A computer model of the atmospheric entry of the Tunguska object

Mathematical models of the entry trajectory for various types of meteors have frequently been applied in an effort to determine the nature of the Tunguska object. This approach has been used to support both a stony asteroid and a cometary object as the most probable cause of the event. An accurate trajectory model must include an evaluation of both the mechanical fragmentation and the aerothermal ablation and must couple these two processes. Inaccuracies in the calculated ablation rate can lead to substantial errors in the predicted terminal altitude of a given entry body, this is particularly true for relatively weak, icy objects such as comets. The present study uses an analytical approximation of the mechanical fragmentation and radial spreading of the bolide and examines aerothermal ablation in some detail, including an evaluation of radiative cooling of the shock layer gases and the effect of radiation blockage by ablation products coming off the meteorʹs surface. Such calculations can be performed only in an approximate manner since the properties of high temperature gases are not well established at the extremc pressures and temperatures involved. It is found that the sudden release of energy approximately 8 km above the surface which was associated with the Tunguska event could have been produced by the disruption of either a comet or an asteroid, although a cometary origin would have required a very steep atmospheric entry angle. Therefore, although an asteroidal origin seems more likely, it is concluded that a trajectory analysis of this type cannot be used at the present time to exclude either type of object with absolute certainty.