What are the chances of a huge meteor smashing us flat?

Dear Cecil:

What are the chances of a huge meteor hurtling through space and smashing us flat? What precautions should I, as a concerned citizen, take? What are the authorities doing about it? Answer quickly--I'm worried.

Cecil replies:

Cecil replies:

Larry, man, I gotta tell you. It’s time to lay off the weed. In the first place, meteors don’t smash anything, flat or otherwise. By definition, a meteor is a meteor only when it’s burning itself up. Before it enters the Earth’s atmosphere, the particle is called a meteoroid; ripping through the upper atmosphere at about 40 miles a second, it vaporizes and becomes visible as a meteor, commonly known as a "shooting star." From any one vantage point, five to ten meteors are visible every morning, adding up to about 200,000 visible meteors worldwide each day. The vaporized matter that passes through the atmosphere adds about ten tons daily to the weight of the earth; "micrometeors"–particles about the size of a grain of salt and too small to be seen–account for another 100 tons of acquired mass every day.

So far, no sweat. But every year, about 150 meteors are hardy enough to survive the friction of passing through the atmosphere and actually strike the ground. At that point, they become "meteorites." Most of them are small and do no damage whatsoever–the Earth is a fairly good sized planet, after all, and the chances of a meteorite landing in a populated area are comfortably remote. It’s estimated that a a meteor strike causing 100 or more fatalities could only occur once in 100,000 years, a striking causing more than 1,000 deaths once in every million years.

The largest meteorite ever found checked in at 132,000 pounds; happily, it struck a remote region of southwest Africa in prehistoric times. The biggest meteor crater in the U.S. is near Canyon Diablo in Arizona, measuring about one mile across and 500 feet deep. The Chubb Crater in northern Quebec, now a lake, has a circumference of seven and a half miles, still narrow enough to spare the suburbs had it landed in, say, downtown Chicago. And of course one must acknowledge the hypothesis, as yet unproven, that a giant meteorite strike in prehistoric times brought about the end of the dinosaurs. So what I’m saying is, a giant meteorite is probably nothing to worry about. But it could mean the end of life as we know it.

Sad to say, not one city in a thousand has an adequately staffed Office of Meteorite Preparedness. I suppose I could see them worrying about this in California. But come on, Larry, get tough. After you’ve spent a winter in Chicago, you’ve got to be pretty used to the idea of horrible things falling from the skies.

Send questions to Cecil via cecil@straightdope.com.

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