A scale for assessing asteroid and comet collision hazard agreed at a June
1999 international conference concerning near-Earth objects held in Torino (Turin), Italy. The brainchild of Professor Richard P. Binzel, from the Massachusetts Institute of Technology (MIT), it is divided into eleven risk intensities in White, Green, Yellow, Orange, and Red bands.
White: Events having no likely consequences
0. Likelihood of collision is zero or well below the chance that random object of the same size will strike the Earth in the next few decades.
Green: Events meriting careful monitoring
1. Chance of a collision extremely unlikely, about the same as the chance of a random object of the same size striking the Earth in the next few decades.
Yellow: Events meriting concern
2. Somewhat close, but not unusual encounter. Collision very unlikely.
3. A close encounter with 1 percent or greater chance of collision causing localized destruction.
4. A close encounter with 1 percent or greater chance of collision causing regional devastation.
Orange: Threatening events
5. A close encounter with a significant threat of collision causing regional devastation.
6. A close encounter with a significant threat of collision causing a global catastrophe.
7. A close encounter with an extremely significant threat of collision capable of causing a global catastrophe.
Red: Certain collisions
8. A collision capable of causing localized destruction. Such events occur on Earth between once per 50 years and once per 1,000 years.
9. A collision capable of causing regional devastation. Such events occur on Earth between once per 1,000 years and once per 100,000 years.
10. A collision capable of causing a global climatic catastrophe. Such events occur on Earth every 100,000 years or less often.