Tuesday, October 26, 2010

NASA Identifies 1,142 Near Earth Objects That Are Potential Collision Hazards, 149 Larger Than One Kilometer Diameter

NASA is with charged the task of protecting the U.S. and the world from a deadly asteroid collision.

Section 804 of the National Aeronautics and Space Administration (NASA) Authorization Act of 2008 directs the Director of the Office of Science and Technology Policy (OSTP) to “(1) develop a policy for notifying Federal agencies and relevant emergency response institutions of an impending near-Earth object threat, if near-term public safety is at risk; and (2) recommend a Federal agency or agencies to be responsible for: (A) protecting the United States from a near-Earth object that is expected to collide with Earth; and (B) implementing a deflection campaign, in consultation with international bodies, should one be necessary.”

John Holdren, director of the White House Office of Science and Technology Policy  (OSTP)  has sent 10-page letters to the House Committee on Science and Technology and the Senate Committee on Commerce, Science and Transportation that detail NASA’s Response to Congress on Near-Earth Objects.

The letters outline plans for  protecting the United States from a near-Earth (NEO)  that is expected to collide with Earth and implementing a deflection campaign, in consultation with international bodies, "should one be necessary."

Current and Prospective Near-Earth Object (NEO) Detection Activities
NEOs are asteroids or comets whose orbits bring them within a set distance of the Earth,’ with a portion of these objects traveling sufficiently close to make an eventual collision a possibility. No NEO large enough to present a hazard is known to be on a collision course with the Earth, and the probability of an impact by such a NEO is extremely low. 

Nevertheless, incidents of this nature have occurred in Earth’s geologic past, and our immediate neighborhood of the Solar System is continually showered by very small, non-hazardous objects. Indeed, a steady stream of these objects enters the Earth’s atmosphere on a daily basis, consisting mostly of dust-sized particles and estimated to total some 50 to 150 tons each day. Thus, however remote it may be, the possibility of a future collision involving a more hazardous object should not be ignored.  In general terms, this distance is equivalent to about one-third the average distance of the Earth from the Sun.
Any strategy for addressing the potential hazard of a future NEO impact depends in the first instance on the detection, precision tracking, and characterization of potentially hazardous space objects. However, there are several challenges involved in first finding NEOs that are coming toward the Earth, and then determining whether a collision is likely. Such a determination is contingent upon factors such as the distance, size, orbit, and reflectivity of these objects, as well as the number and capabilities of the telescopes that are involved in the search. This is further complicated by the prospect that the orbits of known objects can be changed by gravitational or solar radiation perturbations, or even collisions with other objects, meaning that periodic monitoring of known NEOs must also be conducted.

Against this backdrop, Congress has provided direction to NASA to pursue enhanced NEO detection activities in various pieces of legislation, including most recently in the 2005 NASA Authorization Act (in a section labeled The George E. Brown, Jr. Near-Earth Object Survey Act), wherein NASA is directed to detect, track, catalogue, and characterize 90 percent of all NEOs with a diameter of 140 meters or greater by 2020. Earlier Congressional direction in 1998 tasked NASA with locating at least 90 percent of all NEOs with a diameter of one kilometer or greater (i.e., those judged by many experts to have the potential to threaten civilization) within ten years. 

In pursuit of these Congressionally-directed goals, NASA currently sponsors various activities relating to the search for NEOs, including the international Minor Planet Center (MPC), located at the Harvard-Smithsonian Center for Astrophysics and operating under the auspices of the International Astronomical Union, for the collection and correlation of NEO orbit data; research at two radio telescope facilities to help provide precision tracking and characterization of NEOs; surveys conducted by ground-based optical telescopes; and NASA’s NEO Program Office at the Jet Propulsion Laboratory (JPL) for the overall coordination of these efforts and assessments of NEO orbits and impact probabilities.

There are also cooperative projects among NASA, the National Science Foundation (NSF, which has a key role within the United States for ground-based astronomical assets), and the U.S. Air Force (USAF), as well as non-government academic and space research organizations. Within this latter category, an important international collaboration exists with the University of Pisa’s NEO Dynamic Site in Italy, which performs high-precision orbit determination and trajectory prediction in parallel with NASA’s NEO Program Office, allowing analyses from these two organizations to be independently compared and cross-checked.

