How a Near-Earth Object Impact Might Affect Society

The hazard of impacts by meteoroids, asteroids, and comets ranging in size from meters to kilometers should be a matter of practical concern to policy makers in many nations. At worst, the very unlikely case of a 3 km asteroid striking Earth could send civilization into a new Dark Age; this case – with a potential death toll of a billion or more – has an annualized fatality rate comparable to other serious hazards, like earthquakes or airline crashes. At a minimum, the increasing rate of discoveries of Near Earth Asteroids combined with media sensationalism will surely alarm the public and bring the issue of this potentially solvable hazard (e.g. by deflecting an approaching asteroid away from the Earth) to the desks of responsible emergency management officials. In this report, six representative cases of asteroid impact scenarios are described in practical terms, with implications that vary for nations of different sizes, proximity to ocean coastlines, and other characteristics. Some cases, meriting concern and advance preparation for mitigation, are certain to happen in this century; others are quite unlikely, but sufficiently dangerous that responsibility dictates that they should be evaluated to determine the appropriate priority of preparing for such an event. The six cases are described in terms of the anticipated devastation, the probability of happening, the likely warning time, the opportunities (if any) for post-warning mitigation, the nature of post-impact crisis management, and the opportunities for advance preparation. Finally, some important issues are discussed: the role of the media and public perception of an inherently non-intuitive but alarming hazard, the unusual scientific uncertainties associated with predicting impacts, international oversight of asteroid deflection technologies, and a post Sept. 11th perspective on the impact hazard. A devastating impact is likely to manifest itself as the compounded effects of various familiar natural hazards, including tsunami, earthquakes, windstorms, fires, and explosions. Therefore, the additional efforts needed to prepare for an unlikely impact may be considered as relatively low-cost, marginal add-ons to existing approaches for managing civil defense against more common natural and man-made dangers.