A new inclination instability reshapes Keplerian disks into cones: application to the outer Solar System

TL;DR

This paper introduces a new dynamical instability in eccentric Keplerian disks that causes them to evolve into conical shapes, potentially explaining the orbital distribution of minor planets beyond Neptune.

Contribution

It identifies a novel inclination instability in eccentric disks and links it to the observed orbital clustering in the outer Solar System.

Findings

The instability causes exponential growth in orbital inclinations.

Disks evolve into conical shapes with aligned orbital tilts.

Predicted increase in high-inclination minor planet detections.

Abstract

Disks of bodies orbiting a much more massive central object are extremely common in astrophysics. When the orbits comprising such disks are eccentric, we show they are susceptible to a new dynamical instability. Gravitational forces between bodies in the disk drive exponential growth of their orbital inclinations and clustering in their angles of pericenter, expanding an initially thin disk into a conical shape by giving each orbit an identical 'tilt' with respect to the disk plane. This new instability dynamically produces the unusual distribution of orbits observed for minor planets beyond Neptune, suggesting that the instability has shaped the outer Solar System. It also implies a large initial disk mass (1-10 Earth masses) of scattered bodies at hundreds of AU; we predict increasing numbers of detections of minor planets clustered in their angles of pericenter with high inclinations.