Comet Hale-Bopp as a free-rotation rigid body

After considering the advantages of using such a simple mechanical model, the nucleus of Comet Hale-Bopp is treated as a free rotation symmetrical top. Although most authors have rejected the periodicity of more than 20 days, we considered in our analysis a possible complex rotational state with the 11.30 hour and the 20–24 day periods. From our model, a complex rotation could be possible if the large period is the spin around the axis of minimum moment of inertia (long axis) and the accepted 11.30 hour period corresponds to a free precession motion. The motion of precession should be nearly perpendicular to the direction of the long axis of the Comet, and then it should be in conflict with the observed stability of the shell structures. Because this result is independent of the axes ratio for reasonable values, we conclude that the complex rotational state is not compatible with observations.