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 communication 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 an integer 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.
The Torino Scale is defined only for potential impacts less than 100 years in the future.
"For an object with multiple potential collisions on a set of dates, a Torino Scale value should be determined for each date. It may be convenient to summarize such an object by the greatest Torino Scale value within the set."
History and naming 
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, 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:
|NO HAZARD (white)|
|0.||The likelihood of a collision is zero, or is so low as to be effectively zero. Also applies to small objects such as meteors and bodies that burn up in the atmosphere as well as infrequent meteorite falls that rarely cause damage.|
|1.||A routine discovery in which a pass near the Earth is predicted that poses no unusual level of danger. Current calculations show the chance of collision is extremely unlikely with no cause for public attention or public concern. New telescopic observations very likely will lead to re-assignment to Level 0.|
|MERITING ATTENTION BY ASTRONOMERS (yellow)|
|2.||A discovery, which may become routine with expanded searches, of an object making a somewhat close but not highly unusual pass near the Earth. While meriting attention by astronomers, there is no cause for public attention or public concern as an actual collision is very unlikely. New telescopic observations very likely will lead to re-assignment to Level 0.|
|3.||A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of localized destruction. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by public and by public officials is merited if the encounter is less than a decade away.|
|4.||A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of regional devastation. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by public and by public officials is merited if the encounter is less than a decade away.|
|5.||A close encounter posing a serious, but still uncertain threat of regional devastation. Critical attention by astronomers is needed to determine conclusively whether a collision will occur. If the encounter is less than a decade away, governmental contingency planning may be warranted.|
|6.||A close encounter by a large object posing a serious but still uncertain threat of a global catastrophe. Critical attention by astronomers is needed to determine conclusively whether a collision will occur. If the encounter is less than three decades away, governmental contingency planning may be warranted.|
|7.||A very close encounter by a large object, which if occurring this century, poses an unprecedented but still uncertain threat of a global catastrophe. For such a threat in this century, international contingency planning is warranted, especially to determine urgently and conclusively whether a collision will occur.|
|CERTAIN COLLISIONS (red)|
|8.||A collision is certain, capable of causing localized destruction for an impact over land or possibly a tsunami if close offshore. Such events occur on average between once per 50 years and once per several thousand years.|
|9.||A collision is certain, capable of causing unprecedented regional devastation for a land impact or the threat of a major tsunami for an ocean impact. Such events occur on average between once per 10,000 years and once per 100,000 years.|
|10.||A collision is certain, capable of causing global climatic catastrophe that may threaten the future of civilization as we know it, whether impacting land or ocean. Such events occur on average once per 100,000 years, or less often.|
No object has ever been rated above level 4; the currently highest-scaled objects are only level 1 (see below).
Actual impacts and impact energy comparisons 
The Chicxulub impact, believed by many to be a significant factor in the extinction of the dinosaurs, has been estimated at 100 million (108) megatons, or Torino Scale 10. The impacts which created the Barringer Crater or the Tunguska event in 1908 are estimated to be in the 3–10 megaton range, corresponding to Torino Scale 8. The 2013 Chelyabinsk meteor had a total kinetic energy prior to impact of about 0.4 megatons, corresponding to Torino Scale 0 (but not far from Scale 8).
The comet C/2013 A1, which might impact Mars in 2014, is estimated to have a potential impact energy of 5 million to 24 billion Mt, and with an impact probability of ~1:1250 would be at the Martian analogue of Torino Scale 6.
Objects with non-zero Torino ratings 
Currently non-zero 
- 2007 VK184 is an asteroid which is listed on the Near Earth Object Risk List with a Torino Scale of Level 1. The object was discovered on 12 November 2007, by the Catalina Sky Survey. It has about a 1 in 1820 chance of impacting the Earth during June 2048. This translates into a 0.055% chance to hit (or 99.945% to miss). The asteroid is estimated to have a diameter of 130 meters, and travels through space with a speed of 15.63 km/s relative to the Earth.
Downgraded to zero 
- (99942) Apophis (a ≈350 m near-Earth asteroid) became the first object rated level 2 on 23 December 2004, and was subsequently upgraded to level 4 — the current record for highest Torino rating. It will pass quite closely to the Earth on 13 April 2029 without an impact. It retained a rating of level 1 for a 2036 encounter due to the orbital uncertainties introduced by the gravitational deflection until August 2006, when Apophis was downgraded to 0.
- (144898) 2004 VD17 (using an observation arc of 475 days) was upgraded to level 2 in February 2006 for a possible 2102 encounter, making it the second asteroid rated above level 1. It was downgraded to 0 after further observations.
