[meteorite-list] Assessing and Reporting Impact Risks

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:22 2004
Message-ID: <200209062038.NAA20215_at_zagami.jpl.nasa.gov>

http://skyandtelescope.com/news/current/article_728_1.asp

Assessing and Reporting Impact Risks
By David L. Chandler
Sky & Telescope
September 6, 2002

Reports of possible impacts by comets or asteroids are not exactly a new
thing. Edmond Halley, long before the comet that bears his name made its
first predicted return, suggested that a comet might eventually strike Earth
with possibly devastating results.

It wouldn't be surprising if, back in 1690, a few press reports blew
Halley's warning way out of proportion, and astronomers worried that their
credibility would be undermined as a result. That's what regularly happens
nowadays. Faced with this problem, some of the astronomers at this week's
Workshop on Scientific Requirements for Mitigation of Hazardous Comets and
Asteroids presented ideas about how to improve public communications
surrounding the increasingly high-profile impact prediction process.

Today's astronomers use numerical yardsticks to assess impact risk. The
Torino Scale ranks every near-Earth object on a zero-to-ten basis, with zero
representing the risk of impact being lower than that of a random unknown
object hitting Earth in the same time frame. The Torino rankings were
designed with the general public in mind, with higher values representing
both a higher probability of impact and worse damage. By contrast, the
Palermo Scale was created for astronomers' use. It assigns zero to any
object that has the same probability of hitting Earth in a given time period
that a random object would. But it also assigns negative values to objects
that pose less risk than random impacts. And its rankings are assigned
differently too, with no distinction between small impacts and big ones.

Clark Chapman (Southwest Research Institute) and Brendan Mulligan (Queen's
University, Canada) investigated a wide variety of hazard scales that have
been used to communicate everything from hurricanes and forest fires to
nuclear war and terrorism. Chapman says that with some modification, the
Torino Scale for impact risk seems to hold up well, and he suggested it
should be used consistently in communicating with the public about new
possibly-hazardous asteroids. And, he says, astronomers should avoid
references to the Palermo Scale - whose usage figured prominently in the
reports six weeks ago about a low-probability possible impact in 2019 by
asteroid 2002 NT7.

Some of those reports, Chapman says, were "confusing and inappropriate,"
since they stressed the fact that this was the first object ever to get a
positive, greater-than-zero Palermo rating. Since the scale was barely a
year old, he says, that's "like calling the Queens air crash last fall the
worst transportation disaster of the century, when the century was barely a
year old!"

David Morrison (NASA/Ames Research Center) says that on the one hand, such
reports do help raise public awareness of the issue, but they also have
"demeaned the credibility of astronomers in the public's eye." While
astronomers should not suppress information, he suggests, they should make
sure that a good, responsible report of the facts is quickly available on
the Internet, even "in a few sentences, to give our view." But he criticizes
recent suggestions for a military-run warning center for asteroid impact
predictions. Because real, substantiated warnings of a serious asteroid
danger will be so rare - perhaps one every 50 to 100 years - "this is not a
credible option," he says.

Duncan Steel (University of Salford, United Kingdom) suggested his own
analogy to help the public understand the risk and how to put it in
perspective: comparing the asteroid threat to the risk of cancer. For any
individual, the risk is low on any given day, but must be taken seriously;
early detection is crucial - if one is detected, suddenly the high cost of
mitigation becomes irrelevant. And if it is detected early enough, the
treatment can be highly effective.
Received on Fri 06 Sep 2002 04:38:18 PM PDT