[meteorite-list] Scientists See No Asteroid Threat ... Yet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:27 2004
Message-ID: <200302141801.KAA04818_at_zagami.jpl.nasa.gov>

http://www.upi.com/view.cfm?StoryID=20030213-074016-8554r

Scientists see no asteroid threat ... yet
By Phil Berardelli
UPI
February 13, 2003

DENVER -- Of about 650 large, near-Earth asteroids that have
been identified and tracked so far, none poses a direct threat to the planet
within the next century or two, astronomers reported Thursday.

However, the astronomers added, those objects represent only about 60 percent
of the largest bodies estimated to have the potential to strike the planet,
and comets also comprise a threat that will remain unquantifiable for some
time to come.

"We just don't know about the (450 or so other large bodies) and we know
nothing about the small ones," said David Morrison, senior scientist at
NASA's Astrobiology Institute at the Ames Research Center in Mountain View,
Calif.

However, Morrison said, the current assessment represents substantial
progress in identifying potentially dangerous near-Earth objects -- of which
a new one is found almost once a day -- over what was known a decade ago,
when the program called the Spaceguard survey was begun. He delivered his
remarks at a panel discussion on near-Earth asteroids at the American
Association for the Advancement of Science's annual meeting.

Spaceguard is a 25-year effort to identify and track objects, both asteroids
and what are called short-period comets, that potentially endanger Earth. The
first part of the effort requires identifying objects that have a diameter of
about 1 kilometer (about 0.62 mile) or greater. Objects of that size could
strike Earth with a force to wipe out most of civilization.

Future surveys could be designed to locate objects as small as about 50
meters (160 feet) in diameter, such as the one that struck the Tunguska area
of Siberia in 1908 and leveled a circular area nearly 40 kilometers (25
miles) in diameter. Such objects strike Earth about once every thousand
years.

Lee Clarke, a sociologist with Rutgers, the State University of New Jersey,
said perhaps the most challenging problem in the search for dangerous objects
is how to communicate prospective events to the public -- an application he
and the other panels said has relevance to America's current heightened state
of alert. He urged government officials to discount the possibility of mass
panic because of possible acts of terror.

"Probably the single most important reason there weren't more World Trade
Center fatalities (during the attack of Sept. 11, 2001) was because people
did not panic," Clarke said. "If you give people specific and credible
warnings, they will follow the instructions," he added. "Just upping the
(alert) level to orange and telling people to buy plastic is not effective,"
he said, referring to recent instructions to citizens in certain U.S. cities
to prepare for a possible chemical or biological attack.

Clarke cited the examples of fire drills held regularly in every school
building, the hurricane evacuation plans issued in coastal areas and,
historically, the air raid alerts given to citizens of London during the
Blitz in World War II.

Just as in dealing with terror, authorities responsible for asteroid impact
warnings would face twin dilemmas, Clarke continued. They would have to
communicate the risks of a catastrophe and then, perhaps, react to its
aftermath. However, they would face an additional problem: the possibility of
a very long lead time.

"Who is going to think it through if we have (to wait) 200 years?" Clarke
asked.

Geoff Sommer, a policy analyst with the RAND Corporation in Santa Monica,
Calif., said a continuing problem associated with the search for dangerous
objects is the challenge of communicating just the right amount of warning.

"We've already had several asteroid scares," Sommer said, referring to news
reports over the past couple of years involving possible impacts, arriving
anywhere from 18 years to more than 100. "We need to counteract the social
costs of warning," he added.

Clark Chapman, a planetary scientist with the Southwest Research Institute in
Boulder, Colo., described how, given enough warning, the technology already
exists to nudge an errant asteroid out of its collision course with Earth.

The process would involve sending a spacecraft to rendezvous with the object
as long before a potential impact as possible. Then, using rocket engines or
other, non-explosive means, the craft would disrupt the asteroid's orbital
path just enough to avoid disaster. At least, Chapman said, that is the
possibility for asteroids.

"Comets are another story," he said, explaining the icy blobs originate in
the outer solar system where they are extremely difficult to detect. Instead
of years or even decades of warning, as with the asteroids that have been
detected, comets travel at a much higher velocity, and new ones would be
detected only months ahead, at best.
Received on Fri 14 Feb 2003 01:01:36 PM PST