William F. Bottke, Jr
Center for Radiophysics and Space Research
Cornell University
Ithaca,
NY 14853-6801
Tel: (607) 255-3934
Fax: (607)
255-9002
bottke@astrosun.tn.cornell.edu
Paper for 23rd Meeting of the International Seminars on Planetary Emergencies
Erice, Italy
September 10, 1998