He walks through the close approach of asteroid 2001 YB5, an object large enough that atmospheric detonation would not have been an option. Unlike smaller impactors that break apart or explode before reaching the surface, this one would have struck the ground with full force. The comparison to the Tunguska object, which flattened 2,000 square kilometers of Siberian forest in 1908, provides a sobering reference point. Tunguska was an airburst. This would have been a direct impact. The difference in energy release and ground effect would have been catastrophic on a regional scale, and the transcript sets up that comparison to help visualize the real threat posed by near-Earth objects of this size class.