Scientists didn't visit the site until 19 years later and when they finally did they found utter devastation.
Astonishingly, one eyewitness to the cataclysm still survives.GRIGORY VERKHOTUROV, now 96, remembers the day that the fire came by. "Everything shook. There was a flash, a roar. The sun went in. We ran to a neighbour's house. Everyone was just sitting there. People came round to ask what had happened. Where had it come from? No one knew."
Today, the scientists know a little more about The Day The Earth Got Hit. They believe an object penetrated the Earth's atmosphere from outer space, blowing up about 6 kilometres above the ground with a force of 15 megatons, many times greater than the nuclear bomb dropped on Hiroshima. But what that object was exactly remains a mystery.
Now every summer a team of Russian scientists struggles to reach Tunguska, one of the remotest places on earth, in the hope of solving that mystery. Their mission is vital and urgent - for any information on cosmic impact could help save this planet from destruction. The expedition's goal lies deep in the trackless forests of Siberia, on the banks of the Tunguska River, 2000 miles from Moscow and two-and-a-half days' walk from the nearest settlement, the tiny trading post of Vanovara. Equinox joined the scientists on their latest trek - the first western documentary team allowed into one of the former Soviet Union's most secret areas.
Countless questions remain about the impact and there are many rival theories about what the object from outer space consisted of. What was it? The stone or iron core from an asteroid? The nucleus of a comet? Or something in between, perhaps a stray fragment from a meteorite shower that regularly orbits the earth?
The race is now on to find the answers. Scientists have realised that the Tunguska explosion is the latest of a series of collisions between the Earth and objects from outer space. "It's the only thing we can point to and say directly where a large object struck the Earth," says Dr DAVID MORRISON of NASA. "Indeed, if it hadn't been for Tunguska, we might not be aware today that there's an impact hazard at all."
Astronomer DUNCAN STEEL believes knowing exactly what happened at Tunguska will help mankind decide what to do when - as it inevitably will, perhaps today, perhaps in 300 years time - another object takes aim at our planet.
"We need to understand what happened there," he says. "Was it an asteroid? Was it a comet? How fast was it coming in? How did it detonate? What debris did it leave behind if any? And we need to do that in order to build up a total understanding of the cosmic shooting gallery which the earth happens to move through."
At Tunguska itself, Equinox follows an investigation that began as long ago as 1927, when a pioneering meteorite expert, LEONID KULIK, first reached the area. His expedition, brought to life in the programme through archive film, searched for fragments of the object but found nothing. Today, the hunt continues, with the Russian scientists meticulously combing through samples of peat from the bog at the explosion's epicentre. Others continue to map the strange butterfly-shaped pattern of the fallen trees in the hope of establishing the size of the explosion with greater precision. And a geneticist is examining strange anomalies in the plant life of the blast area.
In the West, astronomers and NASA experts have begun their own Tunguska research programmes, among them ballistics expert MARK BOSLOUGH of Sandia Laboratories in New Mexico. Using one of the world's most powerful computers, he has simulated this extraordinary event with surprising results. The scientists, he suggests, have been searching for the fragments of the cosmic invader in the wrong place. The answer may lie hundreds of miles away beneath the waters of Lake Baikal, the world's deepest freshwater lake.
And in California, perhaps the greatest of all explosion experts keenly awaits results, in the hope that news from this remotest of places on the surface of the Earth may help avert a far greater cataclysm in a more populated place sometime in the future. DR EDWARD TELLER, 'father' of the H bomb, hopes that mankind will be better prepared the next time the planet is hit:
"And I think that whenever it should occur," he says, "whether it is ten people in the middle of Siberia or a hundred thousand people in a city or a hundred million people on a continent or the whole human race, we should do what we can to prevent it."
Prod/Dir: Stephen White
Prod: Armorer Wason
Exec Prod: Simon Welfare
Prod Co: Granite Produtions
Reviewed by Benny J. Peiser