Edward Teller, arguably the world’s most influential scientist in the second half of the twentieth century, died a month ago. Late in his life Teller became a powerful advocate for defending the Earth against asteroids, although few of those writing about his death take note of this final chapter in his life. This news item is devoted to remembering Teller’s role in advocating for the development of defenses against asteroids. Most of what follows deals with my own interactions with Teller between 1992 and 1995. I begin with the opening comments from the New York Times obituary.
NEW YORK TIMES OBITUARY
September 11, 2003, opening paragraphs
By William J. Broad and Walter Sullivan
Edward Teller, a towering figure of science who had a singular impact on the development of the nuclear age, died late Tuesday at his home in Stanford, Calif. He was 95.
Widely seen as a troubled genius, Dr. Teller generated hot debate for more than a half century, even as he engendered many features of the modern world.
A creator of quantum physics who loved to play Bach and Beethoven as an amateur pianist, the Hungarian-born physicist helped found the nuclear era with his work on the atom bomb, played a dominant role in inventing the hydrogen bomb (though he often protested being called its father), battled for decades on behalf of nuclear power and lobbied fervently for the building of antimissile defenses, which the nation is now erecting.
His antimissile efforts, obsessive by most accounts and dismissed by critics as doomed to failure, were his way of trying to protect his adopted country from the horrors he helped bring into the world.
Dr. Teller's actions split scientists into warring camps and created huge, lingering controversies over his legacy, including whether his work in the cold war had fostered a dangerous nuclear arms race or an uneasy peace that helped crush Soviet Communism.
TELLER AT LOS ALAMOS, January 1992
Notes from David Morrison with Clark Chapman
(adapted from an unpublished book manuscript)
In 1991 Congress had charged NASA to develop a specific plan for an asteroid survey, through its Spaceguard Working Group, which I chaired. The second part of the Congressional request asked for an analysis of the technology that might be used for asteroid protection, if a threatening object were actually discovered. To address the technology issues, John Rather of NASA Headquarters convened a single brainstorming meeting in January 1992 where ideas on defense technologies could be brought forward. Rather invited many of his former colleagues from the nuclear weapons laboratories (Los Alamos and Livermore), and he held his workshop at Los Alamos National Laboratory in New Mexico. A few of us astronomers also were invited to this defense technology workshop at the last minute.
From the perspective of the astronomers, the meeting got off to a bad start by featuring a 1990 report by Teller’s protégé Lowell Wood and colleagues, which asserted that any asteroidal projectile larger than 4 m in diameter would penetrate through the atmosphere and impact explosively, with a potential for widespread damage and many fatalities. Wood estimated that the Earth was struck by projectiles of 4 m or larger diameter about annually, producing property damage of about $60 million and hundreds of deaths per year, on average. In his words, "it's the stuff between a truck and a house in scale which rains down on our fair planet at rates of dozens to hundreds of strikes per century." These assumptions were so obviously inconsistent with the real world that we were perplexed. Some of us wondered if it was coincidental that the 4-m asteroidal adversaries that dominated Wood's paper were about the same size as an ICBM.
Wood's interest in shooting down small asteroids was initially supported by Teller, whose presence dominated the Los Alamos workshop. This was our first contact with Teller, who had only recently become interested in defenses against asteroids. Leaning on his staff -- a thick wooden pole with a leather grip at shoulder height -- Teller immediately commanded attention. His gravelly voice was clear and authoritative, and his cadence was exceptionally slow, with each word enunciated precisely in a Hungarian accent. We saw that he was treated with extraordinary deference. Once, when Rather, as chair of a session, began to comment after a speaker had finished, Teller's rumble became audible. Rather instantly interrupted himself in mid-sentence to give his mentor the floor: "Oh, Dr. Teller, I am so sorry...I believe you want to speak?" He was always formally addressed as "Dr. Teller", and at Los Alamos he had the final word on any issue.
