The surface dynamics and geophysical environment of asteroid (3200) Phaethon

Context . (3200) Phaethon is a ∼5-kilometer-diameter near-Earth asteroid with a small perihelion distance of 0.14 au. It is the parent body of the Geminids. JAXA’s DESTINY + mission will fly by Phaethon in the near future. Aims . To support the preflight planning for the DESTINY + mission, we performed a geophysical analysis of Phaethon’s surface and near-surface environment utilizing the latest shape model, which is based on numerous observations. Methods . We employed the soft-sphere discrete element method code PKDGRAV to construct a “mascon” model of Phaethon and determine its gravity. We then computed the geopotential on Phaethon and derived various physical quantities related to its surface and near-surface dynamics. Results . We calculated geophysical quantities for the surface, including surface acceleration and slope. To assess whether surface objects could be launched off the surface, we computed the escape speed, return speed, Jacobi speed, and the location and stability of equilibrium points around Phaethon, and conducted a simple dynamical simulation of launched particles. Conclusions . Our results suggest that a large depression feature in the northern hemisphere could harbor exposed subsurface material and the freshest material on Phaethon. We propose that this depression be considered a key area for observation by the DESTINY + mission.