One hundred years ago today, a large object entered the Earth’s atmosphere and exploded over a remote area of Siberia with a force greater than 1,000 Hiroshima A-bombs; if it had happened in a populated region, there could have been millions dead: Fire in the sky: Tunguska at 100.

The cause was an asteroid or comet just a few tens of metres across which detonated 5-10km above the ground, 100 years ago today. Eyewitnesses recalled a brilliant fireball resembling a “flying star” ploughing across the cloudless June sky at an oblique angle.

The plume of hot dust trailing the fireball gave rise to descriptions of a “pillar of fire”, which was quickly replaced by a giant cloud of black smoke rising over the horizon.

“The sky split in two and fire appeared high and wide over the forest. The split in the sky grew larger, and the entire northern side was covered with fire,” one local remembered.

“At that moment I became so hot that I couldn’t bear it, as if my shirt was on fire … I wanted to tear off my shirt and throw it down, but then the sky slammed shut. A strong thump sounded, and I was thrown a few yards.”

This eyewitness was lucky, but an elderly hunter who was much closer to the explosion died after being flung against a tree by the blast. That the airburst did not cause more casualties was in large part due to the remoteness of the area.

The University of Bologna may have identified the impact crater for the object: Tunguska Home Page (Bologna, Italy).