TOTAL ABLATION OF THE DEBRIS FROM THE 1908 TUNGUSKA EXPLOSION

THE Origin of the explosion over Tunguska, central Siberia, in 1908 ha s long been an enigma. Models(1-3) of the disruption of solid objects entering the atmosphere indicate that the Tunguska explosion occurred at an altitude of 6-10 km, and that the source object was probably a s tony asteroid(4). But important questions concerning the nature of the object remain(5,6), particularly as no fragments have been identified in the area of the explosion. Unlike smaller objects (such as meteori tes), which decelerate high in the atmosphere and can thus escape comp lete ablation and/or pulverization(7), a Tunguska-sized object penetra tes deeper into the atmosphere, where it will experience a greater aer odynamic load: the object should be disrupted into a vast number of fr agments, each no larger than about 10 cm (ref. 2), which are then wide ly dispersed. Here I calculate the flux of radiation both inside and o utside the fireball associated with the fragmenting object, and show t hat this is sufficient to totally ablate the dispersing fragments. The apparent absence of solid debris is therefore to be expected followin g the atmospheric fragmentation of a large stony asteroid.