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On Tuesday 12 April it was announced that a revised version of the Torino scale has been formally published. The scale is used to rate the risk from Near Earth Objects (NEOs), and has been modified to make it easier to understand.
The scale runs from zero to ten, where ten is the most hazardous. A Torino rating of zero represents no hazard, whereas a rating of ten represents a certain collision, capable of causing global climatic catastrophe.
On the original scale, objects ranked two to four were described as "meriting concern." The revised scale describes them as �meriting attention by astronomers�, but not necessarily the public.
In December 2004 an object designated 2004 MN4, reached four on the scale � the highest rating ever reached. Further observations of the object have allowed astronomers to rule out many of the orbits that could have posed a risk, and the rating has now dropped to one.
Objects are often spotted in this way. When the object is initially identified, astronomers have very little data with which to extrapolate the rest of the object�s orbit. They calculate all of the potential orbits and determine how many of those may approach the Earth. In the following weeks they make further observations, allowing them to rule out many of those �virtual� orbits. An object ranked higher than zero on the Torino scale is usually reduced down the scale within weeks of the first sighting.
Donald Yeomans, manager of Nasa's Near Earth Object Program Office, said: "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."
More info: Revised Torino scale
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