Duck and Cover

I saw on an online news site--for politeness' sake, it shall go unnamed--that some respectable folks in academia have resumed lobbing ideas back and forth for what to do in the event that a cataclysmic piece of cosmic debris should happen to be on a collision course with our beloved home planet. Well, let me just say that I had a wonderful, riotous laugh at their expense and began hunting through my bookshelves for the nuts and bolts that would justify my laughter. The search did not take long.

The plain truth, folks, is that if a cosmic rock decides to smack into us, we won't be able to do anything but wring our hands. Crying shame, isn't it?

I should give some background information to start with. You see, impacts of these extraterrestrial projectiles are actually quite frequent--and, as it happens, typically unnoticed by all the crowds of us who are too deeply engaged in contemplating our next trip to the drugstore to care. As a matter of fact, the very idea that these impacts should occur has only relatively recently ascended from the level of Chicken Little absurdity. As late as 1807, none other than the illustrious Thomas Jefferson said, "I would find it easier to believe that two Yankee professors would lie than that rocks should fall from the sky."

Why two Yankee professors? Did Mr. Jefferson already know one that was a liar?

Consider the hard data. In 1990 one of these rocks walloped the Pacific Ocean with the explosive force of the atomic bomb that decimated Nagasaki. In 1947 another one with ten times that strength impacted less than 400 kilometers from Vladivostok. And in 1908, if we accept the recently reached scientific consensus that it was a cometary impact and not the UFO suggested by other quarters, then such a collision occurred in Siberia with a strength of 20 megatons. Forget the atomic bombs of World War II; we've now begun talking about modern ICBM's with multiple thermonuclear warheads.

And by the way, if that last one had waited a few hours, it would have waylaid populated Russia, not the boonies.

Now here's the rub. All three of these fellows were actually pretty darned small. Thanks go to Robert Zubrin for compiling the data in one place (his book, Entering Space), and it is compelling. That first class of impact happens as frequently as once a year; the second, once a decade; and the third, once every 400 years. But we've only gotten up to asteroids about 40 meters in diameter! No, it's nothing to sneeze at, but it's downright tiny compared to a lot of what's hurtling around out there.

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