[meteorite-list] Revised Asteroid Scale Aids Understanding of Impact Risk

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Apr 12 14:22:10 2005
Message-ID: <200504121821.j3CILfp23740_at_zagami.jpl.nasa.gov>

http://www.eurekalert.org/pub_releases/2005-04/miot-ras041205.php

Public release date: 12-Apr-2005

Contact: Elizabeth Thomson
thomson_at_mit.edu
617-258-5402
Massachusetts Institute of Technology

Revised asteroid scale aids understanding of impact risk

Goal is to assuage public's concerns about a potential doomsday collision

CAMBRIDGE, Mass.--Astronomers led by an MIT professor have revised the
scale used to assess the threat of asteroids and comets colliding with
Earth to better communicate those risks with the public.

The overall goal is to provide easy-to-understand information to assuage
concerns about a potential doomsday collision with our planet.

The Torino scale, a risk-assessment system similar to the Richter scale
used for earthquakes, was adopted by a working group of the
International Astronomical Union (IAU) in 1999 at a meeting in Torino,
Italy. On the scale, zero means virtually no chance of collision, while
10 means certain global catastrophe.

"The idea was to create a simple system conveying clear, consistent
information about near-Earth objects [NEOs]," or asteroids and comets
that appear to be heading toward the planet, said Richard Binzel, a
professor in MIT's Department of Earth, Atmospheric and Planetary
Sciences and the creator of the scale.

Some critics, however, said that the original Torino scale was actually
scaring people, "the opposite of what was intended," said Binzel. Hence
the revisions.

"For a newly discovered NEO, the revised scale still ranks the impact
hazard from 0 to 10, and the calculations that determine the hazard
level are still exactly the same," Binzel said. The difference is that
the wording for each category now better describes the attention or
response merited for each.

For example, in the original scale NEOs of level 2-4 were described as
"meriting concern." The revised scale describes objects with those
rankings as "meriting attention by astronomers"--not necessarily the
public.

Equally important in the revisions, says Binzel, "is the emphasis on how
continued tracking of an object is almost always likely to reduce the
hazard level to 0, once sufficient data are obtained." The general
process of classifying NEO hazards is roughly analogous to hurricane
forecasting. Predictions of a storm's path are updated as more and more
tracking data are collected.

According to Dr. Donald K. Yeomans, manager of NASA's Near Earth Object
Program Office, "The revisions in the Torino Scale should go a long way
toward assuring the public that while we cannot always immediately rule
out Earth impacts for recently discovered near-Earth objects, additional
observations will almost certainly allow us to do so."

The highest Torino level ever given an asteroid was a 4 last December,
with a 2 percent chance of hitting Earth in 2029. And after extended
tracking of the asteroid's orbit, it was reclassified to level 0,
effectively no chance of collision, "the outcome correctly emphasized by
level 4 as being most likely," Binzel said.

"It is just a matter of the scale becoming more well known and
understood. Just as there is little or no reason for public concern over
a magnitude 3 earthquake, there is little cause for public attention for
NEO close encounters having low values on the Torino scale." He notes
that an object must reach level 8 on the scale before there is a
certainty of an impact capable of causing even localized destruction.

The Torino scale was developed because astronomers are spotting more and
more NEOs through projects like the Lincoln Near Earth Asteroid Research
project at MIT's Lincoln Laboratory. "There's no increase in the number
of asteroids out there or how frequently they encounter our planet.
What's changed is our awareness of them," Binzel notes.

As a result, astronomers debated whether they should keep potential NEO
collisions secret or "be completely open with what we know when we know
it," Binzel said. The IAU working group, of which Binzel is secretary,
resoundingly decided on the latter.

The revised wording of the scale was published last fall in a chapter of
"Mitigation of Hazardous Comets and Asteroids" (Cambridge University
Press). The revisions were undertaken through consultation with
astronomers worldwide for nearly a year before being published.

Binzel concludes that "the chance of something hitting the Earth and
having a major impact is very unlikely. But although unlikely, it is
still not impossible. The only way to be certain of no asteroid impacts
in the forecast is to keep looking."

###

For more information on the revised Torino scale go to:
neo.jpl.nasa.gov/torino_scale.html .

 
Received on Tue 12 Apr 2005 02:21:41 PM PDT