Torino scale

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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.

Contents

Near-Earth objects with a Torino scale of 1 are discovered several times a year, and may last a few weeks until they have a longer observation arc that eliminates any possibility of a collision. The only objects on the Torino Scale that have ever ranked higher are asteroids 99942 Apophis, which had a rating of 4 for four days in late 2004, the highest recorded rating, (144898) 2004 VD17 , with a historical rating of 2 from February to May 2006, and 2024 YR4 , with a current rating of 3 from 27 January 2025. [1]

Overview

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 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." [2]

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.") [2] This version was published in a subsequent peer-reviewed article. [3]

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. [4]

Definition

Ratings are assigned based on the parameters of impact calculations. Each rating has a defined meaning which is to inform the public.

Calculation of ratings

Torino Scale. The scale in metres is the approximate diameter of an asteroid with a typical collision velocity. Torino scale.svg
Torino Scale. The scale in metres is the approximate diameter of an asteroid with a typical collision velocity.

Ratings are determined on the basis of the impact probability (p), expressed as a real number between 0 for no chance of impact and 1 for a certain impact; and the estimated impact energy (E), expressed in megatons of TNT.

RatingCondition
0⁠log10E + 1/3⁠ + ⁠log10p + 2/2⁠ < 0  OR log10E < 0
1⁠log10E + 1/3⁠ + ⁠log10p + 2/2⁠≥ 0  AND log10E≥ 0  AND ⁠log10E − 2/3⁠ + ⁠log10p + 2/2⁠ < 0  AND log10p < −2
2⁠log10E − 2/3⁠ + ⁠log10p + 2/2⁠≥ 0  AND ⁠log10E − 5/3⁠ + ⁠log10p + 2/2⁠ < 0  AND log10p < −2
3log10p≥ −2  AND  log10E≥ 0  AND p < 0.99  AND  log10E < 2
4log10p≥ −2  AND  log10E≥ 2  AND ⁠log10E − 5/3⁠ + ⁠log10p + 2/2⁠ < 0  AND p < 0.99
5⁠log10E − 5/3⁠ + ⁠log10p + 2/2⁠≥ 0  AND p < 0.99  AND  log10E < 5
6⁠log10E − 5/3⁠ + ⁠log10p + 2/2⁠≥ 0  AND log10p < −2
7log10p≥ −2  AND  + log10E≥ 5  AND p < 0.99
8p≥ 0.99  AND  + log10E≥ 0  AND  log10E < 2
9p≥ 0.99  AND  + log10E≥ 2  AND  log10E < 5
10p≥ 0.99  AND  + log10E≥ 5

Meaning of ratings

The Torino Scale also uses a color code scale: white, green, yellow, orange, red. Each color code has an overall meaning: [5]

No hazard (white)
0The 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.
Normal (green)
1A routine discovery in which a pass near Earth is predicted that poses no unusual level of danger. Current calculations show a collision is extremely unlikely with no cause for public attention or public concern. New telescopic observations very likely will lead to reassignment to Level 0.
Meriting attention by astronomers (yellow)
2A discovery, which may become routine with expanded searches, of an object making a somewhat close but not highly unusual pass near Earth. While meriting attention by astronomers, there is no cause for public attention or public concern as an actual collision is still very unlikely. New telescopic observations very likely will lead to reassignment to Level 0.
3A 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 reassignment to Level 0. Attention by public and by public officials is merited if the encounter is less than 10 years away.
4A 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 reassignment to Level 0. Attention by public and by public officials is merited if the encounter is less than 10 years away.
Threatening (orange)
5A close encounter posing a serious, but still uncertain threat of regional devastation. Even though most objects of this level will be lowered to Level 0, critical attention by astronomers is still needed to determine conclusively whether a collision will occur. If the encounter is less than 10 years away, governmental contingency planning may be warranted.
6A 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 30 years away, governmental contingency planning may be warranted. Some objects of this level may be lowered to Level 1 or 2, if the chances of collision decrease.
7A 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 the next 100 years, international contingency planning is warranted, especially to determine urgently and conclusively whether a collision will occur.
Certain Collisions (red)
8A 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 a century and once per 10,000 years.
9A 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 few hundred thousand years.
10A collision is certain, capable of causing global catastrophes that may threaten the future of civilization and life as we know it. Oceanic impacts can cause tsunamis hundreds, or even thousands of feet high while land impacts can cause major firestorms. Such events occur on average once every few hundred thousand years. Larger objects of this size may strike less often.

