A Meteor glowing as it enters the Earth's atmosphere. (solarseven/iStock)

June 30 is the 107th anniversary of the biggest asteroid strike on the Earth in recorded history.

In 1908, an asteroid measuring perhaps 90-190 meters across struck Siberia, damaging over 2,000 square kilometers of Russian forest – an area that measures larger than New York’s five boroughs. Scientists estimate that the energy of that explosion was about 1,000 times that of the atomic bomb the U.S. dropped on Hiroshima in 1945.

This is far from the only close call that humans have had with asteroids. In 2004, an asteroid big enough to have its own small moon narrowly missed the planet. In 2013, an asteroid struck the Russia countryside with many times the force of the Hiroshima bomb, and was widely captured on video.

And of course, it was an asteroid, smashing into the Earth with the force of more than billion Hiroshima bombs, which nixed the dinosaurs and allowed humans to take over the Earth in the first place.

Asteroids are the greatest threat of planetary extinction that we’re all not talking about, and that is partly due to a principle of economics, argue Alex Tabarrok and Tyler Cowen, two economists at George Mason University who run the blog Marginal Revolution.

The probability that you’ll die from an asteroid may be surprisingly large -- about the same probability as dying from a plane crash, according to research cited by Tabarrok and Cowen. That’s because, while a large asteroid hitting the Earth is a relatively low probability event, it’s a very high death event. In other words, the chance that it will happen is small, but if it does, it's very likely that we’re all going to die.

And yet, while we've put a lot of money into airplane safety, we're put very few resources into asteroid defense. Tabarrok and Cowen say this is largely because asteroid defense is what economists call a "public good." A public good is an economics term for something that is a) non-excludable, meaning that people who don’t pay can’t be prevented from using it and b) "non-rival," meaning that when I use it, it doesn't reduce your ability to use it.

If that sounds confusing, consider the difference between blue jeans and asteroid defense, say Tabarrok and Cowen. Jeans are both excludable and rival. People who pay for jeans get to wear them, while people who don't pay for jeans don't. And if I'm wearing a pair of jeans, chances are that you're not wearing that same pair.

Asteroid defense is different. If the U.S. government, or a private company, pays for asteroid defense, other people in other places will enjoy the benefits, too.

“This is a classic case of a public good," Tabarrok said in a phone interview. "Meaning that, if you protect one person, you basically protect the entire planet. If we push the asteroid away, we’ve saved everyone. But for that very reason, no one really wants to pay for it. They want the other guy to pay for it."

Markets are great at providing excludable, rival goods, like jeans, hamburgers and contact lenses. But they are not as good at ensuring that people have access to public goods -- such as national defense, asteroid systems and disease control. For most people, the incentive is to be a "free rider" -- to enjoy the benefits of a service without paying for it personally. (If you've ever listened to public radio and then ignored their pleas for donations, you understand the principle.)

Since most people still consider things like national defense and disease control to be important, we typically turn to governments to provide these services, and allow governments to finance them with taxes. But this can result in another, less-discussed problem: so-called forced riders. A lot of liberals may wish they paid fewer taxes toward U.S. national defense, while conservatives may feel the same way about public radio.

Asteroid defense is a particularly pernicious example of a public good, since neither the market nor the government is yet providing it, says Tabarrok.

Tabarrok argues that the easiest way to guard against asteroids is just by improving our tracking of them. If an asteroid is headed straight for Earth, humans ultimately have three options, he says: "You can blow it up, you can kick it, or you can tug it. The one Hollywood likes, the Armageddon proposal, is to put a nuclear weapon up there and blow it up. However, that’s what we should do at the last minute. If we discover it earlier, then you can just make tiny pushes or pulls would be enough to knock it off course.” Now that humans have successfully landed a probe on a comet, we know that we have the technology to do this.

NASA has put some effort into mapping asteroids whose orbits bring them within approximately 31 million miles of Earth's orbit around the sun through the Near-Earth Object Camera, and has discovered many of the largest asteroids out there.

But there are still many that measure between 50 and a few hundred meters in diameter, large enough to wipe out a city. According to an Asteroid Day Declaration signed by scientists including Bill Nye and dozens of NASA scientists and astronauts, we've discovered fewer than 10,000 of the estimated million asteroids that could strike the Earth, or less than 1 percent.

Data released by NASA in late 2014 showed that small asteroids hit the Earth’s atmosphere and disintegrate with surprising frequency – about every other week. These asteroids, called bolides or more commonly “fireballs,” aren’t large enough to make it all the way to the ground – they burn up in the atmosphere. According to NASA, more than 550 bolides have burned up in the atmosphere in the last 20 years.


(NASA)

There are a few private efforts to fund asteroid defense, but Tabarrok says he doubts they will succeed because of the strong incentive to free ride. "I actually did donate money to the cause, but I don’t expect it to be terribly successful, because I don’t expect other people to pay for it. The chance that your donation would make the difference between a successful asteroid prevention and an unsuccessful is so small that you may as well keep your money and buy a pair of jeans.”

Part of the problem is that our understanding of the threat of asteroids is relatively new, and it is very difficult to convince the public of the reality of a threat they haven't seen in action, says Tabarrok. People vaguely understood the threat of a massive tsunami or a terrorist hi-jacking a plane before the earthquake and tsunami in the Indian Ocean in 2004, or 9-11. But they didn't have enough motivation to act on it.

Tabarrok says his hope is that private efforts in space will one day soon focus on mining asteroids for valuable resources. If you have miners and private developers working with asteroids in space, that could inadvertently make it easier to defend the planet against an asteroid collision.

And of course, there is the option that people on Earth could somehow get the motivation to work together, and asteroid defense might ultimately be a reason for unifying the world, says Tabarrok.

"The idea that the whole planet is potentially under threat from an asteroid does make us think that the world is our home, and we’re all in this together – Spaceship Earth, to get a little crunchy granola. And that makes us think a little more about our fellow travelers, our fellow world residents, that we’re all in this together.”

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