THE INFLUENCE OF REACTIVE TORQUES ON COMET NUCLEUS ROTATION

Abstract. Reactive torques, due to anisotropic sublimation on a comet nucleus surface, produce slow variations of its rotation. In this paper the secular effects of this sublimation are studied. The general rotational equations of motion are averaged over unperturbed fast rotation around the mass center (Euler-Poinsot motion) and over the orbital comet motion. We discuss the parameters that define typical properties of the rotational evolution and discover different classifications of the rotational evolution. As an example we discuss some possible scenarios of rotational evolution for the nuclei of the comets Halley and Borrelly. Key words: comet nucleus, rotational dynamics, non-gravitational perturbations 1. Statement of the Problem and Main Assumptions In the classical model of a comet nucleus proposed by Whipple (1951), aniso-tropic ice sublimation due to solar radiation produces reactive torques, Mr, that act on the nucleus. The goal of the present paper is to study the possible secular effects produced by Mr on the rotational dynamics of the nucleus. Unlike previ-ous studies, based primarily on numerical modeling of nucleus rotation evolutio