Mini-Oort clouds: Compact isotropic planetesimal clouds from planet-planet scattering

TL;DR

This paper demonstrates through simulations how planetary system instabilities can create large, isotropic clouds of planetesimals, called mini-Oort clouds, which may be observable and linked to hot Jupiter formation.

Contribution

It introduces a new formation mechanism for mini-Oort clouds resulting from planet-planet scattering and planetary ejections in evolving planetary systems.

Findings

Mini-Oort clouds can form from planetesimal scattering after planetary ejections.

These clouds have long collisional lifetimes, exceeding 10 Gyr.

Potential observational signatures include dust emission at 70 microns.

Abstract

Starting from planetary systems with three giant planets and an outer disk of planetesimals, we use dynamical simulations to show how dynamical instabilities can transform planetesimal disks into 100-1000 AU-scale isotropic clouds. The instabilities involve a phase of planet-planet scattering that concludes with the ejection of one or more planets and the inward-scattering of the surviving gas giant(s) to remove them from direct dynamical contact with the planetesimals. "Mini-Oort clouds" are thus formed from scattered planetesimals whose orbits are frozen by the abrupt disappearance of the perturbing giant planet. Although the planetesimal orbits are virtually isotropic, the surviving giant planets tend to have modest inclinations (typically ~10 degrees) with respect to the initial orbital plane. The collisional lifetimes of mini-Oort clouds are long (10 Myr to >10 Gyr) and there is a window of ~100 Myr or longer during which they produce spherical clouds of potentially observable dust at 70 microns. If the formation channel for hot Jupiters commonly involves planetary close encounters, we predict a correlation between this subset of extrasolar planetary systems and mini-Oort clouds.