Asteroids: Why Earth needs a defence system against incoming asteroids - by Bob McDonald

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.

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.

Read more: Why Earth needs a defence system against incoming asteroids - Quirks and Quarks