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Project Progress

We developed a new technique and a new code (called “SMACK”) for modeling the collisions and dynamics of debris disks. SMACK will help us interpret images of planetary systems and understand how planetesimals transport material around young planetary systems. SMACK (Superparticle Model/Algorithm for Collisions in Kuiper belts) combines an N-body integrator with a novel superparticle-based algorithm that tracks several orders of magnitude in planetesimal size and runs fast enough to model the entire lifetime of a typical observed debris disk in a feasible number of CPU cycles. With SMACK, we can derive improved estimates of the masses and orbital parameters of exoplanets from high spatial resolution images of debris disks, and better understand the history of the solar system, e.g. by calculating the effects of collisions on predictions of late heavy bombardment events in the context of the Nice dynamical model.

Before we could publish a new kind of disk model, we had to show that it was stable and accurate. So we spent the bulk of the year subjecting SMACK to a series of numerical tests. We showed that SMACK conserves angular momentum at an acceptable level. We showed that it is stable to numerical viscosity and numerical heating over 10 Myr time scales. We also compared SMACK models to one-dimensional analytical models of disk evolution, and showed that SMACK can reproduce them.

Then, we used SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit. We found that differential precession creates a transient spiral structure as the ring evolves, but that collisions subsequently break up the spiral, leaving a narrower eccentric ring.

We saw that the ring acquires a forced eccentricity from the planet, but that (in 10 Myr) it never quite stops precessing – in contrast with common assumptions made by previous modelers. A paper describing the SMACK code, our numerical tests, and these initial models was prepared and accepted for publication in the Astrophysical Journal during this reporting period (Nesvold, Kuchner, Rein, & Pan 2013).