Chapter 1: is the earth worth saving?

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The United States Congress took a bold initiative in asking NASA to study the impact hazard. At that time, most NASA managers were skeptical of becoming involved in the issue, warned by unfavorable press reactions to comments by Vice President Quayle on this topic, but they had no choice but to follow congressional instructions. One of us (Morrison) was appointed to head the international working group that defined the hazard and studied ways to increase the discovery rate of NEOs. This group met throughout 1991, as recounted in this chapter, determining for the first time how the danger is related to the size of the impacts. We found that the greatest risk is from impacts near the threshold for global ecological catastrophe (about 1 million megatons, corresponding to a mile-wide asteroid or comet), rather than from the much more frequent smaller blasts (like Tunguska). With these results in hand, we designed an international astronomical survey system to find these objects, which we called the Spaceguard Survey (borrowing the name from a science-fiction novel by Arthur C. Clarke). The cost of the Spaceguard Survey was estimated at $250 million, spread over the 20 years that would be required to discover all the near-Earth asteroids larger than a mile across. Our Spaceguard Working Group completed its report to NASA and the Congress in January 1992.


Needs opening quote.

Congress had charged NASA, through its Spaceguard Working Group, to develop a specific plan for an asteroid survey. The second part of their request was less well defined, asking only for an analysis of the technology that might be used for asteroid protection, if a threatening object were actually discovered. In addressing this assignment, John Rather took a different approach from that adopted by the Spaceguard team. He decided to hold 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 meeting at Los Alamos National Laboratory in New Mexico, the home of "The Bomb".

A few astronomers also attended the defense technology workshop. Except for Gene Shoemaker, who had been invited early on, the Spaceguard members had received their invitations at the last minute, reportedly at the insistence of NASA officials who wanted balance. Most of us had never visited Los Alamos, constructed in the remote mountains of New Mexico during World War 2 for the sole purpose of designing and constructing the first nuclear bombs. It was apparent from the beginning that the environment here would be different from that of NASA scientific meetings and workshops. A prominent sign set the tone for the meeting: "By Invitation Only." John Rather barred several reporters who showed up, even though the meeting was unclassified. We entered the meeting room past a long gallery of portraits of such great atomic physicists as Robert Oppenheimer, Niels Bohr, Enrico Fermi, Hans Bethe -- and Edward Teller, who was also present in person. As we describe in this chapter, a new constituency interested in asteroid defense was about to make itself heard -- the bomb builders.

Since most of the people who assembled in Los Alamos were new to the asteroid defense issue, John Rather had sent them each a package of background reading. This package included an unpublished 1990 report by Lowell Wood and his colleagues at Livermore National Laboratory, called "Cosmic Bombardment II: Intercepting the Bomblets Cost-Efficiently." In this report, Wood asserted that any asteroidal projectile larger than 4 m in diameter would penetrate though the atmosphere and impact explosively, with a potential for widespread damage and many fatalities. He 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." Since these smaller impacts are much more frequent than large ones, Wood recommended that any defensive system should concentrate on the 4-m projectiles. He went on to outline such a system, featuring nuclear-tipped interceptor rockets that could be launched on short notice, rather similar to some proposals for defense against enemy nuclear attacks. He concluded that "erecting such defenses should be commenced at the earliest practicable date."

We Spaceguarders were incredulous when we read Wood's paper. Not only had he made a basic technical error in his calculations of the threshold for atmospheric penetration, he had also apparently failed to test his hypothesis against simple common sense. How could he assert that cosmic bomblets were killing all these people and doing hundreds of millions of dollars in property damage, when there were no newspaper or historical reports of even one such destructive event having taken place? Obviously, there was some fallacy here. During the days before flying to New Mexico, we wondered: why had Rather included this erroneous report in his collection of background reading? Was it coincidental that the 4-m adversaries that dominated Wood's paper were about the same size as an ICBM?

We had heard of Lowell Wood before. A burley man with a red beard and booming voice, he was famous in the defense community as a favorite of Edward Teller's who had achieved a high position at Livermore and considerable prominence in Washington. He had also gained national notoriety as the chief advocate of the x-ray space laser that had provided the original justification for President Reagans' Star Wars policy, a technically flawed concept that was ultimately withdrawn as unworkable after the expenditure of hundreds of millions of dollars. More recently Wood had taken command of the defense programs at Livermore called "brilliant pebbles" and "brilliant eyes", and he was touting these as the answer to the challenge of an impenetrable missile defense.

