EXCERPTS FROM: WHAT TO DO ABOUT BOLTS FROM THE BLUE
by Steve J. Marcus WATCHING OUT FOR ASTEROIDS
by Michael Paine, The Planetary Society Australian Volunteers: http://www1.tpgi.com.au/users/tps-seti/ ISSUES ON RISK ASSESSEMENT AND NEO IMPACT PREDICTION
by Clark R. Chapman WHY ARE WE STILL TALKING ABOUT ASTEROID XF11?
by David Morrison
By Steven J. Marcus IEEE Spectrum December 1998 Chicken Little's deduction that "the sky is falling" when her head was struck by an acorn has long seemed the perfect metaphor for misplaced alarm. But a far bigger and faster object from the sky, packing a lot more wallop, could one day confirm her hasty forecast with a vengeance. Just last March a terrifying warning of such an event a few decades hence turned out to be a false alarm, but not by much. That scare, together with some recent near misses of the earth and an actual crash into a sister planet, have helped alert the public and some political leaders to what a cadre of activist scientists has long maintained is no fairy tale. The facts are these. Eventually a sizable asteroid or comet could come screaming down to earth -- perhaps in our lifetimes, though more likely not. The slender probability per year of that event, offset by the enormous devastation (possibly global-scale catastrophe) it would wreak, renders it just as risky as many other natural and more frequent threats that are taken seriously indeed. Astronomers have the ability to detect such an asteroid or comet -- generally referred to as a "near-earth object" (NEO) -- and to accurately predict the date it would cross the earth's path. And the technology to fashion a reasonable defense against earth-intersecting NEOs is in hand,though with some additional thinking, experimentation, design, international cooperation, and planning, over time better alternatives and strategies could be devised. Two Hollywood movies last summer dramatized the issue, and one of them, Deep Impact, did a fair amount of scientific homework. Its simulated comet surface conformed to much of what is known about such objects; and the special effects deployed for a tsunami destroying New York City and other consequences of the impact were plausibly, and terrifyingly, presented. But the merciful last-minute "save" was way off base. Pulverizing the comet with a few nuclear weapons only hours before it hit, most scientists agree, would actually have fried everyone to a crisp. The single huge threat would have been broken into numerous still-large threats that would not only hit the earth but probably have triggered global firestorms as the resulting fireballs coalesced. The other film, Armageddon, in the thrill-a-minute tradition, paid little heed to scientific fact. Its asteroid was "the size of Texas" (about a million times larger than any [earth-approaching] asteroid). Its wrong-stuff crew consisted mostly of space newcomers who, with merely a week's training, flew off to save the world. And the nuclear explosive they implanted some 250 meters down in the gigantic object, which somehow splits into two neat pieces that both obligingly proceed to miss the earth, would have had the barely appreciable effect of a mosquito bite. All the same, Deep Impact's and Armageddon's depictions of the planet's vulnerability could render a public service. "Whatever [the films'] technical strengths or weaknesses, they should sensitize the public to the existence of an impact danger, and perhaps also to the fact that we could mount a defense against an incoming object and thus avert the disaster entirely," said astronomer David Morrison. Though there is no need for immediate alarm, those who maintain the sky is not failing base their optimism largely on blissful ignorance. As an editorial in The Economist (11 September 1993) put it: "No known rock is on a collision course at the moment -- but most of the rocks are unknown." Thus the primary task, from which, if indicated, all else would follow, is detection. From analyzing the geological records of the asteroid/comet flux in the earth's vicinity (manifested in the moon's craters) and from sampling the heavens directly, scientists estimate that some 2000 NEOs out there both have orbits that might eventually bring them into collision with the planet and are big enough (more than 1 km across) to cause global catastrophe. So far, astronomers have identified about 10 percent of them, but at the present rate of discovery, it will take a century, they maintain, before they have cataloged a total of 90 percent. The [current] detection system, such as it is, consists of a few virtuosos doing solos, not an orchestra. . . The circumstances and styles of the research efforts vary. Some programs look where the asteroids are brightest, while others concentrate on the fainter magnitudes of farther-off objects; some scan wide chunks of the sky at a rapid rate, while others home in on smaller sections for a more sustained look. If in principle the waterfront is being covered, in reality that coverage is superficial. In March 1993, the then-[House] Science Committee Chairman George E. Brown (D-Calif.) declared: "If some day in the future we discover well in advance that an asteroid that is big enough to cause a mass extinction is going to hit the earth, and then we alter the course of that asteroid so that it does not hit us, it will be one of the most important accomplishments in human history." [In September 1995, the position paper of the American Institute of Aeronautics and Astronautics] said: "AIAA and its cooperating