Sunday, April 6, 2008

Asteroids will kill us all!

Well, not really, I suppose. A new article in the journal Icarus describes how we might attempt to deflect near earth asteroids if they were on a collision course with Earth (purchase required).

There is a pretty good write up of the article at Ars Technica, which is free-er to read than the actual journal article (that is to say, it is free).

It is comforting to report that the basic gist of the article is that it is possible to save ourselves from a collision if we were watching the asteroids sufficiently far in advance to be able to deflect them decades before their actual collision with the Earth. At that point, we could apply a relatively small amount of force in order to knock the asteroid off its intercept course (that sounds Star Trekkie).

This brings up a good point, brought up by a friend a few years ago, when he attended a lecture about the statistics of destruction, and found that chances of dying by asteroid impact (1 in 20K) were higher than dying by tornados (1 in 60K). Since my home town just had horrible twisters late last week and my family spent the night in the hallway, this is especially timely for me. You are probably thinking, "how could dying by asteroid impact be common? I've never met anyone who's died by asteroid, but I know people die in tornadoes."

Well, it comes down to statistics, and the amount of destruction that an asteroid can inflict. Let's take easy numbers, and take a look. We know from geological evidence about how often large meteors hit the earth. There was a meteor in Russia in 1908 that knocked trees down in an 800 square mile area. Let's assume that one of these events happens every 100 years and can kill 50% of the inhabitants in a city. Let's also assume that for the next 1000 years cities will average about 10% of the land coverage in the world, and that over the next 1000 years the average size of a city will be 10 million people. So, over the next millennium, 10 large-ish meteors will hit the Earth, 70% will fall in the ocean, and 30% will hit the land. Of the 30% that hit the land, 3% will hit cities (because cities cover 10% of land). The 3% meteors will kill 50% of 10 million, so 150K on average over the 1000 years. This contrasts the 50 people per year who are killed by tornadoes, which would only mean 50K deaths from tornadoes over 1000 years. All of this should make asteroids scarier than tornadoes, but in this situation we don't really fear the unknown asteroids, we fear the tornadoes.

My numbers of course are all rough estimations, but it shows how important the work is to attempt to safeguard humanity against meteors. The tens of meter sized objects (like in Russia), are not really all that concerning (unless you are caught underneath it), but the hundreds of meter sized objects are. We might not get a second chance after something like that.

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