- 2006 XG1 was rated level 1 on December 22, 2006, but removed from the Sentry Risk Table on February 7, 2007.
- 2007 CA19 was rated level 1 for one week ending 19 February 2007.
- 2008 AF4 was rated level 1 until 14 February 2008.
- 2009 KK was rated level 1 after its discovery in May 2009, and downgraded to 0 on 17 June 2009.
- 2009 WM1 was rated level 1 after its discovery on 17 November 2009, and downgraded by the end of November.
- 2009 YG was rated level 1 after its discovery on 17 December 2009, and downgraded to 0 by the end of December.
- (308635) 2005 YU55 was rated level 1 in February 2010, and downgraded to 0 on 9 April 2010. The chances of an actual collision with an asteroid like 2005 YU55 (~400 meters in diameter) is about 1 percent in the next thousand years.
- 2010 XC25 was rated level 1 in December 2010, and downgraded to 0 on 2 January 2011.
- 2011 CA21 was rated level 1 in February 2012.
- 2012 MU2 was rated at Torino scale 1 in June 2012. With an observation arc of only 6 days it showed a 1 in 7140 chance of impact on 1 June 2015. It was removed from the Sentry Risk Table on June 25.
- 2011 AG5 was rated at Torino scale 1 from February 2011 to December 2012, for an impact on 5 February 2040. It was downgraded thanks to observations collected in October 2012 with telescopes on Mauna Kea, Hawaii.
See also 
- http://impact.arc.nasa.gov/torino.cfm Torino Impact Scale (NASA Ames)
- "The Torino Impact Hazard Scale". NASA/JPL Near-Earth Object Program Office. 13 Apr 2005. Retrieved 2011-11-05.
- "Sandia supercomputers offer new explanation of Tunguska disaster". Sandia National Laboratories. December 17, 2007. Retrieved 2008-01-29. "The asteroid that caused the extensive damage was much smaller than we had thought,” says Sandia principal investigator Mark Boslough of the impact that occurred June 30, 1908."
- "2007 VK184 Impact Risk". Near Earth Object Program. NASA. Retrieved 2011-10-19.
- "Impact Probability". Near Earth Object Program. NASA. Retrieved 2011-10-19.
- "Asteroid 2003 QQ47's Potential Earth Impact in 2014 Ruled Out". NASA/JPL Near-Earth Object Program Office. September 3, 2003. Retrieved 2011-11-06.
- "NEOs Removed from Impact Risks Tables". Near Earth Object Program. NASA. 2009-06-17. Retrieved 2009-06-17.
- Don Yeomans, Steve Chesley and Paul Chodas (December 23, 2004). "Near-Earth Asteroid 2004 MN4 Reaches Highest Score To Date On Hazard Scale". NASA/JPL Near-Earth Object Program Office.
- David Morrison (March 1, 2006). "Asteroid 2004 VD17 classed as Torino Scale 2". Asteroid and Comet Impact Hazards (NASA). Retrieved 2011-11-06.
- "2009 WM1 Earth Impact Risk". Near Earth Object Program. NASA. Retrieved 2009-11-26.
- "2009 YG Earth Impact Risk". Near Earth Object Program. NASA. Retrieved 2009-12-28.[dead link]
- "2005 YU55 Impact Risk". Near Earth Object Program. NASA. Archived from the original on 2010-04-12. Retrieved 2010-02-25.
- Elizabeth K. Gardner (October 31, 2011). "Large asteroid to pass by Earth Nov. 8, but what if it didn't?". Purdue University. Retrieved 2011-11-07.
- "2010 XC25 Impact Risk". Near Earth Object Program. NASA.[dead link]
- "2011 BM45 Impact Risk". Near Earth Object Program. NASA. Retrieved 2011-02-25.[dead link]}
- "2011 SM68 Impact Risk". Near Earth Object Program. NASA. Retrieved 2011-09-29.[dead link]
- "2011 UL21 Impact Risk". Near Earth Object Program. NASA. Retrieved 2011-10-27.[dead link]
- "2011 AG5 Impact Risk". Near Earth Object Program. NASA. Retrieved 2011-02-07.
- The Torino Impact Hazard Scale
- NASA Ames: Asteroid and Comet Impact Hazards: The Torino Scale
- NEODyS Impact Risk Page – NEODyS current risk list
- NEODyS 2006 XG1 Impactor Table
- NASA Near Earth Object Program: Impact Risk – NASA Near Earth Object Program current risk list
- Torino Scale
- New Scientist: "Row erupts over asteroid press scare" (18 September 2003)
- The Torino Scale