Gene Shoemaker and I spoke in the first session at Los Alamos, describing the results from the Spaceguard Working Group. In particular, we noted that small asteroids did not penetrate the Earth's atmosphere, in contradiction to Lowell Wood's paper. No questions were asked from the audience, and we assumed that we had made our points. When the weapons scientists began their presentations, however, we found that most of them dealt with ways to locate, track, intercept, and destroy 4-m asteroids shortly before they would plunge down to Earth. Following Wood's lead, each speaker assumed that the greatest danger was from these 4-m "bomblets," which could be located only at the last moment, hence requiring a virtually instantaneous response -- interceptors on the launch-pad -- to shoot them down.
Those of us from the Spaceguard team were not sure what was happening. It seemed to us that the weapons scientists did not conduct their business through the open questioning and dialog that astronomers were used to. Outwardly, everyone seemed polite and deferential toward each other, never questioning the presentations publicly, no matter how outlandish some of them seemed. We wondered if Teller’s dominating presence and support for Wood contributed to suppressing open debate. Only in private discussions with the weapons lab scientists were we able to penetrate below this apparent unanimity and begin to explore alternative ideas.
Several schemes were suggested for exploding asteroids into billions of small fragments. In one approach, it was necessary to get a large nuclear bomb into the center of the asteroid. This would be accomplished by launching a series of closely spaced nuclear warheads, like firecrackers on a string. The first one would be detonated at the surface, excavating a hole. The second warhead, following a fraction of a second behind, would explode within the hole, deepening it. After a dozen or more such explosions, the hole would be deep enough for a large bomb to penetrate and provide the coup de grace. An alternative was suggested by Teller himself, who noted that a sufficiently large bomb detonated at the surface could disintegrate any comet or asteroid. The challenge was to make the bomb big enough. He noted that for the larger asteroids, a bomb would be required that was a million times more powerful than any that had yet been developed. Such a multi-million-megaton weapon would have no use in terrestrial warfare, of course, but Teller suggested it might be appropriate to develop such a bomb as part of a cosmic defense system.
After the meeting, the astronomers compared notes. One thing that struck us was the contrast between Teller and Shoemaker, as the senior scientists from the two groups. Both were widely honored scientists, with Shoemaker often called the “father of planetary geology” just as Teller was the “father of the H-Bomb”. Shoemaker, however, was a pleasant and unassuming man who dressed informally and readily smiled and laughed. To all of us he was plain “Gene”, a friend and colleague, and very American in style. In contrast, Teller projected the image of a European professor, always formally dressed, treated with something akin to awe (or perhaps fear), who gave speeches rather than engaging in dialog. It is hard to imagine more different personalities or scientific styles.
TELLER’S LOS ALAMOS SPEECH, January 1992
One of the highlights of the Los Alamos Meeting was an after-dinner speech in which Teller outlined his thoughts on asteroid defense in more detail. Following is a transcript of that talk as recorded by Clark Chapman.
There are two answers to the question "Why Now?"
First, in the last three years very remarkable changes have occurred in the world. One of them is that I can visit Hungary. What has happened? Nobody present, nobody in the world, had foreseen it. Now, for the first time, incredible things can really happen, including international cooperation on a subject like defense against asteroids.
I cannot pass over, in talking about this subject, the indirect and powerful ways our national laboratories contributed to what has happened. Nuclear energy did not have the possibility of remaining undiscovered. That it has been discovered and has been used - probably not without mistakes, but without major mistakes - has persuaded people who had been previously impotent and unforthcoming to find leaders to take them one big step toward peace. That the Russian people stood up in incredible numbers to defend their own freedom and that of others... this was made possible by the magnificent fact that nuclear power rested in the hands of those who did not misuse it in a truly major way, in the hands of our government which is in fact dedicated to peace. It is a reason to say that we can work on all knowledge leading to technology in the confidence that people will use it properly...the role of the national laboratories in bringing this about cannot go unmentioned. The big changes in the world give a reason for "why now," and "why here" (at Los Alamos).
There is another reason: because of a remarkable number of technological developments which have made it possible to do something about meteorites. Computers, radar, lasers, nuclear energy... you will see how each of these has contributed. We are now facing a problem that before the Tunguska meteorite could not be addressed. These methods were not available. Now they are.
