Do We Need a Crash Effort to Thwart Killer Asteroids?

Astronomers’ recent announcement that an asteroid has about a 1-in-25 chance of smashing into the surface of Mars brought back the memory of those alarming headlines in 2002, when a 1,000-to-1,300-foot-long rock named 2001 YB5 hurtled toward Earth. What CNN labeled the "killer asteroid" turned out to miss our planet by 375,000 miles, about 1.5 times the distance between Earth and the moon. But by asteroid standards, that’s way too close for comfort.

Sure, sizeable asteroids don’t strike the Earth very often — on average, an object 1 kilometer (.6 miles) or larger hits every 500,000 years. But when they do, all hell usually breaks loose. Scientists believe an asteroid 6 miles in diameter struck the Yucatan peninsula 65 million years ago, releasing energy that was the equivalent of 100 million megatons of TNT and generating a planet-wide heat pulse so intense that according to one recent study, it probably killed off the dinosaurs in a matter of hours. In 1908, another asteroid probably caused the Tunguska Event in Siberia, a mysterious aerial explosion that generated enough force to level 80 million trees and cause an earthquake estimated at 5 on the Richter scale.

Nobody is sure how many potential killer asteroids are out there, but astronomers already have discovered more than 5,000 Near Earth Objects (NEOs) — that is, asteroids, comets and meteors whose orbits bring them within 124 million miles of Earth. About 900 of these have been classified as Potentially Hazardous Asteroids (PHAs), objects at least 500 feet in diameter that come within 46.5 million miles of our planet (about half the distance between Earth and the sun).

Even the least imposing PHAs have the potential to cause a devastating tsunami, while the bigger ones could wipe out an entire city and kill millions of people. (Imagine, for example, what would have happened if the Tunguska Event object had exploded over Moscow.) But it’s the exceedingly remote but nevertheless possible collision with a Yucatan Event-sized asteroid that really gives cause for concern, because it could wipe out the great majority, if not all, of the living creatures on Earth.

So if we’re threatened with the prospect of annihilation from the cosmos, what are we doing about it? If life were a Hollywood movie — say, the 1998 Hollywood disaster flick Armageddon — NASA simply would launch Bruce Willis and his intrepid team into space on a mission to land on the giant asteroid, drill an 800-foot-deep hole, drop in a nuclear bomb, and then remotely detonate it, cutting the PHA precisely in half so that both pieces narrowly miss Earth. (As the Bad Astronomy blog notes, splitting an asteroid in half might well cause one of the pieces to hit Earth with even greater velocity.) In reality, NASA isn’t doing much at this point beyond surveying space and attempting to identify and chart the NEOs and PHAs out there, a project for which the government has allocated a relatively minuscule $4.1 million a year. (NASA hopes to have that job 90 percent complete by 2020.) A 2007 NASA report to Congress only briefly touches upon possible killer-asteroid mitigation strategies. Instead of trying to split an asteroid into pieces, scientists have contemplated using the gravitational attraction of a giant spacecraft to pull the asteroid in a different direction, or using a giant mirror to focus solar energy on the asteroid’s surface and boil off material, creating thrust that would change its path.

In order to actually be able to do any of these things in the foreseeable future, however, we’d likely have to allocate many billions of dollars to an effort vastly more ambitious than the Manhattan Project or the Apollo program to put men on the moon. Developing effective asteroid-diverting technology might well divert resources and attention away from other important priorities, such as the efforts to mitigate global warming. On the other hand, if a killer asteroid strikes Earth, we might not be around to worry about climate change any more. So what do you think? Should we launch a crash program to deal with the threat of killer asteroids? Offer your opinion below.