Discovery of probable Tunguska cosmic body material: anomalies of platinumgroup elements and rare-earth elements in peat near the Explosion Site (1908)

Ten Spagnum fuscum peat samples collected from different depths of a core i ncluding the layer affected by the 1908 Tunguska explosion in the Tunguska area of Central Siberia, Russia, were analyzed by ICP-MS to determine the c oncentrations of Pd, Rh, Ru, Co, REE, Y, Sr, and Sc. The analytical results indicate that the Pd and Rh concentrations in the event- and lower layers were 14.0-19.9, and 1.23-1.56 ppb, respectively, about 3-9 times and 3 time s higher than the background values in the normal layers. In addition, the patterns of CI-chondrite-normalized REE in the event layers were much flatt er than in the normal layers, and differed from those in the nearby traps. Hence, it can be inferred from the characteristics of the elemental geochem istry that the explosion was probably associated with extraterrestrial mate rial, and which, most probably, was a small comet core the dust fraction of which was chemically similar to carbonaceous chondrites (CI). In terms of the Pd and REE excess fluxes in the explosion area, it can be estimated tha t the celestial body that exploded over Tunguska in 1908 weighed more than 10(6) t, corresponding to a radius of > 60 m. If the celestial body was a c omet, then its total mass was more than 2 x 10(7) t, and it had > 160 m rad ius, and released an energy of > 10(7) t TNT. (C) 2000 Elsevier Science Ltd . All rights reserved.