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imported_Morpheus · #7 (**permalink**) 26-October-2003, 05:39 PM

On Aug. 6, 1945, an atomic bomb was dropped on Hiroshima with an estimated equivalent explosive force of 12,500 tons of TNT. This bomb killed in the region of 200,000 people and decimated the surrounding area.

In June 2002, scientists were caught unaware when an asteroid measuring about 300 ft across hurtled past Earth at a distance of only 75,000 mi—less than a third of the distance to the Moon. The asteroid, which was provisionally named 2002 MN, was only discovered three days after its closest approach. It is the sixth known asteroid to pass within the Moon's orbit.

Think about the above two paragraphs.

At about 7:17am on June 30th 1908 a meteor about 200 feet across travelling at a speed of about 10-20 miles per second entered the atmosphere above the Tunguska River region in Siberia. It produced a brilliant fireball in the sky that set the forest on fire and even burned the shirts off peoples backs. When it reached an altitude of about 5 miles it exploded into billions of smaller fragments that burned up in the atmosphere. This meteor exploded with the force of between 10 and 20 megatons of TNT. This is a blast about 1,000 times greater than that expereinced at Hiroshima. Trees burst into flame over an area of about 1,000 sqaure miles around the epicentre, people and houses many miles away were carried away in the blast wave, the jolt was measured on seisometers in Britain and the atmospheric shock wave circled the Earth twice before it was spent.

Can you imagine the devastation if the above meteor had exploded over a densley populated region of the planet ? Utter chaos would reign. Countries and governments would fall.

Now bear in mind that we have no way of tracking all the lumps of rock that hurtle about the Solar System, and certainly could not be expected to spot a lump about the size of that which exploded over Tunguska.

Now imagine that by some chance a lump of rock about 400ft across was spotted on a collision course with Earth. Chances are that we would not spot this rock more than a few days before impact. What would the government do ? Most governments would resist any idea that the rock would hit, they would expect the scientific community to produce absolute proof that it would impact before they would take any action. Unfortunately, the scietific community is such that for every scientist who agrees with a theory, you can usually find one who disagrees. Therfore you could never expect to convince a government in time to avoid disaster, especially as the government would probably not want to beleive it anyway, and would therfore be more likely to follow the advice of those who say it will miss. Even if the impact was plotted to be in an industrialised modern country, no government is about to evacuate an area the size of which would be required (several thousand square miles) in only a few days, even if they had the will to do so. One thing is certain. No government, on learning of the coming impact, would alert its population. Why ? Well think about it. No astronomer could give absolute proof that the meteor would strike, and certainly not calculate it's impact site to the level of acuracy required. No government is about to set terror among its populace without that proof. Even if the evacuation could take place, where would the probable hundreds of thoudands of people go ? Rioting and looting would sky rocket, the emergency services would be overwhelmed, the armed forces would be called in to keep the peace. Also, bear in mind that to most people the idea of being hit by a metoer is so fantastical that they would have great difficulty beleiving it, even if their government did tell them. Sadly, it is likely that even if a government did release the information, did mobilise all it's resources to evacuate the vast area required, that human nature is such that most people would not beleive it until it was too late to reach safe distance.
The other side of the coin is what would happen if a government did take action and the meteor then missed. During the process of evacuation it is inevitable that many millions, possibly billions, of pounds would need to be spent. There would be massive damage caused by the fires, vandalism, rioting, looting etc that would undoubtedly accompany a evacuation on the scale required. The final bill would likely run into trillions. That's without even considering the hundreds or thousands of deaths that would be caused by panic. No government is about to risk itself and it's population to this scale for what to many politicians would likely be thought of as a mere chance. The repercussions of such actions would bankrupt a country.

It's these smaller asteroids that hold a greater risk for mankind than the much talked about mega-impacts. The really big rocks we can probably see coming, it is very likely that a rock 1-2 miles wide would be spotted fairly early on by astronomers, especially the amateur ranks. Once it has been discovered anything that big would eventually reflect enough light to be impossible to keep secret. It's the small ones, for which at most we could expect only a few days notice, we could nothing about. It's likely that when the next Tunguska sized meteor hits, we wont know about it until it's too late.