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 Earth's atmosphere intact. A 10 indicates that a collision is certain, and the impacting object is large enough to precipitate a global disaster.
An object is assigned a 0 to 10 value based on its collision probability and the kinetic energy (expressed in megatons of TNT) of the possible collision.
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".
The Torino Scale has served as the model for the Rio Scale which quantifies the validity and societal impact of SETI data.
The Torino Scale also uses a color code scale: white, green, yellow, orange, red. Each color code has an overall meaning:
No object has ever been rated above level 4.
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 impact which created the Barringer Crater, and the Tunguska event in 1908 are both 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 0.5 megatons, corresponding to Torino Scale 0. Between 2000 and 2013, 26 asteroid impacts with energy of 1-600 kiloton were detected.
The biggest hydrogen bomb ever exploded, the Tsar Bomba, was around 50 megatons. The 1883 eruption of Krakatoa was the equivalent of roughly 200 megatons.
The comet C/2013 A1, which passed close to Mars in 2014, was originally estimated to have a potential impact energy of 5 million to 24 billion Mt, and in March 2013 was estimated to have an impact probability of ~1:1250, corresponding to the Martian analogue of Torino Scale 6. The impact probability was reduced to ~1:120000 in April 2013, corresponding to Torino Scale 1 or 2.
This is a partial list of near-Earth asteroids that have been listed with a Torino Scale rating of 1+ and been lowered to 0 or been removed from the Sentry Risk Table altogether. Most objects that reach a Torino Scale of 1 have a short observation arc of less than 2 weeks and are quickly removed as the observation arc gets longer and more accurate.
2002
(163132) 2002 CU11 was rated level 1 on 20 March 2002, and completely removed from the Sentry Risk Table on 26 April 2002.
2003
(177049) 2003 EE16 was rated level 1 on 2 April 2003, and removed from the risk table on 28 May 2003.
(387746) 2003 MH4 was rated level 1 on 7 July 2003 with an observation arc of 10 days. There was roughly an estimated 1 in 19,000 chance of impact on 9 June 2077. It was removed from the risk table on 29 July 2003.
(143649) 2003 QQ47 was rated level 1 on 30 August 2003 and removed from the Sentry Risk Table on 14 September 2003.
(143651) 2003 QO104 was rated level 1 in early October 2003, and removed on 13 October 2003.
(164121) 2003 YT1 was rated level 1 on 27 December 2003 with an observation arc of 8.7 days. It was removed from the risk table on 29 December 2003.
2004
(144332) 2004 DV24 was rated level 1 on 1 March 2004 with an observation arc of 7.8 days. It was removed on 5 March 2004.
2004 FU4 was rated level 1 on 27 March 2004 with an observation arc of 6.9 days. It was lowered to 0 on 2 April 2004. It was removed on 13 April 2004.
(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 close to 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.
2006
(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. It was removed from the Sentry Risk Table on 14 February 2008.
(433953) 1997 XR2 was a lost asteroid from December 1997 that had an observation arc of 27 days. From early 2002 until 24 February 2006 it was estimated to have a 1 in 10,000 chance of impacting Earth on June 1, 2101. It was removed from the risk table on 24 February 2006 when it was serendipitously rediscovered.
(292220) 2006 SU49 (with an observation arc of 7 days) showed a 1 in 42000 chance of impacting Earth on 22 January 2029. It was removed from the Sentry Risk Table on 23 November 2006.
(417634) 2006 XG1 was rated level 1 on December 22, 2006, when it had an observation arc of 25 days, but was removed from the Sentry Risk Table on February 7, 2007.
2007
2007 CA19 was rated level 1 for one week ending 19 February 2007. The asteroid was estimated to be roughly 970 meters (3,180 ft) in diameter and had a virtual impactor listing a 1 in 625,000 chance of impact on 14 March 2012. It was removed from the risk table on February 22.
