Spencer Wallace (University of Washington)

Planetesimals are the smallest gravitationally bound objects to play a role in the planet formation process, and act as the building blocks for both terrestrial planets and giant planet cores. Because of the vast disparity between the timescales for dynamical interaction and growth during this process, it is extremely computationally expensive to model this process from beginning to end with N-body simulations, unless one approximates collections of smaller bodies using superparticles. In this talk, I present the first-ever direct N-body simulations of planetesimal growth using realistic-sized bodies and show that some crucial dynamical mechanisms are only activated with sufficiently fine resolution. By using a tree-based algorithm to approximate gravitational self-interactions and handle collisions, we are able to achieve a resolution nearly 100x finer than previous studies. We also use this algorithm to follow the formation of a system of tightly-packed inner planets (STIP) all the way from planetesimals to full-sized planets. This allows us to trace the building blocks to their initial locations in the disk and make predictions for the final compositions of the planets under an in-situ model.