Wood's interest in shooting down small asteroids was supported by his mentor, Edward Teller. Teller biographer and critic William Broad of The New York Times has characterized him as a major architect of the Cold War and probably the most influential scientist of the 20th century. Broad believes that isolation from collegial criticism has become a problem for Teller and has encouraged him into major mistakes such as his support for the x-ray laser. But in spite of the x-ray fiasco, Teller remains a formidable presence (following the Republican Congressional victory of 1994, House Speaker Newt Gingrich, himself a space supporter, invited Teller to present the opening keynote address to the newly-elected members of Congress).

Now in his waning years, Teller is stooped and peers through nearly-closed eyelids; his famous eyebrows are white and less prominent. Leaning on his staff -- a thick pole made of a light-colored wood, with a leather grip at shoulder height -- Teller immediately commands attention, even from those who are not his disciples. His gravelly voice is clear and authoritative, and his cadence is exceptionally slow, which makes his delivery all the more dramatic. Each sentence is grammatically perfect, each word is enunciated precisely in a Hungarian accent, still perceptible after five decades in the United States.

From the moment he entered the Los Alamos conference room, Teller's presence dominated the asteroid defense workshop. He was treated with obsequious deference and always given priority in speaking. 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 always had the final word on any issue.

Both Morrison and Shoemaker 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, and could not, penetrate the Earth's atmosphere, in contradiction to Lowell Wood's paper. No questions were asked, 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. In the discussion period the astronomers again explained that Wood's analysis was in error, that small projectiles were not the problem, and that if the Spaceguard Survey were carried out we would have a warning time of many years, not just a few hours, before an impact. The audience stared back blankly, refusing to accept the heresy of a challenge to Teller or his protoge, Wood.

Those of us from the Spaceguard team were not sure what was happening. We were already struggling with the unfamiliar vocabulary of the weapons builders, where a nuclear bomb is a "device", a rocket is a "vehicle", and a spy satellite is an "asset". More fundamentally, however, we saw that the weapons scientists did not conduct their business through the open questioning and discussions that astronomers were used to. Outwardly, everyone seemed excessively polite and deferential toward each other. Statements made by speakers went unchallenged even when they seemed contradictory or technically ill-founded. Perhaps this was because so much of the research done by this community is classified and thus not appropriate for public discussion and debate. Or maybe they were just more polite, and less critical in public, than astronomers. Or possibly it was Teller's inhibiting presence that stifled open debate.

John Rather had invited a wide range of participants, and there was no shortage of ideas to lay on the table. Many of the Los Alamos and Livermore technologists seemed like kids with their hands in the cookie jar. The bombs, lasers, and miniature spacecraft had been their playthings through the era of Star Wars, and they welcomed an opportunity to keep playing. The concepts they proposed often seemed outrageous to the NASA scientists. One idea, for example, was to focus giant laser beams on an incoming asteroid, using lenses in space that were several miles in diameter and laser systems that consumed more power than an entire city. Another scheme was to deploy a phalanx of thousands of high-speed "darts" against an asteroid, striking it so fast that they would slice it apart like a potato in a vegetable dicer. Most of the plans, however, depended on nuclear weapons to disrupt or destroy cosmic projectiles.

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.

All this talk of potential uses for nuclear weapons was well received by most of the participants, many of whom had been involved in the design and testing of nuclear bombs. This spirit was best captured by Lowell Wood, who noted in a comment made from the back of the room that there was considerable convergence of ideas from Los Alamos and Livermore scientists on the need to develop nuclear devices to deal with the impact hazard -- "but that is not surprising, since we share the same motivation: Nukes Forever!". The phrase "Nukes Forever!", later quoted in The New York Times and other newspapers, came to symbolize the Los Alamos meeting.

Although overshadowed by the seemingly outrageous proposals, a number of good ideas were presented at Los Alamos, and the meeting served to introduce the astronomers and weapons lab scientists to each other. Each group had previously been pursuing their interests in asteroid defense in isolation. A great deal of time was wasted, however, in consequence of Wood's cosmic bombardment paper and its focus on small bomblets. Wood's analysis had been accepted by Teller, Rather, and almost all of the other bomb-builders, who received the counter-arguments from the astronomers with open skepticism and resistance. Only late in the meeting, when Wood's colleagues from Livermore gave a talk in which they admitted that the atmosphere would block most small asteroids, did the majority of the audience consider backing off from their preoccupation with a short-range defense founded on a "shoot-first, look-later" philosophy. But by then the meeting was nearly over.