organizations strongly believe that Congressman BrownÕs [1993] statement is true as well as its converse: If some day an asteroid does strike the earth killing not only the human race but millions of other species as well, and we could have prevented it but did not because of indecision, unbalanced priorities, imprecise risk definition, and incomplete planning, then it will be the greatest abdication in all of human history not to use our gift of rational intellect and conscience to shepherd our own survival, and that of all life on earth." For now, most scientists in the NEO community confine their advocacy to adequate cataloging of potentially threatening objects. Provided that a sufficient detection effort is mounted for people to be confident about what's out there and for warning times to be as long as possible, they generally do not recommend a crash program (pardon the expression) for deploying a defense or even for doing much of the prerequisite research, unless it is determined that an actual threat is on the way. In their 1994 Nature article, [Clark] Chapman and [David] Morrison asserted that "preparation of a mitigation system would be premature and not cost-effective," particularly "if the system involves controversial and potentially hazardous elements, such as nuclear weapons, [because] society would surely require further expense to lessen the potential for dangerous accidents involving (or misuse of) the mitigation system itself." And such a generic system could be downright useless. [Alan] Harris pointed out that defense against an asteroid or comet would necessarily "be very case-specific," tailored to the size, composition, and orbit of the actual threat. Take the case of last MarchÕs false alarm over asteroid 1997FX11, and imagine it had been bound for the earth after all. We would have had 30 years' warning, "a long time to think things over," said Harris. "We'd fly a mission out there to poke it, probe it, land on it, drill holes in it, and think about it. Then we'd come back home and think some more. And then we'd decide what to do and devise a deflection." But having the luxury of that "long time to think things over" critically depends on the thoroughness of the detection efforts. The Government at present appears unlikely to support a full-blown version of Spaceguard, the systems for using telescopes to search the sky, but it may be missing an important bet. "Just as we sometimes make a small investment in a high-risk chance of winning big in the stock market," Chapman testified to the House subcommittee last May, "we can make a comparatively small national investment in protecting civilization from the small chance of a global catastrophe." In that way, "planetary protection [could] be elevated from a sideline activity of a few astronomers, and some passionate amateurs, and be put on a sound, appropriately funded footing." In Armageddon, the doomsday asteroid is due to intercept the earth only 8 days after its discovery. "Why didn't you detect it much earlier?" a senior (though salty) space scientist is asked. Our "object collision budget," he responds, in one of the film's few plausible explanations, covered only about "three percent of the sky. And it's a big-ass sky."
The following was published in the December 1998 (Vol. 70, No. 12) issue of Engineers Australia. The Editor, Engineers Australia. Audiences who saw the movies Deep Impact and Armageddon no doubt came away thinking that we don't need Bruce Willis to save the world because there is a dedicated band of scientists staring at the skies looking out for an asteroid "with our name on it". Sorry - think again. The worldwide detection effort is at most, about one tenth of that needed to meet the realistic goals of the proposed international Spaceguard Survey. The shameful fact is that Australia's contribution is essentially zero. Government funding for a low-budget but highly successful asteroid search program was cut in 1996 - probably because it straddled ministerial portfolios and there was no appropriate budget pigeonhole. In the next 50 years there is a 1 in 2,000 chance of a 1 kilometre diameter asteroid impacting the Earth at a speed of around 70,000km/h. At this speed the object has more energy than its equivalent mass in TNT. The consequences would be global and catastrophic - this would not be an "extinction event" but perhaps one quarter of the world's population would die and civilization would collapse. Impacts by smaller objects occur more frequently and could threaten the fragile global economy. Why I am raising this issue in an engineering magazine? I am a mechanical engineer with a background in road safety research. When I applied the cost-effectiveness procedures that are used to justify road safety initiatives to the Spaceguard proposal I realized that the project was highly cost-effective. Furthermore this was based on very conservative estimates because it only considered Australian lives saved; it did not consider global fatalities, the economic consequences of an impact or the effects of tsunami hitting low-lying coastal areas. This is clearly a government responsibility but it appears that Australian politicians are not prepared to consider an issue that, in their judgement, is not likely to have an effect before the next election. I am hopeful, however, that corporate Australia is more prepared to look to the longer term and will sponsor an Australian Spaceguard program. This has occurred in the USA with the successful Spacewatch project.