I would like to make my main statement. It will be brief, but the consequences are long. Here is my recommendation about what to do with the opportunity that is here. We must do this in four separate phases, one at a time. Therefore, we must give the lion's share of attention to the first phase: knowledge.
We must find out about meteorites. A lot has been found out. Very much more remains to be found out. In what ways? Many are obvious. I'll mention two special points, which have not received detailed emphasis as yet in this meeting. One is the incredible developments in Livermore in the improvement of lasers. We can now concentrate a lot of illumination in a narrow spectral region for a short time, with laser pulses a hundred times cheaper than before (in terms of megabuck per megawatt). Powerful lasers have already focused on the moon. With the help of rockets, or even from the Earth, we can illuminate a meteorite that passes closer than the moon. We could heat up the surface and watch it cool, yielding information about its conductivity. The importance of this subject is now evident to me, although not before yesterday.
A second example. Shall we look at them from Earth or from space? I don't know. But I will give an argument to look at them from space, because it is not completely obvious. If we put the telescope on a (low) orbiting satellite, it can see all of the sky and with no disturbance from the atmosphere. Clearly one of their important
properties is their changing brightness because of their rotation and changing position. These intensities can be measured from the ground. They can be measured more quantitatively if the atmospheric disturbances are corrected, but the disturbances cannot be eliminated as completely as if you didn't have them in the first place.
I have a practically religious belief that the most important thing is knowledge, which is in principle good. We need to measure intensities to 0.1%, which can be done by CCD's. Unlike photographic plates, which are clumsy and old-fashioned, CCD's report directly to a computer, and then you can perform miracles. With 50 bits to a hundred bits you can get accurate positions of stars and spectral lines. The Sun changes intensity up to 1% every eleven years. We have similar information to date on a few dozen stars. Let's get stellar variability to 0.1% for a million of them, 10^8 bits. Ask the computer to check the catalog. We don't want to know this to find out about the long-term energy variation in stars - it has been a million years from the production of energy to when it is emitted. What we see on the short term is due to hydrodynamics, which we don't understand (except for Cepheid variables). We're ignorant about the smaller variations. Why do we want to know about them? I'll tell you after I find out. Galileo said look first, then find out what the problems are. From space you have a better possibility of learning about meteorites and also about this entirely different branch of science.
This project might be done internationally; a national effort would be difficult and expensive. But the public interest exists for this first step of knowledge.
The second step is experimentation. Every year one of these potentially dangerous meteorites (it is not actually dangerous) comes closer than the moon. We should send out satellites to discover them, try to do what you would do for defense if you needed to, whether nuclear or non-nuclear. We can give an absolute guarantee that we will have no detectable radioactivity on the Earth. These could be stones, rubble piles, a comet, chondrites, iron meteorites - whatever - you take the best look at them and experiment, so if and when a real danger occurs, you have already practiced. Do it internationally. The United States should pay less than half the cost; this is not to save dollars, but criticism from other nations would be much more constructive if they were paying. The planning, the money, the actions should all be international. If a threat occurs, the knowledge from our experimentation can be used.
The third phase is defense against a meteorite that is going to hit. One might think about starting to make plans about who decides what to do when it happens. Perhaps it is good to make plans. I'll say why it might not be good. I hope that we will have more than three months' notice, not about a hypothetical object, but about a real one that will hit. Maybe we should evacuate 1,000 people or maybe we should use one of the methods we have already practiced. If the decision on how to decide is made in advance, it will be made by bureaucrats. If the threat is happening, the people will decide; I trust the people better. If the object is deflected, then we have step number four.
As step four, we can make plans for the safety of the whole future. I would like to practice on a small one because there is a 99% chance that a small one will come before a big one, so it is the optimal approach.
In this extraordinary time, which is the end of three years of miracles, we are looking into only the possibility of a better future, because there are big and different changes for different people in 1992 (like starvation). This is a crisis for which the Chinese symbol that means both danger and opportunity applies. Defense against meteorites is one way to make the opportunity more and more real.
