The Torino Scale

The Torino scale is a classification (similar to the Ritcher scale for earthquakes) to quantify the impact hazard of a certain NEO. This classification has been introduced, for the first time, at an International Conference on Near-Earth objects held in June 1999 in the city of Torino, as a revised version of the "Near-Earth Object Hazard Index" created by Professor P.Binzel of the MIT.
The Torino scale is a two parameters scale: it utilizes numbers form 0 to 10 to indicate the chance of a collision, while the color is used as a second parameter to give an information about the danger of the event (going from white, non dangerous bodies, to red, catastrophic events) .
The parameters that lead to the classification of an object, aside to its position and its dimension, are its kinetic energy and its collision probability. This means that, an object that will make several different close approaches of Earth, will have a different Torino scale value for each approach. Normally, only the highest of these values is considered to identify an object.
Another important thing about the Torino scale value, is that it will change in time. This change will be the result of better measurements of the object's orbit (see probability of impact).


The Torino and the Palermo scale (taken from T.S. number 7)

Since the Torino scale is a function of the impact energy and probability of the event, the time of the possible impact does not matter (provided it is within 2100). No special consideration is given to the possibility of impacts in the very near future, as in this case. This feature of the Torino scale had already been the subject of discussion among the specialists, in particular Rick Binzel, the author of the Torino scale, and Hans Rickman, the General Secretary of the IAU. In a meeting of the Working Group on Near Earth Objects (WGNEO) of the IAU, chaired by D.Morrison, held in Palermo during the Asteroids 2001/Piazzi meeting, the consensus was that the current IAU procedure for impact announcements, based upon the Torino scale, should not be formally changed, but the people concerned should use their common sense to handle each different case in the way most effective to obtain observations capable of solving the problem. For us this includes to begin experimenting with a new scale, sometimes nicknamed 'Palermo technical scale', which was presented at the Palermo meeting by Chesley et al. In this new scale the risk posed by one Virtual Impactor is compared to the 'background risk' posed by all NEO between now and the time of possible impact. Thus in this formula the shorter the time span, the larger the relative risk: understandably, a possibility of impact in two years results in a comparatively large value, and this well reflects our intuitive feeling, that such an immediate risk is worse than one remote in time.


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