or regional effects near the time and place of the impact, but could include, for large impacts, global climate change or tsunamis. But how large an impact and what kind of impact could cause these effects is still uncertain. A research program is needed to address all of these issues in order to assess and quantify the risks associated with the NEO impact hazard.

The ability to mitigate the impact hazard, or even to define appropriate strategies for mitigating the hazard, likewise depends on the acquisition of the new knowledge and understanding that could be gained through a research program. Even if the only viable mitigation approach to an impending impact is to warn the population and to evacuate, better information is needed for making sound decisions. Under what conditions should warning be provided and when, and who should evacuate? If, however, there are available active mitigation options, like changing the orbit of an impactor, again better information is needed: One must be able to predict with confidence the response of an impactor to specific forms of applied forces, impacts of various types and speeds, or various types of radiant energy, such as x rays. The required information goes beyond the basic physical characterization that determines the size and mass of the impactor and includes surface and subsurface compositions, internal structures, and the nature of their reactions to various inputs.

Just as the scope of earthquake research is not limited only to searching for and monitoring earthquakes, the scope of NEO hazard mitigation research should not be limited to searching for and detecting NEOs. A research program is a necessary part of an NEO hazard mitigation program. This research should be carried out in parallel with the searches for NEOs, and it should be broadly inclusive of research aimed at filling the gaps in present knowledge and understanding so as to improve scientists’ ability to assess and quantify impact risks as well as to support the development of mitigation strategies. This research needs to cover several areas discussed in the previous chapters of this report: risk analysis (Chapter 2), surveys and detection of NEOs (Chapter 3), characterization (Chapter 4), and mitigation (Chapter 5). The committee stresses that this research must be broad in order to encompass all of these relevant and interrelated subjects.

Recommendation: The United States should initiate a peer-reviewed, targeted research program in the area of impact hazard and mitigation of NEOs. Because this is a policy-driven, applied program, it should not be in competition with basic scientific research programs or funded from them. This research program should encompass three principal task areas: surveys, characterization, and mitigation. The scope should include analysis, simulation, and laboratory experiments. This research program does not include mitigation space experiments or tests that are treated elsewhere in this report.

Some specific topics of interest for this research program are listed below. This list is not intended to be exhaustive:

  • Analyses and simulations of ways to optimize search and detection strategies using ground-based or space-based approaches or combinations thereof (see Chapter 3);

  • Studies of distributions of warning times versus sizes of impactors for different survey and detection approaches (see Chapter 2);

  • Studies of the remote-sensing data on NEOs that are needed to develop useful probabilistic bases for choosing active-defense strategies when warning times of impacts are insufficient to allow a characterization mission (see Chapter 4);

  • Concept studies of space missions designed to meet characterization objectives, including a rendezvous and/or landed mission and/or impactors;

  • Concept studies of active-defense missions designed to meet mitigation objectives, including a test of mitigation by impact with the measurement of momentum transfer efficiency to the target (see Chapter 5);

  • Research to demonstrate the viability, or not, of using the disruption of an NEO to mitigate against an impact;

  • The technological development of components and systems necessary for mitigation;

  • Analyses of data from airbursts and their ground effects as obtained by dedicated networks, including military systems and fireball (brighter than average meteor) observations; also analyses and simulations to assess

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