How to deflect an asteroid hurtling toward Earth

A massive space rock enveloped in fire and hurtling toward Earth at warp speed may be something we’ve only seen in movies. But asteroids do collide with planets all the time – including our own.

Most of what hits Earth is small and burns up in the atmosphere. But something the size of a football field plunges through the atmosphere and causes local damage every 2,000 years or so. And once every few million years, a space rock big enough to cause global devastation hits. 

So what would we do if scientists identified a big one on a collision course with Earth? Although humans have never deflected an asteroid before, there are plenty of ideas. 

The National Aeronautics and Space Administration (NASA) may actually test a possible solution for the first time soon. The Double Asteroid Redirection Test (DART), as the mission is called, moved to the preliminary design phase in June.

It would use a technique called the “kinetic impactor” to change the speed of an asteroid ever so slightly. Think of it this way, explains Lindley Johnson, NASA’s planetary defense officer: If two cars are driving on a highway side by side at the same speed and they have to merge into one lane, they will collide unless one vehicle changes how fast it is going. Earth and an asteroid are the two cars. 

What NASA wants to do is see if it can change the velocity of the rock to prevent it from smashing into Earth. If the DART mission gets the full go-ahead and funding, it would test this technique by slamming a spacecraft into an asteroid in orbit around another asteroid. Should that prove successful, the idea would be to apply the same concept to a rock orbiting the sun that is on a trajectory to hit us. 

Among other ideas to avoid an asteroid Armageddon:

• The gravity tractor. A spacecraft would station itself alongside the asteroid and, over time, the gravity of the probe would tug the asteroid into a slightly different orbit. 

• The hair dryer effect. This would involve using some heat source, such as lasers or sun reflected off a solar mirror, to evaporate material from one spot on an asteroid, creating a sort of propelling jet that would alter the rock’s orbit.

• Nuclear explosion. This would not be like what people see in the movies, Mr. Johnson says. Scientists wouldn’t send up a bomb to incinerate an asteroid. It would be something much more modest and targeted – a bomb strike intended to take just enough material off a space rock to alter its path. Still, Johnson adds, if they were out of time, scientists could try to blow up the asteroid. But pieces would likely still rain down on the planet.

• Celestial graffiti. Since solar radiation gives small bodies a bit of a nudge in orbit, scientists could change an asteroid’s trajectory by painting it white or black. 

“The key to all this is finding [potentially dangerous asteroids] as early as we can,” Johnson says. Given enough time, these technologies could be tested, or new ones dreamed up.

This article first as a sidebar to the Monitor cover story Chasing Asteroids.