NEWS & REVIEWS, by Clark R. Chapman, from the Nov./Dec. 1998 issue of The Planetary Report I've just attended a workshop on public policy implications of predictions about natural hazards (like earthquakes, hurricanes) and about environmental degradation (global warming, nuclear waste storage) ["Workshop on Prediction in the Earth Sciences: Use and Misuse in Policy Making," organized by the Geological Society of America and the National Center for Atmospheric Research.] The participants included philosophers, ex-staffers of the congressional House Science Committee, the operations director of Fargo who dealt with the 1997 floods, an ex-Emergency Management Director for Los Angeles, economists, structural engineers, social scientists, a Nebraska rancher (who relies on climate forecasts), a public utility official, a science journalist, a National Science Foundation official, a reinsurance analyst, and experts in the predictive earth and environmental sciences. Prediction Councils I attended the workshop to present a case study of the asteroid/comet impact hazard. I felt a bit out of place. Most of the other nine case studies dealt with hazards for which institutions and protocols have long existed. For example, the problematic selection of Yucca Mountain (Nevada) as the permanent repository for nuclear wastes during the next 10,000 years was the outgrowth of an elaborate, two-decade-long governmental process. Forecasts about whether the mountain will or won't contain the wastes successfully emanate from an official deliberative body, the Nuclear Waste Technical Review Board. When and if California seismologists dare again to make any short-term earthquake predictions (like the failed Parkfield prediction of 1985), they will be endorsed by the governor of California only after being vetted within the California Earthquake Prediction Evaluation Council (CEPEC). Space scientists, on the other hand, are woefully unprepared to deal with the social impacts of their science. The heavens normally play little role in earthly affairs, despite the quackery of astrologers. Solar flares were the unique exception until the recent recognition of the impact hazard. Eight years after a congressional mandate to evaluate the hazard, NASA has only begun to augment the limited funding of telescopic searches for hazardous objects. I am hard-pressed to think of any research project on the nature and consequences of the modern-day impact hazard that has been funded by NASA. Among well-funded earthquake, hurricane, and climate-change researchers at the workshop, I felt alone in relying on my employer's overhead to pay for my participation. Lack of institutionalized experience led, no doubt, to the mistaken forecast last March of an impact impending in 2028. A South Carolina banker at the workshop recalled his anger upon hearing the retraction two days after the apocalyptic headlines. We now know, as reported at the October meeting of the American Astronomical Society/Division for Planetary Sciences in Madison, Wisconsin, that the positions of asteroid 1997XF11 observed just two weeks after its early-December discovery were already sufficient to rule out an impact in 2028. Those data, given normal celestial mechanics, imply a chance of impact less than the chances of a poker player in an honest game being dealt seven royal flushes in a row. This reassuring information would have been available, had anyone been adequately funded to use existing software to evaluate the probabilities. Calculations and Protocols Obvious lessons from this fiasco are that (1) NASA should fund experts to make valid impact probability calculations and (2) formal protocols should be established for evaluating impact predictions before entities like the American Astronomical Society publicly endorse them. The widely promulgated, face-saving story that the unearthing of pre-discovery (1990) images of 1997XF11 saved the day might lead NASA to conclude that all it needs to do is fund more observations (benefiting observers and those who archive observations) when in fact we really need better early calculations. Case studies presented at the Prediction Workshop document that economic and institutional biases often strongly influence predictions as well as conclusions drawn from them. As for protocols, much discussion on the Internet has chided NASA for proposing to "censor" impact predictions. But consider this: NASA's establishment of an impact prediction evaluation council would no more censor the predictions of quacks (or of mistaken professionals) than CEPEC has censored amateur earthquake predictions (including one based on prophecies of Nostradamus), but it would provide a forum for evaluating predictions to which responsible