A Primer on Unifying Debris Disk Morphologies

TL;DR

This paper presents a unified, minimal model for debris disk morphologies that can explain a wide variety of observed shapes through simple physical principles, aiding interpretation of real debris disk images.

Contribution

It introduces a unifying minimal model that reproduces diverse debris disk shapes and explains their features from first principles, serving as a reference for detailed system-specific models.

Findings

Five broad disk shape categories identified.

Disk morphology depends on planet eccentricity and dust orbit alignment.

Eccentric planets influence the outer regions of planetary systems.

Abstract

A "minimum model" for debris disks consists of a narrow ring of parent bodies, secularly forced by a single planet on a possibly eccentric orbit, colliding to produce dust grains that are perturbed by stellar radiation pressure. We demonstrate how this minimum model can reproduce a wide variety of disk morphologies imaged in scattered starlight. Five broad categories of disk shape can be captured: "rings," "needles," "ships-and-wakes," "bars," and "moths (a.k.a. fans)," depending on the viewing geometry. Moths can also sport "double wings." We explain the origin of morphological features from first principles, exploring the dependence on planet eccentricity, disk inclination dispersion, and the parent body orbital phases at which dust grains are born. A key determinant in disk appearance is the degree to which dust grain orbits are apsidally aligned. Our study of a simple steady-state (secularly relaxed) disk should serve as a reference for more detailed models tailored to individual systems. We use the intuition gained from our guidebook of disk morphologies to interpret, informally, the images of a number of real-world debris disks. These interpretations suggest that the farthest reaches of planetary systems are perturbed by eccentric planets, possibly just a few Earth masses each.