(435159) 2007 LQ19 was rated level 1 on 3 July 2007 with an observation arc of 19 days. The asteroid was estimated to be 930 meters (3,050 ft) in diameter and there was a 1 in 556,000 chance of impact on 11 July 2082. It was removed from the risk table on 15 July 2007.
2008
(332446) 2008 AF4 was rated level 1 until 14 February 2008. It was removed from the risk table on 19 December 2009.
2009
2009 KK was rated level 1 after its discovery in May 2009 (with a 15-day observation arc), and downgraded to 0 by 11 June 2009. It was removed 17 June 2009.
2009 WM1 was rated level 1 after its discovery on 17 November 2009, and downgraded by the end of November. It was not removed from the risk table until 26 June 2013.
(359369) 2009 YG was rated level 1 on 28 December 2009 (with an observation arc of 10 days). It was downgraded to 0 by the end of December.
2010
(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 JU39 was rated level 1 on 18 May 2010 with an observation arc of 7 days. There was roughly an estimated 1 in 77,000 chance of impact on 26 June 2058. It was removed on 23 May 2010.
2010 XC25 was rated level 1 in December 2010, and downgraded to 0 on 2 January 2011.
2011
2011 BM45 was rated level 1 on 13 February 2011 with an observation arc of 13.8 days. There was a 1 in 24,000 chance of impact on 18 January 2086. It was removed from the risk table on 10 March 2011.
2011 SM68 was rated level 1 on 28 September 2011 with an observation arc of 2.6 days and listed virtual impactors in 2016 and 2019. But it was quickly downgraded to 0 a few days later and was removed from the risk table on 7 October 2011.
(415029) 2011 UL21 is an asteroid with a diameter of 2.6 km, which was rated level 1 on October 27, 2011 (with an observation arc of 9.6 days.) It was downgraded to 0 a few days later.
(436724) 2011 UW158 was rated level 1 on 4 November 2011 with an observation arc of 9 days. There was a 1 in 56,000 chance of impact on 8 July 2079. It was removed 17 November 2011.
2012
2012 CA21 was rated level 1 on 21 February 2012 (with an observation arc of 8.9 days). It was removed from the risk table on 3 March 2012.
2012 MU2 was rated at Torino scale 1 on 23 June 2012 with an observation arc of 4 days. 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.
(367789) 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.
2013
2013 TV135 (a ≈450 m near-Earth asteroid) was rated level 1 on 16 October 2013 (with an observation arc of 7.3 days). It was downgraded to 0 on 3 November 2013. It was completely removed from the Sentry Risk Table on 8 November 2013 using JPL solution 32 with an observation arc of 27 days.
2014
2014 DA with an estimated diameter of 100 meters was rated level 1 on 23 February 2014 with an observation arc of 5 days. It was estimated to have a 1 in 5,560 chance of impact on 2 February 2027. It was lowered to Torino Scale 0 on the next day (24 February 2014).
2007 VK184 was listed on the Near Earth Object Risk List with a Torino Scale of Level 1 from after its discovery in November 2007 until recovered in March 2014. With an observation arc of 60 days, it had about a 1 in 1800 chance of impacting Earth on 3 June 2048; the probability went to effectively zero when the 2014 recovery observations were taken into account. The asteroid is estimated to have a diameter of 130 meters (430 ft), and travels through space with a speed of 15.6 km/s relative to Earth.
2015
2015 NK13 was listed on the JPL Near Earth Object Risk List with a Torino Scale of Level 1 on 22 July 2015 and again on 11 August 2015, while the NEODyS Risk List had it at a slightly lower impact probability, sufficient to classify it as Torino Scale Level 0. In July and August it was downgraded to Level 0 the following day. With a 13-day observation arc, it had an estimated 1 in 36,000 chance of impacting Earth on 5 October 2096. It was discovered on 12 July 2015 by Pan-STARRS. The asteroid is estimated to have a diameter of 310 meters (1,020 ft), and would impact Earth at a relative speed of 14.35 km/s (32,000 mph).
