By Greg Bear
February 13, 2013
In January, this commentary was posted on CNN.com. Since then, the passage of another asteroid has been announced, this one much smaller but coming much closer, than Apophis, the asteroid that provoked the first flurry of publicity.
Called 2012 DA 14, this hurtling mass is less than 150 feet long, but will pass closer than twenty thousand miles. It will not hit the Earth this time around. Its impact would not be an extinction-level event, but it could easily wipe out several hundred square miles--that is, it could easily leave a major metropolitan area a smoking, cratered ruin.
Here is my original piece on Apophis, uncut, with text quoted from J.A. Enever’s excellent 1966 article.
Look up at our nearest neighbor, the Moon, and you’ll see stark evidence of the dangerous neighborhood we live in. The man in the Moon was sculpted by large-scale events, including many meteor and asteroid impacts.
In 1994, the comet Shoemaker-Levy 9 dove into Jupiter. The result was awesome. The impact caused a brilliant flash, visible in Earth telescopes, and left an ugly dark scar on Jupiter’s cold, gaseous surface.
With the recent passage a thousand-foot-wide asteroid labeled 99942 Apophis, one of a class of space rocks referred to as “Near-Earth Objects” or “Earth-grazers,” scientists have revised their worst estimates of its chances of striking Earth. Current thinking is, we’re safe. For the next couple of decades.
But this does not mean the danger is over. Far from it.
Named after a very bad, no good Egyptian serpent god, lord of chaos and darkness, Apophis flies past Earth every seven years. This year, its thousand-foot bulk approached to within nine million miles. In 2029, it will swoop in close enough to put some of our orbiting satellites in peril--20,000 miles. In that year, no doubt Apophis will arouse even more attention, because it will be visible in the daytime sky. In 2036, it will probably pass by at a reassuring fourteen million miles.
Yet there’s always a possibility we still don’t have these measurements exactly right. What could happen at any point in Apophis’s orbit to modify its course--just a smidgen? A tiny collision with another object, way out beyond Mars? What could change between now and 2029, or during any orbit thereafter?
Apophis masses at more than twenty million tons. If it hit Earth, the impact would unleash a blast the equivalent of over a billion tons of TNT. That’s not a so-called extinction event, but it could easily result in billions of deaths and months if not years of climate disruption.
The potential risk is huge. And Apophis is far from alone. Life in our solar system has always been dangerous. As kids we learn about the Barringer Crater in Arizona, a relatively recent formation--fifty thousand years old--caused by a rock weighing several times more an aircraft carrier. That impact released the equivalent of twenty megatons of TNT and left a crater four thousand feet wide.
Both Mars and Earth were long ago hit by planet-sized objects, one spinning off our Moon, the other shaping two distinctly different hemispheres on Mars. To this day, a steady rain of meteors falls on Earth--some of them left-over pebbles and dust from worn-out comets, others from random impacts out in the “asteroid belt,” still others from big strikes on the Moon and Mars.
Since oceans cover two-thirds of the Earth’s surface, water impacts are much more likely than impacts on land. It was the blast of a six-mile-wide asteroid off the coast of Mexico some sixty-four million years ago that changed Earth’s weather for years and hastened the departure of the dinosaurs. Ocean impacts are worse than land impacts, not just because of immense tidal waves, but because of the vast quantities of super-heated water vapor and dust that spread from the impact to shroud the entire Earth.
In March 1966, J.E. Enever published his ground-breaking article, “Giant Meteor Impact” in ANALOG SCIENCE FICTION/SCIENCE FACT. Enever surveyed the current material on meteor and asteroid impacts, then published his own calculations and analysis of what such strikes could do, and have done, to the Earth, with cinematically vivid prose and equally terrifying physics. He was the first to put it all together and publish in a respected and widely available forum. Even though geology was still reluctant to admit to any form of “catastrophism,” eschewing Biblical explanations, many read and pondered... seriously.
In the decades since Enever’s article, writers, scientists, and engineers have proposed various ways to avert such impacts. Some have suggested we strap rocket motors to a threatening rock and nudge it away. A steady pulse of projectile “paintballs” could also do the trick. Others have suggested we use nuclear weapons to “kick” an asteroid from its orbit, or even to shatter it into smaller debris--a rather dim idea that misleads us into believing a single bullet is worse than the blast from a shotgun. Our atmosphere provides little protection against meteors larger than a truck.
Moreover, many asteroids are chunky masses of rock and dust loosely held together by very little gravity, like loosely-packed peanut clusters. Attempting to attach a rocket to one of these might merely dislodge a few “peanuts,” leaving the rest to do the dirty work. Wrap one of these peanut clusters in a giant steel net, then drag it off its deadly course? Intriguing, but for now--like deploying tractor beams from the starship Enterprise--just so much super-science.
Not all asteroids are loose conglomerates. Many are more solid and made of valuable minerals and metals like nickel and iron. These classic nickel-iron bodies could be harvested, possibly to great profit, by mining operations conducted in deep space, or by swinging the bodies closer to the Earth or Moon. But the public outcry against such maneuvers could cause real headaches for less hardy entrepreneurs, and even for Bond villains.
As for Apophis, twenty thousand kilometers is definitely a miss--but it’s still too damned close. Once again we are warned that we have to seriously consider spending a LOT more money on keeping track of our neighbors. After all, the dinosaurs were only slightly less serious about watching the sky than we are.
And in one way, the dinosaurs are still with us--in the form of walnut-brained voters and politicians. We spend more money on guns to protect our homes than we do on asteroid detection, and waste far more time thinking about the Mayan calendar than we do about the very real threat of asteroids and giant meteors.
What if there is no next election? No “trending” cult craziness? Only a spreading plume of super-heated steam and molten rock igniting a world-wide firestorm, shrouding the Earth for thousands of years.
Nothing left to worry about... Ever again.
It’s happened before, right here on Earth.
It’s happened many times.