Although much of the talk at Los Alamos concerned ways to blow up an asteroid, the defense strategy of choice is deflection, not destruction. Any effort to blow apart an incoming projectile might well make things worse, transforming (in effect) a cannon ball into a cluster bomb. If, however, an offending asteroid could be gently nudged while still a long way from the Earth, it would be possible to change the orbit so that it would miss the Earth entirely. Two academic scientists, Tom Ahrens of Caltech and Alan Harris of NASA's Jet Propulsion Laboratory, presented a report on deflection requirements at Los Alamos and subsequently published their paper in the journal Nature, making theirs one of the first published papers to deal with asteroid defense issues. It is characteristic of the two cultures that Ahrens and Harris, the "outsiders", would publish their research findings in a widely available technical journal, while Wood and his colleagues produced only internal reports (such as the "Cosmic Bombardment" series, which had grown to "Cosmic Bombardment IV" by 1994) with circulation limited to a few colleagues in the weapons labs.

One of the unique aspects of the impact threat is that, as a natural hazard, it alone can be eliminated totally -- at least in principle. We cannot stop an earthquake or hurricane, but we can avoid an impact, given sufficient warning. The purpose of the Spaceguard Survey is to provide that warning. If a complete survey of the larger asteroids is carried out, any threatening object could -- most likely -- be identified decades before it actually struck the Earth. We would not need to have rockets and bombs ready on the launch pad. We would have many years during which to plan a defense strategy, study the object in detail, develop and build the necessary hardware, and perhaps try several ways to nudge it into a different orbit.

How can one nudge an asteroid? If it is small enough, then simply impacting its surface with a high-speed rocket might provide sufficient energy to change its orbit slightly. If a lot of energy must be provided, however, either because the threatening asteroid is large or the time available is short, then a nuclear device is the only choice. A one-ton conventional (non-nuclear) warhead has the chemical energy of one ton of TNT, but a one-ton nuclear warhead can pack a million tons -- a megaton -- of energy. Since any mitigation device must be launched into space from the surface of the Earth, the enormous advantage of nuclear defense schemes in the amount of wallop they carry per pound is clear.

How does one use a megaton of energy to change an asteroid's path? Simply detonating a megaton bomb on an asteroid's surface won't do the trick. It risks breaking the asteroid apart, especially if the asteroid is small (or fragile) and the bomb is large. We can provide a gentler nudge if the bomb is exploded in space near the asteroid, perhaps at a distance from the surface equal to the radius of the asteroid.

When a bomb explodes in the Earth's atmosphere, it releases much of its energy in the form of shock waves and supersonic winds composed of superheated air rushing outward from the fireball. If the bomb is exploded in the vacuum of space, there is no air to form such a blast wave. Instead, neutrons -- sub-atomic particles that are copiously produced in nuclear reactions -- slam into the surface of the asteroid, heating it and boiling off the rock. As the rock vapor flows away into space, it exerts a reaction force against the asteroid to move it in the opposite direction. This is an example of Newton's Third Law of an equal and opposite reaction, which accounts for the operation of jet engines and rockets.

Rough calculations presented at Los Alamos indicated that a megaton-size device would do the trick, assuming it was used several years in advance of the predicted impact. Even gentler accelerations could be provided by a series of smaller explosions. The most efficient approach is to use neutron-rich bombs, devices that had been discussed for several years by cold warriors as a way to kill people without damaging structures. The NASA astronomers wondered if such neutron bombs actually existed; the physicists from the weapons labs simply smiled.

Whatever its technical merits, the Los Alamos meeting was a public relations disaster. Having been barred from attending, the press heard indirectly about the discussions of nuclear weapons and Wood's "Nukes Forever!" outburst, and they were quick to attack. When NASA managers read the press reports and saw the weird ideas that Rather was promoting under the banner of new technologies, they moved quickly to disassociate themselves from the meeting. NASA released a sanitized summary that omitted most mention of nuclear weapons and Star-Wars technology, and the space agency refused to sanction publication of the more detailed reports that had been presented at Los Alamos. This task was delegated to the Department of Energy, which published a report a year later.

