Palermo Technical Impact Hazard Scale
|99942 Apophis||1.10||12.6x greater|
|(89959) 2002 NT7||0.18||1.51x greater|
|(29075) 1950 DA||0.17||1.48x greater|
|(144898) 2004 VD17||-0.25||1.78x less|
|(410777) 2009 FD||-0.44||2.75x less|
|2022 AE1||-0.66||4.57x less|
|2013 TV135||-0.73||5.37x less|
|(367789) 2011 AG5||-1.00||10x less|
The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-Earth object (NEO). It combines two types of data—probability of impact and estimated kinetic yield—into a single "hazard" value. A rating of 0 means the hazard is equivalent to the background hazard (defined as the average risk posed by objects of the same size or larger over the years until the date of the potential impact). A rating of +2 would indicate the hazard is 100 times as great as a random background event. Scale values less than −2 reflect events for which there are no likely consequences, while Palermo Scale values between −2 and 0 indicate situations that merit careful monitoring. A similar but less complex scale is the Torino Scale, which is used for simpler descriptions in the non-scientific media.
As of January 2022, two asteroids have a cumulative Palermo Scale value above -2: 101955 Bennu (-1.41) and (29075) 1950 DA (-1.42). A further three have cumulative Palermo Scale values above -3: 1979 XB (-2.73), 2000 SG344 (-2.79), and 2007 FT3 (-2.93). There are 24 that have a cumulative Palermo Scale value above -4, three of them were discovered in 2021: 2021 QM1 (-3.01), and 2021 EU (-3.18) and 2021 GX9 (-3.40).
The scale compares the likelihood of the detected potential impact with the average risk posed by objects of the same size or larger over the years until the date of the potential impact. This average risk from random impacts is known as the background risk. The Palermo Scale value, P, is defined by the equation:
- pi is the impact probability
- T is the time interval over which pi is considered
- fB is the background impact frequency
The background impact frequency is defined for this purpose as:
where the energy threshold E is measured in megatons, yr is the unit of T divided by one year.
In 2002 the near-Earth object (89959) 2002 NT7 reached a positive rating on the scale of 0.18, indicating a higher-than-background threat. The value was subsequently lowered after more measurements were taken. 2002 NT7 is no longer considered to pose any risk and was removed from the Sentry Risk Table on 1 August 2002.
In September 2002, the highest Palermo rating was that of asteroid (29075) 1950 DA, with a value of 0.17 for a possible collision in the year 2880. By December 2015, the rating had been reduced all the way to −1.42.
For a brief period in late December 2004, with an observation arc of 190 days, asteroid 99942 Apophis (then known only by its provisional designation 2004 MN4) held the record for the highest Palermo scale values, with a value of 1.10 for a possible collision in the year 2029. The 1.10 value indicated that a collision with this object was considered to be almost 12.6 times as likely as a random background event: 1 in 37 instead of 1 in 472. With further observation through 2021 there is no risk from Apophis for the next 100+ years.
- Asteroid impact avoidance
- Asteroid impact prediction
- Earth-grazing fireball
- Impact event
- List of asteroid close approaches to Earth
- List of Earth-crossing asteroids
- Torino scale
- Time-domain astronomy
- "THE PALERMO TECHNICAL IMPACT HAZARD SCALE". NASA/JPL Near-Earth Object Program Office. 31 August 2005. Retrieved 9 March 2021.
- "Sentry: Earth Impact Monitoring - Impact Risk Data". Jet Propulsion Laboratory. Retrieved 9 January 2022.
Use Unconstrained Settings, sort by Palermo Scale (cum.)
- "How A/CC broke the 2002 NT7 story". hohmanntransfer. 29 March 2003. Archived from the original on 6 November 2020. Retrieved 25 April 2019.
- "Sentry Risk Table - Removed Objects". NASA/JPL Near-Earth Object Program Office. Retrieved 9 March 2021.
- "Asteroid 1950 DA". NASA/JPL Near-Earth Object Program Office. Archived from the original on 1 October 2002. Retrieved 14 October 2011.
- "Sentry: Earth Impact Monitoring: 29075". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 April 2017. Retrieved 20 June 2017.
- Daniel Fischer (27 December 2004). "2004 MN4 Earth Impact Risk Summary (computed 27 December 2004)". The Cosmic Mirror. Archived from the original on 14 March 2005. Retrieved 4 November 2011.
- Math: 101.10 = 12.589
- "Predicting Apophis' Earth Encounters in 2029 and 2036". NASA/JPL Near-Earth Object Program Office. Archived from the original on 18 November 2007. Retrieved 28 December 2007.
- The primary reference for the Palermo Technical Scale is "Quantifying the risk posed by potential Earth impacts" by Chesley et al., Icarus 159, 423-432 (2002).