Wednesday, December 19, 2007

Asteroid Threats to our Planet


Whether you call it the Big One, the Great Exterminator, Lucifer's Hammer, or Extinction Level Event -- there's much to be said about big chunks of space rock slamming into the earth. One thing's for sure, however. It happened so many times before, that it's only likely it will happen again...

It all comes about within moments. Suddenly, there's a big, fiery ball in the sky, just for a few seconds. And then: impact.

The atmosphere will be on fire. A huge column of fire and debris towers up miles into the sky. Hundreds of thousands die instantaneously. For thousands of miles around, everyone outdoors is incinerated. People nearby simply evaporate.

The impact sends out a shockwave around the globe, just like a stone thrown into a pool makes a circle of waves. But this wave rolls through the Earth's crust itself, causing death and destruction everywhere. There are massive earthquakes. Huge tsunamis. Volcanoes popping open. Millions die, cities are shaken into oblivion. On the opposite side of our planet, the waves of destruction slam into each other again, causing the earth's crust to tower up, forming a massive mountain-ridge within seconds.

And that's just the beginning. As the tremor and the seas calm down and the fires extinguish, there's more to deal with: the huge, black cloud of debris that's thrown up into the stratosphere from the impact site. The debris spreads through the stratosphere, covering the Earth with a thick blanket of burnt carbon, dust and debris. The Sun is blackened.For months or even years to come, the world is covered in darkness, the Sun being no more than a vague blot of light in the pitch-black sky. Temperatures drop about twenty to forty or even fifty degrees everywhere. The Earth's surface freezes. Plants cannot produce oxygen anymore by photosynthesis and die. Animals relying on the plants die too. And we -- relying on both the animals and the plants -- are in BIG trouble.

Oh, there are a few pockets of people still hanging on. They're hiding in bunkers, or in caves. They hold on for years, as long as their supply of tin cans lasts. But when they return to the surface after the endless winter night, they find their planet is turned into a barren, lifeless sheet of land, with only some deserted ruins reminding of what once was.

Sure: in the end, the Sun returns and temperatures start rising again. So there may be a new beginning for mankind after all? Think again. The odds run against such optimism. The only thing alive is bacteria and mosses and -- if we're lucky -- some insects, rodents and fish. With luck, civilization is `only' thrown back into the Stone Age. More likely however is that humanity becomes extinct.

A Brief History of Meteors Going Whammo

Oddly, until twenty years ago, no one took meteors quite serious. It was widely believed that those mean clumps of rock and ice that zoom across the galaxy are not a real threat to our planet. A comet entering our atmosphere would instantly burn up, and that would be it.
All that changed in 1978, when two paleobiologists, Louis and Walter Avarez, went to Italy to study the so-called K/T barrier: the transition between the Cretaceous period (the age of the dinosaurs) and the next prehistoric era, the Tertiary period. The K/T Barrier had always been a big mystery. Within only several thousands of years -- a twinkling of an eye, in geological terms -- all the dinosaurs suddenly vanished and nature switched from one geological period to the next.

Digging around in the Apennine Mountains, father and son Avarez suddenly realized something extraordinary must have happened. Everywhere on Earth, the K/T Barrier is marked by a tiny layer of iridium in the ground -- `iridium' being a rare chemical substance mostly found in meteorites. It began to dawn on Louis and Walter that the dinosaurs didn't just die out because of some evolutionary reason. The dinosaurs were simply squashed by a huge meteorite!

The killer meteorite must have slammed into our planet 65 million years ago. It must have been an event much like the one described above. There was a long, mean period of darkness, while it rained iridium all over the world. Life on our planet was almost completely wiped out. All plants and animals bigger than a blade of grass became extinct. Just picture that! No wonder the Avarezes coined the killer meteor `The Great Exterminator'.

For the decade to come, the Exterminator theory was highly controversial. If a meteor big enough to kill all the dinosaurs really went boom on our planet, surely you should notice an impact crater somewhere? Then, in 1991, Nasa sattelites indeed spotted the crater.

It was a huge scar known as the `Cenote Ring', underneath the Mexican peninsula of Yucatan, almost impossible to detect by the eye because of millions of years of erosion and tectonic movement. Judging by the size of the impact crater, scientists calculated the Great Exterminator must have had the size of a mountain.

It hammered the world of those poor dinosaurs with the impact force of about 100 million megaton of TNT. That's the equivalent of 5,000,000,000 atomic bombs! By now, some people really started to get itchy about meteors.

Next came the impact of the comet Shoemaker-Levy 9 on Jupiter. For the first time in history, man could see what actually happens when a colossal comet starts to mess around with your planet. In July 1994, the meteor slammed into Jupiter's atmosphere, snapped into pieces, and bombarded the planet for days. Huge balls of fire and dust rose up from the planet's surface, and the debris darkened parts of Jupiter's atmosphere for weeks.

The biggest impact crater, carved out by the piece of meteor known as Hale-Bopp, had a size no smaller than the entire Earth! By now, everyone realized that the danger of a meteor suddenly ending your world is as real as can be. It could happen next year, or next month. And well, it could also happen tomorrow.

From those days on, attention for meteors grew and grew. Were the dinosaurs just unfortunate? The troublesome answer is a loud and clear `no'. As a matter of fact, the meteor that killed the dino's wasn't the first big piece of rock hitting our planet -- and not even the biggest, scientists began to realize.

