Haven’t had anything to worry about for a while? Here, let me fix that…
Sometime around the end of the ’70s I read a book called Lucifer’s Hammer, by Jerry Pournelle and Larry Niven. It was a good book (a bestseller, in fact), but out of all its memorable scenes the one I remember best is is the one of the surfer whose ultimate dream had come true: he was riding the biggest wave in the world, a wave hundreds and hundreds of feet high, riding it longer than anybody had ever ridden a wave before. He proved once and for all who was the best surfer in the world–at least, right up until the wave swatted him against the side of a downtown Los Angeles skyscraper.
Lucifer’s Hammer, you see, was the name given by Pournelle and Niven to a hypothetical asteroid that collided with Earth, and the mile-high wave was the result of the impact of a large chunk of that asteroid in the Pacific Ocean.
If you’re like most people, you probably don’t worry much about the possibility of a giant asteroid ruining your whole day, but a recent article in the science magazine Discover came up with an interesting (if that’s the word) figure: your chances of dying in an asteroid impact are roughly six times as great as your chances of dying in an airplane disaster.
Here’s how the figures work: about 130 Americans are killed each year in airline disasters (sorry, no figures for Canadians, so pretend you’re an American for a moment, just for me, OK?). Assuming you’re an average American who flies an average amount, your chance of dying in such a disaster in any given year is 130 divided by the total U.S. population of 250 million–about one in two million. Assuming also that, as an average American, you have about another 50 years to live, your chance of dying in an airline disaster is roughly one in 40,000.
On the other hand, astronomers estimate an asteroid about a mile wide strikes the Earth about once every 300,000 years, exploding with a force of 100,000 megatons of TNT–10 times the force of the world’s entire nuclear arsenal. Such an asteroid would leave a crater at least 10 miles wide and might trigger “nuclear winter,” kicking up such a pall of dust that agriculture would collapse and most people would die.
So in any given year there’s a one-in-300,000 chance of such an asteroid hitting the Earth, or a one-in-6,000 chance over the next 50 years–making it roughly six times as likely that you’ll die as a result of an asteroid collision as an airplane disaster. (And we won’t even talk about how much more likely it is than you winning the lottery.)
Now, depending on your temperament, you can use this data in two ways: either to berate your non-flying friends with yet another statistic showing how safe it is to fly commercially or as an excuse to start laying in foodstuffs and thinking about fortifying the old homestead against the starving hordes of asteroid-shocked survivors.
The fact is, we’re far too complacent about the possibilities of something really nasty falling out of the sky (or as Discoverput it, “Chicken Little was right!” We think of Earth as somehow hanging alone in pristine, empty space, when in fact we are surrounded by swarms of bits of dust, pebbles, rocks, chunks of metal–and much bigger things.
These “bigger things” have hit the Earth in the past, and sooner or later will do so again. The famous Meteor Crater in Arizona, for example, three-quarters of a mile wide and 600 feet deep, was the result of a collision a mere 50,000 years ago between the Earth and a tiny asteroid, hardly worthy of the name, only 150 feet across. (It has been suggested that Hudson Bay was the result of an asteroid impact. Think about THAT for a minute.)
The asteroids we have to worry about aren’t the ones safely orbiting out in the asteroid belt between Mars and Jupiter, of course; they’re the others whose orbits bring them across the Earth’s orbit. Before 1970 only a couple of dozen of these were known. Since then nearly 170 have been catalogued, and a new one is discovered every few weeks.
NASA recently discovered an asteroid whose orbit swings from just inside Jupiter’s orbit to just beyond Earth. Made of metal, it’s 1.6 miles wide. Some day we’ll probably want to mine it (it’s mostly iron, about eight percent nickel, and, based on what we know of metal meteorites, probably also contains about 100,000 tons of gold). But that doesn’t mean we want it to pay us a visit.
NASA scientists also estimate that, during the Earth’s first billion years or so, it may have been struck twice by REALLY large bodies. How large? Well, would you believe the size of California? Imagine something the size of California, travelling at 40,000 miles per hour, striking the Earth. Go on, I dare you.
So what? You ask. What can we do about this threat from space?
Well, in the absence of Dr. Who, not a heck of a lot. With enough warning, we might be able to launch nuclear missiles to deflect asteroids before they got here (we wouldn’t want to shatter them–getting hit with twenty medium-sized rocks instead of one big one might be a case of the cure being worse than the disease).
Trouble is, unless we spend more time and money searching for these asteroids, we may not see the one that gets us until it’s too late, and then–oops! There goes New England! As an example: just two years ago a rock as wide as the Empire State Building is tall missed Earth by just twice the distance to the moon–and no one saw it until several nights after it had gone by. How many have come even closer and never been seen at all?
Scientists are beginning to talk very seriously about near-Earth asteroids and the hazard they present. And if you think worrying about something like this is a waste of time–well, check those figures at the start of the column again, and ask yourself if you think worrying about airline safety is a waste of time.
After all, you can always choose not to ride an airplane, but you can’t choose not to ride the Earth.