The Torino Scale is a method for categorizing the impact hazard associated with near-Earth objects (NEOs) such as asteroids and comets. It is intended as a tool for astronomers and the public to assess the seriousness of collision predictions, by combining probability statistics and known kinetic damage potentials into a single threat value. The Palermo Technical Impact Hazard Scale is a similar, but more complex scale.
The Torino Scale uses a scale from 0 to 10. A 0 indicates an object has a negligibly small chance of collision with the Earth, compared with the usual "background noise" of collision events, or is too small to penetrate the Earth's atmosphere intact. A 10 indicates that a collision is certain, and the impacting object is large enough to precipitate a global disaster. Only integer values are used.
An object is assigned a 0 to 10 value based on its collision probability and its kinetic energy (expressed in megatons of TNT).
The Torino Scale was created by Professor Richard P. Binzel in the Department of Earth, Atmospheric, and Planetary Sciences, at the Massachusetts Institute of Technology (MIT). The first version, called "A Near-Earth Object Hazard Index", was presented at a United Nations conference in 1995 and was published by Binzel in the subsequent conference proceedings (Annals of the New York Academy of Sciences, volume 822, 1997.)
A revised version of the "Hazard Index" was presented at a June 1999 international conference on NEOs held in Torino (Turin), Italy. The conference participants voted to adopt the revised version, where the bestowed name "Torino Scale" recognizes the spirit of international cooperation displayed at that conference toward research efforts to understand the hazards posed by NEOs. ("Torino Scale" is the proper usage, not "Turin Scale.")
Due to exaggerated press coverage of Level 1 asteroids such as 2003 QQ47, a rewording of the Torino Scale was published in 2005, adding more details and renaming the categories: in particular, Level 1 was changed from "Events meriting careful monitoring" to "Normal".
Current Torino Scale
The Torino Scale also uses a color code scale: white, green, yellow, orange, red. Each color code has an overall meaning:
Objects with high Torino ratings
The current record for highest Torino rating is held by 99942 Apophis, an about 350 m near-Earth asteroid, which was later downgraded to 0. On December 23, 2004, NASA's Near Earth Object Program Office announced that Apophis (then known only by its provisional designation 2004 MN4) was the first object to reach a level 2 on the Torino Scale, and it was subsequently upgraded to level 4. It is now expected to pass the Earth on Friday, April 13, 2029 quite closely but with no possibility of an impact. Future uncertainties in the orbit of Apophis will occur because of gravitational deflection during the 2029 encounter, so a Torino rating of 1 (for an encounter in 2036) applied until August 2006, when Apophis was downgraded to 0.
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