The first scientific results of the italian scientific expedition Tunguska99 will be presented at the 31st Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society (Padova, Italy, October 10-15 1999). The poster will be presented in the Session 59 (late papers) on Thursday 14 october (6:00-7:30 PM). Moreover, the abstract will be published on the Bulletin of the American Astronomical Society, vol. 31, n. 5, (1999) and is available on the web at the Tunguska99 home page.
Processing of the data is in progress, but preliminary analysis of data collected on the lake suggests that the origin of the lake be not related to the 1908 event. It constitutes, more likely, an ancient volcanic depression filled up by a more than 50 m thick sedimentary deposit of fluviatile origin. The future work will focus on the core analysis, and on the detection of possible physical effects within the sedimentary successions (i.e. gravitative failures of the slopes) that could give important insights on the energy of the event.
An aerial photographic survey covering a surface of 235 kmē has been carried out. Contemporarily we measured on the ground the geographical coordinates of some points in the same area. The results of the aerial survey and topographic measurements are being processed to check whether the 1908 explosion was single or multiple and to verify a recent hypothesis on the explosion mechanism.
Gamma rays from cosmic and environmental radiation have been continuously recorded on time scale of one minute and in the 0.05-3 MeV, 3-5 MeV and 5-20 MeV energy bands. The in-flight measurements indicate great gamma ray variations in dependence on altitude, longitude and latitude. Nearby the lake Cheko daughter radionuclides from the 238U and 232Th chains have been recorded. The data are being processed to find other natural or man-made radionuclides.
Bologna, 12 October 1999
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