Saturday, January 09, 2010

The Tunguska Event

The morning of June 30, 1908, dawned crisp and clear at the tiny village of Vanavara, deep in the Siberian wilderness. Situated on the apex of an acute northern bend of the Stony Tunguska River, Vanavara was a muddy little trading post for natives and Russian settlers in the remote, forested region.

Vanavara on the shores of the Stony Tunguska River

Already a week into summer, it was mild in the tundra region of Vanavara that morning, and Semen Semenov, a local farmer, stood outside his cabin preparing for the days’ work. Though only a few minutes past 7 o’clock, the sun was already arcing into the dome of the sky; late June sunrise in that northern latitude would have been around 3:45 a.m.

As he stood in the lee of his little ramshackle dwelling, he suddenly saw an immense bright light split the sky to the north.

An artist's rendition

As he watched in horror, he saw fire billowing up above the trees in the distance, and within seconds he was knocked down by a wind so hot that it seemed to flay his skin. It felt as though his very clothes were on fire.

Struggling to regain his feet, he began to hear thunderclaps like an artillery barrage. He instinctively covered his head, the superheated furnace blast of wind still whipping around him like the breath of hell.

His wife came staggering out of their little cabin, reaching for him to drag him inside as a sound like fifty freight trains roared down from the distant taiga. The ground shook like an earthquake and the flames billowed higher and higher into the northern sky, turning the forested landscape into an inferno.

* * *

What Semenov and countless other eyewitnesses experienced in the hinterlands of central Siberia that day has baffled scientists for over a century. Semenov’s story is even more amazing when you learn that he was not at the epicenter of the explosion; the village of Vanavara was roughly forty miles away.

As with any major event, the eyewitness accounts vary dramatically, but a general sense of what happened can be pieced together from their stories. Around 7:15 a.m. local time, a massive fireball – as bright as the sun, certainly too bright to look at directly – streaked through the cloudless sky trailing an enormous cylinder of smoke behind it. It seemed to crash into the earth where it set the horizon on fire. Rushing hot wind tore across the landscape, and numerous eyewitnesses described the accompanying sounds the same way Semen Semenov did – like an artillery barrage. Not just a single explosion, but a series of explosions. The explosions caused an earthquake that registered 5.0 on the Richter scale. The subsequent cloud of dust and debris rose so high into the atmosphere that it created a phenomenon known as “bright nights” all across Europe. For several nights subsequent to the blast, cities as far away as London reported such brightness levels at night that one could stand outside and read a book. This phenomenon is caused by the divergent rays of the sun – coming from the other side of the globe – reflecting off dust high in the atmosphere.

Odd as it seems, no scientist – even in Russia – seems to have taken much of an interest in this singular event. It occurred in a deeply rural area of Russia many hundreds of miles from civilization; in fact, the area was so sparsely populated, there were no known fatalities from the blast. Furthermore, the region was inhabited mostly by native Evenki people, and the Tsarist government of St. Petersburg was not particularly concerned about the plight of natives on the backwater tundra of its empire.

It seems to have created somewhat of a stir for several weeks throughout Europe, then it was mostly forgotten.

It was not until the 1920’s, after the Russian Revolution and the fall of the empire, that the first scientists began to legitimately study the Tunguska Event.

These first scientists found the locals in Tunguska highly superstitious about the area, refusing even to guide them to the epicenter for fear of godly wrath. Scientists, however, did eventually find their way to the epicenter, and what they found there shocked them.

It had long been assumed that the explosion was caused by a crashing meteor. Based on eyewitness testimony and newspaper accounts, that seemed to make the most sense.

Yet there was no crater at the epicenter site.

Indeed, no crater has ever been found to this day. Instead, scientists found only miles of mown down trees, splayed out around the center in a butterfly pattern covering over 800 square miles.

Photograph taken in the 1920's

Paradoxically, many of the trees near ground zero were still standing, stripped of bark and foliage and burnt black. How could a meteor create a blast zone of over 800 square miles, have enough force to knock people to the ground forty miles away, set off an earthquake that measured 5.0 on the Richter scale, and create a dust cloud that lit up cities some four thousand miles away, yet leave no visible crater and even leave trees standing upright in the vicinity of the epicenter itself?

