Yesterday, February 15, 2013, a meteorite flashed over a city in Siberia and exploded. No one was killed, but over a thousand people were injured. That was bad. The scary videos (collected in this New York Times piece) attest to the power of the explosion, which according to another Times piece may have been 20 times more powerful than the nuclear bomb that destroyed Hiroshima (or even more). But it could have been worse. That meteorite may have weighed around 7000 tons. Meanwhile a far larger piece of space rock, known to its friends as 2012 DA14 and weighing an estimated 195,000 metric tons, according to Wikipedia, whizzed by Earth on the same day, about 17,000 miles from the surface -- closer than some of our own satellites.
We know that a serious satellite hit would be a disaster. The dinosaurs may have died from one, and so could we. So the question is, do we try to do something to forestall the end of (our) world?
One answer might be that there simply is nothing we can do. But that isn't true. We're already tracking a lot of stuff flying by us in space. (The Times reports that we have "cataloged 95 percent of near-Earth asteroids 0.6 miles wide or wider, but fewer of the smaller ones." We didn't see the Siberian one coming -- it was much smaller and, as the Times story also notes, it couldn't be seen because it was approaching "from the dayside," so that the light of the sun overwhelmed it.) We could, potentially, figure out ways to block objects that are on their way towards us. Doing so wouldn't be easy, and today might not even be possible, but the basic idea -- push the stuff away before it gets too near us -- seems straightforward enough. Or we could hedge our species-wide bets, by creating colonies off the earth -- in earth orbit, on the Moon, or even further out. Even more expensive, of course, but again by no means beyond imagining.
But should we spend even one penny on these efforts? That's an interesting issue. The chances that human civilization, or the human race, will be extinguished by an asteroid strike are extremely small. Not zero, but extremely small. The chance that human beings will die of treatable diseases, or of starvation, or of criminal or military action, are all far greater, in fact all of these are certainties. Apparently yesterday's Siberian explosion was unprecedented because it actually caused many injuries; meteors enter our atmosphere all the time, some of them as big as a car, and normally do no harm at all. So it would certainly make sense to say that any resources we have for improving the lot of humanity should go to dealing with the ills of our own world rather than the perils outside it.
And yet I do think we should make an effort to prevent the end of the world. The likelihood is very, very low; but the stakes are very, very high. As a matter of sheer mathematics, any possibility of a harm of infinite magnitude (I think from our point of view our own extinction would qualify as of infinite magnitude) would amount to a significant matter, the kind of thing one shouldn't ignore.
I don't mean to say that we should treat the end of the world as nigh. A tiny risk of disaster is nothing like as big a problem as an imminent likelihood of merely very bad conditions. So we should absolutely not make this danger a top priority, and instead should continue the modest, pragmatic task of attending to life in the here and now. But not without an eye -- and some concrete work -- directed to outer space.