February of 2013 may prove to be one of the more important months in recent human history. The meteor that streaked across the skies of Siberia, and the close brush just a day later with a much larger asteroid, brought home as Hollywood itself never has how dangerous a place the solar system can be. We can hope that the Chelyabinsk meteor, which produced injuries but no deaths, will be enough to seize the attention of the public. Because we need to be thinking about stopping potential impacts, and developing the technologies that can ensure our defense.
The stakes could not be higher. The 1908 event at Tunguska, also in Siberia, was caused by an object at least 60 meters in diameter, as opposed to the assumed 15-20 meter object that terrified Chelyabinsk. The asteroid 2012 DA14, which flew by the Earth on Feb. 15, is thought to have been about 45 meters wide, close to the size of the Tunguska impactor. At Tunguska, the air burst occurring above the Earth’s surface has been estimated to have been 1000 times more powerful than the bomb that leveled Hiroshima. This largest impact event in human history knocked down trees over an area greater than 2000 square kilometers.
Commentators on the Feb. 15 meteor at Chelyabinsk and the passage of asteroid 2012 DA14 generally overlooked the active strategies we can pursue to prevent such impacts. There are many, and many of them are far more creative, and a good deal less problematic, than trying to blow it up with a nuclear warhead. Even so, using a nuke to deflect the asteroid’s trajectory should work, although we run the risk of breaking the object up into a series of smaller objects that could still wreak havoc on our planet. The outcome would depend on what kind of object we’re dealing with, which puts the priority on studying and categorizing asteroids.
But nuclear weapons may be overkill. The world watched with fascination in July of 2005 as NASA’s Deep Impact mission slammed an impactor into comet Tempel 1, ejecting clouds of ice and dust debris. A similar strike on an asteroid determined to be on a collision course with Earth could alter its course enough to miss us, depending on the size of the impactor and the asteroid itself. The other key variable: We would need to hit the asteroid many years before the predicted impact on Earth, which means the premium is on early asteroid and comet detection. Waiting until the asteroid is only weeks — even a few months — away could be fatal.
A number of projects are now underway to catalog the asteroids deemed most dangerous to our planet, but as we proceed, we need to continue the active search for solutions in case something turns up on a collision course. An intriguing possibility that would likewise need time to work is the so-called ‘gravity tractor,’ which works by using nature’s weakest force to do the job. Remarkably, a spacecraft orbiting an asteroid could, over the course of time, cause its trajectory to be altered enough to miss us. This assumes we find the asteroid in time and can get a hefty payload to it even if it is coming from a long way out in the solar system.
Other ideas abound, and we can be sure, as we approach the yearly Planetary Defense Conference in Flagstaff, Ariz., this April, that they will be talked out at some length. Some asteroids may respond to being heated by carefully placed solar concentrators that could beam the Sun’s energy straight at a small portion of the asteroid’s surface. Enough heat could create an outflow of vapor and other materials that could act as a jet to move the asteroid off its course. This assumes we build the technology to reach the asteroid and construct the needed concentrators.
Or how about killing multiple birds with a single stone? At the University of California at Santa Barbara, scientists are developing a concept that would use lasers fed by solar energy to beam enough energy at an incoming asteroid that it would be obliterated over the course of a year. A system like this could be an invaluable tool in our defense arsenal, but it would also generate vast amounts of power for peaceful uses here on Earth’s surface, helping us wean ourselves off dwindling supplies of fossil fuels. It could even, in conjunction with large space ‘sails,’ be used to beam a spacecraft deep into the outer solar system.
These are a handful of the more intriguing ideas about how to stop a future impact. 65 million years ago, the dinosaurs had no space program to protect them and could only suffer the consequences of the huge asteroid strike that occurred in what is today’s Yucatan peninsula. Their demise helped mammals like ourselves become the dominant species on our planet. If we have the wisdom to begin building a deep space infrastructure that can not only find dangerous asteroids but deflect them, we will be guaranteeing that we will not meet the same fate.