Potentially hazardous object

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The asteroid Toutatis is listed as a potentially hazardous near-Earth asteroid, yet poses no immediate threat to Earth. (Radar image taken by GDSCC in 1996.) Toutatis.jpg
The asteroid Toutatis is listed as a potentially hazardous near-Earth asteroid, yet poses no immediate threat to Earth. (Radar image taken by GDSCC in 1996.)

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 is large enough to cause significant regional damage in the event of impact. [1] They are defined as having a minimum orbital intersection distance with Earth of less than 0.05 astronomical units (19.5 lunar distances ) and an absolute magnitude of 22 or brighter. [2] 98% of the known potentially hazardous objects are not an impact threat over the next 100 years. [3] Only about 32 potentially hazardous objects are listed on the Sentry Risk Table as objects that are known not to be a threat over the next hundred years are excluded. [4] Over hundreds if not thousands of years, "potentially hazardous" asteroids have the potential for their orbits to evolve to live up to their namesake.

Contents

Most of these objects are potentially hazardous asteroids (PHAs), and a few are comets. As of March 2021 there are 2,173 known PHAs (about 9% of the total near-Earth population), of which 158 are estimated to be larger than one kilometer in diameter (see list of largest PHAs below). [5] [6] [lower-alpha 1] Most of the discovered PHAs are Apollo asteroids (1,730) and fewer belong to the group of Aten asteroids (171). [7] [8]

A potentially hazardous object can be known not to be a threat to Earth for the next 100 years or more, if its orbit is reasonably well determined. Potentially hazardous asteroids with some threat of impacting Earth in the next 100 years are listed on the Sentry Risk Table. As of March 2021, only about 32 potentially hazardous asteroids are listed on the Sentry Risk Table. [4] Most potentially hazardous asteroids are ruled out as hazardous to at least several hundreds of years when their competing best orbit models are sufficiently constrained, but recent discoveries whose orbital constraints are little-known have divergent or incomplete mechanical models until observation yields further data. After several astronomical surveys, the number of known PHAs has increased tenfold since the end of the 1990s (see bar charts below). [5] The Minor Planet Center's website List of the Potentially Hazardous Asteroids also publishes detailed information for these objects. [9]

In May 2021, NASA astronomers reported that 5 to 10 years of preparation may be needed to avoid a potential impactor based on a simulated exercise conducted by the 2021 Planetary Defense Conference. [10] [11] [12]

Overview

Plot of orbits of known potentially hazardous asteroids, with sizes over 140 metres (460 ft) and that pass within 7.6 million kilometres (4.7x10
^
mi) of Earth's orbit. Epoch as of early 2013. Potentially Hazardous Asteroids 2013.png
Plot of orbits of known potentially hazardous asteroids, with sizes over 140 metres (460 ft) and that pass within 7.6 million kilometres (4.7×10^ mi) of Earth's orbit. Epoch as of early 2013.

An object is considered a PHO if its minimum orbit intersection distance (MOID) with respect to Earth is less than 0.05  AU (7,500,000  km ; 4,600,000  mi ) – approximately 19.5  lunar distances – and its absolute magnitude is brighter than 22, approximately corresponding to a diameter above 140 meters (460 ft). [1] [2] This is big enough to cause regional devastation to human settlements unprecedented in human history in the case of a land impact, or a major tsunami in the case of an ocean impact. Such impact events occur on average around once per 10,000 years. NEOWISE data estimates that there are 4,700 ± 1,500 potentially hazardous asteroids with a diameter greater than 100 meters. [13]

Levels of hazard

The two main scales used to categorize the impact hazards of asteroids are the Palermo Technical Impact Hazard Scale and the Torino Scale.

Potentially hazardous comets

Short-period comets currently with an Earth-MOID less than 0.05 AU include: 109P/Swift-Tuttle, 55P/Tempel–Tuttle, 15P/Finlay, 289P/Blanpain, 255P/Levy, 206P/Barnard–Boattini, 21P/Giacobini–Zinner, and 73P/Schwassmann–Wachmann.