news media would (hopefully) turn before printing scary headlines. Predictive Space Science It is odd that space scientists should be so unfamiliar with risk assessment and prediction. After all, astronomers are renowned for accurately predicting eclipses, and NASA engineers routinely predict the arrival of spacecraft at targets years in the future. The occasionally less successful predictions of comets and meteor storms "of-the-century" at least have no social consequences, other than causing would-be watchers to lose a few hours of sleep. Yet there are real social and economic costs in the use and misuse of predictions in the space sciences that extend beyond impact prediction. The Challenger astronauts were lost in part because of NASA's failure to heed a cold-weather forecast. The successes or failures of expensive spacecraft depend not only on space-qualified engineering but also on predictions from scientific models about planetary radiation belts, micrometeoroid fluxes, and planetary surface environments. Space scientists should catch up with other scientific disciplines and learn about risk assessment and the pitfalls of predictive science.
By David Morrison [See also the note on XF11 in the News Archive for June 1998] People continue to be interested in near-Earth asteroid 1997XF11, which created a brief media storm in mid-March 1998 when newspapers suggested that this object might impact the Earth in 2028, only to have the "prediction" withdrawn a day later. The previous stories by Marcus and Chapman both mention the XF11 affair. This asteroid played an important role in alerting the public to the hazard of NEO impacts. Unfortunately it has also involved the asteroid scientific community in an unprecedented level of pettiness. Science is filled with entirely human errors and misjudgments, and most of the time these are quickly forgotten with no harm to anyone's reputation. Scientifically the XF11 issue is a tempest in a teapot, and the main reason we still hear about it is that distorted versions of the story continue to appear in the press. The simple fact is that Brian Marsden's reasonable announcement (from the International Astronomical Union Minor Planet Center, which he directs) that XF11 would pass close to the Earth in 2028 was quickly distorted into a prediction of possible impact. Brian had calculated an orbit that turned out to be not quite correct, so that the pass in 2028 is not as close as he predicted. More to the point, neither he nor anyone else had calculated the uncertainties in the orbit, and Brian's speculations to the press about a chance of impact were just that -- speculation. As soon as the orbit and its uncertainties were calculated by Don Yeomans and Paul Chodas of JPL (within a few hours of Brian's announcement), it was clear that no impact was possible. In retrospect we see that such a calculation, ruling out impact, could have been done from existing observations weeks before Brian's announcement. As Clark Chapman has pointed out in the story above, however, no one in the science community is supported by NASA or any other Agency to make such risk calculations. It is common for the preliminary orbit of a newly discovered NEO to be uncertain, and the various data sets used in the calculations to be inconsistent. I see no fault in any of this except that Brian would have been wise (in retrospect) to consult with colleagues and try to evaluate the risk of impact before making any announcements to the press. Since last March, however, there has been an unseemly effort on the part of a handful of individuals to revise or reinterpret the facts. The first piece of misinformation, widely reported in the press, was that only by finding additional prediscovery observations of XF11 was it possible to rule out an impact in 2028. The second episode concerns the miniscule possibility that XF11 might pose an impact hazard later in the 21st century. The question of events after 2028 was not a part of the original press interest in XF11, and it should not be confused with questions of how to avoid the mistakes in media relations of March 11, 1998. I believe that extensive discussions of the hazard post-2028 also suggest a lack of perspective on the danger of impacts. This hazard is dominated, in our present level of ignorance, by objects not yet discovered. The chance of impact by an undiscovered object during the 21st century is much greater than that of an impact by XF11. In this sense, the discovery of XF11 reduced the probability of impact for the 21st century by moving this NEO from the "unknown" to the "known" category. The rest is splitting hairs. Much better for us to get on with discovering the unknown cousins of 1997XF11! David Morrison |