With respect to the Congressional direction to identify 90 percent of the objects that are one kilometer or greater in diameter, NASA advises that it is now closing in on that objective after twelve years of conducting surveys (updates are provided on the NEO Program website).  As of October 1, 2010, search teams have discovered 903 of these objects (out of an estimated total population of 1,050 NEOs that are one kilometer or larger in diameter) and have determined that only 149 of these objects are in orbits that could ever pose a collision hazard with the Earth -- with none presenting a threat of impact on Earth within the next century. NASA anticipates reaching the 90 percent detection goal for this category of NEOs by the end of

More generally, this twelve-year search effort has increased the total number of known NEOs from 499 to 7,319, of which 1,142 are thought to be traveling in potentially hazardous orbits (including the 149 objects larger than one kilometer in diameter mentioned above and 993 objects smaller than one kilometer). This represents genuine and notable progress (see Figure 1).
Figure 1. Cumulative history of all NEA discoveries

NASA notes that a large number of the NEOs predicted to exist still remain undiscovered, and many of these could present a potential future hazard to the Earth. To help illustrate this point using the data provided above, 6,416 of the NEOs detected thus far are smaller than one kilometer in diameter, including the 993 objects in this category that are traveling in potentially hazardous orbits. 

However, the latest estimates for the total population of NEOs below one kilometer in size indicate that these 6,416 known objects represent less than five percent of the total number of NEOs projected in this size category (see Figure 2 for a depiction of the status of detection efforts for various size categories). Thus, based upon simple probability, it seems quite likely that there are more than 993 objects of this smaller size traveling in orbits potentially hazardous to the Earth.

Figure 2. Known Near-Earth Asteroids January1980 through August 2010 
In light of such considerations and consistent with its Congressional direction, NASA has continued to pursue additional capabilities for a NEO surveillance program able to detect, track, catalogue, and characterize NEOs down to 140 meters in diameter. In particular, NASA has been seeking to leverage partnerships with various dual-use facilities and spacecraft to further the goal of NEO detection and characterization. For example, NASA has supported the enhancement of the capabilities of the MPC to enable it to process all NEO observations received from worldwide facilities and disseminate the resulting orbit information without fees via the Internet. With these enhancements, the MPC should be able to accommodate the anticipated significant increase in NEO observation data from world-wide “next generation” search efforts. 

In addition, NASA has partnered with the USAF Panoramic Survey Telescope and Rapid Response System (PanS TARRS) program to utilize this system for detection of NEOs that are a few hundred meters in diameter. Although Pan-STARRS has experienced some delays in final development, it is expected to begin regular NEO survey operations soon. As noted earlier, NASA also continues to support interplanetary radar capabilities for precision tracking and characterization of NEOs at its Goldstone Solar System Radar facility in California (part of NASA’s Deep Space Network for communication with interplanetary spacecraft) and now also at the NSF’s Arecibo radio telescope in Puerto Rico.

In a recent development along these lines, NASA has expanded the utility of its Wide-field Infrared Survey Explorer (WISE) satellite, which was launched in December 2009 for the primary purpose of scanning the sky in infrared frequencies, to help support NEO detection and characterization activities. Under a project known as NEO-WISE, modifications of the ground data processing functions of WISE have enabled automated searches for NEOs using already- collected WISE images. 

These efforts have resulted in the observation of tens of thousands of asteroids (most of which orbit the Sun in the Main Asteroid Belt, which is located between Mars and Jupiter) and hundreds of known NEOs, as well as the discovery of 119 new NEOs. Nineteen of these newly identified objects are considered potentially hazardous, and seven are greater than one kilometer in diameter. WISE has reached the expected end of its on-board supply of coolant, and NEO-WISE mission operations will conclude by the end of January 2011.

At the same time, NASA is exploring whether other planned wide-field space surveillance systems being developed by U.S. Government (USG) agencies can be utilized in support of NEO detection and tracking efforts. Two planned ground-based facilities of particular interest are the USAF’s next generation Space Surveillance Telescope (SST), which is being developed by the Defense Advanced Research Projects Agency and is in the final stages of development, and the proposed Large Synoptic Survey Telescope (LSST), which currently is aiming to begin operations by the end of the decade if approved by NSF and the U.S. Department of Energy, and if funded by Congress.

Both systems could provide significant contributions to the search for NEOs, although adapting them for this purpose might require some modifications, and involved agencies likely would need to reach agreements on how the NEO survey mission would be balanced against the primary missions of these systems. Other options include a possible observing spacecraft tailored to the search for NEOs and operating in a solar orbit interior to that of Earth. 

Recent analyses both by NASA and a National Research Council (NRC) study team suggest that such a spacecraft could significantly accelerate the detection of NEOs L00 meters or larger in diameter, and NASA’s experience with space-based telescopes such as Spitzcr, Kepler, and WISE indicate that existing technologies should be sufficient for this purpose. Nonetheless, it should be noted that a project of this nature would likely be much more costly than Earth-based telescopes. No plans are in place to pursue such a mission, though evaluations of the costs and benefits of this approach relative to other capabilities (such as the SST and LSST) will continue as NEO survey activities progress.

