From Hale-Bopp's activity to properties of its nucleus

Abstract

Because of the outstanding brightness of comet Hale-Bopp reliable production rates of several molecules could be measured over a wide range of heliocentric distances. The H2O-activity of a comet is closely connected with the energy balance and the composition of its surface. It is often assumed that more volatile molecules originate from subsurface regions. The CO observations provided an important data base for a better understanding of this matter. A thermal model has been applied to calculate gas production rates of Hale-Bopp. The strong obliquity of the spin axis causes pronounced seasonal effects and, therefore, an asymmetry of water activity with respect to perihelion. By comparing measured and calculated rates properties of the nucleus have been derived.