2015 PU228 was listed on NEODyS with a Torino Scale of Level 1 on 23 August 2015. Sentry also listed it with a Torino Scale of Level 1 on 24 August 2015. With a 10-day observation arc, it had an estimated 1 in 84,000 chance of impacting Earth on 15 January 2081. It was downgraded to level 0 on 8 September 2015. It was discovered on 13 August 2015 by the Space Surveillance Telescope. The asteroid is estimated to have a diameter of 340 meters (1,120 ft).
2016
2016 BE was rated at level 1 for a day on 25 January 2016 by the NEODyS system, and downgraded to level 0 the following day. On the Sentry system it never crossed the threshold between the two levels, due to a lower computed impact probability.
2016 EU85 was rated at level 1 by NEODyS on 25 March 2016, but subsequently lowered to zero thanks to prediscovery observations by the Pan-STARRS survey. The asteroid is estimated to have a diameter of about 440 meters (1,440 ft).
2016 WJ1 was listed on the JPL Near Earth Object Risk List with a Torino Scale of Level 1 on 25 November 2016, while the NEODyS Risk List has it at a lower impact probability, sufficient to classify it as Torino Scale Level 0. With a 10-day observation arc, it had an estimated 1 in 8000 chance of impacting Earth on 12 June 2065. It was discovered on 19 November 2016 by Mt. Lemmon Survey. The asteroid is estimated to have a diameter of 180 meters (590 ft), and would have impacted Earth at a relative speed of 18.61 km/s (42,000 mph). It was removed from the Sentry Risk Table on 2 December 2016, when prediscovery images by Pan-STARRS from October 2016 and precovery images taken from Mauna Kea in July 2003 where located and included in the impact calculations.
2016 XP23 was listed on the JPL Near Earth Object Risk List with a Torino Scale of Level 1 on 25 December 2016, while the NEODyS Risk List has it at a lower impact probability, sufficient to classify it as Torino Scale Level 0. With a 15-day observation arc, it was listed with an estimated 1 in 105,000 chance of impacting Earth on 1 November 2110. The asteroid is estimated to have a diameter of 360 meters (1,180 ft), and would have impacted Earth at a relative speed of 27 km/s (60,000 mph). It was removed from the Sentry Risk Table on 7 January 2017 with a 29-day observation arc.
2017
2017 AM4 was listed on the JPL Near Earth Object Risk List and NEODyS Risk List with a Torino Scale of Level 1 on 19 January 2017. With a 14-day observation arc, it had an estimated 1 in 59,000 chance of impacting Earth on 1 August 2024. The asteroid is estimated to have a diameter of 500 meters (1,600 ft), and would impact Earth at a relative speed of 33 km/s (74,000 mph). With a 16-day observation arc, the odds of impact were reduced to 1 in a million. It was removed from the Sentry Risk Table on 23 January 2017 with a 19-day observation arc.
2017 BL30 was listed on the JPL Near Earth Object Risk List and NEODyS Risk List with a Torino Scale of Level 1 on 3 February 2017. With a 5-day observation arc, it had an estimated 1 in 1610 chance of impacting Earth on 3 August 2029. With a 6-day observation arc, the odds were 1 in 1270. With a 7-day observation arc, the odds were 1 in 909. With a 10-day observation arc, the odds were 1 in 826. The asteroid is estimated to have a diameter of 70 meters (230 ft), and would impact Earth at a relative speed of 13 km/s (29,000 mph). The value decreased to 0 with further observations on February 11, with a cumulative impact chance of 1 in 4258.
2017 CH1 was listed on the NEODyS Risk List with a Torino Scale of Level 1 on 8 February 2017. It is estimated be 900 meters in diameter with a 1 in 500000 chance of impact on 4 June 2095. Such an impact could create a crater 10 km in diameter. Follow-up observations on February 10 eliminated the chances of impact on every date except for 4 June 2044, with a 4.59E-10 chance of impact on that date, or less than a 1 in 2 billion chance of impact. It was removed from the Sentry Risk Table on 15 February 2017.
