Evolution of Primordial Kuiper Belt Binaries Through a Giant Planet Instability

TL;DR

This study uses N-body simulations to investigate how early giant planet encounters disrupted primordial Kuiper Belt binaries, explaining the scarcity of wide binaries in the hot classical belt.

Contribution

It demonstrates that planetary encounters during early solar system instability effectively disrupted wide binaries, accounting for observed binary distributions in the Kuiper belt.

Findings

Planetary encounters disrupted binaries with separations >1% of Hill radius.

Widest observed binaries are unlikely to survive encounters, but some tighter binaries can be widened.

Encounters can produce the small population of very wide binaries in the HCB.

Abstract

The non-resonant Kuiper belt objects (KBOs) between the 3:2 and 2:1 Neptunian mean motion resonances can be largely divided between a cold classical belt (CCB) and a hot classical belt (HCB). A notable difference between these two subpopulations is the prevalence of widely spaced, equal-mass binaries in the CCB and a much smaller but non-zero number in the HCB. The primary reason for this difference in binary rate remains unclear. Here using N-body simulations we examine whether close encounters with the giant planets during an early outer solar system instability may have disrupted primordial Kuiper Belt binaries that existed within the primordial Kuiper belt before they attained HCB orbits. We find that such encounters are very effective at disrupting binaries down to separations of ~1% of their Hill radius (as measured in the modern Kuiper belt), potentially explaining the paucity of widely spaced, equal mass binaries in the modern HCB. Moreover, we find that the widest binaries observed in the modern HCB are quite unlikely to survive planetary encounters, but these same planetary encounters can widen a small subset of tighter binaries to give rise to the small population of very wide binaries seen in today's HCB.