This new NASA map shows all 556 times an asteroids or meteors entered Earth's atmosphere since 1994 — and gives you an idea of just how regular these events are:
The good news is that virtually all of these objects burned up in the Earth's atmosphere, and most posed no danger to us.
That even includes the largest of these impacts: the meteor that exploded over Chelyabinsk, Russia in February 2013 (shown as a relatively large yellow circle on the map). Though the explosion released about as much energy as the detonation of 500 tons of TNT, shattered windows, and caused about a thousand injuries, the meteor itself broke up in the air and landed in small pieces on the ground.
But the bad news is that a slightly larger object could cause a much more destructive explosion, whether it burned up in the air or hit the ground. And though we've done a good job locating all the truly massive asteroids that would lead to global annihilation, we haven't done nearly as good a job of tracking mid-sized objects that could still cause a lot of damage. In 2005, NASA was tasked with spotting 90 percent of all near-Earth asteroids that could cause significant damage by 2020, but so far, they've only located an estimated 10 percent.
Asteroids are an overlooked risk
When most people consider asteroid impacts, they think of the enormous, 10-kilometer wide one that hit Earth some 65 million years ago and likely led to the extinction of the dinosaurs. However, we know about pretty much all of the objects of this size, and none of them are on track to hit us.
But it doesn't take a kilometer-sized one to cause a lot of damage. In 1908, an asteroid that was somewhere between 60 and 190 meters in diameter exploded over a remote corner of Siberia. This modest asteroid discharged an amount of energy 1,000 times greater than the atomic bomb dropped on Hiroshima, scientists estimate, and flattened some 80 million trees over a roughly 830 square mile area.
In any given year, the odds of an impact of this size are quite small: it probably only happens every few centuries or so. But the problem is that, given enough time, it will occur.
Earlier this year, I interviewed Alexander Rose, the direction of the Long Now Foundation, an organization that thinks our species has failed to engage in truly long-term thinking. He felt an epitome of this was the way we largely disregard the threat of asteroids.
"We know that, at some point, a catastrophic meteor or asteroid will impact this planet," he said. "For the first time in human history, we have the capability to detect and potentially divert it. Yet we aren't really putting any money into that."
How we could defend ourselves from asteroids
The first step to protect ourselves from asteroids is seeing them. Currently, we have a few different telescopes here on Earth devoted to spotting near-Earth objects (the Catalina Sky Survey and Pan-STARRS in Hawaii), and they've spotted more than 90 percent of the ones big enough to cause a global catastrophe.
However, to see smaller ones, you need telescopes in space, because they don't have to deal with interference from the atmosphere and the sun's glare.
NASA has proposed launching one of these, called NEOCam, and a private organization called the B612 Foundation is currently raising $450 million for a complementary mission, called Sentinel, that would survey a different area of the sky.
If both these missions happen, they'd dramatically increase our ability to spot mid-sized asteroids that pose a threat and give us enough time to actually do something. But the NASA mission is still just a proposal — one that is reportedly short on money — and the B612 mission is also short of its fundraising goal.
Further, if we did spot an asteroid heading our way, we don't have any proven means of stopping it. The simplest way would probably be sending a craft crashing into the asteroid, nudging it off its path enough so that it'd miss Earth. The UN has proposed designing and testing a network of small probes that would be capable of doing so, but it's still waiting on the necessary funding from various national space agencies, with an estimated price tag of about $2.5 billion.
That might sound like a lot. But the cost of doing nothing could be infinitely larger. Not long ago, the B612 Foundation produced this map: what it would look like if the 1908 Tunguska asteroid landed squarely in Washington, DC.
Odds are, an asteroid of this size will never land in Washington, DC. But when thinking about this issue, the important thing to remember is that, given enough time, it will happen again somewhere on the planet.
When it comes to asteroids, we're talking about natural disasters that are probably preventable. Figuring out how to do so would be a relatively cheap insurance plan that would benefit the entire species.
- These calculators let you see what would happen if an asteroid hit Earth
- Earth's history of meteorite strikes, in one awesome visualization: