Excerpt:
The following text is adapted from a major review on Comets, prepared by Michel C. Festou (Observatoire Midi-Pyrenees, Toulouse, France), Hans Rickman (Astronomiska Observatoriet, Uppsala, Sweden) and Richard M. West (European Southern Observatory, Garching, Germany) and published in the review journal Astronomy & Astrophysics Reviews (A&AR) (Part I, Vol. 4 pp. 363-447, 1993)