I will make a more general remark about how the opportunity should be used. The right solution was proposed in early 1946 to the U.N. Its outstanding characteristic was to seek security in cooperation and openness (not secrecy) in the ashes of the Lilienthal report. It was proposed by Oppenheimer, who was not a right-winger; and by Baruch, who was not a left-winger, and presented to the United Nations. All political parties supported it, the right solution, but it went to naught due to the veto of Stalin. It involved an International Atomic Development Authority with limited but sufficient powers. I think we can succeed now.
Two last things. First, you might call me over-optimistic. We should be daunted by neither war nor meteorites. Man has been called a problem-solving animal. Man and woman are called problem-creating animals. We will have new problems to solve. I am optimistic, however, and not only because it is my birthday.
Second, a pessimist is a person who is always right, but gets no enjoyment. An optimist imagines that the future is uncertain. Our duty is to be an optimist. Then we are prepared to do something about any threats.
TELLER AT ERICE, April 1993
Notes from Clark Chapman David Morrison
(adapted from their unpublished book manuscript)
In the months following the Los Alamos meeting, the astronomers and the weapons builders continued their dialogue. At Los Alamos, Teller had focused on the problem of defending against small asteroids, which could not be detected more than a few days in advance of their collision with the Earth. Later in the spring of 1992, however, when he and I gave back-to-back keynote lectures at a meeting of the National Space Society in Colorado Springs, Teller had accepted the argument that small projectiles were not a problem and that some sort of comprehensive asteroid survey (the Spaceguard Survey) should be carried out to find the larger ones. At that time he advocated conducting a space-based search for NEOs using Star Wars technology. A series of small satellites would be placed in Earth orbit to scan the sky for asteroids, transmitting their observations to the ground for analysis. By the time of the next hazard meeting, held in Tucson in January 1993 (see below), Teller was apparently reconciled to the cost-effectiveness of a ground-based asteroid survey like Spaceguard.
Looking ahead to the problems of deflection, however, Teller expressed concern about our lack of knowledge of the physical properties of comets and asteroids. He advocated a major program of spacecraft visits to explore the comets and asteroids, using small and relatively inexpensive probes based on the "brilliant eyes" surveillance system being proposed by Lowell Wood at Livermore. He also suggested that initial spacecraft visits should be followed by active testing, including the experimental deflection of asteroids and comets to develop the technology that might someday be needed for defense against a real impact threat.
Although he remained in the background during the early interactions between astronomers and weapons scientists, one of the most influential figures in the impact hazard debates was Col. Pete Worden of the U.S. Air Force. With Teller's support, Worden decided to organize another conference on asteroid defenses for the spring of 1993. This meeting would focus on near-term issues, rather than "new technology" schemes. Worden’s meeting would be international, with the participation of leaders from the Russian defense establishment. And far from banning the press as Rather had done at Los Alamos, Worden invited not only science reporters but also leading critics of the Star Wars program from a number of Washington space and peace advocacy groups. For a location, he chose the picturesque town of Erice, perched atop a mountain on the west coast of Sicily. In this environment, Teller was much more wiling to join in discussion and exchange of ideas, although he still retained his aloof professorial persona. The discussions were constructive, and gradually agreement emerged among the participants, in spite of their different backgrounds. The Russians seemed especially anxious to share their decades of experience with nuclear weapons in the service of a new, international cause.
On the final day of the Erice conference, we all gathered in the main monastery building to agree upon a statement that summarized the conclusions we had reached. The first four points of the statement were relatively straightforward. The group agreed that "cosmic impact is an environmentally significant phenomenon which has played a major role in the evolution of life on Earth", and that "the threat is real and requires further internationally coordinated public education efforts." We also agreed that "gathering of additional physical knowledge of NEOs and their effect on the Earth is a scientifically and socially important endeavor," and that "dedicated international astronomical facilities similar to the proposed Spaceguard System should be developed."
