This Day in Scientific History (Mysterious Cosmic Body Explodes in Siberia)

June 30, 1908—In central Siberia, shortly after 7 a.m., a comet or asteroid entered Earth’s atmosphere and exploded between five and 10 kilometers above ground, devastating an entire forest and leaving behind a century-old mystery that haunts scientists to this day.

Why should the so-called “Tunguska explosion”—an event that happened in the middle of nowhere, practically—concern us? Because similar past disturbances in the atmosphere have had major effects on the evolution of the world, scientists say. Moreover, because the fireball flew through the atmosphere in a largely unpopulated region, the world lucked out then. We might not be so fortunate next time—and, according to the best calculations, “next time” might not be all that far off.

I learned about this event in the June 2008 issue of Scientific American, a magazine that, when I had to read it for some projects in my high school biology class with Larry Chinnock in St. Cecilia High School, really made my eyes glaze over. Something must have happened in the intervening years, though, because the articles made more sense to me. My guess is that they simplified it for the likes of me. (I did, after all, pick this up at a newsstand.) You won’t be able to read the full text online, but even this excerpt, I believe, will be enough to make you want to read the whole thing.

The atmospheric disturbance registered the largest impact of a cosmic body to occur on the Earth during modern history, according to the article. What was it like to experience this extraordinary event? According to one Russian eyewitness, at the closest human habitation, a trading station:

"I was sitting on the porch of the house at the trading station, looking north. Suddenly in the north...the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire. I felt a great heat, as if my shirt had caught fire... At that moment there was a bang in the sky, and a mighty crash... I was thrown twenty feet from the porch and lost consciousness for a moment.... The crash was followed by a noise like stones falling from the sky, or guns firing. The earth trembled.... At the moment when the sky opened, a hot wind, as if from a cannon, blew past the huts from the north. It damaged the onion plants. Later, we found that many panes in the windows had been blown out and the iron hasp in the barn door had been broken."

Far away, even in lands as distant as Britain, the effects could be felt:

* Instruments recorded seismic vibrations as much as 1,000 km (600 miles) away.

* Closer, around 60 km away, observers were thrown to the ground or knocked unconscious.

* The closest human observers (if they could be called “observers”—maybe were asleep in their tents at the time) were reindeer herders, some of whom were blown into air and knocked unconscious. At lease one man died.

* Londoners could see a pink, phosphorescent night sky.

* An Israeli scientist estimated in 1975 that the explosion was between 10 and 15 megatons in magnitude—the equivalent of 1,000 Hiroshima atomic bombs.

Believe it or not, it was 19 years before the authorities could mount a serious scientific investigation into what happened. The lapse is unfortunate, but a bit more understandable when one considers what was happening in Russia during those years. For the first nine years, the country was wracked by internal unrest, mobilization for WWI, then the Russian Revolution. Then after 1917 came invasion by Russia’s former Western partners in WWI, civil war, and the beginning of the “dictatorship of the proletariat.”

The authors of the Scientific American article will be conducting further investigations into the origins of the disturbance this year. By better understanding what kind of event this was, they hope to be better prepared the next time it happens—which could be within our lifetime.