For instance, just over 4,5 billion years ago, when our planet was still very young, an enormous body hit Earth with such unimaginable force our planet literally broke up. A huge piece of Earth was launched into space. You can still see that lump of earth when you look out of your window: the debris rolled up into a ball, and is what we today call the Moon.

The next massive space attack came a half billion years later: our planet was bombarded so heavily with asteroids that the entire crust actually melted. That would explain why the oldest rocks on Earth are only 3,9 billion years old, while the planet itself is five billion years old.

And then there was another apocalyptic event, some 590 million years ago. One day, a meteorite of incredible proportions slammed hard into what's now South Australia, digging a crater about four kilometers deep and some 40 kilometers wide (currently known as Lake Acraman). Within seconds the whole thing vaporized into a huge firestorm. The impact was so devastating, it must have created massive earthquakes and 100-meter high tsunamis even hundreds of kilometers away. Oh boy!

Actually, it literally rained Big One's on our little planet. As recently as January 2002, geologists discovered a huge impact crater out of the Australian coast: no less than 120 kilometers wide. The meteor that carved out the crater slammed into our planet 360 million years ago, wiping out 85 percent of all species.

And in 2001, Norwegian researchers suddenly realized that their coast had once been the scene of a similar event. A huge meteor went kaboom over Norway 150 million years ago - speaking in geological terms, right before the Great Exterminator. The explosion slammed a 40-kilometer wide bump in the seabed of the Barents Sea, the so-called `Mjoelnir Crater'. Researchers still wonder how it was possible that anything survived.

Oh, and even when humanity was around, the meteors kept hitting us. For example, according to some researchers, the legendary floods of Deucalion, the Sumerian Gilgamesh-epos and the biblical Deluge may very well have been caused by a big comet plunging into sea somewhere.

More recent, in the year 1490 A.D., the city of Ch'ing Yang in Central China was the scene of a weird disaster. The event was recorded in at least ten ancient textbooks, all claiming that the event killed many thousands of people as it `rained stones and fire'. Likely cause: an asteroid as big as a modest sky scraper, going kaboom high up in the Earth's atmosphere.

On June 30th of 1908, a loud explosion shook the village of Tunguska in Middle-Siberia. Local inhabitants saw a huge blast of fire in the sky. There was a sudden temperature rise, and a blazing forest fire, lighting up the horizon. No less than two thousand square miles of forest were devastated. As we know now, a twelve story building sized piece of rock hit the atmosphere over Siberia and exploded at a height of some eight kilometers. The energy set free at the event was equivalent to 15 megatons of TNT -- a thousand atomic bombs!

So, it's no pessimistic estimate that our planet can bounce into a freaky piece of space rock again. Cosmologists estimate an extinction type comet hits the earth once every 20 million years. The odds for a smaller, Tunguska-type impact are much higher. On average, this kind of thing happens once in every 300 years.

Of course, the effect of a meteor impact depends on the place where it hits the Earth. The meteor that killed the dinosaurs, for example, hit a soil loaded with sulfuric rock, which enormously boosted the comet's devastating effect. Had it hit the planet several hundreds of miles westwards, it would have plunged into the ocean -- and the dinosaurs probably would have survived.

On the other hand, if a Tunguska-type meteor happens to hit an inhabited area, it will definitely wipe it off the face of the Earth entirely. Considering that some 10 percent of our planet is inhabited, you could assume that once in every 3,000 years a meteorite will destroy an inhabited area.

Meanwhile, the people at Nasa try to reassure us, by claiming they keep an open eye to the sky. The message they propagate is that a meteor that wants to hit our planet surely will be spotted in time and destroyed -- whether it is by a nuclear bomb or by a team of Bruce Willis-like he-men going out in a space shuttle.

No offense -- but that's pure propaganda. The harsh fact is that such `protection' is far less reliable than Nasa wants us to believe. For example, in March 1998, a BIG comet nearly hit us. Remarkably, no one saw it coming. Because it came straight at us, the thing was only visible as a tiny speck in the sky, not as a distinct, moving object traversing the cosmos from left to right. Consequently, no one noticed it -- until it passed.

(Meteor Size) (Impact Force) (Destruction) (Chance)
(50m) (15 Megaton of TNT) (City sized) (1:300)
(200m) (100 Mt TNT) (Continent sized)
(1,000m) (100,000 Mt TNT) (Half of the world) (1:2,000,000)
(10,000m) (100,000,000 Mt TNT) (Extinction level event) (1:30,000,000)

The Norwegian meteor was 2 Kilometers across; the meteor that carved out Lake Acraman in Australia 4 Kilometers, and the comet that killed the dinosaurs 10 Kilometers. The impact force also depends on the velocity of the object, which ranges roughly from 50,000 to 100,000 Kilometers per hour.

Then there's the eerie problem of ice comets. Many comets are in fact `dirty snowballs' made of dust and ice. The problem is we cannot really detect these comets, because conventional equipment sees right through them. You can only spot an ice comet when it comes so close to the Sun that it begins to melt. We'll recognize it by its tail by then. But according to many critical astronomers, this will be much too late to take any action.

Besides, there are no reliable ways of getting rid of a comet racing at us. Pleas for a kind of `space shield' protecting us from big pieces of rock have not yet raised any political backing. And it is doubtful whether Bruce Willis is willing to go out to kill the Big One if it's coming.

Oh, and talking about Big One's: in 2039, another HUGE comet will pass us by `only' some millions of Kilometers. However, this estimate is not completely fireproof, for one thing because comets are very sensitive to variations in their trajectory.

Here's what to do. Put on your best helmet -- and keep your fingers crossed.

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