Asteroid Comet Impact Hazards - Florida International University

Report on the Tunguska International Workshop Bologna, Italy, July 14-17, 1996
E.M. Shoemaker, Z. Sekanina, J.G. Hills, B.G. Marsden, and A.W. Harris, also to name only a few.
Conspicuous by his absence, but hardly overlooked, was C. Chyba, whose 1993 stony asteroid model
generated more heat than light and came under heavy fire by both the Russians and Americans,
especially the mechanical aspects of his model.
Chairman Vasilyev's report about the history of Tunguska investigations, research strategies and
methods, and publications by Russian investigators revealed the enormous research effort exerted by the
Russians over the decades to solve the Tunguska puzzle. His report is must reading for anyone who
wishes to compile a data base about the Tunguska event. The following is excerpted from his exhaustive
report:
"Today the Tunguska problem can be considered an important part of the larger problem of the possible
collision of Earth with those cosmic bodies called Near Earth Objects (NEO). To estimate the scale of
collision danger threatening our planet, one should base research not only on the calculations of the
probability of collisions, but also on the investigative results of such events in Earth's history.
"The volume of information about the Tunguska Event obtained during approximately 90 years of
investigations is enormous. However, most of it derives from work done after 1945 and is published
only in Russian and, therefore, has not been available to scientists of the West. We consider it important
to present a brief overview of the existing Tunguska information and to discuss its more important
aspects, which may play a key role in a final solution to the problem."
A sampling of paper presentations will show the wide range of topics discussed: Veteran Tunguska
investigator W.H. Fast (Tomsk State University, Russia) reviewed the extent and implications of fallen
and damaged forest. G. Andreev (also of Tomsk) described the data base of some 900 testimonials of
eyewitnesses of the Tunguska explosion. G. Longo, M. Galli, and R. Serra (University of Bologna)
described their search for elemental constituents of the Tunguska body trapped in the 1908 annual ring
resins of trees that survived the explosion. E.M. Kolesnikov (Moscow State University) spoke on his
more than 15 years of field work in the chemical and isotopic investigation of peat and spherules from
the region of the explosion. V.D. Goldin (Tomsk) addressed the problem of the Tunguska event being
not a single explosion but a series of several explosions, the local centers of which can be determined on
the basis of data from fallen trees.
Z. Sekanina (Jet Propulsion Laboratory, Caltech) attempted to leave no doubt in anyone's mind that the
Tunguska object was a stony asteroid and could in no possible way have been of cometary origin. He
was alone in this contention, except for the missing Chyba. Hot on Sekanina's heels came S.S. Grigorian
(Moscow State University) who just as strongly argued for the Tunguska object being a small comet.
Had it been a stony asteroid, he maintained, by now we would have found stony debris somewhere. Jack
Hills (Los Alamos National Laboratory), who discussed damage from the impacts of small asteroids,
agreed that if the object had been a stony asteroid by now a swarm of loose gravel about a kilometer in
diameter should have been found somewhere in the epicenter area. Hills, perhaps more than any other
participant, avoided the sticky dichotomy of comet versus asteroid and instead spoke of "objects" over a
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