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SOME HIGHLIGHTS FROM THE TORINO INTERNATIONAL SPACEGUARD WORKSHOP: IMPACT (INTERNATIONAL MONITORING PROGRAMS FOR ASTEROID AND COMET THREAT)

June 1-4, 1999

By David Morrison (david.morrison@arc.nasa.gov)
June 11, 1999

  • Nature of the Impact Hazard: For any given size (energy) of potential impactor, there is a "background probability" of impact from unknown objects. As more NEOs are discovered, this background probability decreases. However, occasionally a newly discovered NEO is found to be on an orbit that repeatedly brings it close to the Earth, and that has a non-zero chance of impact at one or more discrete times in the future. As the orbit is refined, these discrete moments of risk will generally disappear. There are no more than a handful of truly threatening NEOs (D >1 km) in any century, and perhaps none. The progress of Spaceguard can then be thought of as a replacement of a general background risk with discretely identified risks from a very small number of NEOs, which will of course be carefully tracked to determine their future orbits with high precision.

  • Appreciation of the Risk: Although the public is broadly aware of the impact hazard, and there has recently been evidence of increased interest in the U.S. Congress and the UK Parliament, it appears that the reality of the impact hazard has still not been accepted by many decision-makers, including most professionals in the risk assessment profession. Geof Sommer of RAND provided the workshop a provocative discussion of how we might formulate some of our issues in terms that can communicate better with policy makers and perhaps enhance the credibility of NEO impacts as a risk issue.

  • Search and Discovery: The rate of discovery of NEAs has greatly accelerated, with the bulk of the recent discoveries coming from the MIT LINEAR program using a single 1-m telescope. Grant Stokes reported that a second identical LINEAR telescope is about to begin regular operations, and other systems are also working, as described in previous NEO News notes. However, to meet the Spaceguard objective of discovering 90% of NEAs >1 km in diameter by 2009, it will be necessary to extend the search down to approximately visual magnitude 20.5, which has not been demonstrated for LINEAR or other systems that use 1-m telescopes. Thus it is not yet clear whether an expanded network of 1-m telescopes can do the full job.

  • Follow-up Observations: NEA discoveries must be rapidly followed up to determine orbits. Many groups, including amateur astronomers, now contribute to follow-up observing programs. This work is quite effective, but most of the present observers do not have large enough telescopes to observe discoveries that reach to magnitude 20.5. Thus as the discovery rate of faint NEAs increases, there may be a crises in follow-up. We also lack follow-up capability in the Southern Hemisphere, which could lead to the loss of many NEAs that are moving south at the time of discovery.

  • Availability of data: As the number of NEA observers increases, and as more people have the capability to calculate orbits and impact probabilities, it is essential to move toward more rapid dissemination of data on NEA positions. Probably a system can be developed soon to provide automatic, essentially instantaneous posting of observational data on the Internet.

  • Cooperation and Coordination: A successful Spaceguard program requires detailed coordination of observations to avoid redundancy and make full use of the available resources. Some observers are already posting their observing plans on the Internet. Better coordination will be required, however, as the rate of discovery continues to increase.

  • Physical Characterization: There is a continuing need for physical characterization of NEOs, primarily using ground-based telescopes and radar. In addition, a number of spacecraft missions to comets and asteroids are planned or underway, which should greatly increase our knowledge of the nature of these objects.

  • Impact Hazard Scale: A new Torino Impact Hazard Scale, developed by Rick Binzel, was endorsed by attendees at the workshop. This scale, ranging from 0 (risk well below background level) to 10 (certain catastrophic impact), will be described in detail in a future message.

  • Verification of Threatening NEOs: The workshop attendees recommended that the International Astronomical Union take responsibility for establishing a system for voluntary rapid peer review of predictions or announcements of any NEO with significant impact risk (level 1 or higher on the Torino risk scale). This review will also be described on NEO News when the IAU works out the details.

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