A SMACK Model of Colliding Planetesimals in the $\beta$ Pictoris Debris Disk

Abstract

We present a new model of the $\beta$ Pictoris disk-and-planet system that simulates both the planetesimal collisions and the dynamics of the resulting dust grains, allowing us to model features and asymmetries in both thermal and scattered light images of the disk. Our two-part model first simulates the collisional and dynamical evolution of the planetesimals with the Superparticle-Method Algorithm for Collisions in Kuiper belts (SMACK) and then simulates the dynamical evolution of the resulting dust grains with a standard Bulirsch-Stoer N-body integrator. Given the observed inclination and eccentricity of the $\beta$ Pictoris b planet, the model neatly ties together several features of the disk: the central hole in the submillimeter images, the two-disk "x"-pattern seen in scattered light, and possibly even the clumpy gas seen by ALMA. We also find that most of the dust in the $\beta$ Pictoris system is likely produced outside the ring at 60-100 AU. Instead of a birth ring, this disk has a "stirring ring" at 60-100 AU where the high-velocity collisions produced by the secular wave launched by the planet are concentrated. The two-disk x-pattern arises because collisions occur more frequently at the peaks and troughs of the secular wave. The perturbations of the disk in this region create an azimuthally and vertically asymmetric spatial distribution of collisions, which could yield an azimuthal clump of gas without invoking resonances or an additional planet.