* * * * * *

Congress had asked for written reports from the two asteroid studies, and eventually it received them. The next step was to hold a hearing on the results. In March of 1993, a meeting of the Space Subcommittee of the House Committee on Science, Space and Technology was duly announced on the subject of "the threat of large Earth-orbit crossing asteroids". Letters of invitation were sent to David Morrison and John Rather as chairs of the two NASA studies, as well as to the headquarters offices of NASA and the Secretary of the Air Force. The Air Force demurred, pleading that the Clinton administration team had not had time to consider this matter, but on March 25 the three NASA witnesses presented themselves in the plush, high-ceilinged hearing room of the Rayburn House Office Building and sat down under the bright television lights to talk about asteroid impacts.

Presiding at the hearings was tall, courtly Congressman Ralph Hall of Texas, the chair of the Space Subcommittee and a strong supporter of the Space Station. Next to him sat Congressman George Brown of California, chair of the parent committee and one of the most knowledgeable members of Congress on matters of science and technology. Congressman Brown was the most vocal advocate of the Spaceguard Survey in the Congress, and he was especially anxious that the Air Force should join with NASA in pursuing asteroid searches. Other members of the subcommittee wandered in and out, apparently curious to see whether this strange topic was something that should actually be taken seriously by the official representatives of the American people.

Brown began the proceedings by noting that "for Members who are hearing about this subject for the first time, I know that the tendency is to be somewhat skeptical . . . None of our friends, relatives, or constituents have ever been killed by an asteroid." After enumerating some of the evidence that the Earth is struck occasionally by cosmic projectiles, he continued: "But why should Congress be involved? I think that it is the duty of the Congress to provide periodic oversight of all matters that relate to the health and welfare of the citizens of this country. This is particularly true for those issues where Congressional oversight might spur the Administration forward to take some appropriate action. I believe that the topic of Earth-threatening asteroids is just such an issue . . . I believe that the initiatives that are now getting underway to deal with this issue in a thorough and scientific manner have the potential for being one of the most important things that mankind has ever done."

Several other committee members also entered positive statements into the record, and then Morrison and Rather summarized the results of their two studies, followed by NASA Associate Administrator Wesley Huntress who spoke officially for the space agency. Huntress took a cautious tone, praising the two reports but declining to endorse their specific recommendations. Noting that NASA was doubling its support for astronomical studies of asteroids to $1 million per year, he mentioned the upgrade of Gehrel's Spacewatch Program and the funding of a new search telescope at Lowell Observatory to be used by Gene Shoemaker and Ted Bowell. The NASA objective was "to systematically and prudently increase the detection rate of NEOs and to enhance our understanding of these objects."

In the discussion that followed these statements, many of the questions were more concerned about scientific facts than programmat­ic issues -- questions about the nature of comets and asteroids, and about the evidence for historical impacts and their effects. The scientific exchange, which extended long beyond the scheduled time for the hearings, was a major departure from the usual business conducted in Congressional meetings.

At the end, Chairman Hall seemed somewhat bemused by the whole experience. Looking quizzically at the three witnesses sitting before him in their identical grey suits, he mused: "I think it's been a very interesting bit of testimony. I think it's obvious that you men and those with whom you work know what you're doing, and I guess it must be stressful to you to know some of the things that ought to be done . . . because you have no funds and no infrastructure [to discover and track potentially threatening objects]. You seem like pleasant men, but you must lead a frustrating life knowing that you're not likely to get any funds out of Congress at this time."

3500 words (3/27/97)


Congress had charged NASA, through its Spaceguard Working Group (described in Chapter 11), to develop a specific plan for an asteroid survey. The second part of their request was less well defined, asking only for an analysis of the technology that might be used for asteroid protection, if a threatening object were actually discovered. This charge formed the topic of a workshop, held in January 1992 at Los Alamos. This technology workshop was attended primarily by defense department scientists, many of them involved in the design and testing of nuclear bombs. A few astronomers, ourselves included, were invited, apparently as an afterthought. This chapter tells of our Los Alamos confrontation with the "star warriors" and describes the technologies proposed for a defense against asteroids and comets. It also introduces Edward Teller, the "father of the H Bomb" and a strong proponent of asteroid defense, together with his protege, Lowell Wood. We found the style of the star warriors very different from our own experience -- more secretive and apparently less critical of technical issues. The were also much more hierarchical, especially in the obsequious deference given to Teller. On defense issues, we describe how explosives could be used to deflect or destroy incoming NEOs, given adequate warning time. Nearly all of the suggested approaches involved nuclear technology, and Wood's outburst "We all agree on one thing -- Nukes forever!" has come to symbolize the Los Alamos workshop. The chapter concludes with a description of the 1993 testimony before Congress by Morrison and two other NASA witnesses.


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