters contribute at least 5% to long-period comets and introduces a simple proxy to identify significant stellar encounters affecting the Oort cloud.

Findings

Past stellar encounters injected at least 5% of known long-period comets.

Galactic tide is the dominant factor in producing long-period comets.

Strong stellar encounters like HIP 89825 and HIP 14473 contribute significantly to comet flux.

Abstract

The solar system's Oort cloud can be perturbed by the Galactic tide and by individual passing stars. These perturbations can inject Oort cloud objects into the inner parts of the solar system, where they may be observed as the long-period comets (periods longer than 200 years). Using dynamical simulations of the Oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. We find that past encounters were responsible for injecting at least 5% of the currently known long-period comets. This is a lower limit due to the incompleteness of known encounters. Although the Galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong -- but as yet unidentified -- stellar encounters or other impulses. The strongest individual future and past encounters are probably HIP 89825 (Gliese 710) and HIP 14473, which contribute at most 8% and 6% to the total flux of long-period comets, respectively. Our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. Our analysis also indicates a smaller population of the Oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories.