A new report from the U.S. National Science and Technology Council outlines the steps needed to prevent an asteroid from hitting Earth, and if that's not possible, what to do if one does hit.

The dinosaurs learned a hard lesson 66 million years ago about the deadly consequences of a large object from space crashing into our planet. The impact changed the climate so quickly and so dramatically, Earth became inhospitable to many species of the time and the course of evolution was changed.

And that was not the only one. Records show Earth has been hit at least five times throughout its history, with some of the impacts wiping out 90 per cent of life on land and in the oceans. In other words, our living world has been virtually sterilized by encounters with large space rocks that have slammed into us. And there are a lot of others still out there that could have our name on them. Fortunately for us, life is incredibly tenacious, and given enough time, always comes back, albeit in a different form.

Now we have the technology to prevent such a disaster from happening again, which the report lays out in several steps: find them, deflect their path away from the Earth, prepare for an impact in case we fail to deflect, and have international co-operation in place to assist in disaster recovery.

astroid

Could Earth be slated for another devastating asteroid impact? (Credit: iStock/Getty Images)

The first step, spotting near-Earth objects (NEO) is already under way. NASA has its Near Earth Object Program that uses telescopes to track objects that could hit us, and Canada has a satellite called NEOSSat which is in space looking for potential threats.

Strangely, the very large, mountain-sized objects that are 15 to 20 kilometres across or larger, and can cause mass extinctions, are the easiest to spot but strike least often. Already, more than 90 per cent of the big ones estimated to be out there have been identified, and none are heading our way any time soon. Ironically, the objects that could cause the greatest damage pose the least threat.

Smaller objects, those the size of a house or a car, are much more difficult to see in telescopes and carry enough kinetic energy to wipe out an entire city. In 2013 an object only 20 metres across exploded high in the atmosphere above Chelyabinsk, Russia, with a force 20 to 30 times greater than the first atomic bombs. And no one saw it coming.

There are an estimated 10 million objects in the 20-metre category out there, most of them undetected. More powerful telescopes in space will be needed to spot them when they are farther away, giving us time, as in a few years, to go out and meet one before it strikes and nudge it off course.  As in any type of shooting, the farther away from a target you are, the harder it is to hit, so a small nudge from a long distance can avoid disaster. The closer it is to us, the more you have to push, and if that doesn't work, you could try to blow it into tiny fragments that would still rain down on Earth, but over a wider area, with much of the debris burning up in the atmosphere.

Tricky business

The deflection technology is where things get a little tricky. While a few robot spacecraft have been sent out to asteroids and comets, none have tried to move one out of its orbit in a significant way. A rocket meant to deflect an asteroid would have to be ready to fly at a moment's notice, be very fast, extremely manoeuvrable, and possibly carry a nuclear warhead. That's called a space weapon and goes against the UN Space Treaty of 1967 that prohibits nuclear or other weapons of mass destruction in space.

Asteroid 2012 DA14

The passage of asteroid 2012 DA14 through the Earth-moon system, is depicted in this handout image from NASA. On February 15, 2013, the asteroid, 45 metres in diameter, passed Earth. (NASA/Reuters)

Even if an exemption to the treaty was made for the sake of protecting Earth against a natural disaster, the very existence of such a potent device that could fly circles around existing rockets — and built by the United States — could be perceived as a threat by other nations, possibly triggering another arms race.  

It is interesting that many members of this report are from the U.S. Department of Defence. Could this be a way of getting around the space treaty by developing a space weapon under the guise of protecting Earth?

It might be perceived that way and fought against by rival nations. It would be a sad ending if humanity was wiped out by an asteroid because we didn't trust each other enough to build a protective shield.

That is why developing a protective shield for Earth has to be a truly international project. Asteroids can come from any part of the sky and strike any part of the planet, including the oceans. The threat is global, so it will take a global effort to prepare for or recover from a strike, no matter where it happens.