By the 1940’s and the dawn of the nuclear age, scientists began to take note of the similarities between the blast pattern of the Tunguska Event and the blast pattern created by nuclear tests. One researcher during that time went so far as to speculate that a nuclear-powered spacecraft from Mars had crashed there in the Siberian tundra.

Researchers eventually concluded that the explosion was equal to roughly 15 megatons of TNT – or about 1000 times more powerful than the nuclear explosions that destroyed Nagasaki and Hiroshima. Furthermore, it happened, like a nuclear explosion, in midair – roughly 5 miles above the earth’s surface.

But what was it?

Modern scientists believe that the Tunguska Event was caused by a “low-density asteroid.” This is a fancy way of saying that it was sort of a mix between an asteroid and a comet. An asteroid differs from a meteor in that a meteor is space debris, usually metallic, left over from the formation of the galaxy, while an asteroid is a piece of rock from a larger, planetoid body. A comet, on the other hand, is made up of ice and various gasses and may have a rocky core.

The asteroid hit the earth’s atmosphere at a very low angle of deflection. This is the reason why it didn’t detonate on contact with the atmosphere, as most space rocks do. It skimmed through like a stone on a pond. Speeding through the upper atmosphere, the asteroid’s shape caused an enormous amount of drag against its surface, heating it into a virtual fireball. Because of the low density composition of the asteroid, it was unable to withstand this immense heat and exploded. The “artillery barrage” reported by so many eyewitnesses indicates that not just one, but many explosions occurred, breaking the asteroid up into virtual dust before it impacted the surface of the earth. Roughly the size of a small office building, the midair explosion caused a blast pattern not unlike what is seen with a nuclear detonation – the pressure from above is exerted equally on the surfaces of the trees directly below the blast, leaving many of them standing upright. But as the blast radiates outward, trees farther away from the epicenter are knocked down like matchsticks. In the case of Tunguska, an estimated 80 million trees were felled by the blast.

The most disturbing aspect of this event, of course, is its intensity. The Tunguska Event, in fact, is the most intense earth impact by an extraterrestrial body in all of known human history. Had it occurred above a major metropolitan area, millions of lives would have been lost. Most of the earth’s surface, of course, is water, and even most of earth’s land surface is not densely populated like an urban area. Still, a Tunguska-like event over Chicago, for instance, would level every structure and kill every living thing in a 35-mile radius.

Modern observatories, of course, monitor near-earth objects in an effort to stay ahead of the curve and identify any potential city-killers like the Tunguska asteroid, or even planet-killers like the meteor that helped put an end to the dinosaurs.

But it’s hard not to wonder if one might not slip through the cracks. Indeed, is there any reason to suppose that in all the vastness of space, we would manage to get a glimpse of an approaching mega-meteor before it hit?

The epicenter of the Tunguska Event as it looks today


Luna said...

Don't try to confuse me with your SCIENCE and so-called ASTRONOMY! I know signs of an alien invasion cover up when I see them!

But seriously, now I have another thing to worry about! Sheesh!

Scott said...

Maybe Nicky II had a nuclear program way earlier than anyone else, but his science and research was all lost in 1917, thus putting off the Cuban Missile Crisis for an extra 40 years. :)

Seriously though, you'd be surprised, probably, to discover that meteors cause Hiroshima-sized explosions about once a year or so in the atmosphere. They happen high up because the meteors typically hit the atmosphere directly. It takes a really oblique angle for a meteor to actually get through the atmosphere, and even then it would have to be quite large in order to not burn up before getting down low to the earth to make any difference or even be visible.

Of course, Tunguska was 1000 times stronger than Hiroshima. But even a Tunguska-sized impact occurs every few hundred years. But again, they don't typically make it through the atmosphere like at Tunguska. Meteor Crater, Arizona, however, was a Tungusaka-sized meteor that actually hit the earth. But it happened, of course, 40,000 years ago.

You also have to remember that the earth is really, really big relative to you and your particular geographic region. Even if a Tunguska-sized asteroid made it through the atmosphere and hit the earth every single year, it would probably take hundreds of years before one actually hit a highly-populated area - just going by the immense size of the earth and the fact that most of the earth is water and most of the earth's population is packed into a tiny percentage of the earth's total landmass.

Now, something like the Mt. Everest-sized meteor that hit the Yucatan 65 million years ago...yeah, that would probably wipe us all out, more or less.

moses said...

Thanx Scott. You should be an astronomer.

Scott said...

Thanks for reading Moses.

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