Future international collaboration may also help enhance efforts to discover and characterize NEOs. For example, NASA is sponsoring a science team to work with the Canadian Space Agency (CSA) on collection and processing of data from the CSA’s Near Earth Object Surveillance Satellite, which is scheduled for launch in 2011, and a potential bilateral partnership also is being discussed with respect to Germany’s planned Asteroid Finder mission. More broadly, NASA, the Department of State (DOS), and other USG agencies are actively engaged in the NEO Working Group of the Scientific and Technical Subcommittee of the United Nations (UN) Committee on the Peaceful Uses of Outer Space (COPUOS), which is promoting more involvement by other nations in dealing with the threat of potentially hazardous NEOs.

Various Administration policy and budgetary decisions made this year have addressed the subject of NEOs in some form and are expected to buttress ongoing detection and tracking activities going forward. For example, the President’s FY20 1 1 budget request for NASA calls for more than a 3.5-fold increase from the enacted FY20 10 level (from $5.8 million to $20.3 million) for NEO detection activities. 

Further, the President’s new National Space Policy specifically directs NASA to “pursue capabilities, in cooperation with other departments, agencies, and commercial partners, to detect, track, catalog, and characterize near- Earth objects to reduce the risk of harm to humans from an unexpected impact on our planet and to identify potentially resource-rich planetary objects.” This guidance reinforces NASA’s roles and responsibilities in this arena and makes clear that cooperation with other organizations will be a key aspect going forward. Finally, the President’s new plan for NASA’s human space flight activities establishes a goal of conducting a human mission to an asteroid by 2025 — an effort that relates to NEO detection and possible mitigation activities in several ways.

Among other things, NEO detection and tracking efforts should provide more candidates for human and robotic exploration programs, allowing NASA to choose a more optimal trajectory and target for this mission. Moreover, the opportunity to comprehensively survey an entire object through both human and precursor robotic missions (and relate carefully collected samples to that object) will represent a scientific milestone in human exploration and could also reveal important information about asteroid composition and structure. The planning, required capabilities, and ultimate execution of such a mission also would parallel most aspects of a potential robotic asteroid deflection mission, providing valuable experience in asteroid rendezvous techniques. As such, considerations relating to potential asteroid mitigation or deflection activities are envisioned as part of the overall mission planning and objectives for this effort. ‘

Notification Procedures for a Potential NEO Threat
OSTP has been working closely with several departments and agencies to determine the plans, mechanisms, and procedures that should he used for notifying local, state, and Federal authorities and emergency response institutions in the unlikely event of an impending NEO threat to the United States. As will be described in more detail below, the essence of the planned notification approach is to utilize existing communications resources and mechanisms resident at the Federal Emergency Management Agency (FEMA) in the Department of Homeland Security (DHS) for this purpose, once an initiating notice has been received from NASA regarding a potential NEO threat. Such domestic notification efforts would be supported by the diplomatic mechanisms of DOS for international communications as needed. These notification procedures have been exercised and implemented regularly over the last few years, particularly for re-entering human-made space objects (with a prominent recent example being the successful Burn! Frost Joint Task Force effort to engage and destroy the non-functioning “USA-l93” spacecraft in February 2008). FEMA considers these procedures to be well-understood and applicable to the emergency notifications needed for a potential NEO threat.

FEMA Emergency Notification Procedures.
For FEMA to initiate its notification process, it must itself first receive notice of a potential NEO threat from NASA, which will have coordinated the NEO threat information from other organizations within the NEO detection community. This initial notice must be given to the FEMA Operations Center (FOC), the Joint Space Operations Center (JSpOC) within the U.S, Department of Defense (DOD), DOS, appropriate organizations in the Executive Office of the President (EOP), and other relevant Federal officials and organizations, and would include information regarding the predicted time and location of the potential NEO impact, along with an assessment of the uncertainty regarding that prediction. NASA already has instituted communications procedures aimed at this purpose, including direction with regard to public release of such information. 

These NASA procedures would be set in motion only after the necessary observations, analyses, and characterization efforts had taken place within the NEO community to determine that a space object indeed represented a sufficiently credible threat. Depending upon the perceived level of risk and urgency, such activities could well unfold over the course of many years after initial detection of an object and often would entail various combinations of’ increased monitoring, cross-checks of any potentially hazardous trajectories as needed, and accelerated orbit-determination efforts in cases where a potential hazard is considered nearer term in nature. 

For a complete copies of the OSTP Response to Congress on Near-Earth Objects: House (pdf) - Senate (pdf)

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