It was an amazing spectacle, a rapid succession of giant asteroids blazing across the sky. First, on Feb. 15, Russia was hit with the biggest asteroid in 100 years. Barely a few hours later, an even bigger one made the closest approach to Earth ever recorded for an asteroid of its size. Then the residents of San Francisco, Cuba, and south Florida looked up and saw meteors streak across the sky, rattling their nerves.
It was a historic display of nature’s cosmic firepower, something I never expected to see in my lifetime. Mother Nature was showing Hollywood who’s boss.
The city of Chelyabinsk in Russia bore the brunt of the celestial fireworks. A piece of rock, about 50 feet across and weighing more than 7,000 tons, came crashing to Earth. Traveling at a blinding speed of over 40,000 miles per hour, it created a sonic boom and shockwave that shattered windows across the city: 1,200 people were injured, mainly by the flying pieces of glass, and 52 were hospitalized, two of them in serious condition. Chelyabinsk, once known as one of the most polluted places in the world due to its storage of nuclear waste, will now be known as “meteor city.”
The asteroid packed a huge punch, the power of 20 Hiroshima bombs. It was a “city buster,” capable of flattening a modern metropolis and reducing it to rubble. It was a miracle that the asteroid exploded roughly 10 to 15 miles above ground: had there been a ground burst, it would have caused tens of thousands of casualties. If that asteroid had hit just a few seconds later, it would have created a tragedy on Earth.
While Russia was still reeling from the shock of this meteor impact, just a few hours later, 17,200 miles in space, an asteroid three times larger than the Russian one came within a whisker of hitting Earth. Called 2012 DA14, it actually sailed about 5,000 miles closer to Earth than our communications satellites (which orbit at 22,000 miles). If the asteroid had arrived just a few minutes earlier, it might have hit Earth, with truly cataclysmic consequences.
To see what might have happened in the case of a collision with DA14, one can study the 1908 Tunguska impact, which hit Siberia with the force of 1,000 Hiroshima bombs, giving Earth a black eye. That meteorite was about the same size as DA14, i.e., the size of an apartment building. The energy of the impact was so great that it devastated 830 square miles of Siberia, including 80 million trees. Pictures of the area show millions of trees lying on their sides, as if a giant hand came down and flattened every tree in sight. The impact was so spectacular that the blast was heard hundreds of miles away, and strange lights were seen as far away as Europe.
Fortunately, the 1908 and 2013 asteroids that hit Russia missed hitting a major metropolitan area like Moscow. However, because of the similarity with nuclear blasts, one can imagine what might happen if such an object had hit, say, New York.
First, one would see a blinding flash of light as the asteroid smashed into Earth. Midtown Manhattan would be instantly vaporized by the impact, leaving a crater almost a mile wide. Seconds later, the blast wave would spread out from the crater, toppling all the skyscrapers in the city as if they were made of twigs. Minutes to hours later, there would be a rain of fiery meteors falling from the sky, created by debris blown out of the original crater. Then, for hours and days, firestorms would incinerate an area roughly 30 miles from the impact site. Large swaths of Long Island, Connecticut, Westchester County, and New Jersey would be set on fire. At Hiroshima, about 100,000 people died in the opening phase of the blast. An asteroid impact could have casualties in the millions.
All this sounds like overheated science fiction, but the reality is actually much worse. Lurking in space are asteroids even bigger than the city busters—to wit, “nation busters” big enough to destroy Germany or England. The most dangerous one is called Apophis, which is 1,000 feet across and will come dangerously close to Earth in 2029 and again in 2036. The most recent calculations show that Apophis will barely miss Earth in 2029, but will actually graze our atmosphere. But because of the uncertainty of its path as it whizzes past, there is a small possibility that its orbit may be perturbed so it might actually hit Earth in 2036. NASA scientists are reasonably confident it will still miss Earth in 2036, but the head of the Russian space agency takes the threat of a collision seriously, stating that we have to prepare for the worst. If Apophis hits Earth, it would have the force of approximately 20,000 Hiroshima bombs.
But of all the threats that face the planet, only one can actually destroy all life on Earth in almost an instant, and this is a “planet buster.” An object several miles across that has enough energy to kill everything on Earth.
The most famous planet killer is the asteroid or comet that plowed into the Yucatán Peninsula of Mexico 65 million years ago, creating a crater about 110 miles in diameter. The impact created a huge tsunami and firestorms that raged throughout the Caribbean and North and South America. The impact was so great that the dirt and debris sent into the atmosphere cut off the sun, darkening Earth until temperatures plunged around the world, eventually killing off the dinosaurs.