No incoming object has ever been rated above level 4, though over all of Earth's history impacts have spanned the full range of damage described by the scale.

Actual impacts and impact energy comparisons

Burned and flattened trees after the Tunguska event. Tunguska Ereignis.jpg
Burned and flattened trees after the Tunguska event.

The Chicxulub impact, believed by most scientists to have been a significant factor in the extinction of the non-avian dinosaurs, has been estimated at 100 million (108) megatons. Were an equivalent impact predicted with a probability of 99% or more, it would rate 10 on the Torino Scale. The impacts that created the Barringer Crater and the 1908 Tunguska event are both estimated to have been in the 3–10 megaton range, [6] thus, if a similar impact had been predicted with near certainty, it would correspond to Torino Scale 8. The 2013 Chelyabinsk meteor had a total kinetic energy prior to impact of about 0.5 megatons, thus, regardless of impact probability, it would only rate 0 on the Torino Scale. Between 2000 and 2013, 26 atmospheric asteroid impacts with an energy of 1–600 kilotons were detected by the network of infrasound sensors operated by the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization. [7]

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 megatons, and in March 2013 was estimated to have a Mars impact probability of ~1:1250, corresponding to the Martian equivalent of Torino Scale 6. [8] The impact probability was reduced to ~1:120000 in April 2013, corresponding to Torino Scale 1 or 2. [9]

Objects with non-zero Torino ratings

Typical evolution of impact probability in three stages: as the uncertainty region gets progressively smaller with additional observations, the probability of impact can increase because Earth covers a larger percentage of the shrunk uncertainty region, but drops to 0 once Earth is no longer inside the uncertainty region Apophis ellipse.svg
Typical evolution of impact probability in three stages: as the uncertainty region gets progressively smaller with additional observations, the probability of impact can increase because Earth covers a larger percentage of the shrunk uncertainty region, but drops to 0 once Earth is no longer inside the uncertainty region

Currently non-zero

Downgraded to zero

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.

See also

Related Research Articles

(143649) 2003 QQ47, provisionally designated: 2003 QQ47, is a kilometer-sized asteroid and synchronous binary system, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. It became briefly notable upon its discovery in late August 2003, when media outlets played up a very preliminary report that it had a 1 in 250,000 chance of impacting into Earth on 21 March 2014. The discovery of a companion, approximately 310 meters (1,000 ft) in diameter, was announced in September 2021.

<span class="mw-page-title-main">Sentry (monitoring system)</span> JPL program to monitor the Minor Planet Centers catalog for Earth impacts

Sentry is an automated impact prediction system started in 2002 and operated by the Center for Near Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ years. Whenever a potential impact is detected, it will be analyzed and the results immediately published by CNEOS. However, alerts do not imply certainty about future impacts, as the small amounts of optical data that can trigger an alert are not enough to conclusively identify an impact years in the future. In contrast, eliminating an entry on the risk page is a negative prediction.

(292220) 2006 SU49, provisional designation 2006 SU49, is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group that had a small chance of impacting Earth in 2029.

(144898) 2004 VD17 (provisional designation 2004 VD17) is a sub-kilometer asteroid, classified as near-Earth object of the Apollo group once thought to have a low probability of impacting Earth on 4 May 2102. It reached a Torino Scale rating of 2 and a Palermo Technical Impact Hazard Scale rating of -0.25. With an observation arc of 17 years it is known that closest Earth approach will occur two days earlier on 2 May 2102 at a distance of about 5.5 million km.

<span class="nowrap">2007 VK<sub>184</sub></span>

2007 VK184 is a sub-kilometer asteroid, classified as a near-Earth object of the Apollo group, and estimated to be approximately 130 meters (430 ft) in diameter. It was listed on the Sentry Risk Table with a Torino Scale rating of 1 for a potential impactor in June 2048. It was removed from the Sentry Risk Table on 28 March 2014.

