An asteroid or comet fragment around 60 meters across is believed to have been behind the Tunguska Event, a powerful explosion that took place over Russia in 1908.

据信，1908年俄罗斯上空发生的强劲爆炸——通古斯大爆炸背后，有一个直径约六十米的小行星或慧星碎片。

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But even if Spaceguard does succeed, another problem remains smaller asteroids, of the size believed to have caused a huge explosion above Tunguska, in Russia, in 1908.

ECONOMIST: A large asteroid sweeps by Earth. Where are the others?

Siberia time in the morning in June of the year 1908 high in the sky above the Forest in the remote wilderness of Tunguska Siberia heard an explosion that laid flat more than 800 square miles of the forest with all the trees pointing away from the center of the blast with most all the trees laying on their side.

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