Complex Rotators: Asteroid 4179 Toutatis

Abstract

In this chapter the assumption of uniform rotation is removed. Many asteroids are non-uniform rotators, potentially due to several different causes. These include spin-down due to the YORP effect, which can make an asteroid more susceptible to perturbing torques, and tumbling due to a close planetary flyby, an asteroid fission event, or an impact. Comets are also believed to often be in such a spin state due to outgassing jets on the surface that are activated around every perihelion passage. Strong evidence exists for several comets being in non-uniform rotation states including Halley and Encke [149, 12]. Once in a tumbling mode, we assume that the body will approximately follow the torque-free rigid-body dynamics described earlier. While this is not exactly true, due to solar radiation pressure torques, gravitational perturbations, and internal dissipation effects, over timespans of interest for the motion of a particle or spacecraft in the asteroid frame this is a good assumption.