Close TNO Passages as a Driver of the Origin and Evolution of Ultra-Wide Kuiper Belt Binaries

TL;DR

This study investigates how close gravitational passages of TNOs, rather than impacts, influence the formation and evolution of ultra-wide Kuiper Belt binaries, revealing their significant role over billions of years.

Contribution

It introduces a new model focusing on gravitational perturbations from close TNO passages as a key driver in the evolution of ultra-wide Kuiper Belt binaries.

Findings

Close passages can significantly widen binary separations.

Simulated binaries match observed eccentricity and inclination distributions.

The process explains some properties of known wide binaries.

Abstract

Within the dynamically cold low inclination portion of the Classical Kuiper Belt, there exists a population of weakly bound binary systems with a number of unusual properties; most notable of which is their extremely wide orbital separations; beyond 7% of their Hill radii. The stability and evolution of these Ultra-Wide Trans-Neptunian Binaries (TNBs) have, in the past, been studied extensively under the assumption that the primary evolving mechanisms are interactions between the binary components and impacting Trans-Neptunian Objects (TNOs). Here, we instead study their evolution as driven by the gravitational perturbations of close passing but non-impacting TNOs. By simulating these passages, we show that the aggregate effects of encounters over billions of years have a significant effect on Kuiper Belt binary evolution. Such processes can lead to tight binaries widening significantly over time, approaching and sometimes surpassing the separation of the widest known TNBs. We also find that the eccentricity and inclination distributions of observed Ultra-Wide TNBs can be sampled from such widened binaries. While we are unable to produce enough wide binaries to explain their abundance, the orbital properties of ones we do produce are consistent with known wide binaries.