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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. 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 highest rating ever assigned on the Torino Scale was given to the asteroid 99942 Apophis, which had a rating of 4 for four days in late 2004.
99942 Apophis is a near-Earth asteroid and a potentially hazardous object with a diameter of 370 metres that caused a brief period of concern in December 2004 when initial observations indicated a probability up to 2.7% that it would hit Earth on April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth in 2029. Until 2006, a small possibility nevertheless remained that, during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole of no more than about 800 kilometres (500 mi) in diameter, which would have set up a future impact exactly seven years later on April 13, 2036. This possibility kept it at Level 1 on the Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small and Apophis' rating on the Torino scale was lowered to zero. By 2008, the keyhole had been determined to be less than 1 km wide. During the short time when it had been of greatest concern, Apophis set the record for highest rating ever on the Torino scale, reaching level 4 on December 27, 2004.
Sentry is a highly automated impact prediction system operated by the JPL Center for NEO Studies (CNEOS) since 2002. 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 the Center for Near-Earth Object Studies. However, several weeks of optical data are not enough to conclusively identify an impact years in the future. By contrast, eliminating an entry on the risk page is a negative prediction.
(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.
(481482) 2007 CA19 is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. It led the impact hazard list, with a Torino Scale impact risk value of 1, for one week, ending on February 19, 2007. Before and after 2007 CA19, 99942 Apophis was the object with the highest Palermo Scale rating. With an observation arc of 4.8 days, it had a Palermo Scale of −0.88.
2006 RH120 is a tiny near-Earth asteroid and fast rotator with a diameter of approximately 2–3 meters that ordinarily orbits the Sun but makes close approaches to the Earth–Moon system around every twenty years, when it can temporarily enter Earth orbit through temporary satellite capture (TSC). Most recently, it was in Earth orbit from July 2006 to July 2007, during which time it was never more than 0.0116 AU (1.74 million km) from Earth. As a consequence of its temporary orbit around the Earth, it is currently the second smallest asteroid in the Solar System with a well-known orbit, after 2021 GM1. Until given a minor planet designation on 18 February 2008, the object was known as 6R10DB9, an internal identification number assigned by the Catalina Sky Survey.
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.
(410777) 2009 FD is a carbonaceous sub-kilometer asteroid and binary system, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, discovered on 24 February 2009 by astronomers of the Spacewatch program at Kitt Peak National Observatory near Tucson, Arizona, in the United States.
(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.
(85640) 1998 OX4, also written 1998 OX4, is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group.
2003 BR47 is a sub-kilometer asteroid classified as near-Earth object and potentially hazardous asteroid of the Apollo group. It was discovered on 31 January 2003 by the LINEAR program. As of 19 March 2013, its orbit is based on 170 observations spanning a data-arc of 939 days.
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.
2011 XC2 (also written 2011 XC2) is a near-Earth asteroid roughly 60–140 meters (200–460 ft) in diameter that passed less than 1 lunar distance from Earth on 3 December 2011.
2014 DX110 is a sub-kilometer asteroid, classified as near-Earth object of the Apollo group, approximately 30 meters in diameter. It passed less than 1 lunar distance from Earth on 5 March 2014. With an absolute magnitude of 25.7, this asteroid is potentially the largest asteroid to come inside the orbit of the Moon since 2013 PJ10 on 4 August 2013. The close approach was webcast live by Slooh and Virtual Telescope.
2014 UR116, also known as 2008 XB, is an eccentric sub-kilometer asteroid, categorized as a near-Earth object and potentially hazardous asteroid of the Apollo group with a diameter of approximately 400 meters (1,300 ft). It was first observed on 1 December 2008, by the Mount Lemmon Survey at Mount Lemmon Observatory in Arizona, United States.
2011 GA is a small asteroid that is a Near-Earth object and an Apollo asteroid.
2016 PQ is an approximately 20-meter sized asteroid and near-Earth object of the Apollo group, with one of the smallest known minimum orbital intersection distances with Earth.
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.
1979 XB is a lost asteroid with a short observation arc of 3.9 days that cannot be recovered with targeted observations and awaits serendipitous survey observations. It is classified as a near-Earth object and potentially hazardous asteroid of the Apollo group and is estimated to be 660 meters in diameter. The unnumbered minor planet has a poorly constrained orbit and has not been observed in 40 years. It has been listed on the Sentry Risk Table since the list started in 2002. With a cumulative Palermo Technical Impact Hazard Scale of −2.72, the poorly known orbit and assumed size place 1979 XB third on an unconstrained listing of the Sentry Risk Table.
2019 PG1 is a sub-kilometer near-Earth object and potentially hazardous asteroid of the Apollo class, discovered by Pan-STARRS on 8 August 2019, two weeks after it passed Earth at 62 LD. With an observation arc of 103 days, Earth approach dates become divergent by 2042 as the date of closest approach in 2042 has an uncertainty of ±3 days.
References
- 1 2 3 4 5 "JPL Small-Body Database Browser: 433953 (1997 XR2)" (2017-02-16 last obs.). Jet Propulsion Laboratory . Retrieved 2 June 2017.
- 1 2 3 4 5 "433953 (1997 XR2)". Minor Planet Center. Retrieved 1 March 2017.
- 1 2 "Absolute Magnitude (H)". NASA/JPL. Archived from the original on 2 March 2001. Retrieved 1 March 2017.
- 1 2 3 4 "1997 XR2 Earth Impact Risk Summary". Wayback Machine. Archived from the original on 7 February 2006. Retrieved 13 January 2013.
- ↑ "JPL Close-Approach Data: (1997 XR2)" (last observation: 2007-01-15; arc: 9.1 years). Retrieved 3 September 2013.
