The 1908 Tunguska Explosion: Discovery of Indium and Other Element Anomalies

摘要

The 15 peat samples collected from the layers affected by the 1908 Tunguska explosion in Tunguska area of central Siberia, Russia, were analyzed by NAA to determine the contents of Ir, REE, Ni, Co, Fe and Sb. The analytical results indicate that Ir concentrations in and above the event layer were 0.54-0.24 ppb, about 10-20 times higher than that in layers below, and other elements were all enriched by a factor of 2 to 5. In addition, the variation of Ni concentration was closely related with Ir in the explosive layer, and the patterns of chondrite-normalized REE are almost flat with a ratio of about 1. Hence, it can be inferred from the characteristics of elemental geochemistry that the explosion likely was associated with extraterrestrial material. Due to its explosion before reaching the ground, the density of the explosion body must have been quite low, the chemical composition of which was probably similar to the carbonaceous chondrite (Cl). In terms of the Ir flux in the explosion area, it can be estimated that the celestial body exploded weighed about 1.9 x 10'" tons, corresponding to 1-1.5km in radius, and might have released energy equal to - 101 megatons.