What is it for?

The Torino Scale is a "Richter Scale" for categorizing the Earth impact hazard associated with newly discovered asteroids and comets. It is intended to serve as a communication tool for astronomers and the public to assess the seriousness of predictions of close encounters by asteroids and comets during the 21st century.

Why is the Torino Scale needed?

When a new asteroid or comet is discovered, predictions for where the object will be months or decades in the future are naturally uncertain. These uncertainties arise because the discovery observations typically involve measurements over only a short orbital track and because all measurements have some limit in their precision. Fortunately, for the majority of objects, even the initial calculations are sufficient to show that they will not make any close passes by the Earth within the next century. However, for some objects, 21st century close approaches and possible collisions with the Earth cannot be completely ruled out.

How does the Torino Scale Work?

The Torino Scale utilizes numbers that range from 0 to 10, where 0 indicates an object has a zero or negligibly small chance of collision with the Earth. (Zero is also used to categorize any object that is too small to penetrate the Earth's atmosphere intact, in the event that a collision does occur.) A 10 indicates that a collision is certain, and the impacting object is so large that it is capable of precipitating a global climatic disaster.

The Torino Scale is color coded from white to yellow to orange to red. Each color code has an overall meaning:

WHITE SHADING: "EVENTS HAVING NO LIKELY CONSEQUENCES"

0. The likelihood of a collision is zero, or well below the chance that a
random object of the same size will strike the Earth within the next few
decades. This designation also applies to any small object that, in the
event of a collision, is unlikely to reach the Earth's surface intact.

GREEN SHADING: "EVENTS MERITING CAREFUL MONITORING"

1. The chance of collision is extremely unlikely, about the same as a random
object of the same size striking the Earth within the next few decades.

YELLOW SHADING: "EVENTS MERITING CONCERN"

2. A somewhat close, but not unusual encounter. Collision is very unlikely.

3. A close encounter, with 1% or greater chance of a collision capable of
causing localized destruction.

4. A close encounter, with 1% or greater chance of a collision capable of
causing regional devastation.

ORANGE SHADING: "THREATENING EVENTS"

5. A close encounter, with a significant threat of a collision capable of
causing regional devastation.

6. A close encounter, with a significant threat of a collision capable of
causing a global catastrophe.

7. A close encounter, with an extremely significant threat of a collision
capable of causing a global catastrophe.

RED SHADING: "CERTAIN COLLISIONS"

8. A collision capable of causing localized destruction. Such events occur
somewhere on Earth between once per 50 years and once per 1000 years.

9. A collision capable of causing regional devastation. Such events occur
between once per 1000 years and once per 100,000 years.

10. A collision capable of causing a global climatic catastrophe. Such
events occur once per 100,000 years, or less often.

How does an object get its Torino Scale number?

An object is assigned a 0 to 10 value on the Torino Scale based on its collision probability and its kinetic energy (proportional to its mass times the square of its encounter velocity). Categorization on the Torino Scale is based on the placement of a close approach event within a graphical representation of kinetic energy and collision probability. An object that is capable of making multiple close approaches to the Earth will have a separate Torino Scale value associated with each approach. (An object may be summarized by the single highest value that it attains on the Torino Scale.) There are no fractional values or decimal values used in the Torino Scale.

Can the Torino Scale value for an object change?

Yes! It is important to note that the Torino Scale value for any object initially categorized as 1 or greater will change with time. The change will result from improved measurements of the object's orbit showing, most likely in all cases, that the object will indeed miss the Earth. Thus, the most likely outcome for a newly discovered object is that it will ultimately be re-assigned to category 0. Any object initially placed in category 0 is unlikely to have its Torino Scale value change with time.

How did the Torino Scale get its name?

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 near-Earth objects 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 near-Earth objects. ("Torino Scale" is the proper usage, not "Turin Scale.)

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