The Palermo Technical Impact Hazard Scale for asteroids 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 greater than 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.
On Jan. 27, 2020 scientists using a telescope on Mauna Loa in Hawaii spotted an asteroid that has been classified as a potentially hazardous asteroid. It is called 2020 BX12 and it passed within 2.7 million miles and will not get any closer pass over the next century. 2020 BX12 also has a moon. The larger rock is at least 540 feet (165 meters) across, and the smaller one is about 230 feet (70 m) wide. They appeared to be separated by about 1,200 feet (360 meters).
As of December 2019, two asteroids have a cumulative Palermo Scale value of above -2: (29075) 1950 DA (-1.42) and 101955 Bennu (-1.71). A further three have cumulative Palermo Scale values of above -3: 1979 XB (-2.82), 99942 Apophis (-2.83), and 2000 SG344 (-2.86). 25 more have a cumulative Palermo Scale value of above -4, three of them having been discovered in 2019.
Bennu has a cumulative 1-in-2,700 chance of impacting Earth between 2175 and 2199. It is named after the Bennu, the ancient Egyptian mythological bird associated with the Sun, creation, and rebirth. 101955 Bennu has a mean diameter of 490 m (1,610 ft; 0.30 mi) and has been observed extensively with the Arecibo Observatory planetary radar and the Goldstone Deep Space Network. If an impact were to occur, the expected kinetic energy associated with the collision would be 1,200 megatons in TNT equivalent (for comparison, TNT equivalent of Little Boy was approx 15 kiloton).
(29075) 1950 DA, provisional designation 1950 DA, is an asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 1.1 kilometers (0.68 miles) in diameter. It has about 5 times the mass of Bennu.
1950 DA had the highest known probability of impacting Earth. In 2002, it had the highest Palermo rating with a value of 0.17 for a possible collision in 2880. Since that time, the estimated risk has been updated several times. In December 2015, the odds of an Earth impact were revised to 1 in 8,300 (0.012%) with a Palermo rating of −1.42. As of 2018, It is listed on the Sentry Risk Table with the highest cumulative Palermo rating. 1950 DA is not assigned a Torino scale rating, because the 2880 date is over 100 years in the future. As of the 7 December 2015 solution, the probability of an impact in 2880 is 1 in 8,300 (0.012%).
The energy released by a collision with an object the size of 1950 DA would cause major effects on the climate and biosphere, which would be devastating to human civilization. The discovery of the potential impact heightened interest in asteroid deflection strategies. It would impact with about 10 gigatons of force.
The near-Earth object (89959) 2002 NT7 was the first near-Earth object detected by NASA. It was given a positive rating on the scale of 0.06 which indicated 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.
For a brief period in late December 2004, with an observation arc of 190 days, asteroid (99942) Apophis 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 2016 there is no significant risk from Apophis at any of the dates in question.
SOURCES – NASA JPL Center for NEO Studies (CNEOS), Wikipedia
Written By Brian Wang, Nextbigfuture.com