Monday, November 24, 2008

The great Canadian fireball of 2008

At approximately 5:31 PM local time last Thursday, residents of Edmonton Alberta got a bit of a fright. The skies lit up over much of central Canada as a large fireball streaked across the heavens, flaring and fragmenting, seemingly striking somewhere over the horizon. It startled a number of residents and was inadvertently caught on surveillance cameras at several locations (a google search will reveal a number of these). While it hasn't been definitively identified, it was NOT: A. the lost tool bag from the international space station, or B. a crashing UFO. It was most likely a nickel iron or stony meteorite ranging in size from an orange to a small desk which broke up as it entered the atmosphere The breakup resulted from the overpressure which results from the force exerted on the meteor by air pushed ahead of it that can no longer get out of its way due to its great speed (around 17 kilometers per second) It was an amazing albeit somewhat rare event, which scientists term a bollide, and count yourself lucky if you ever get to see one (a small one at least) I witnessed one in my lifetime, on new years 1973, over central Florida, around 1:30 AM. It was bright, beautiful, and scary, it lit the sky up with pink, white and green light.
The Canadian event when witnessed on video is stunning, and one wonders if this is the effect of a small meteor what would the effect of a larger one, one large enough to strike the surface with considerable force be? I decided to do just that, using the University of Arizona's asteroid impact effects calculator, available online at The object I modelled for my hypothetical hit was a really nasty one, an iron asteroid approximately 2 miles in diameter, coming in at around the typical speed of 17 kilometers per second, and at at a rather steep 45 degree angle and striking the Edmonton metropolitan area.
The results of such an impact are not suprisedly, total destruction.
A fireball of superheated gas and vaporized rock with a diameter of 8 miles would be created, lingering for approximately 16 minutes, and incinerating anyone or anything unlucky enough to be in its general vicinity. when the fireball dissipated,the excavated crater with a diameter of around 40 miles would become visible, completely obliterating Edmonton.
Then I wondered what the effects would be some distance away, Say, Seattle Washington, around 500 miles away from the impact. Again, even at some distance, the level of destruction is almost surreal. Around 3 minutes after the impact in Canada, the people of Seattle would experience a magnitude 9.4 earthquake, the seismic shock wave caused by the impact ( the fault induced great San Fransisco Earthquake of 1906 was estimated at 7.8) causing severe structural damage all buildings . Around 8 minutes after the impact, material ejected by the formation of the crater would start to rain from the sky, most probably semi molten fragments of rock and dust , which would start numerous fires. As the before mentioned earthquake would probably destroy most plumbing,and thus water pipes, the fires would be difficult if not impossible to extinguish. 45 minutes after the impact, the air blast would hit, with a hurricane level wind velocity of around 200 mph, blowing down 90 percent of the trees, shattering windows and knocking down whatever buildings left standing. The sound of the impact from 500 miles away would be around 93 decibels . Loss of life would be great. It would be the most catastrophic event in human history. And this level of destruction would extend out in all directions for thousands of miles, as the seismic wave and ejecta propagate out from the impact point.
How likely is this to happen? A 2 mile asteroid striking our planet is fortunately a very rare event, happening on the order of tens of millions of years.But it has occurred throughout the history of our planet and will continue to do so The number of people worldwide searching for these objects is the same as the crew of one McDonald's restaurant, and the amount of money allocated for searching is minuscule. But it is a threat, and if it does happen, the only hope we would have of averting it is to get as much warning time as possible, if the asteroid is detected early enough, we might have decades to react, and there that could be developed that could theoretically deflect an asteroid from its path (blowing it up would only turn it from one impact into multiple ones) Hopefully we will see more money thrown at detection in the future. And hopefully we will get more warning time then the Canadians did on Thursday.

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