This post examines the consequences of the impact of a large stony or nickel-iron asteroid or a large ice and rubble comet upon the earth. For precedents see ‘Dinosaur Demise 65 million years ago’. That should pretty well cover the consequences. Now I’d like to move on to scientifically proposed preventive methods.
There have been several entertaining motion pictures and “scientific” television programs recently describing supposedly realistic methods of protecting the earth from planet-killing asteroids or comets. I have watched in disbelief as prominent scientists expounded on methods to save the earth from these wanderers in space. Their supposedly educated and well-thought-out concepts range from blowing them up with nuclear weapons, to blasting them with space borne lasers or focused light beams or attaching rockets to change their path away from an impact with earth. At the risk of being accused of the scientific version of heresy, I'd like to state my objections to these methods and propose one of my own that I think could be effective.
The Nuclear Option
First I’d like to discuss the ‘blasting them with nuclear weapons’ option. As I understand the physics, the blast effect of nuclear weapons is created by the 7000-plus-degree fireball superheating the air in which the explosion occurs. This causes the air to expand at an incredible rate. This expanding bolus of air actually constitutes the blast wave. Since there is no air in space a blast wave cannot be created. The explosion of the bomb would probably just look like a super-sized flashbulb. No noise, of course for the same reason. (No air – no sound.) The asteroid would be pelted with x-rays, gamma rays, infrared radiation and the remains of the bomb casing and vehicle, which would have been pretty much vaporized. Since Force = Mass times Velocity, the miniscule amount of mass left after the explosion would probably not be able to move much more than a basketball-sized piece of asteroid if even that. Now a nuclear bomb could probably have a significant effect on a rubble-filled snowball-type comet. The infrared radiation could cause the ice to flash into steam and, for an instant, expand it against the rubble and push the rocks away in a somewhat different direction.
Bits and Pieces or All in One?
One of the caveats expressed by some scientists is that if we do blow up an asteroid in some manner, we would be in greater danger than if we left it alone and let it strike the earth. I would like to explore this concept thusly: assume you and I are standing 50 yards apart in a field. I have a 12-gauge shotgun with which I inform you I am about to shoot you. I give you the choice as to the ammunition I will use. Your choices are: bird shot or a rifled deer slug. I don't know about you but I would jump on the bird shot like a pit bull on a T-bone. Why you say? Of course you already know. Bird shot fired even at that short distance would be greatly affected by the air through which it passes. Also, F = M x V comes into play because each very low mass piece of shot will strike you with very little impact. You would probably be completely safe with a hunting jacket and protective goggles. A prime example of this is the hunting accident involving Dick Cheney, our former vice president. The cumulative impact of the many pellets would be spread over a large area. A rifled deer slug, at that range, will still carry (F = M x V) considerable power to penetrate clothing, skin and organs. You will be dead meat.
One For All and All For One
Unless I am mistaken, the same would be true in comparing the impact of one large asteroid as opposed to many small asteroids entering the atmosphere and eventually striking the earth. The broken pieces would expose a very much larger surface to the atmosphere for ablation and, because of their greatly reduced mass, would be significantly slowed. Note that in free-fall parachuting, terminal velocity is determined by both the weight (mass) and total area of the falling individual. Each piece of the asteroid being smaller would carry much less force than the complete asteroid. Furthermore, since our planet is covered primarily by water, this group of smaller asteroid remains would mostly impact in the oceans. The sum total affect of their individual impacts would be orders of magnitude smaller than that of the original intact asteroid.
Finally, there are the methods proposed for changing the trajectory of an asteroid. Some of these methods include firing a powerful laser at the asteroid so that surface matter would ablate and fly off into space and move the asteroid slightly. (Newton's third law.) A second and similar proposal is to launch a huge space mirror and focus the rays of the sun on the surface for the same ablative effect. A third is to attach rockets to the surface of the asteroid and nudge it into a slightly differently path so that it misses the earth entirely. I do not believe that any of these methods would work. This is simply because they all assume that the asteroid is moving along in space without any rotating motion at all. This assumption is necessary so that this long-term firing onto the surface (months or even years) would be impacting the same spot for all this time. This is the only way an ablative effect could change the velocity or direction of the asteroid. From the information and photos I've seen, these travelers are usually tumbling erratically. The reason that they come our way is most likely because they have collided with another object in the asteroid belt or the Oort cloud. Such an impact would impart changes in both velocity and rotation. Because of this rotation neither a laser nor a light beam would be able to blast an area long enough to have any significant directional effect. Since rocket motors take a significant time to develop thrust they would probably just cause the asteroid to spin even more erratically.
The Hope For A Solution?
One method that I believe could have a reasonable chance of success is as follows. A series of deep holes would be drilled perpendicular to the long axis of the asteroid, regardless of its rotational motion. Powerful explosives would then be inserted in the holes. The explosives would, of course, need to be preheated and super insulated so that they would not radiate their heat into space, preventing the necessary chemical action from taking place. Each explosive device would be equipped with an electronic detonator. A triggering wire would lead from the holes to an electronic receiver. Each of the holes would then be partially filled with the rubble from the excavations. The charges would then be triggered simultaneously by a radio signal. The signal must be accurately timed so that the exits of the drilled holes would be facing in the opposite direction from the desired movement. When the charges explode, Newton would strike again. The explosion would press against the bottom of the drilled holes and, simultaneously, project the rubble out of the hole at a very high velocity. Our friends F = M x V and Newton come into play and the thrust of the blast would move the asteroid in the opposite direction much as a jet engine moves an aircraft and the recoil of a shotgun presses back onto the shoulder of the shooter.
The Time Crunch
In this manner, I believe sufficient force could be applied to an asteroid to divert it slightly from its orbital path. The success of any method, however, is dependent upon detecting the asteroid months, or even years before impact, so that there would be time enough for such an effort to be effective. The bottom line is that many more resources must be devoted to detection of these intruders to provide sufficient time to act. The last figure I heard was that the total number of individuals devoted to this search world wide was the approximate equivalent of the staff of one MacDonald’s restaurant. Considering the possible consequences, I honestly think we can afford to do better.