Averting a collision with asteroids

Chicken Little was right. The sky fell again, this time over the city of Chelyabinsk, Siberia, on the morning of Feb. 15, 2013 when a meteor exploded, injuring almost 1,500 people and damaging more than 7,200 buildings. Some of the startled Russians immediately thought that it was an American ICBM and that a third world war had started.

But they were lucky, and they knew it. Another meteor blew up over Tunguska, also in Siberia, on June 30, 1908. It flattened millions of trees over 800 square miles.

Had that event occurred over Chelyabinsk, the dead would have numbered in the many thousands.

A world war is indeed under way. It is between this world and so-called Near-Earth Objects, or NEOs in astronomical shorthand — asteroids (also called minor planets), meteors (shooting stars), meteorites, meteoroids (they are named according to size, their distance from Earth, or whether they hit it) and comets — that get too close, and it has been going on since this solar system formed.

Earth exists in an abidingly dangerous neighborhood. The late Eugene Shoemaker, a geologist and the first de facto planetary scientist, said that NEOs amount to a “hail of bullets.” The home planet has more than 130 known impact craters and countless others that are on the ocean floor or have been covered by shifting land masses.

The robotic solar system exploring spacecraft of the 1970s and ’80s, and chiefly Voyager 2, which went on a sensational 12-year grand tour of four of the outer planets, sent imagery home showing that every solid body that they passed had craters or other scars that were evidence of unimaginably powerful collisions. The “Big Splat” theory has it that something huge once slammed into Earth with such force that it broke off a huge chunk that became the Moon.

The violence is not all theoretical, however. The remnants of a crater at Chicxulub, off Mexico’s east coast, which is 110 miles in diameter and was discovered in the late ’70s, is believed to be from the impactor that killed off the dinosaurs and most other life 66 million years ago. Meteor Crater near Flagstaff, Ariz., where Shoemaker “hailed” the barrage, is a popular tourist attraction.

Astronomers calculate that we are not due for another catastrophic hit or close encounter for at least a century, but a large undetected rock that blew up over the eastern Mediterranean on June 6, 2002 with the force of a small atomic bomb was a reminder that the danger persists.

With the Cold War over and territorial disputes among the developed nations settled for the first time in modern history, Earthlings are looking upward and outward instead of across borders to spot potential impactors that could obliterate a city, an entire region or bring on Doomsday.

Several surveys have been undertaken to get a clear idea of the danger, including a comprehensive, congressionally mandated, NASA Spaceguard Survey that catalogued 90 percent of NEOs larger than 140 meters, and others at MIT, the Lowell Observatory and elsewhere. And several organizations have been created for planetary defense, the most notable being the B612 Foundation, which was created by former astronauts Ed Lu and Rusty Schweickart and others. They plan to put an infrared telescope named Sentinel in a Venus-like orbit in 2017-18 from where it will watch Earth for impending danger.

The United Nations is also working on the problem by creating an International Asteroid Warning Group and the Japanese space agency is actively watching the sky, too. But the most ambitious project is called NEOShield, run by several European nations and the United States. It would involve using a gravity tractor to nudge the approaching impactor off course without touching it and, failing that, using a kinetic impactor to hit it or an explosive device, possibly a nuke, to obliterate it.

Planetary defense requires the ultimate Strategic Defense Initiative, to borrow a term from President Ronald Reagan’s ill-fated (and ill-conceived) 1983 Star Wars program. The potential impactor has to be spotted and precisely tracked at least two decades ahead of time. Then a spacecraft could be sent out to gently nudge it off course.

Failing that, or in the event of a surprise “attack,” so-called directed energy weapons, such as lasers or particle beams, rocket-propelled missiles, and very high-speed pellet guns could be used to destroy it far enough out so there would be no collateral damage to the cradle of life in this solar system.

The observation system would not only require infrared sensors like Sentinel, but powerful ones that look out in all directions from Earth. The program should have an entirely appropriate name: Watch Your Asteroid.

William E. Burrows is the author of The Asteroid Threat: Defending Our Planet From Deadly Near-Earth Objects, which was published this month.