You are not going to die.
A NASA diagram depicting the passage of asteroid 2012 DA14 past the Earth on February 15, 2013. (Credit: NASA/JPL-Caltech) Fear of death is, of course, the most exciting thing about asteroids. But the asteroid known as 2012 DA is not going to hit the Earth tomorrow. Oh, it will pass close—about 17,150 miles away at 2:25PM EST, closer than many of our communications satellites—but the odds of a collision are zero. Zilch. Nada. (As my friend Phil Plait has just pointed out, we also are not going to be hit by a different asteroid in 2106.) We know the orbit of 2012 DA very precisely, so this is one of life's rare sure things. ** But see update below. While we are contemplating death, though, just for fun let’s think for a moment about what it would be like if 2012 DA did hit. We don’t have to guess. This asteroid is about 150 feet in diameter, similar to the inferred size of an object that exploded over the Tunguska River in Siberia in 1908. The resulting Tunguska blast flattened about 750 square miles of forest. Let’s round that out and say its blast area was about 1,000 square miles. If another impact like that occurred today, what are the odds that you, dear reader, would perish in the process? (It’s worth noting that there are no known fatalities associated with the Tunguska event.) One way to do the calculation is to look at how much of the Earth’s surface is populated. 71 percent of our planet is covered with ocean. Of the remaining 29 percent, only about 2 percent is densely populated (ie, consists of extended urban areas). Just by pure odds, a city is very unlikely to get hit. There’s another, more personal way to go after the question. The total surface area of the Earth is about 200 million square miles. The likelihood that any particular spot would lie within the 1,000 square mile blast area of DA 2012, then, is about 1/200,000. That is your likelihood of feeling the blast. The odds of being killed is much lower. The real probability is very hard to estimate, but let’s pick a fairly high number and say that 1 in 10 people within the blast zone perish. Your odds of dying would therefore be 1/2,000,000. Now back to the real world. Asteroids the size of 2012 DA hit every 1,000 years on average. That means that over your lifetime (I’m giving you another 50 years, which seems reasonable), your odds of dying due to the impact of a small, Tunguska-scale asteroid are about 1 in 40,000,000. This is well into winning-the-Lotto territory. You are much more likely to be struck by lightning (1/100,000), and much much much more likely to die in an auto accident (1/100). In fact, here’s a weird thing about asteroids. Although there are far more small ones than large ones, the large ones are probably more dangerous. The kind of giant impact that killed the dinosaurs happens every 50 million years or so, on average, but an event that devastating might easily kill half the people on the planet. So there is a 1 in a million chance of impact in your (50 year) remaining lifetime, and then perhaps 50-50 odds of death, meaning that your chance of death due to a dino-killer are about 1 in 2,000,000. Still remote, but a lot scarier than the risk from little ones like 2012 DA. The good news is that big asteroids are much easier to find and track; if one were headed our way, we would probably know it decades ahead of time. We don’t yet know how to deflect such objects, but we may soon. In 2016 NASA is sending up a spacecraft called OSIRIS-REx to learn more about the structure of the small near-earth asteroid 1999 RQ36, with an eye toward learning how to deal with one on a collision course. And two competing companies, the B612 Foundation and Deep Space Industries, are looking at ways both to deflect Earth-approaching asteroids and to mine them for resources. If those efforts get more support, there may be some real, quite positive fallout from the near-miss of 2012 DA. UPDATE: Nature has a way of making fools of anyone who confidently proclaims about "sure things." This morning a meteor explosion over Russia reportedly injured 500 people, 14 of them seriously. Strangely, this event seems to be unrelated to 2012 DA; the incoming object appears to have followed an entirely different trajectory. But the event does offer a reminder that asteroids may be surrounded by debris fields, and that small objects may come in swarms--as is the case with meteor showers, although the evidence is less clear for larger objects like the one that struck over Russia. All of the basic argument I laid out above still stands. In all of history there are no recorded fatalities due to a meteorite impact, and thankfully that still seems to be true. Nevertheless, the impact risk is complicated, and for small objects our predictions are based on little more than historical statistics. The other crucial message: Hubris is never a good idea in a world full of unknowns.
