Hypotheses ranging from a black hole to a falling UFO have been offered, but scientists have narrowed the field down to asteroids and comets. The debate whether the strike was an asteroid or comet is ongoing today. Scientists did not venture to Tunguska for another 19 years. They anxiously searched the area for a crater but found none. They then searched for fragments of a meteorite, an asteroid or a chunk of one, but once again, …showed first 75 words of 728 total…

…showed last 75 words of 728 total…would have been similar to a global catastrophe. Zdenek Sekanina of the Jet Propulsion Laboratory at Caltech said, "It would have been a global catastrophe comparable to a nuclear winter. The effects on mankind would have been so overwhelming that we could not discuss the topic, because we would not be here. Computer modeling done also shows that a cometary object would have exploded far too high to cause the damage that occurred at Tunguska.