Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. [1] [2] It is defined as the distance between the closest points of the osculating orbits of two bodies. Of greatest interest is the risk of a collision with Earth. Earth MOID is often listed on comet and asteroid databases such as the JPL Small-Body Database. MOID values are also defined with respect to other bodies as well: Jupiter MOID, Venus MOID and so on.
An object is classified as a potentially hazardous object (PHO) – that is, posing a possible risk to Earth – if, among other conditions, its Earth MOID is less than 0.05 AU. For more massive bodies than Earth, there is a potentially notable close approach with a larger MOID; for instance, Jupiter MOIDs less than 1 AU are considered noteworthy since Jupiter is the most massive planet. [1]
A low MOID does not mean that a collision is inevitable as the planets frequently perturb the orbit of small bodies. It is also necessary that the two bodies reach that point in their orbits at the same time before the smaller body is perturbed into a different orbit with a different MOID value. Two objects gravitationally locked in orbital resonance may never approach one another. Numerical integrations become increasingly divergent as trajectories are projected further forward in time, especially beyond times where the smaller body is repeatedly perturbed by other planets. MOID has the convenience that it is obtained directly from the orbital elements of the body and no numerical integration into the future is used. [3]
The only object that has ever been rated at 4 on the Torino Scale (since downgraded), the Aten asteroid (99942) Apophis, has an Earth MOID of 0.00026 AU (39,000 km ; 24,000 mi ). This is not the smallest Earth MOID in the catalogues; many bodies with a small Earth MOID are not classed as PHO's because the objects are less than roughly 140 meters in diameter (or absolute magnitude, H > 22). Earth MOID values are generally more practical for asteroids less than 140 meters in diameter as those asteroids are very dim and often have a short observation arc with a poorly determined orbit. As of September 2023, there have been seven objects detected and their Earth-MOID calculated before the Earth impact. [4] The first two objects that were detected and had their Earth-MOID calculated before Earth impact were the small asteroids 2008 TC3 and 2014 AA. 2014 AA is listed with a MOID of 0.00000045 AU (67 km; 42 mi), [5] and is the second smallest MOID calculated for an Apollo asteroid after 2020 QY2 with an Earth-MOID of 0.00000039 AU (58 km; 36 mi). [6]
Object | Earth MOID (AU) | Size (m) (approximate) | (H) |
---|---|---|---|
2016 FG60 | 0.000076 AU (11,400 km ; 7,100 mi ) [8] | 300 | 21.1 |
(177049) 2003 EE16 | 0.000107 AU (16,000 km; 9,900 mi) | 320 | 19.8 |
2012 HZ33 | 0.000131 AU (19,600 km; 12,200 mi) | 260 | 20.4 |
2010 JE88 | 0.000148 AU (22,100 km; 13,800 mi) | 180 | 21.5 |
(137108) 1999 AN10 | 0.000153 AU (22,900 km; 14,200 mi) | 1300 | 17.9 |
2022 BX1 | 0.000177 AU (26,500 km; 16,500 mi) | 170 | 21.7 |
2003 EG16 | 0.000179 AU (26,800 km; 16,600 mi) | 490 | 19.4 |
2021 NQ5 | 0.000187 AU (28,000 km; 17,400 mi) | 210 | 21.2 |
(442037) 2010 PR66 | 0.000238 AU (35,600 km; 22,100 mi) | 695 | 19.3 |
(216985) 2000 QK130 | 0.000252 AU (37,700 km; 23,400 mi) | 200 | 21.3 |
99942 Apophis | 0.000257 AU (38,400 km; 23,900 mi) | 370 | 19.7 |
(89958) 2002 LY45 | 0.000261 AU (39,000 km; 24,300 mi) | 1300 | 17.2 |
(35396) 1997 XF11 | 0.000305 AU (45,600 km; 28,400 mi) | 704 | 17.0 |
162173 Ryugu | 0.000315 AU (47,100 km; 29,300 mi) | 896 | 19.6 |
(143651) 2003 QO104 | 0.000321 AU (48,000 km; 29,800 mi) | 2300 | 16.1 |
(85236) 1993 KH | 0.000335 AU (50,100 km; 31,100 mi) | 500 | 18.8 |
(471240) 2011 BT15 | 0.000368 AU (55,100 km; 34,200 mi) | 150 | 21.4 |
Object | Epoch | Earth MOID (AU) |
---|---|---|
3D/Biela | 1832 | 0.0005 AU (75,000 km ; 46,000 mi ; 0.19 LD ) |
109P/Swift-Tuttle | 1995 | 0.0009 AU (130,000 km; 84,000 mi; 0.35 LD) |
55P/Tempel–Tuttle | 1998 | 0.0085 AU (1,270,000 km; 790,000 mi; 3.3 LD) |
255P/Levy | 2007 | 0.0088 AU (1,320,000 km; 820,000 mi; 3.4 LD) |