On a final question, however, consensus broke down. Teller insisted that defense issues also be addressed. He was convinced that nuclear experiments on deflecting real asteroids and comets were necessary. He had two reasons. One was technical: the need to learn how to accomplish such a task in advance of any actual emergency. His second reason was political. He argued that it would be extremely difficult to obtain international agreement for any use of nuclear devices in space, and that we had better start now to work out ways to deal with this problem. Teller considered the social experiment of forging international consensus in support of experimental deflections to be even more challenging than the technical problems of accomplishing the deflection once it was approved.
In the Erice environment, Teller did not automatically get his way. Opposed by Worden, Shoemaker, and all of the Spaceguard astronomers attending the conference, Teller found himself engaged in a real debate. Most of us wanted to say explicitly that we did not favor experimentation at this time, but Teller stood his ground. He would not agree to any statement that called for deferring experiments, while the majority would not sign any statement that endorsed such experiments. After heated arguments, the stalemate was resolved in the waning minutes of the conference and compromise wording was approved: "The study of potential mitigation systems should be continued. Many of us believe that unless a specific and imminent threat becomes obvious, actual construction and testing of systems that might have the potential to deflect or mitigate a threat may be deferred because technology systems will improve." The "many" referred to in the statement was nearly everyone at the meeting except Teller.
TELLER AND THE HAZARDS BOOK, 1993-94
Teller participated in what was undoubtedly the most important scientific conference on the impact hazard, organized by Tom Gehrels in January 1993, one year after the Los Alamos meeting. One product was the 1200-page book Hazards Due to Comets and Asteroids (University of Arizona Press, 1994), which contains 46 technical papers covering many aspects of impacts, ranging from the population of asteroids and comets to defense approaches. The presence of the two old adversaries, Teller and Carl Sagan, added to the interest of this meeting.
Tom Gehrels hoped that Teller and Sagan would collaborate on a short policy chapter for his book, but this proved impossible. Teller would consider the possibility of such a collaboration, but not with Sagan. Accordingly, Greg Canavan of Los Alamos served as facilitator to bring me together with Teller to discuss writing a joint chapter, focusing on the areas in which we agreed. It was exciting for me to face the opportunity to try to find common ground with Teller. I took notes from my discussions with Teller and made use of the consensus resolotion from Erice described above. In this basis I wrote a first draft, subsequently refining the chapter with him at his office at Stanford University.
The only areas in which we had difficulty agreeing where those that dealt with experiments to develop defense technologies. I recall discussions, for example, concerning where such experiments should be carried out. Teller advocated working with an asteroid that came very close to the Earth in order to see the effects from the ground. I pointed out that the debris from any asteroid that was disrupted near the Earth would return to menace the planet later, and that we should experiment on as asteroid with an orbit that brought it nowhere near our planet. I won the argument here, although in his autobiography (see below) Teller returned to advocating that experiments be done using asteroids that come between the earth and the moon.
Teller was anxious to argue in this forum for an open international approach to defending our planet. The final two paragraphs of our paper (Morrison & Teller 1994) stated:
“In the present situation, there can be little doubt that the important decisions connected with the danger of asteroid impact should be made by open democratic means. Under these circumstances, scientists and engineers should limit themselves to the finding and publication of relevant facts. Of course, interpretations and value judgments are useful and important as well. But the resolution of points of disagreement and the formation of policies to deal with the impact issue must reside with the population at large through their legitimate representatives….
“Our actions should be widely publicized and explained, with secrecy restrictions abolished as completely and rapidly as possible. This principle holds particularly for issues associated with the use of nuclear energy…. All parts of the world are equally at risk from impacts, and we all share a common interest in our self-protection from such cosmic catastrophes. One of us (E.T.) urges that experimentation should not be delayed except for strong reasons, since procedures for protection need to be decided on the basis of data on comets and asteroids, part of which can be obtained only through experimentation.”
The fact that Teller’s iniaials were E.T. led to some humorous comments. Teller noted that in fact extraterrestrials were among us, but that we called them Hungarians!
