A multidisciplinary investigation in the site of the Tungska explosion

In July 14-30, 1999, an Italian scientific expedition ("Tunguska99") was carried out in Central Siberia, in the site of the 1908 explosion of a cosmic body. The disruption of the body occurred in the atmosphere between 5 and 10 km above ground, producing energy between 10 and 20 million tons TNT and more than 80 millions of trees were uprooted on an area of 2150 km². Data on forest devastation and records of the atmospheric and seismic waves have made it possible to deduce the main characteristics of the Tunguska explosion, i. e. its exact time, 00h 14m 28s UT and the coordinates of the point usually called "epicenter", 60° 53' 09" N, 101° 53' 40" E. No macroscopic fragments of the cosmic body, neither impact craters have ever been found. In spite of the vast amount of theoretical and experimental work done up to now (see 1 and references therein), the nature and composition of the cosmic body and the dynamic of the event have not yet been clarified. To search for traces of the cosmic body, the "Tunguska99" expedition was organized by the Department of Physics of the University of Bologna, in collaboration with the Turin Astronomical Observatory and the Institute of Marine Geology (CNR Bologna) and with the local support of Russian personnel and researchers, mainly from Tomsk. The participants and the equipment of the expedition were transported from Italy to Krasnoyarsk by a Russian Iljushin IL-20M aircraft of the "State Research Institute of Aviation Systems" (GosNIIAS) and from Krasnoyarsk to Tunguska by a Russian MI-26 helicopter. To perform the expedition tasks, a camp has been built in the taiga at some hundred kilometers from centers connected by roads. To plan the construction of the base camp, four of the authors (A. C., M. D. M., G. L., R. S.) together with Victor Chernikov made an in situ recognition on July 1998 2. The recent expedition had broader tasks in comparison with those of the first Italian expedition organized by the University of Bologna in 1991 to search in tree resin for microparticles from the cosmic body 3 4 5 6 7. The main tasks of the "Tunguska99" expedition were: 1) to study the structure and sediments of the lake Cheko, a small lake located at 8 km from the epicenter of the Tunguska event; 2) to carry out an aerial photosurvey of the explosion site; 3) to collect wood, peat and rock samples; 4) to monitor gamma rays during the flights Italy-Siberia-Italy and in the Tunguska National Reserve. The analysis of the data and samples collected during the "Tunguska99" expedition will make it possible to deduce important characteristics of the Tunguska event and to refine, verifying their accuracy, the mathematical models concerning the interaction with atmosphere of cosmic bodies having different composition and dimensions. The "Tunguska99" expedition is a contribution to the international programs on the detection and physical study of asteroids and comets potentially dangerous to humankind.