15P/Finlay | 2015 | 0.0092 AU (1,380,000 km; 860,000 mi; 3.6 LD) |
73P–BW | 2022 | 0.0093 AU (1,390,000 km; 860,000 mi; 3.6 LD) [9] |
252P/LINEAR | 2016 | 0.0122 AU (1,830,000 km; 1,130,000 mi; 4.7 LD) |
460P/PanSTARRS | 2016 | 0.0163 AU (2,440,000 km; 1,520,000 mi; 6.3 LD) |
289P/Blanpain | 2019 | 0.0165 AU (2,470,000 km; 1,530,000 mi; 6.4 LD) |
21P/Giacobini–Zinner | 2017 | 0.0179 AU (2,680,000 km; 1,660,000 mi; 7.0 LD) |
Object | Earth MOID (AU) |
---|---|
6 Hebe | 0.975 AU (145.9 million km ; 90.6 million mi ; 379 LD ) |
7 Iris | 0.850 AU (127.2 million km; 79.0 million mi; 331 LD) |
8 Flora | 0.873 AU (130.6 million km; 81.2 million mi; 340 LD) |
12 Victoria | 0.824 AU (123.3 million km; 76.6 million mi; 321 LD) |
18 Melpomene | 0.811 AU (121.3 million km; 75.4 million mi; 316 LD) |
84 Klio | 0.798 AU (119.4 million km; 74.2 million mi; 311 LD) |
228 Agathe | 0.657 AU (98.3 million km; 61.1 million mi; 256 LD) |
(444004) 2004 AS1, provisional designation 2004 AS1, and also known by the temporary name AL00667, is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 300 meters in diameter.
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.
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and which is large enough to cause significant regional damage in the event of impact. They are conventionally defined as having a minimum orbit intersection distance with Earth of less than 0.05 astronomical units and an absolute magnitude of 22 or brighter, the latter of which roughly corresponds to a size larger than 140 meters. More than 99% of the known potentially hazardous objects are no impact threat over the next 100 years. As of September 2022, just 17 of the known potentially hazardous objects listed on the Sentry Risk Table could not be excluded as potential threats over the next hundred years. Over hundreds if not thousands of years though, the orbits of some "potentially hazardous" asteroids can evolve to live up to their namesake.
(4953) 1990 MU is a large Earth-crossing asteroid (ECA) belonging to the Apollo group of near-Earth objects which also cross the orbits of Mars and Venus. At approximately 3 km in diameter, it is one of the largest known ECAs. It has been assigned a permanent number from the Minor Planet Center (4953) indicating that its orbit has been very well determined. With an observation arc of 45 years, the asteroid's trajectory and uncertainty regions are well known through to the year 2186.
(7888) 1993 UC is a near-Earth minor planet in the Apollo group. It was discovered by Robert H. McNaught at the Siding Spring Observatory in Coonabarabran, New South Wales, Australia, on 20 October 1993. The asteroid has an observation arc of 34 years and has a well determined orbit. Its estimated size is 2.3 to 5.2 km.
(523662) 2012 MU2, provisional designation 2012 MU2, is a sub-kilometer asteroid on an eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. It was discovered on 18 June 2012 by astronomers of the Catalina Sky Survey at an apparent magnitude of 19.9 using a 0.68-meter (27 in) Schmidt–Cassegrain telescope. It has an estimated diameter of 240 meters (790 ft). The asteroid was listed on Sentry Risk Table with a Torino Scale rating of 1 on 23 June 2012.
(388188) 2006 DP14, provisional designation 2006 DP14, is a sub-kilometer sized, peanut-shaped asteroid on a highly eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. This contact binary was discovered on 23 February 2006, by astronomers of the LINEAR program at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. On 10 February 2014, it passed 6.25 lunar distances from Earth. The asteroid is approximately 400 meters in diameter and has a rotation period of 5.77 hours.
2004 TN1 is a sub-kilometer near-Earth asteroid and potentially hazardous object of the Apollo group, approximately 180 meters (600 ft) in diameter. It was first observed by the Near-Earth Asteroid Tracking at Palomar Observatory on 5 October 2004. The asteroid has a notably low sub-lunar Earth-MOID of 0.38 LD. As of 2019, it has only been observed in Fall 2004.