TELLER IN RUSSIA, September 1994
Notes from David Morrison with Clark Chapman
(adapted from an unpublished book manuscript)
Two groups of Russian scientists were interested in asteroid defense issues. The Russian astronomers (centered in St Petersburg) had been interested in asteroids and asteroid orbital dynamics for many decades. Now, however, some of the Russian weapons scientists also began to explore the possibility of testing nuclear explosives against asteroids, the same “experimental” approach that Teller advocated. For many years the defense strategists and weapons builders from the U.S. and Russia had worked together, first as cold-war rivals and more recently in a spirit of international cooperation. Within Russia the astronomers and the weapons scientists initially pursued their interests independently (as they had in the United States), but by 1994 they had begun to talk to each other, largely at the initiative of nuclear physicist Vadim Simonenko.
Simonenko worked at the Institute of Technical Physics of the Russian Federal Nuclear Center -- the Russian equivalent of Livermore National Laboratory in the United States. For decades the existence of this Federal Nuclear Center had been a military secret, and the city in the southern Urals where it was located did not even have a name -- just a postal code, Chelyabinsk-70. It was a milestone in the emergence of this secret city when Simonenko obtained permission to host an international conference on asteroid defense there. The conference was named "Space Protection of the Earth 1994", and both Teller and Wood accepted invitations to attend, as did five other Americans, myself included.
The American party arrived at the Ekaterinburg Airport in the small hours of September 25, having crossed 12 time zones in the flight from California. Soon we were in a bus, following the blinking blue light of a police escort through endless miles of white birch trees to our destination: a closed city that appears on no map of Russia. Only during the preceding year had it obtained a name: Snezhinsk, which means "snowy" in Russian. When we finally arrived, we entered Snezhinsk through barbed wire fences guarded by soldiers with automatic weapons and unsheathed bayonets. Here, isolated from the rest of the world, lived the 15,000 workers at the nuclear institute and their families. A huge bronze statue of Lenin still dominated the central square, and several of us spoke with students in the schools who had never before seen an American. These talented people, who have spent two generations building nuclear bombs in this closed society, were looking for alternatives. Shooting down asteroids seemed like a possibility.
The Space Protection meeting was attended by about 150 Russians, the majority of whom had not previously worked with foreigners. For a week we met to discuss asteroids, with particular emphasis on schemes for interception and nuclear deflection or destruction of NEOs. Teller, as "father of the H-bomb", was idolized by the Russian nuclear community, and he and Wood had come to Russia with a message that this audience was happy to hear. The Teller-Wood thesis was simple: we must build an international defense system against cosmic impacts, and an urgent part of that effort is to conduct nuclear tests to learn how to deflect or destroy NEOs. Teller emphasized that such an experimental program was the only way to obtain the required data, and that nuking asteroids represented the most cost-effective kind of experimentation. In case anyone missed the message, Wood also told the audience that there were no international prohibitions against nuclear explosions in space, since the existing treaties dealt only with "weapons of mass destruction", not peaceful uses of nuclear explosives intended to develop a capability to protect the Earth. Teller added that “only fear-mongers oppose the peaceful use of nuclear explosives.”
One of the interesting experiences of this week was a visit to the nuclear museum at Snezhinsk, which included several exhibits dealing with peaceful applications of nuclear explosives. The centerpiece was the mock-up of a 100-megaton bomb, the largest ever built and tested. Teller posed next to this bomb, and pictures of him with this monster have been widely published, including in Teller’s autobiography.
TELLER AT LIVERMORE, May 1995
A third planetary defense meeting (following those at Los Alamos and in Russia) was held at Livermore, California, in May 1995. Following is Teller’s talk, one of the last public statements he made on defense against impacts. He did not attend the SPE-96 meeting the next year in Russia. Note that in this talk Teller has accepted the impact-frequency estimates from the Spaceguard Survey Report and has also adopted the 1-km threshold for global disasters, which he had not mentioned in previous talks.
