[meteorite-list] Science Workshop Reveals Evolving Perspective on Asteroid Threat

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:22 2004
Message-ID: <200209062318.QAA25264_at_zagami.jpl.nasa.gov>

http://www.noao.edu/outreach/press/pr02/pr0208.html

FOR IMMEDIATE RELEASE: Friday, September 6, 2002
RELEASE NO: NOAO 02-08

Science Workshop Reveals Evolving Perspective on Asteroid Threat

For More Information:

Douglas Isbell
Public Information Officer
National Optical Astronomy Observatory
Phone: 520/318-8214
E-mail: disbell_at_noao.edu

Prof. Erik Asphaug
University of California at Santa Cruz
Phone: 831/459-2260
E-mail: asphaug_at_es.ucsc.edu

Direct measurements of the surface properties and interior structures of
asteroids and comets should be fundamental elements of future spacecraft
missions to these primitive solar system bodies, according to participants
in a scientific workshop held in Arlington, VA, from September 3-6.

Such information is vitally important for preparing a variety of approaches
for the diversion of Near-Earth Objects which may someday threaten Earth.
Evidence presented at the workshop suggests that gentle thrusts applied for
decades, rather than traditional explosives, are likely to be needed to
change their orbital paths. This will require early detection together with
knowledge of their geologic properties.

Sponsored by NASA, the workshop was designed to find common ground among
researchers on the reconnaissance and exploration of Near-Earth Objects.
"Unlike volcanoes or earthquakes, the NEO hazard was only recently
identified, and we have just begun to understand its implications," said
meeting organizer Erik Asphaug of the University of California at Santa
Cruz. "This is the only major natural hazard which can, in principle, be
made predictable and even eliminated if we find the dangerous ones and learn
how to modify their orbits over time."

Astronomers have determined precise orbits and estimated the sizes of
approximately 1,500 Near-Earth Objects (NEOs), according to conference
presentations. More than 600 of the estimated 1,000 asteroids larger than
one kilometer in diameter (a size that could cause widespread calamity on
Earth) have been detected so far. This represents good progress toward the
goal mandated by Congress for NASA to discover 90% of these objects by 2008.
While no known asteroid is on collision course with Earth, ongoing detection
should alert us to serious threats.

Significant topics of discussion at the workshop included large
uncertainties in the state of scientific knowledge of asteroid surfaces,
despite great advances in recent years. There is increasing evidence that
most asteroids larger than a few hundred meters have complex interiors and
may be loosely bound conglomerates which might resist explosive diversion.
To almost everyone's surprise, about a sixth of NEOs are now observed to
have moons, which would complicate any effort to change their orbits.

While scientific goals of researching the early history of the solar system
and mitigation goals of protecting the Earth are very different, the kinds
of asteroid studies needed to address both goals are largely identical,
several participants noted. "Learning more about them is the first step,"
Asphaug said. Gathering a wide variety of measurements is critical for fully
understanding the history and properties of NEOs, given their great
diversity and their many observed dissimilarities from presumed analogues
like the surface of the Moon.

Because we know so little, physical characterization was seen by researchers
as going hand-in-hand with potentially useful technological developments.
For example, a large, lightweight solar concentrator was discussed that
could vaporize a small surface area for measurements of composition; thrust
from the escaping material could be measured to test concepts for
solar-powered asteroid deflection.

Because close-calls are far more likely than actual impacts, attendees also
discussed the deployment of radio transponders for precision tracking of
dangerous objects. Many researchers expressed the need for high-performance
propulsion systems that could power a spacecraft to a rapid rendezvous with
an NEO.

Ground-based observatories such as the proposed 8.4-meter Large Synoptic
Survey Telescope (a high priority in the most recent Decadal Survey of
astronomy by the National Academy of Sciences) can be effective tools to
detect 80-90% of the NEO population down to a diameter of 300 meters within
about a decade of full-time operations. A spacecraft orbiting close to the
Sun and looking outward in tandem with such a telescope might reduce this
time to five years. NEOs in this size range can cause widespread regional
damage on Earth, although the workshop scientists agreed that the detailed
effects of impacts of any size remain poorly understood.

Ground-based radar observations of close-approaching NEOs will also remain a
uniquely important and flexible method to study a variety of objects,
attendees agreed. Radar is capable of imaging and accurately tracking the
closest Earth-approachers.

Few countries outside of the United States are spending significant
resources on the NEO hazard, and this international imbalance must be
remedied if the threat is to be fully understood within the next few
decades, according to several speakers. For example, there are currently no
active ground-based NEO searches in the Southern Hemisphere. Despite the
spectacular success of NASA's recently concluded Near Earth Asteroid
Rendezvous mission, and excitement surrounding Japan's upcoming MUSES-C
mission (the first-ever sample return from an asteroid, to be launched in
December), researchers agreed that more substantial investigations are
required if we are to learn how to change an asteroid's orbit.

Scientists must take better advantage of opportunities to explain new
detections and their related risks to the media and the public, attendees
agreed. With advanced search systems coming on line, asteroids will be
discovered at an increasing rate, with orbits which may initially appear
dangerous. Only detailed follow-up on a case-by-case basis can prove each
new discovery to be non-threatening. This process must be communicated more
carefully, scientists agreed, in the manner that hurricanes are tracked by
the weather service until the "all-clear" is announced.

The workshop was attended by 70 scientists from the United States,
Australia, Europe and Japan. It was co-sponsored by Ball Aerospace, Science
Applications International Corp., Lockheed Martin Corp., the National
Optical Astronomy Observatory and the University of Maryland. A formal
report on the workshop will be submitted to NASA by the end of 2002.

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Received on Fri 06 Sep 2002 07:18:41 PM PDT