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.
(456938) 2007 YV56, provisional designation 2007 YV56, is a sub-kilometer asteroid on an eccentric orbit, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 190–360 meters (620–1,200 ft) in diameter. It was discovered on 31 December 2007, by astronomers of the Catalina Sky Survey conducted at the Catalina Station in Arizona, United States.
(549948) 2011 WL2 is a sub-kilometer asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group. It was discovered on 16 November 2011, by astronomers with the LINEAR at the Lincoln Laboratory ETS near Socorro, New Mexico, in the United States.
(415029) 2011 UL21, provisional designation 2011 UL21, is an Apollo class potentially hazardous asteroid discovered on October 17, 2011, by the Catalina Sky Survey project. The asteroid is estimated to have a diameter of 2.5 kilometres (1.6 mi). It was rated at Torino Scale 1 on October 27, 2011, with an observation arc of 9.6 days.
(16960) 1998 QS52 (provisional designation 1998 QS52) is a stony asteroid on a highly eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 4.1 kilometers (2.5 mi) in diameter. It was discovered on 25 August 1998, by astronomers of the LINEAR program at Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. This asteroid is one of the largest potentially hazardous asteroid known to exist.
(52768) 1998 OR2 (provisional designation 1998 OR2) is an asteroid on an eccentric orbit, classified as a near-Earth object and potentially hazardous asteroid of the Amor group, with a diameter of 2 kilometers (1.2 mi). It was discovered on 24 July 1998, by astronomers of the Near-Earth Asteroid Tracking (NEAT) program at the Haleakala Observatory, Hawaii, it passed very near to earth on 29 April 2020 at around 4:15am. It is one of the brightest and therefore largest potentially hazardous asteroids known to exist. With an observation arc of 35 years, the asteroid has a well-determined orbit, and its trajectory is well known through the year 2197. The asteroid's orbit is only potentially hazardous on a time scale of thousands of years.
(143651) 2003 QO104, provisional designation 2003 QO104, is a stony asteroid, slow rotator and suspected tumbler on a highly eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Amor and Apollo group, respectively. It was discovered on 31 August 2003, by astronomers of the Near-Earth Asteroid Tracking program at the Haleakala Observatory in Hawaii, United States. The Q-type asteroid has a rotation period of 114.4 hours and possibly an elongated shape. It measures approximately 2.3 kilometers (1.4 miles) in diameter and belongs the largest potentially hazardous asteroids known to exist.
(85182) 1991 AQ is a stony asteroid on a highly eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 1.1 kilometers in diameter. It was discovered on 14 January 1991, by American astronomer Eleanor Helin at the Palomar Observatory in California. Based on its brightness variation of 0.69 magnitude, this Q-type asteroid is likely elongated. It belongs to the small group of potentially hazardous asteroids larger than one kilometer.
2017 YE5 is a binary pair of asteroids of approximately equal size and mass, each about 0.9 km (0.56 mi) in diameter. Classified as a near-Earth asteroid and potentially hazardous object of the Apollo group, 2017 YE5 was discovered by amateur astronomer Claudine Rinner at the Oukaïmeden Observatory on 21 December 2017. On 21 June 2018, the pair of asteroids passed within 15.5 lunar distances or approximately 6 million km (3.7 million mi) from Earth. During the close encounter, 2017 YE5 was resolved in high detail by concurrent radar observations by the Arecibo and Green Bank observatories, along with individual observations by the Goldstone Solar System Radar. 2017 YE5 is likely an extinct or dormant comet due to its distant elliptical orbit and dark red surface.
(696513) 2016 NL56 (provisional designation 2016 NL56) is a near-Earth object (NEO) and a potentially hazardous object (PHA), meaning that it has an orbit that can make close approaches to the Earth and large enough to cause significant regional damage in the event of impact. It is an Apollo asteroid, meaning that it is an Earth-crossing asteroid that has an orbit larger than the orbit of the Earth. It was first observed on 12 July 2016, when the asteroid was more than 1 AU from Earth and had a solar elongation of 163 degrees.
2019 BE5 is a sub-kilometer near-Earth asteroid classified under the Aten group. It was discovered on 31 January 2019, by the Zwicky Transient Facility at the Palomar Observatory. The asteroid was discovered one day after it had made a close approach to Earth from a distance of 0.00784 AU (1.173 million km; 3.05 LD).
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.