How to prevent collisions of asteroids with the Earth
Steve Chesley, JPL/Caltech
The Earth’s neighborhood is not the empty space it was once thought. Subtle gravitational and thermal forces are continually shepherding main belt asteroids into the inner solar system where they encounter Earth. These so-called near-Earth asteroids can and do impact the Earth, causing a wide range of effects ranging from harmless lightshows to global devastation. The frequency of significant impacts is low enough that human experience of such events is almost nonexistent, and so many consider it to be an ignorable threat. And yet in an actuarial sense, the hazard posed by asteroid impact is at a level that approaches or exceeds many more common disasters, both natural and man-made, which are widely recognized as worthy of significant investment to mitigate their effects.
The asteroid impact hazard is unique among natural disasters because impacts can be prevented once the threat is recognized. The most important step in mitigating the asteroid hazard is to recognize that it is impossible to deflect an asteroid that has not yet been discovered. Once the object has been discovered we can identify any potentially threatening Earth encounters in the future, and if necessary prepare a response to prevent an impending collision. Thus the impact mitigation process has three crucial steps: discovery, recognition and avoidance.