New ideas for deflecting Earth-threatening asteroids

third option: gently nudging the asteroid away from Earth without breaking it apart, either by exploding a nuclear device at a distance or zapping it with high-powered lasers. 

Astronomers have found thousands of asteroids that pass near Earth’s orbit, and a few of these are on trajectories that give them a small chance of hitting Earth. The most worrying is a 270-meter-wide asteroid named Apophis, which has a 1 in 45,000 chance of hitting us in 2036 (see 30 April 2008 HS Daily Wire). 

To investigate the best way to deflect this and other asteroids onto a harmless path, a team led by David Dearborn of the Lawrence Livermore National Laboratory in California has modeled the impact of a nuclear explosion on an object’s trajectory. Their virtual asteroid was 1 kilometer in diameter and made of rocky rubble loosely bound together by gravity, which is considered by many planetary scientists to be the most likely composition for small asteroids.

Thirty years before the asteroid was set to collide with Earth, a nuclear blast, equivalent to 100 kilotons of TNT, was set off 250 meters behind it. The nudge from the explosion increased its velocity by 6.5 millimeters per second, a slight change but enough for it to miss us. 

Shiga writes that he technique also reduced the risk of a break-up — just 1 percent of the asteroid’s material was dislodged by the blast, and of that only about 1 part in a million remained on a collision course with Earth. Dearborn adds that the technology for this method is already established, unlike for the use of a heavy object to shove the asteroid onto a different path — the “kinetic impactor” strategy. “Should an emergency arise, we should know that [the technology] is available, and we should have some idea of how to properly use it,” he says. 

He has now begun simulating the effect of nudging an asteroid with a smaller nuclear explosion — less than 1 kiloton — 1 meter below its surface. This would reduce the device’s weight, making it easier and quicker to launch. He will discuss the work next month at the 1st IAA Planetary Defense Conference in Granada, Spain. 

A less established and gentler approach would be to nudge the asteroid away from Earth using lasers. In this theory, being investigated by Massimiliano Vasile of the University of Glasgow in the United Kingdom