Death from the Skies! Read Online Free PDF Page B

probe slammed into the comet Tempel 1, creating a flash seen by hundreds of scientific instruments across the world. The impactor was an 800 pound block of copper, which was steered into the comet at over six miles per second. The resulting explosion was the equivalent of about five tons of TNT detonating. The size of the resulting crater is unknown; the flash and debris hid the impact from the spacecraft’s camera.
    Steering a probe into an object moving at several miles per second is an engineering triumph. There were no second chances, and even the exact shape of the comet nucleus was unknown until the probe got there.
    On the other hand, the comet itself was three by five miles in size, which is pretty big. Had it been a small asteroid, it’s unclear whether the NASA engineers would have been able to hit it. Still, it was a first shot, and a successful one. Much was learned from the attempt that can be applied to ramming a potentially dangerous asteroid.
    But it must be stressed that the impacting scenario suffers from most of the same issues as bombing an asteroid: it might shatter the asteroid, producing many smaller impactors; if the asteroid is porous it will simply absorb the impactor; and again we cannot control the resulting orbit, so we might just be pushing it into some other future impact event. While this might change the orbit enough to miss the Earth, it can’t be known in advance just how much, and in this game inches matter.

VIRTUAL TETHER
    Still, there may be other ways to rid ourselves of a potential planet-buster. Perhaps, instead of blowing one up, we can instead gently persuade the asteroid to change its trajectory.
    The B612 Foundation—named after the asteroid home of Antoine de Saint-Exupéry’s titular Little Prince—is, for lack of a better description, a kind of doomsday think tank, consisting of dozens of scientists, engineers, and astronauts whose express purpose is to figure out a way to save humanity from the threat of giant impacts. The foundation has held meetings, written papers, and had members (such as Apollo 9 astronaut Rusty Schweickart) testify before Congress about doomsday rocks.
    Their Web site reads like a science-fiction novel, full of ways to stop an asteroid from hitting us. However, the emphasis is on the science. While many of the methods would be difficult to execute and are clearly only in the very early stages, others involve mature technology or adapting what we already have.
    For example, one method is to physically land a rocket on an asteroid, secure it in place upside down, and then start firing it. Over time, the thrust will push the asteroid into a new orbit, making the rock miss us.
    This may be the safest method, and it certainly makes sense, but in reality it would be pretty hard to do. For one thing, it’s not entirely clear how you would secure the rocket to the surface of the asteroid. What if the surface is powdery, or it’s a rubble pile, or it’s metal? For another, every asteroid spins, which means you can only fire the rocket for short periods of time when it’s pointed in the right direction. That means you need more lead time, and in many cases time is precious. Worse, some asteroids tumble chaotically, and for those a rocket would be nearly useless.
    These problems kept the B612 Foundation members thinking . . . and they came up with an answer that is really quite surprising. What if you don’t land the rocket at all?
    Asteroids are small compared to planets, but they still have mass. And any object with mass, said Isaac Newton, has gravity. The rocket itself has mass, and therefore gravity as well. So imagine this: a rocket is placed in a parking orbit near the asteroid, but not physically in contact with it. The asteroid’s gravity will pull on the rocket, making it fall toward the asteroid. In the same way, the rocket’s mass will pull on the asteroid. Now the rocket is fired, but very, very gently, just enough to counteract the fall