The Need for Experiments on Comets and Asteroids
paper given at the Planetary Defense Workshop
Lawrence Livermore National Laboratory, May 22-26, 1995
I would like to say a few things in a straightforward and very serious manner. I believe we are here -- in fact, we all know we are here -- to look into a situation that is unique in the size of the trouble we are looking at and in the improbability of these big troubles. For mathematicians, it is easy to multiply the two and to say that this trouble is like other troubles because the product is the same. For politicians who are trained to look carefully at what happens during their terms of office and less carefully at everything beyond, the same does not hold as for the mathematicians. And we, in turn, depend on the politicians to make it possible for us -- in the form of dollars, or rubles, or anything else -- to do what is needed to be done.
I think it is extremely important that we present a credible case so we can go ahead. I would like to suggest a few points of view on how to present the case that we are talking about -- presenting it very truthfully but emphasizing the things that ought to be emphasized.
Here is the situation that, in my mind, is a scandal, and I think people can understand that it is a scandal: There is a probability of a few percent in the next century of the arrival of a stony asteroid -- not the biggest possible but a fairly big one, approximately a hundred meters in diameter. It delivers on impact maybe 100 megatons. It is a practical certainty that, when and if such an object should bump into us, it will come completely unannounced. We won't have any indication of it. Yet such an object is apt, with a fairly high probability, to do a lot of damage -- for instance, cause a tsunami if it falls into the ocean. Damage would be concentrated on the shores region, where people like to aggregate. So in effect of the asteroid and the people are attracted to the same meeting point -- hence, a lot of damage. Just in dollars it could be billions, and in lives it might reach millions. Yet, no warning whatsoever.
What we need to rectify this situation is half a dozen arrays of CCDs and appropriate (not very big) telescopes, amounting to probably not much more than ten million dollars altogether. If such a catastrophe should occur, afterwards we'll be able to point out on existing pictures where the asteroid has approached, but we wouldn't know it ahead of time because nobody would have looked at those pictures. I shouldn't have said nobody; I should have said hardly anybody. And actually, to find them would be extremely difficult. The CCDs can be systematically trained to scream when there is something suspicious, and in this way we could have information a week ahead of time. To my mind, such action would correct a very large incompleteness in our safety system. And I think that should be a very salable item.
So, we know ahead of time that something is coming. What do we do about it? We would know ahead of time with sufficient accuracy, for instance, what shorelines have to be evacuated. A week is not plenty of time, but it is very considerably more than nothing.
I was interviewed today and the question was asked: Is the international situation ripe for such action? I'm answering with every confidence: It is. I have no doubt that if there is such a danger from outside, if we know that people in certain spots will have to move to save their lives and can't move to save their property, then it will be psychologically not only a necessary thing but an easy thing to get help from all over the world to whoever has to evacuate. I hope that the same thing holds for all the other measures that we might be willing and able to take in order to improve the situation, because I certainly don't want to stop at the point of just saying "evacuate."
The next point that I feel is a real necessity is to know what more to do. We have the power to reach out into space and to deliver what is needed. But we don't know how the objects behave that will arrive. Very particularly, we will know rather little about the actual object that has been a mere spot on the best photographic plate and that has grown for the last couple of days a little more to not very much more than a bigger spot.
What do we do about it? I claim that the next thing we ought to do is to gather knowledge about what can be done. What is the variety of things that can be done? Such knowledge can be obtained in a number of different ways. The one I prefer (and that all of us will not necessarily prefer) is to make experiments -- one or two or three per year -- on objects that are getting close to the Earth, to the approximate distance of the Moon, more or less one light-second away from the Earth. Whatever we do can be observed from the Earth very easily. And to get out there is not very difficult.
And what do we do there? Well, we can do a number of things. I would recommend that, to begin with, we do the very simplest thing on which we can agree: Put up sharp tungsten knives for the purpose of cutting up the incoming object if it's of an appropriate size-something like 300 feet or 100 meters in diameter. Of such objects, approximately a few approach in a year. We make experiments on them. Can every one of them be sliced up sufficiently so that if the fragments fall on the Earth, they will be burned up in the high atmosphere in a completely harmless manner? This certainly can be found out by experiments on objects that have already passed the Earth. I think such experiments will contribute, to a considerable extent, to safety in the one-percent-per-century case that such a danger might actually occur.
