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 scale has been introduced 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 and presented at a United Nations conference in 1995.

How do you read the Torino scale?
The Torino scale utilizes numbers form 0 to 10 to indicate the chance of a collision (where 0 means that the object has no chance to impact Earth, while 10 indicates a certain collision). In this classification the dimension of the NEO is also very important: 0 is also used to classify objects that are too small to penetrate the Earth's atmosphere, even in the case a collision with these objects could actually occur, while 10 indicates that the impacting object is big enough to determine a climatic disaster.
The Torino scale is a 2 parameters scale, in fact each body, besides being classified by a number, also corresponds to a a color that identifies the probability of the impact event:
White - "events with no consequences" : in this case the object is certain to miss Earth or is too small to penetrate atmosphere. This color corresponds to 0.
Green - "events meriting careful monitoring": these objects have very small chances of collision. Normally, it is better to follow them to eventually redefine these chances with other measures. Green corresponds to 1.
Yellow - "events meriting concern": objects with higher probability of impacts, for which refinement of the orbit is necessary. Yellow corresponds: to 2- a close encounter where collision is still unlikely, 3- a close encounter with probability > 1% of local destruction, and 4- a close encounter with probability > 1% of regional destruction.
Orange - "threatening events": close encounters with objects that are large enough to cause regional or even global destruction. Refinement of orbits is in this cases, of extreme importance. Orange corresponds to: 5- a close encounter with a significant threat of collision causing regional devastation, 6- a close encounter with a significant threat of collision causing global devastation, 7- a close encounter with an extremely significant threat of global catastrophe.
Red - "certain collisions": these objects are certain to collide with Earth and have a big enough size to cause damage. This color corresponds to: 8- a certain collision with localized destruction , 9- a certain collision with regional devastation, 10- a certain collision with global climatic effects.

How is an object classified using the Torino scale?

The parameters that lead to the classification of an object are its kinetic energy and its collision probability (click here to know more about how impact previsions are made). This means that, an object that will make several different close approaches to Earth will have a different Torino scale value for each approach. Normally, only the highest value is considered.
Another important thing about the Torino scale value of a NEO is that it will change in time. This change will be the result of better measurements of the object's orbit. Due to the definition of the parameters, it is clear that if the parameter of an object initially ranges above 1, it will probably decrease with further measurements.