Observational and dynamical constraints on the rotation of Comet P/Halley

Abstract

We have carried out an extensive search to determine all rotational states of the nucleus of Comet P/Halley which are capable of explaining a wide variety of observational data. We find that the orientation of the large end of the long axis during the Vega-1 encounter must be reversed from that suggested by Sagdeev et al. (1989) in order to satisfy some of the constraints. Neither pure rotations nor short axis modes (SAMs) are capable of satisfying the constraints. The most likely solutions are long axis modes (LAMs). In the most likely modes for the rotational state, the long axis executes a precessional motion around the space-fixed total rotational angular momentum vector with a period near 3.7 days while performing a rotational motion around itself with a period of about 7.3 days. The direction of the total rotational angular momentum is indicative of prograde rotation, but the exact coordinates are not well determined.