Now, if we find that the biggest or toughest of these objects will not be completely sliced up, then, after we have become familiar with the slicing up, we should take the big step -- using a nuclear explosive. If, for instance (which I think is a plausible situation), on a 300-meter-diameter object, we have succeeded in slicing up 20 meters of the surface, we can then put a nuclear explosive close to the surface, which will irradiate the rubble that we have already created. This tends to homogenize this rubble and push it one way, while, by reaction, the remaining ninety percent of the material is pushed the other way. The reaction on the main body will be very powerful, and there can be no doubt that appropriate deflections can be arranged.
Objects a kilometer or more in diameter are apt to create worldwide disaster. On the average, they are expected once in a million years. We hope to discover them several months in advance. The use of nuclear explosives as outlined might or might not suffice to deflect them. A more radical method of using several nuclear explosives may be needed. We might use them to create the rubble, and this maybe followed by one big blast as mentioned above.
Or we might attempt to bore a hundred-meter-deep hole by successive nuclear explosives and then blow up the object by one big, deeply located explosion. Such methods cannot be relied upon without experimentation on objects that have safely passed the Earth.
One final possibility should be considered. Of the hundred-meter diameter objects, there are approximately a million. They could be discovered, cataloged, and their orbits computed. If a huge, hundred-kilometer object approaches and is apt to hit the Earth within a year, then one of the hundred-meter objects is almost certain
to approach it to within approximately one light second before this can happen Careful deflection of this smaller object could steer it into the path of the bigger one. The expected result would be to prevent a collision with the Earth, which would be the ultimate catastrophe. One must add that collision of a hundred-kilometer object with Earth is not apt to be predicted even in a billion years.
I would like to conclude with emphasizing one obvious principle: We scientists are not responsible and should not be responsible for making decisions. But we scientists are uniquely and absolutely responsible for giving information. We must provide the decision-makers with the data. On the basis of this, they will have the best chance to make the right decisions. That is the main reason why I say that we must pursue and must be given the means to pursue the knowledge as to when and how objects will arrive and the knowledge as to possible ways to deal with them The choice of how to deal with them can be and should be delayed. If need be, it can be done and probably will be done in the last moment. But knowledge -- the firm knowledge, not merely guesses on how asteroids will react but knowledge based on experiments -- should become available. That is our responsibility. And I believe we should argue, in a carefully considered manner, so that we can acquire, in the most efficient manner, as much of the relevant knowledge as is possible.
I can add only two words: Good luck!
Teller published his autobiography in 2001 (Edward Teller, Memoirs: A twentieth century journey in science and politics, Peseus Publishing). The last two pages of this 600-page book deal with the impact hazard. Teller does not mention the meetings in Los Alamos or Tucson or Erice, but begins by describing his 1994 visit to Russia, concluding that “everyone I met [at Chelybinsk-70] was extremely kind, and I thoroughly enjoyed my two-week stay….
“The scientists attending the conference at Chelyabinsk agreed that the more frequent medium-sized impacts [like Tunguska] and the infrequent large impacts are both important. When the probability-weighted damage of all these impacts is considered, meteorite strikes appear to be about as damaging as earthquakes or hurricanes. The practical point is to prevent the great damage caused by large or massive meteorites…..
“It would be valuable to have a system that could intercept a sizable meteor on collision course with the earth. An explosive, detonated an appropriate distance below the meteor’s surface, could expel material from the meteor and either alter its course or break it up. In most cases, conventional explosives would provide a sufficient blast. The only practical way to assure that we could deflect a meteor is to conduct experiments on them by interacting with meteors that pass between the earth and the moon. The experiments should be carried out, of course, when the meteors are beyond their closest approach to earth…”
Teller’s book concludes with the words: “I think that learning cooperatively with other nations how to prevent damage from meteor impact -- becoming knowledgeable enough to prevent a globally catastrophic natural disaster -- would be a worthwhile way to begin the new millennium.”