The Torino Impact Hazard Scale

Newly discovered asteroids and comets have inherent uncertainties in their orbit determinations owing to the natural limits of positional measurement precision and the finite lengths of orbital arcs over which determinations are made. For some objects makings predictable future close approaches to t he Earth, orbital uncertainties may be such that a collision with the Earth cannot be ruled out. Careful and responsible communication between astrono mers and the public is required for reporting these predictions and a 0.10 point hazard scale, reported inseparably with the date of close encounter, is recommended as a simple and efficient tool for this purpose. The goal of this scale, endorsed as the Torino Impact Hazard Scale, is to place into c ontext the level of public concern that is warranted for any close encounte r event within the next century. Concomitant reporting of the close encount er date further conveys the sense of urgency that is warranted. The Torino Scale value for a close approach event is based upon both collision probabi lity and the estimated kinetic energy (collision consequence), where the sc ale value can change as probability and energy estimates are refined by fur ther data. On the scale, Category 1 corresponds to collision probabilities that are comparable to the current annual chance for any given size impacto r. Categories 8-10 correspond to certain (probability >99%) collisions havi ng increasingly dire consequences. While close approaches falling Category 0 may be no cause for noteworthy public concern, there remains a profession al responsibility to further refine orbital parameters for such objects and a figure of merit is suggested for evaluating such objects. Because impact predictions represent a multi-dimensional problem, there is no unique or p erfect translation into a one-dimensional system such as the Torino Scale. These limitations are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.