WASHINGTON — A new report from the National Research Council lays out options NASA could follow to detect more near-Earth objects (NEOs) — asteroids and comets that could pose a hazard if they cross Earth’s orbit. The report says the $4 million the U.S. spends annually to search for NEOs is insufficient to meet a congressionally mandated requirement to detect NEOs that could threaten Earth.
Congress mandated in 2005 that NASA discover 90 percent of NEOs whose diameter is 140 meters or greater by 2020, and asked the National Research Council in 2008 to form a committee to determine the optimum approach to doing so. In an interim report released last year, the committee concluded that it was impossible for NASA to meet that goal, since Congress has not appropriated new funds for the survey nor has the administration asked for them.
In its final report, the committee lays out two approaches that would allow NASA to complete its goal soon after the 2020 deadline; the approach chosen would depend on the priority policymakers attach to spotting NEOs. If finishing NASA’s survey as close as possible to the original 2020 deadline is considered most important, a mission using a space-based telescope conducted in concert with observations from a suitable ground-based telescope is the best approach, the report says. If conserving costs is deemed most important, the use of a ground-based telescope only is preferable.
The report also recommends that NASA monitor for smaller objects — those down to 30 to 50 meters in diameter — which recent research suggests can be highly destructive. However, the report stresses that searching for smaller objects should not interfere with first fulfilling the mandate from Congress. Beyond completion of that mandate, the report notes the need for constant vigilance in monitoring the skies, so as to detect all dangerous NEOs. In addition, the nation should undertake a peer-reviewed research program to better investigate the many unknown aspects connected with detecting NEOs and countering those that could be a threat. The U.S. should also take the lead in organizing an international entity to develop a detailed plan for dealing with hazards from these objects.
In addition, the report recommends that immediate action be taken to ensure the continued operation of the Arecibo Observatory in Puerto Rico. NASA and NSF should support a vigorous program of NEO observations at Arecibo, and NASA should also support such a program at the Goldstone Deep Space Communications Complex. Although these facilities cannot discover NEOs, they play an important role in accurately determining the orbits and characterizing the properties of NEOs within radar range.
THE SCOPE OF THE HAZARD
Near-Earth objects are asteroids and comets that orbit the sun and approach or cross Earth’s orbit. An asteroid or comet about 10 kilometers in diameter struck the Yucatan peninsula 65 million years ago and caused global devastation, probably wiping out large numbers of plant and animal species including the dinosaurs. Objects as large as this one strike Earth only about once every 100 million years on average, the report notes. NASA has been highly successful at detecting and tracking objects 1 kilometer in diameter or larger, and continues to search for these large objects. Objects down to sizes of about 140 meters in diameter — which NASA has been mandated to survey for — would cause regional damage; such impacts happen on average every 30,000 years, the report says.
While impacts by large NEOs are rare, a single impact could inflict extreme damage, raising the classic problem of how to confront a possibility that is both very rare and very important. Far more likely are those impacts that cause only moderate damage and few fatalities. Conducting surveys for NEOs and detailed studies of ways to mitigate collisions is best viewed as a form of insurance, the report says. How much to spend on these insurance premiums is a decision that must be made by the nation’s policymakers.
MITIGATING DAMAGE
The report also examines what is known about methods to defend against NEOs. These methods are new and still immature. No single approach is effective for the full range of near-Earth objects, the committee concluded. But with sufficient warning, a suite of four types of mitigation is adequate to meet the threat from all NEOs, except the most energetic ones.
- Civil defense (evacuation, sheltering in place, providing emergency infrastructure) is a cost-effective mitigation measure for saving lives from the smallest NEO impact events and is a necessary part of mitigation for larger events.
- “Slow push” or “slow pull” methods use a spacecraft to exert force on the target object to gradually change its orbit to avoid collision with the Earth. This technique is practical only for small NEOs (tens of meters to roughly 100 meters in diameter) or possibly for medium-sized objects (hundreds of meters), but would likely require decades of warning. Of the slow push/pull techniques, the gravity tractor appears to be by far the closest to technological readiness.
- Kinetic methods, which fly a spacecraft into the NEO to change its orbit, could defend against moderately sized objects (many hundreds of meters to 1 kilometer in diameter), but also may require decades of warning time.
- Nuclear explosions are the only current, practical means for dealing with large NEOs (diameters greater than 1 kilometer) or as a backup for smaller ones if other methods were to fail.
Although all of these methods are conceptually valid, none is now ready to implement on short notice, the report says. Civil defense and kinetic impactors are probably the closest to readiness, but even these require additional study prior to reliance on them.
Given the significant unknowns about many aspects of the threat and its mitigation, the report recommends that the U.S. start a peer-reviewed, targeted research program on the hazards posed by NEOs, and how to deal with them. Because this is a policy-driven, applied research program, it should not be in competition with basic scientific research programs or be funded from them, the report adds.
The study was sponsored by NASA at the request of Congress. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. They are private, nonprofit institutions that provide science, technology, and health policy advice under a congressional charter. The Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. A committee roster follows.
Copies of DEFENDING PLANET EARTH: NEAR-EARTH OBJECT SURVEYS AND HAZARD MITIGATION STRATEGIES are available from the National Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on the Internet at HTTP://WWW.NAP.EDU. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).
