What caused this mid-air explosion over Russia more than 100 years ago?
On the morning of 30 June 1908, the sky split in two over the forest near the Podkamennaya Tunguska River in Siberia and then a mid-air explosion rocked the area.
It had the estimated energy of a 15-megaton bomb – roughly a thousand times more powerful than the atomic bomb dropped on Hiroshima and millions of times more energetic than any of the man-made explosives of the day. The source of this big bang could only be extra-terrestrial.
The Tunguska event, as it later became known, was most likely a large asteroid or comet up to 100 metres (328 feet) in diameter that – going on the lack of an impact crater – exploded in mid-air about ten kilometres (6.2 miles) up. The resulting fireball and shockwave charred 100 square kilometres (38.6 square miles) and knocked 80 million trees flat in an instant.
The Tunguska object was around five times the size of the Apollo meteor that entered Earth’s atmosphere and exploded over Chelyabinsk in February 2013. Objects of this size enter Earth’s atmosphere only once every few centuries and the Tunguska event is one of the largest in recorded history.
Despite the remote location, there were a few witnesses, who spoke of a light as bright as the Sun, followed by an explosive crack, powerful seismic tremors and a brief, unbearable heat. Indeed the scorching temperatures caused most trees to briefly char, but the proceeding shockwave blew out any flames before they could burn.
Get to know your NEOs
What’s the difference between an asteroid, comet, meteor, meteorite and meteoroid?
They’re not just different names for the same thing, but neither are they completely different near-Earth objects (NEOs). Comets are made mostly of rock and ice that boils off in a gas tail close to the Sun. Asteroids, meanwhile, are small, rocky carbonaceous or metallic bodies that orbit the Sun.
A meteoroid is a small fragment of an asteroid or comet orbiting the Sun; a meteor is a meteoroid that enters Earth’s atmosphere and burns up (ie a shooting star); and, lastly, a meteorite is a meteoroid that passes through Earth’s atmosphere and survives, impacting the surface. Statistically, the larger the rock the less likely an encounter with Earth is. Objects as big as, say, the Chicxulub asteroid hit our planet only once every 100 million years or so.