Some scientists have proposed a rival theory, that volcanic activity near India at around that time might have blackened the skies and killed off the dinosaurs. But other scientists have proposed yet another theory, that perhaps the impact was so great that a shockwave went through Earth and blew out the crust on the other side, creating the volcanic activity in India. In this scenario, the dinosaurs were killed by a one-two punch caused by the original impact.
Fortunately, as frightening as these scenarios are, these big impacts are extremely rare. Small meteors are actually quite common, but a city buster might hit Earth on a time scale of once every several centuries. A nation buster might hit once every few hundred thousand years. And a planet buster might hit once every few tens of millions of years. But we are clueless to say precisely when the next impact might be. We are playing Russian roulette with the planet.
How real is this threat? It’s sobering to realize that we live in the middle of a cosmic shooting gallery. There are about a million asteroids that orbit near the path of Earth. Of these, NASA estimated in 2007 that perhaps 20,000 can one day pose a direct threat to us.
These asteroids have passed by Earth since the dawn of humanity, yet we were blissfully unaware of them. Many asteroids would land in the oceans or in uninhabited areas, where there was no one to record the impact. Today our instruments are revealing how frequent near-misses really are, and the results are deeply disturbing.
What Can Be Done About Them?
Sadly, at present we are sitting ducks. We have no systematic way of detecting these objects, let alone destroying one. Basically, we depend on amateurs as our first line of defense to find these threats. These hobbyists brave the cold every night in hopes of capturing a comet or asteroid in their telescopes. (Only recently have computerized telescopes in Hawaii and the Southwest joined forces with them.)
Basically, we are defenseless.
So it is a no-brainer that our first goal should be to build an early-warning system, a space telescope specifically designed to spot asteroids smaller than a football field. This could be done with off-the-shelf technology and would cost only a few hundred million dollars, which is pocket change compared with a typical space mission. (Just one space-shuttle launch can cost upwards of $800 million.)
With this space telescope, scientists could give a realistic estimate of the true threat posed by these asteroids and identify a handful that might actually hit Earth in the coming decades. Unfortunately, every time scientists present this proposal to politicians, they treat us as if we are space cadets. The “giggle factor” is one reason why this proposal has never been taken seriously by the U.S. Congress. But perhaps the latest Chelyabinsk meteor is a game changer.
However, if, one day, the space telescope actually finds an asteroid with our name on it, there is little we can do with present-day technology. Forget movies like Deep Impact and Armageddon. The space shuttle has been canceled, and moreover, it was never designed to leave Earth’s orbit and go into deep space. An entirely new booster rocket would have to be designed to meet this threat.
U.S. President Barack Obama, canceling the shuttle and the manned mission to the moon and Mars, left open the possibility of one day landing on an asteroid. To lay the groundwork for this mission, NASA plans to launch a probe in 2016 that will eventually intercept an asteroid and in 2023 return a sample back to Earth. If this paves the way for a manned mission, it could be refocused to intercept and eventually deflect an asteroid.
Numerous proposals have been made. The obvious one of blowing up the asteroid with H-bombs might be a bad idea, since it would only create a fleet of baby asteroids—which would, in turn, do more damage than a single asteroid. A more realistic possibility is to land on the asteroid, put a rocket on it, and then gently push the asteroid out of its trajectory by firing the rocket. Even a gentle push, if done when the asteroid is in deep space, could nudge it off of its Earth-killing course. So, Bruce Willis, watch out!
Other possibilities include using the gravity field of the rocket to tug on the asteroid so it is deflected. Yet another possibility is to detonate an H-bomb a safe distance away, so the blast wave pushes the asteroid out of its path.
It is inevitable that one day we will be hit, and hit hard. It’s not a matter of if, it’s a matter of when. We realize this every time we see the pockmarked surface of the moon. Unfortunately, without an early-warning system, we don’t know when such an impact might take place.
Although deflecting a killer asteroid will not be cheap, consider it an insurance policy. There is a historical lesson here. The dinosaurs did not have a space program. That is why we are here and they are not. But without a robust space program, are we next?
Kaku is the Henry Semat Professor of theoretical physics at the City University of New York. He is the author, most recently, of Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100. From our April 19, 2013, issue; Asteroid Apocalypse.