Self-Gravitational Dynamics Within the Inner Oort Cloud

TL;DR

This study investigates the self-gravitational effects within the Inner Oort Cloud, revealing that while such effects can cause orbital modulations, their timescales are too long to impact the solar system's current structure.

Contribution

It introduces a semi-analytic model of IOC self-gravity and demonstrates its negligible influence on solar system dynamics over observable timescales.

Findings

Self-gravity modeled by Miyamoto-Nagai potential

Secular oscillations similar to von Zeipel-Lidov-Kozai resonance

Orbital modulations occur but over timescales longer than the solar age

Abstract

The formation of the Inner Oort Cloud (IOC) - a vast halo of icy bodies residing far beyond Neptune's orbit - is an expected outcome of the solar system's primordial evolution within a stellar cluster. Recent models have shown that the process of early planetesimal capture within the trans-Neptunian region may have been sufficiently high for the cumulative mass of the Cloud to approach several Earth masses. In light of this, here we examine the dynamical evolution of the IOC, driven by its own self-gravity. We show that the collective gravitational potential of the IOC is adequately approximated by the Miyamoto-Nagai model, and use a semi-analytic framework to demonstrate that the resulting secular oscillations are akin to the von Zeipel-Lidov-Kozai resonance. We verify our results with direct $N$-body calculations, and examine the effects of IOC self-gravity on the long-term behavior of the solar system's minor bodies using a detailed simulation. Cumulatively, we find that while the modulation of perihelion distances and inclinations can occur within an observationally relevant range, the associated timescales vastly surpass the age of the sun, indicating that the influence of IOC self-gravity on the architecture of the solar system is negligible.