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Severity Of Asteroid Impact

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Posted by Malcolm McPherson/">Malcolm McPherson on December 10, 1999 11:09:26 UTC

Hi there, People-Who-Know-Stuff

There are a number of things that often puzzle me when I watch documentaries about the effects of asteroid/comet impact on earth. Perhaps someone out there can put me out of my misery on a couple of them. Here goes. (I hope by maths is right)

How could the impact of something so miniscule as an asteroid have such a profound global effect on the biosphere of the earth? An iron-rich asteroid that is one kilometer square (which is bigger than anyone ever talks about) would have a mass of around 6 x 10e12 kg (six trillion kilograms). The earth weighs 6 x 10e24 kg. The ratio of mass of asteroid to mass of earth would therefore be 10e-12, i.e. a ratio of one to one trillion, which seems negligible to me. To put that in perspective by scaling it down to human size, it would be like a 10e-7 gram object (one ten-millionth of a gram) hitting a 10e2 kg (100 kilogram)person, scarcely be a devastating event, one would think. The only reason I can think of is that the damage results from the "ve2" component of the equation KE=1/2mve2, meaning that the (destructive) energy released is proportional to the velocity SQUARED of the object, which would be pretty monumental for an asteroid (~ n x 10e8 meters per second squared). Is this reasoning correct?

On a related topic, by what mechanism would the whole planet be plunged into darkness "in a matter of hours" and stay that way for weeks or months, following a major impact? The rotation of the earth might spread suspended particules latitudinally in a matter of days, given that there was enough suspended material in the first place, but by what mechanism would it spread longitudinally, i.e. from pole to pole? And why wouldn't the particulate matter settle quicker, i.e. in a matter of hours or days, from the atmosphere (like dust from a dust storm)? How high would the impact plume reach?

I guess that's enough for today from the list of things that puzzle me about impact.


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