<span class="nowrap">(367789) 2011 AG<sub>5</sub></span> Near-Earth asteroid in 2040

(367789) 2011 AG5, provisional designation 2011 AG5, is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. It has a diameter of about 140 meters (460 ft). It was removed from the Sentry Risk Table on 21 December 2012 and as such it now has a rating of 0 on the Torino Scale. It was recovered in December 2022 extending the observation arc from 4.8 years to 14 years. As of 2023, the distance between the orbits of Earth and 2011 AG5 is 0.0004 AU (60,000 km; 0.16 LD)

2010 AU118 (also written 2010 AU118) is a potential Amor near-Earth asteroid with an observation arc of only 1.4 days and thus a poorly determined orbit. It was announced on 27 May 2010 based on images taken by the Wide-field Infrared Survey Explorer (WISE) on 13–15 January 2010. It was removed from the Sentry Risk Table on 14 June 2014 as a result of an update to the Sentry software. Another software update restored it to the Sentry Risk Table in 2017. It was again removed from the sentry list on 3 October 2018.

(471240) 2011 BT15, provisional designation 2011 BT15, is a stony, sub-kilometer sized asteroid and fast rotator, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group. It had been one of the objects with the highest impact threat on the Palermo Technical Impact Hazard Scale.

<span class="nowrap">(669555) 2012 YQ<sub>1</sub></span> Asteroid

(669555) 2012 YQ1 is a sub-kilometer asteroid, classified as a near-Earth object and a potentially hazardous asteroid of the Apollo group, approximately 200 meters in diameter. It was first observed on 19 December 2012, by astronomers Andrey Oreshko and Timur Kryachko at the Elena Remote Observatory (G32) located in the Chilean Atacama desert.

2012 KP24 (also written 2012 KP24) is a Chelyabinsk-sized near-Earth asteroid with an observation arc of only 5 days and has a modestly determined orbit for an object of its size. Around 31 May 2023 ±3 days it will pass between 0.19–24 lunar distances (73,000–9,200,000 km) from Earth. Nominally the asteroid is expected to pass 0.026 AU (3,900,000 km; 10 LD) from Earth and brighten to around apparent magnitude 21.6.

(454101) 2013 BP73, provisional designation 2013 BP73, is a sub-kilometer asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 310 meters (1,020 ft) in diameter.

2008 CK70 (also written 2008 CK70) is an Apollo near-Earth asteroid. In 2013 it had the 7th highest impact threat on the Palermo Technical Impact Hazard Scale. It was discovered on 9 February 2008 by Lincoln Near-Earth Asteroid Research (LINEAR) at an apparent magnitude of 19 using a 1.0-meter (39 in) reflecting telescope. It has an estimated diameter of 31 meters (102 ft) and is not large enough to qualify as a potentially hazardous object. Ten precovery images from January 2008 have been located. It was removed from the Sentry Risk Table on 21 December 2013. It may be possible to recover the asteroid in late September 2017, but it will have an apparent magnitude of about 22.

(163132) 2002 CU11, provisional designation 2002 CU11, is a bright, sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. Based on absolute magnitude, it is the second largest asteroid known to have passed closer than the Moon.

2013 TV135 is an Apollo near-Earth asteroid estimated to have a diameter of 450 meters (1,480 ft). On 16 September 2013, it passed about 0.0448 AU (6,700,000 km; 4,160,000 mi) from Earth. On 20 September 2013, it came to perihelion (closest approach to the Sun). The asteroid was discovered on 12 October 2013 by Ukrainian amateur astronomer Gennadiy Borisov with a custom 0.2-meter (7.9 in) telescope using images dating back to 8 October 2013. It was rated level 1 on the Torino Scale from 16 October 2013 until JPL solution 26 on 3 November 2013. It reached a Palermo Technical Impact Hazard Scale rating of -0.73. It was removed from the JPL Sentry Risk Table on 8 November 2013 using JPL solution 32 with an observation arc of 27 days.

2014 XL7 is a near-Earth object and Apollo asteroid, approximately 230 meters (750 feet) in diameter. It was the most dangerous potentially hazardous asteroid on Sentry Risk Table upon its discovery by the Mount Lemmon Survey in December 2014. At the time, the asteroid had a cumulative 1 in 83000 chance of impacting Earth on 4–5 June between the years 2048 and 2084. After the object's observation arc had been extended to 35 days, it was removed from the Sentry Risk Table on 15 January 2015. Since then the asteroid's orbit has been secured. Although it has an Earth minimum orbit intersection distance of less than one lunar distance, there are no projected close encounters with Earth in the foreseeable future, with its closest passage to occur in May 2046, still millions of kilometers away.