[This news release and report are available at HTTP://NATIONAL-ACADEMIES.ORG]
NATIONAL RESEARCH COUNCIL
Division on Engineering and Physical Sciences
Aeronautics and Space Engineering Board
Space Studies Board
COMMITTEE TO REVIEW NEAR-EARTH OBJECT SURVEYS AND HAZARD MITIGATION STRATEGIES
STEERING COMMITTEE
IRWIN I. SHAPIRO1 (CHAIR)
Timken University Professor
Harvard University; and
Senior Smithsonian Scientist
Harvard-Smithsonian Center for Astrophysics
Cambridge, Mass.
MICHAEL A’HEARN (VICE CHAIR)
Professor
Department of Astronomy
University of Maryland
College Park
FAITH VILAS (VICE CHAIR)
Director
MMT Observatory
Mt. Hopkins, Ariz.
ANDREW F. CHENG
Chief Scientist
Space Department
Applied Physics Laboratory
Johns Hopkins University
Laurel, Md.
FRANK CULBERTSON JR.
Senior Vice President
Orbital Sciences Corp.
Dulles, Va.
DAVID C. JEWITT1
Professor
Department of Earth and Space Sciences, and
Institute for Geophysics and Planetary Physics
University of California
Los Angeles
STEPHEN MACKWELL
Director
Lunar and Planetary Institute
Houston
H. JAY MELOSH1
University Distinguished Professor
Purdue University
West Lafayette, Ind.
JOSEPH H. ROTHENBERG
President
Universal Space Network
Darnestown, Md.
SURVEY/DETECTION PANEL
FAITH VILAS (CHAIR)
Director
MMT Observatory
Mt. Hopkins, Ariz.
PAUL ABELL
Research Scientist
Planetary Science Institute
Houston
ROBERT F. ARENTZ
New Business Manager
Ball Aerospace and Technologies Corp.
Boulder, Colo.
LANCE A.M. BENNER
Research Scientist
Jet Propulsion Laboratory
Pasadena, Calif.
WILLIAM F. BOTTKE
Assistant Director
Department of Space Studies
Southwest Research Institute
Boulder, Colo.
WILLIAM E. BURROWS
Independent Aerospace Writer and Historian
Stamford, Conn.
ANDREW F. CHENG
Chief Scientist
Space Department
Applied Physics Laboratory
Johns Hopkins University
Laurel, Md.
ROBERT D. CULP
Professor
Department of Aerospace Engineering Sciences
University of Colorado
Boulder
YANGA FERNANDEZ
Assistant Professor of Planetary Science/Astronomy
Department of Physics
University of Central Florida
Orlando
LYNNE JONES
LLST Fellow
Department of Astronomy
University of Washington
Seattle
STEPHEN MACKWELL
Director
Lunar and Planetary Institute
Houston
AMY MAINZER
Research Scientist
Jet Propulsion Laboratory
Pasadena, Calif.
GORDON H. PETTENGILL1
Professor of Planetary Physics
Department of Earth, Atmospheric, and Planetary Sciences
Massachusetts Institute of Technology
Cambridge
JOHN RICE
Professor
Department of Statistics
University of California
Berkeley
MITIGATION PANEL
MICHAEL A’HEARN (CHAIR)
Professor
Department of Astronomy
University of Maryland
College Park
MICHAEL J.S. BELTOM
President and Deputy Principal Investigator
Belton Space Exploration Initiatives LLC
Tucson, Ariz.
MARK BOSLOUGH
Principal Member
Exploratory Simulation Technologies Department
Sandia National Laboratories
Albuquerque, N.M.
CLARK R. CHAPMAN
Senior Scientist
Department of Space Studies
Southwest Research Institute
Boulder, Colo.
SIGRID CLOSE
Assistant Professor
Department of Aeronautics and Astronautics
Stanford University
Stanford, Calif.
JAMES A. DATOR
Director
Hawaii Research Center for Future Studies
Department of Political Sciences
University of Hawaii
Manoa
DAVID S.P. DEARBORN
Research Scientist
Lawrence Livermore National Laboratory
Livermore, Calif.
KEITH A. HOLSAPPLE
Professor
Aeronautics and Astronautics Department
University of Washington
Seattle
DAVID Y. KUSNIERKIEWICZ
Chief Engineer
Space Department
Applied Physics Laboratory
Johns Hopkins University
McLean, Va.
PAULO LOZANO
Charles Stark Draper Assistant Professor
of Aeronautics and Astronautics
Department of Aeronautics and Astronautics
Massachusetts Institute of Technology
Cambridge
EDWARD D. MCCULLOUGH
Principal Scientist
Boeing (RETIRED)
Riverside, Calif.
H. JAY MELOSH1
University Distinguished Professor
Purdue University
West Lafayette, Ind.
DAVID J. NASH2
President
Dave Nash & Associates LLC
Birmingham, Ala.
DANIEL J. SCHEERES
Professor
Department of Aerospace Engineering Sciences
Colorado Center for Astrodynamics Research
University of Colorado
Boulder
SARAH T. STEWART-MUKHOPADHYAY
John L. Loeb Associate Professor of the
Natural Sciences
Department of Earth and Planetary Sciences
Harvard University
Cambridge
KATHRYN C. THORNTON
Associate Dean
Department of Science, Technology, and
Society
University of Virginia
Charlottesville
RESEARCH COUNCIL STAFF
DWAYNE A. DAY
Study Co-Director
PAUL JACKSON
Study Co-Director
1 Member, National Academy of Sciences
2 Member, National Academy of Engineering