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Near-Earth Object Surveys and Hazard Mitigation Strategies: Interim Report
Finding: The orbit-fitting capabilities of the Minor Planet Center are more than capable ofhandling the observations of the congressionally mandated survey as long as staffing needs are met.
Finding: The Arecibo Observatory telescope continues to play a unique role in characterization ofNEOs, providing unmatched precision and accuracy in orbit determination and insight into size,shape, surface structure, multiplicity, and other physical properties for objects within itsdeclination coverage and detection range.
Finding: The United States is the only country that currently has an operating survey/detectionprogram for discovering near-Earth objects; Canada and Germany are both building spacecraftthat may contribute to the discovery of near-Earth objects. However, neither mission will detectfainter or smaller objects than ground-based telescopes.
In 2008, at congressional direction, NASA and the National Science Foundation asked the National Research Council to undertake a study of the nation’s efforts to survey, discover and characterize, and develop mitigation strategies for NEOs. Near-Earth objects are defined as small solar-system objects whose orbits cross or nearly cross Earth’s orbit.
To date the study’s steering committee, survey/detection panel, and mitigation panel have each met twice. The panels remain in their information-gathering phases. This interim report addresses some issues contained in task 1 of the committee’s charge (dealing primarily with survey and detection efforts) and does not address mitigation issues. The committee will evaluate the particular characteristics of survey strategies in terms of their implications for NEO discovery and/or characterization.
Currently, the U.S. government spends a relatively small amount of money funding a search and survey program to discover and track near-Earth objects, and virtually no money on studying methods of mitigating the hazards posed by such objects.3 Although Congress has mandated that NASA conduct this survey program and has established goals for the program, neither Congress nor the administration has sought to fund it with new appropriations. As a result, NASA has supported this activity by taking funds from other programs, while still leaving a substantial gap between the goals established by Congress and the funds needed to achieve them.
EVOLUTION OF THE STUDY OF NEAR-EARTH OBJECTS
Earth has been impacted by asteroids and comets for billions of years. In the 1980s, after Luis and Walter Alvarez suggested that a massive asteroid impact wiped out the dinosaurs, scientists began to consider the environmental effects—including widespread extinction—that could be caused by large impacts. By the 1990s, available research indicated that the impact of a 1.5- to 2-kilometer-diameter asteroid or comet anywhere on Earth had the potential to produce global effects that would seriously impact human civilization (e.g., a significant reduction in the total food yield, perhaps for several years). Because there were substantial uncertainties in the threshold impactor size needed to produce global effects, a team of NEO experts selected 1-kilometer-diameter objects as the threshold for the most dangerous objects to human civilization.
The uncertainties in the damaging effects of asteroids increase as the size of the asteroid increases. A 1-kilometer-diameter asteroid is generally accepted as the lower boundary for an impactor
The threat posed by long-period comets is not part of the U.S. government effort. Mitigating the threat posed by such comets would be difficult due to the short warning times available for objects in such highly elliptical orbits; these objects are not often visible from Earth until a few months or so before reaching the vicinity of Earth’s orbit.