A huge explosion over the Tunguska River in Russia flattened forest across about 2,000 square kilometres. People 60 km away were knocked off their feet. No crater or large fragments were ever found.
Truth label: Established. Strong evidence and broad agreement among experts.
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The explanation
Most scientists think a space rock or comet tens of metres wide exploded in the air before hitting the ground.
Wild theories
Its mystery invited ideas from crashing spaceships to tiny black holes. The airburst is far better supported.
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- A warning. Had it struck a city, it would have been devastating. It helped inspire today's asteroid tracking.
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Why was there no crater at Tunguska?
It exploded in the air. The object burst in the air above the ground.
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