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Destruction of the object can work, but we have to be careful. If we blow it into pieces, the pieces should be small enough that they'll burn up in the atmosphere. Otherwise, we'll have a bunch of small impacts, rather than one large one. The former may be more destructive than the latter, since it will affect more area. Another possibility is that when we blow the object apart, the pieces have their velocities changed. If the velocities are changed enough, the pieces will miss the earth entirely. If the object is just a pile of rubble, this may be the way to go. If we do decide to blow it up, how do we do it? Nuclear weapons are an obvious choice. But they have disadvantages. People are reluctant to put them into space, for good reason. An orbiting nuclear weapon could destroy Moscow or Washington with essentially zero warning. Warning time, to allow for a counter-attack, was the cornerstone of deterrence throughout the Cold War. Of course, if civilization were at stake, and the nations of the world ensured only one weapon was put into space, that would certainly be acceptable. There is also the risk of a rocket explosion when launching the weapons into space. That could spread radioactivity over a large region of the earth. And if we use nuclear weapons to blow up an asteroid, the pieces would be radioactive. Those that reached the earth would spread the radioactivity as they burned up in the atmosphere. We also might want to avoid making any pieces radioactive, even if they never reach the earth — we might want to mine them someday. So chemical explosives might be preferable, but it's unclear if any would be strong enough to do the job. It's possible some kind of new technology would have to be developed. Perhaps drilling into the asteroid in numerous places, placing explosives deep within it, and detonating all of them at once would do the trick. Or we might divert another asteroid, so that it crashes into the impactor and destroys it. Again, we'll have to explore the object first. We may even have to try out our ideas on another asteroid, not headed for the earth. In fact, I will predict this. When we do find such an object, if we do decide to destroy it, it's much too risky to hope whatever procedure we invent will work the first time we try it. We don't want to create a large number of big, destructive pieces. We will have to try our procedure on several objects. We'll try it with small ones first, then larger ones, then finally one of similar size. And the ones we destroy as experiments won't be headed toward the earth, or even be close to heading toward the earth. We don't want to accidentally divert one into earth's path. Only when we have demonstrated that we can reliably destroy an asteroid, without creating a number of pieces that will survive the earth's atmosphere, will we be willing to destroy one that's headed for earth. (This could all change if we don't have enough time to do the experiments, but still think destruction is the best option. Wasn't that the plot of the movie Armageddon?) Similar statements hold for diversion, if using an explosion. We might be willing to chance an engine, without prior experimentation — at worse we'd just start over with a different or stronger engine, or way to connect it to the object. But we would not want to risk an explosion that might create large, survivable pieces. We'd want to try it first, and be assured that the explosion would move the asteroid, not fragment it. We don't yet have the technology to do this exploration and experimentation with robots. If we found such an object today, we'd have to use astronauts to explore it, and do any drilling. But it's likely we won't find such an object for decades or centuries; we might have satisfactory robot technology then. |
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