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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 (email@example.com)
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
- 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
- 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
- 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.