Computation of a possible Tunguska’s strewn field

Abstract

On June 30, 1908, at about 0h 14.5 m UTC, the Tunguska Event occurred, most likely caused by the fall of a small stony asteroid of about 50–80 m in diameter over the basin of the Tunguska River (Central Siberia). The first expedition was made by the geologist Leonid Kulik 19 years after the event, and macroscopic meteorites have never been found around epicenter. In this paper, we want to establish whether stony macroscopic fragments could have survived the TCB’s airburst (Tunguska Cosmic Body) and where they might have fallen. For this purpose, we have implemented a fall model to describe the mass ablation, pancake expansion, airburst and fragments’s dark flight. In our scenario, the fragments have a higher mean strength than the main body due to Weibull’s law. The results, for a TCB with a kinetic energy of 15 Mt, atmospheric entry speed in the range of 11–20 km/s, trajectory inclination of 35° and average strength in the range of 3–70 MPa, tell us that for a macroscopic fragment with a mean strength between 14–85 MPa would be possible to survive the high pressure and temperature airburst to reach the ground. The falling speed of the fragments is in the range of 0.8–0.5 km/s, which favored their burial in the permafrost. The range of mean strength values for the TCB’s macroscopic fragment appears physically plausible if we consider the fall of Carancas in 2007, with an estimated strength of 20–40 MPa. So our possible strewn field, computed for a typical fragment’s speed of 10±3 km/s, is located about 11 km North-West from the epicenter, with an area of about 140km2. Finally, Cheko Lake, which by some authors is considered an impact crater, falls about 3.5 km outside the strewn fields at 3 sigma level and it is unlikely that it could be a real impact crater: only if the TCB’s trajectory had an azimuth in the range 150∘–180∘ would be in the strewn field area, but this is not consistent with the most likely trajectory azimuth.