Since the details of the asteroid and comet threat are unknown, a planning philosophy will be most effective if it is based on the need to be flexible and generic. This is necessary because of the wide variety of potential hazards, from airbursts through land impacts to tsunamis, with each covering a broad span of possible severities.
The chief unknown with respect to NEO hazards planning will be the size of the need, but if huge, the peril will probably be defined well in advance. In addition to planning a flexible response, a trained cadre of professionals must obtain and set up the equipment and supplies needed to sustain a displaced population. Such preparatory issues are not confined to the asteroid and comet hazard, but have common elements with all other natural hazards, such as earthquakes, fires, and hurricanes. All of the common elements may be treated similarly and by the same personnel.
It makes sense, in any national activity in this civil-defense sphere, to coordinate and collaborate with other nations in the planning and, depending on circumstances, in the implementing of responses to an impending impact event.
The probability of a devastating NEO impact in the United States is small compared to the likelihood of an impact in other nations, most with far fewer resources to detect, track, and defend against an incoming NEO. The NEO hazard, however, is such that a single country, acting unilaterally, could potentially solve the problem. Although the United States has a responsibility to identify and defend against threats with global consequences, this nation does not have to bear the full burden for such programs. There have been several international efforts to characterize objects in the near-Earth environment, but these studies have generally been driven by scientific curiosity and were not designed to address the risk of NEOs. As NEO survey requirements evolve to fainter objects and as mitigation strategies are refined, additional resources will be necessary, and these could be provided by other developed countries. International partnerships can be sought with other science organizations, notably but not exclusively space agencies, in the areas of surveys, characterization, and mitigation technologies. NEO discovery rates and survey completeness could be significantly enhanced through the coordinated use of telescopes owned and operated by other nations. Future NEO space missions, carried out by the United States, by other nations, or through the cooperation of various countries, could be optimized for characterization that enables the development and refinement of mitigation strategies. Space missions to test such strategies could also be developed on a cooperative basis with other nations, making use of the resulting complementary capability. While a coordinated intergovernmental program would be needed to address the full spectrum of activities associated with NEO surveys, characterization, and mitigation, an important first step in this direction would be to establish an international partnership, perhaps of space agencies, to develop a comprehensive strategy for dealing with NEO hazards.
Many scientists, especially among the world’s planetary scientists, have been concerned for well over a decade with the danger posed to Earth from the impact of an asteroid or a comet. Officials from various nations have echoed these concerns. Thus a substantial and important component of the existing international cooperation is the informal contact among professional scientists and engineers, mainly of space-faring nations, but also including some other countries.
International conferences and small meetings, as well as the Internet, have allowed experts in different aspects of space science and technology, including asteroid detection and mitigation, to know their counterparts in other nations personally. Such connections often lead to offers of or requests for aid in the solution of common problems arising in the course of these experts’ work. Veterans of the U.S. or Russian space programs often participate either openly or behind the scenes in the European Space Agency and the Japanese Space Agency and in Indian and Chinese space activities. Nuclear-weapons designers in both Russia and the United States have often met to discuss the use of nuclear explosives to effect asteroid orbit changes.
In the event of a sudden emergency due to the discovery of a threatening NEO, it is likely that people forming this international network would be the first to communicate with one another and to consider responses to the threat. For instance, when an observatory in Arizona discovered NEO 2008 TC3 only 19 hours before its impact in Sudan, the informal network of amateur and professional astronomers in many countries responded in time for thousands of observations of the object to be made and communicated to the MPC, thus allowing an extremely accurate prediction of the time (<1 minute error) and location (<1 kilometer error) of impact.