![]() In all cases, the decision to initiate mitigation is a sociopolitical decision, not a technical decision. ![]() Civil defense and kinetic impactors are probably the closest to deployable but even these require additional study before they can be relied on. Note that Table 5.2 brings in an additional important aspect of the problem, international coordination, which is discussed in more detail in Chapter 7 of this report.Īlthough all of the primary mitigation strategy methods are conceptually valid, none is now ready to implement on short notice. Table 5.2 shows the regimes in which each mitigation method is applicable. The mitigation options are laid out in Table 5.1, which lists the applicability of each option to a given threat. The choice among the three methods-the slow-push and -pull method, kinetic impact, and nuclear detonation-depends both on the mass of the NEO that has to be moved and on how early the NEO is determined to be hazardous, as well as on the details of the orbit. For larger events, actively changing the orbit of the hazardous object is likely desirable. They are also the events that are likely to have the least advance warning. Occurring on average every couple of centuries. Airburst events will also be the most frequent, Events like this cause destruction over areas up to thousands of square kilometers, and evacuation and sheltering are not only plausible but often the most cost-effective approach for saving human lives. Nuclear detonation-delivering a much larger amount of momentum (and energy) instantaneously to an NEO to change its orbit so that it misses Earth.įor impacting NEOs that are sufficiently small (tens of meters to perhaps 100 meters in diameter) and not very strong (typically not iron meteoroids), the destruction on Earth will be caused by an airburst and its associated blast wave and thermal pulse, as was the case of the Tunguska event above Siberia in 1908. Kinetic impact-delivering a large amount of momentum (and energy) instantaneously to an NEO to change its orbit so that it misses Earth, and Slow-push or -pull methods-gradually changing the orbit of an NEO so that it misses Earth, In this chapter the committee considers four categories of mitigation:Ĭivil defense-involving such efforts as evacuating the region around a small impact, For the largest events, from beyond global catastrophe to events that cause mass extinctions, there is no current technology capable of sufficiently changing the orbital path to avoid disaster. ![]() For larger events, changing the path of the hazardous object is the appropriate solution, although the method for changing the path varies depending on the amount of advance notice available and the mass of the hazardous object. ![]() For events of sufficiently low energy, the methods of civil defense in the broadest sense are the most cost-effective for saving human lives and minimizing property damage. Because the range of possible destruction is so huge, no single approach is adequate for dealing with all events. The amount of destruction from an event scales with the energy being brought by the impacting object. Given the inevitability of impacts, and noting that the entire point of surveys is to enable appropriate action to be taken, how can the effects of potential impacting NEOs be mitigated? The risks from these NEOs, or more specifically scientists’ assessment of the risks in the next century, will be changing as surveys are carried out. The impactors range from harmless fireballs, which are very frequent through the largest airbursts, which do not cause significant destruction on the ground, on average occurring once in a human lifetime to globally catastrophic events, which are very unlikely to occur in any given human lifetime but are probably randomly distributed in time. Impacts on Earth by near-Earth objects (NEOs) are inevitable. ![]()
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