Why Earth needs a defence system against incoming asteroids

bobmcdonald-190.jpgBy Bob McDonald, Quirks & Quarks

The Earth was grazed by three space bullets this week in the cosmic shooting gallery that is our solar system. Each small asteroid carried more energy than a nuclear weapon, yet we didn't see them coming until the last minute and there is no system in place to protect us from getting hit.

On Wednesday, Asteroid 2014 DX110, 30 metres wide, whizzed by the Earth closer than the moon. It was followed the next day by 2014EC, a 10-metre space rock that passed even closer, missing us by a mere 65,000 km. That same evening, another surprise visitor, 2014EF, gave us a close encounter. None of these had a chance of hitting the Earth, but by space standards, these fly-bys are incredibly close.

Thursday's first visitor was about half the size of the object that did hit us last February, lighting up the skies over Chelyabinsk, Russia, and causing millions of dollars in damage. All of these objects arrived with very little warning. The first object on Thursday was spotted two days before it came by; the second one in less than 24 hours.

Scientists estimate that these close encounters with small asteroids happen every couple of weeks, which means there are about 25 chances every year that the Earth could get hit by one of them. It is also estimated that there are more than a million small asteroids out there, crossing the Earth's orbit, and so far, only 10,600 have been found.
Perhaps the odds have been on our side so far, but it's obvious that sooner or later, we are going to get pounded by one of these marauders from space. And if one comes down in a major centre, such as New York, Tokyo, Mexico City or Paris, the damage could be worse than a nuclear strike. So, why is there no system in place to protect ourselves from a clear and present danger?

The Hollywood solution - sending brave astronauts out to blow up an object, as portrayed in the movie Armageddon - won't work. It takes years to plan a mission like that, such as the asteroid rendezvous mission currently in development at NASA, which won't get off the ground for at least a decade. Besides, large asteroids, while more damaging, are rarer. We know where they are, and none is heading our way in the foreseeable future. (There is a NASA program that tracks them, which we profiled recently on Quirks.)

It's the small ones, which we only see a day or two before they arrive, that are the problem. To defend against those, we would need a missile system constantly at the ready, with the capability to be programmed quickly for rendezvous with the asteroid and powerful enough to reach out millions of kilometres from Earth. It would take a sizeable multi-stage rocket, such as the kind used to send probes to Mars, in order to reach deep space. That technology already exists, but there are none at the ready to depart on a moment's notice.

Then, there is the issue of what to do with the asteroid once we get to it. A nuclear weapon could blow up a small space rock into tiny pieces that would produce a spectacular meteor shower the following night. But that debris raining down into the atmosphere would also contain radioactive fallout from the bomb. Not a good idea.

A simpler method would be to simply hit it really hard. Asteroids move at tens of thousands of kilometres per hour through space, so a collision with any heavy object at those speeds would either fragment it or knock it off course, so it misses the Earth.

It takes only one or two rockets to provide this defense system at a cost of a few hundred million dollars. In space terms, that's not a lot of money, and since the system is protecting the entire planet, it's a no-brainer to share the costs internationally.

It's puzzling that countries, including Canada, have joined together to build the $100-billion International Space Station and are planning to spend even more to send robots out to the other planets in the Solar System - but no one is thinking about investing in rockets to protect this one.