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Torino Scale - Part 1 of 3

The Torino Scale: Gauging the Impact Threat

Planetary Astronomers unveil a new way to assess hazard predictions for
impacts by asteroids and comets in the 21st century (by J. Kelly Beatty,
Sky & Telescope, October 1999, pp. 32-33):

Caption of  photograph on page 32: The 70-kilometer-wide Manicouagan
structure was formed 210 million years ago when an object 5 to 7 km
across slammed into south-central Quebec, very likely triggering
worldwide consequences. An impact of this magnitude would warrant a
definite 10 on the newly created Torino scale. Courtesy Richard Grieve
(Natural Resources Canada).

Dealing with probabilities is a part of everyday life. When a
meteorologist predicts an 80 percent chance of rain, we take it in
stride. But we all have difficulty appreciating events with very long
odds - like winning a lottery. Consider the hazard to Earth posed by
asteroids and comets passing in our vicinity. In the last two years
astronomers have spotted three mountain-size rocks that initially were
given vanishingly small chances of striking Earth in the coming decades.
But these revelations still made headlines, as much for the confusion
surrounding the prediction process as for the threat itself.
One celebrated case involved asteroid 1997 XF11 (S&T, July 1998, page
30). More recent was the discovery of 1999 AN10 (see page 17); its
chance of striking Earth never climbed higher than one in 500,000, but
it triggered a news-media buzz anyway. Asteroid dynamicist Andrea Milani
(University of Pisa), whose team made the initial prediction, was
perplexed by all the attention. "A probability is only a measurement of
our ignorance" he explains.
Spurred by the recent spate of false alarms, Richard P. Binzel
(Massachusetts Institute of Technology) has unveiled a means for
conveying the impact threat in simple, clear terms. The "Torino scale"
assigns a number that combines the likelihood of being hit by an
asteroid or comet with the potential for damage from objects with a
given energy (which is related to size). In Binzel's scheme, 0 or 1
means there is virtually no chance of impact or damage, while 8 or
higher means that a collision is virtually certain - with 10
corresponding to global climatic catastrophe. In between are values that
variously categorize close asteroid encounters as "events meriting
careful monitoring" to "threatening events." The scale is named for the
Italian city of Torino (Turin), which recently hosted an International
Astronomical Union workshop that brought together impact specialists
from around the world.
The idea for such a hazard index came to Binzel in January 1993, soon
after it was widely reported that Comet 109P/Swift-Tuttle might collide
with Earth in 2126 (another false alarm). Deluged with questions from
reporters, he came to two important realizations: the whole subject of
impact hazard is prone to sensationalism, and the situation will only
get worse as observers step up their efforts to look for near-Earth
objects.


Good Night from Germany,

Bernd

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