(585310) 2017 YZ1, provisional designation: 2017 YZ1, is a sub-kilometer asteroid on an eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 250 meters (800 feet) in diameter. It was first observed on 20 December 2017, by astronomers with the Mount Lemmon Survey at Mount Lemmon Observatory near Tucson, Arizona, in the United States. On 29 January 2018, it passed Earth at 125 lunar distances.

<span class="nowrap">2017 XO<sub>2</sub></span>

2017 XO2, also written 2017 XO2, is a sub-kilometer asteroid and near-Earth object of the Apollo group approximately 110 meters (360 feet) in diameter. The asteroid was discovered by Pan-STARRS in December 2017, after it already had approached Earth at 0.051 AU (7,600,000 km) or 20 lunar distances (LD) on 6 November 2017. On 26 April 2057, it will pass Earth at a similar distance of 21 LD again.

2022 AE1 is a Tunguska event-sized asteroid, classified as a near-Earth object of the Apollo group, approximately 70 meters (230 feet) in diameter. It was discovered by the Mount Lemmon Survey on 6 January 2022, when it was 0.09 AU (13 million km) from Earth. On 9 January 2022 with an observation arc of 3 days, it was rated with a Torino scale of 1 for a virtual impactor on 4 July 2023 16:28 UTC. Nominal approach is expected to occur 1 July 2023 01:13 ± 1 day. With a Palermo scale rating of as high as –0.66 at the European Space Agency on 11 January 2022, the odds of impact peaked at about 4.6 times less than the background hazard level. NEODyS was the first risk-page to drop to Torino scale 0 on 12 January 2022 followed by ESA on 13 January 2022, but by January 14 both returned to Torino scale 1. On 14 January 2022 the waxing gibbous moon was as little as 3 degrees from the asteroid delaying observations of the asteroid from January 12–19. On 20 January 2022 with a 16-day observation arc, using JPL #11 the Sentry Risk Table dropped the asteroid to Torino scale 0 and then later that day JPL #12 resulted in it being removed from the risk table.

2023 DW is a near-Earth asteroid of the Aten group. It is approximately 50 meters in diameter, roughly the size of the asteroid that caused the Tunguska event, and was discovered by Georges Attard and Alain Maury, from the MAP (Maury/Attard/Parrott) asteroid search program in San Pedro de Atacama on 26 February 2023, when it was 0.07 AU (10 million km) from Earth. On 28 February 2023, with an observation arc of 1.2 days, it was rated 1 on the Torino scale for a virtual impactor on 14 February 2046 at 21:36 UTC. The nominal approach is expected to occur about eight hours before the impact scenario at 14 February 2046 13:15 ± 72 minutes. Between 5–8 March, the asteroid was not observed as it was within 40 degrees of the waxing gibbous moon. On 14 March 2023 the European Space Agency was the first to drop to a Torino scale rating of 0. Sentry dropped to a Torino scale rating of 0 on 16 March 2023. It was completely removed from both risk tables on 20 March 2023.

2023 GQ2 is an asteroid roughly 400 meters in diameter, classified as a near-Earth object and potentially hazardous object of the Apollo group. It was first discovered on 12 April 2023, when it was 1.3 AU (190 million km) from Earth, with the Bok Telescope at Kitt Peak National Observatory. On 19 April 2023, with an observation arc of 6.7 days, it was rated 1 on the Torino scale for a virtual impactor on 16 November 2028 at 00:58 UTC. When it had a Palermo scale rating of –0.70, the odds of impact were about 5 times less than the background hazard level and this gave the asteroid one of the highest Palermo scale ratings ever issued. On 20 April 2023 precovery images from May 2019 were announced extending the observation arc to 3.9 years, and the 2028 virtual impactor was removed from the Sentry Risk Table. It is now known the nominal approach will safely occur about 13 hours after the impact scenario on 16 November 2028 13:36 ± 40 minutes.

References

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