The Tunguska Event: Siberia, 1908
1908 · event
Shortly after seven in the morning on 30 June 1908 a fireball crossed the sky above the basin of the Podkamennaya Tunguska River in central Siberia. It ended in an explosion in the air, several kilometres above the taiga. The blast flattened around two thousand square kilometres of forest, an estimated eighty million trees, laying them out in a vast radial pattern. Evenki reindeer herders camped in the region were thrown from their tents, and windows broke in a trading settlement more than sixty kilometres away. Because the area was almost uninhabited, no deaths were ever confirmed.
The object is now generally understood to have been a stony asteroid, perhaps fifty to sixty metres across, that broke apart under the pressure of entry and released its energy as an airburst rather than an impact. Estimates of that energy run into the range of ten to fifteen million tonnes of high explosive. There is no crater, which is why the event was for decades one of the strangest entries in the record of natural history.
Civil war and distance kept scientists away until 1927, when Leonid Kulik led the first expedition to the site. He found no crater but photographed the fallen forest, its trunks pointing outward from an empty centre where the trees still stood upright, stripped of branches. Later expeditions collected microscopic spheres of silicate and magnetite in the soil, consistent with an object that vaporised in the air.
Tunguska is the largest impact event in recorded history, and it happened over one of the emptiest places on the planet. Had it arrived a few hours later, the same object would have met a populated part of Europe or Asia. That thought is why the date is now marked as Asteroid Day, and why the study of near Earth objects is treated as a practical matter rather than an astronomical curiosity.