Should we be Afraid of Asteroids?

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Josh Davis 06 Jul 2015, 19:56

You might have heard that last week, June 30, was Asteroid Day. Ultimately born out of a collaboration between astrophysicist Brian May and filmmaker Grigorij Richters, the campaign aimed to kick-start a global movement calling for greater detection and charting of asteroids in our solar system.

More than 100 events took place all over the world throughout the day, encouraging scientists, the public and governments to unite and raise awareness of these cosmic objects – which, as we all know from the dinosaurs, hold the potential to end life as we know it on our home planet.

While the threat hasn’t changed, such catastrophic events are extremely rare and probably won’t happen in our lifetimes. So what’s changed? Why the resurgence of interest? Should we really be worried about a lump of space rock smashing into Earth’s surface? Keen to find out more, IFLScience attended one of the premier Asteroid Day events, and had the opportunity to delve into the minds of those behind the movement.

According to the experts, the risk of a cataclysmic asteroid hitting Earth in your lifetime is roughly in the same ballpark as you being involved in a fatal car accident on a given day. Not massive, but not insignificant either. “The received wisdom is that we are aware of about one-hundredths of the objects that could hit us,” May told IFLScience.

This is where the 100X Declaration comes in. According to Alan Fitzsimmons, an astronomer at Queen’s University's Belfast Astrophysics Research Center, we have a catalog of around 12,000 asteroids that we know about, but scientists want to be able to expand this by at least 100 times by increasing search efforts. But even this falls way short of the millions of potentially harmful asteroids, or Near Earth Objects (NEOs), estimated to be out there. So how do we know there are so many zooming around if we haven’t found them yet?

“Well, strangely enough, we do know how many are out there,” Fitzsimmons explained to IFLScience. “There are a number of ways to calculate that […] and when we do these calculations, we generally find the same numbers whichever way we do the sums.” For example, scientists calculated that there are approximately 1,000 NEOs greater than a kilometer wide. “And in fact so far, we’ve found about 900 of them, so we’ve actually got about 90% of these objects,” he added.

But as soon as you start to go smaller, the figures begin to balloon. “It’s like pebbles on a beach,” said Fitzsimmons. “For every boulder, you’ve got quite a few large stones, and masses of shingle. It’s the same with asteroids.” So while there might only be 1,000 objects larger than a kilometer, if we go down to the size of the meteorite that exploded over Russia in 2012, which was a relatively tiny 20 meters (66 feet) across, we’re talking of millions. And even that managed to injure more than 1,000 people. Imagine if it happened over, say, London or New York? “Asteroids don’t discriminate,” Richard Crowther, a professor of astronautics, reminds us.

So, we’re realizing the threat, and we have the means to improve our asteroid database. Knowledge is all well and good, but what can we do if a threat appears, whether that is one, 10 or 50 years down the line?

If an asteroid was to hit tomorrow, there’s not much we could do. All we have at our disposal is what’s euphemistically called “civil defense,” or in other words, nuclear bombs. In the grand scheme of things, this isn’t the great idea it might at first seem. What you end up doing is turning one predictable bullet into a random shotgun spray. “All we can do is figure out exactly where it’s going to hit, [and] get some idea of the effects of that hit,” explained Fitzsimmons.   

There are other options in development, though, Asteroid Day science advisor Debbie Lewis explains. The NEOShield project, for example, is working on two different plans. The first is what’s called a “kinetic impactor,” which is as complicated as slamming it with multiple unmanned spacecrafts until it’s been knocked off course, though the mathematics are slightly more delicate than that. The second, the "gravity tractor," is an idea first proposed by two astronauts and relies on the small gravitational pull of a massive spacecraft to ever-so-slightly change the asteroid’s course, effectively dragging it away from us.

The gravity tractor. Airbus Defence and Space.

But it’s not all about the worst case scenario; impacts from smaller objects are more common than big ones that would warrant such methods. And for these, we should be able to prepare – warning, informing and advising communities of the best actions to take, while also empowering people to make a decision based on the information they are given about the situation. In short, asteroid impacts aren’t necessarily a doomsday.

Asteroid Day may be over, but our work is not. According to the experts, we need leadership, we need money, and we need voices to keep this ball rolling. The threat is not going to go away; it is very real. But it is also a hazard that we can predict and do something about, so now is the time for the world to come together and act.

Center image credit: NASA/JPL-Caltech

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