Numbers

Detected NEAs by various projects. The broader class of NEAs includes all PHAs as a subset.
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LINEAR

NEAT

Spacewatch

LONEOS

CSS
Pan-STARRS

NEOWISE

ATLAS

Others Neo-chart.png
Detected NEAs by various projects. The broader class of NEAs includes all PHAs as a subset.
   LINEAR
   NEAT
   Spacewatch
   LONEOS
   CSS
   Pan-STARRS
   NEOWISE
   ATLAS
  Others

In 2012 NASA estimated 20 to 30 percent of these objects have been found. [13] During an asteroid's close approaches to planets or moons other than the Earth, it will be subject to gravitational perturbation, modifying its orbit, and potentially changing a previously non-threatening asteroid into a PHA or vice versa. This is a reflection of the dynamic character of the Solar System.

Several astronomical survey projects such as Lincoln Near-Earth Asteroid Research, Catalina Sky Survey and Pan-STARRS continue to search for more PHOs. Each one found is studied by various means, including optical, radar, and infrared to determine its characteristics, such as size, composition, rotation state, and to more accurately determine its orbit. Both professional and amateur astronomers participate in such observation and tracking.

Size

Asteroids larger than approximately 35 meters across can pose a threat to a town or city. [14] However the diameter of most small asteroids is not well determined, as it is usually only estimated based on their brightness and distance, rather than directly measured, e.g. from radar observations. For this reason NASA and the Jet Propulsion Laboratory use the more practical measure of absolute magnitude (H). Any asteroid with an absolute magnitude of 22.0 or brighter is assumed to be of the required size. [2]

Only a coarse estimation of size can be found from the object's magnitude because an assumption must be made for its albedo which is also not usually known for certain. The NASA near-Earth object program uses an assumed albedo of 0.14 for this purpose. In May 2016, the asteroid size estimates arising from the Wide-field Infrared Survey Explorer and NEOWISE missions have been questioned. [15] [16] [17] Although the early original criticism had not undergone peer review, [18] a more recent peer-reviewed study was subsequently published. [19] [20]

Largest PHAs

With a mean diameter of approximately 7 kilometers, Apollo asteroid (53319) 1999 JM8 is likely the largest known potentially hazardous object, despite its fainter absolute magnitude of 15.2, compared to other listed objects in the table below (note: calculated mean-diameters in table are inferred from the objects brightness and its (assumed) albedo. They are only an approximation.). The lowest numbered PHA is 1566 Icarus. [9]

Brightest Potentially Hazardous Asteroids [9]
Designation Discovery (H) (mag) D (km)Orbital descriptionRemarksRefs
Year Place Discoverer Class a
(AU)
e i
(°)
q
(AU)
Q
(AU)
MOID
(AU)
(4953) 1990 MU 1990 413 R. H. McNaught14.13 km APO 1.6210.65824.40.5552.6870.02640 MPC  · JPL  · catalog
3122 Florence 1981 413 S. J. Bus14.15 km AMO 1.7690.42322.21.0202.5180.04430 MPC  · JPL  · catalog
(16960) 1998 QS52 1998 704 LINEAR14.34 km APO 2.2030.85817.50.3134.0930.01443 MPC  · JPL  · catalog
4183 Cuno 1959 074 C. Hoffmeister14.44 km APO 1.9820.6346.70.7253.2400.02825 MPC  · JPL  · catalog
3200 Phaethon 1983 500 IRAS14.65.8 km APO 1.2710.89022.30.1402.4020.01945 MPC  · JPL  · catalog
(242450) 2004 QY2 2004 E12 Siding Spring Survey14.73 km APO 1.0840.47737.00.5671.6010.04686 MPC  · JPL  · catalog
(89830) 2002 CE 2002 704 LINEAR14.93.1 km AMO 2.0770.50743.71.0233.1310.02767 MPC  · JPL  · catalog
(137427) 1999 TF211 1999 704 LINEAR15.12.9 km APO 2.4480.61039.20.9553.9420.01787 MPC  · JPL  · catalog
(111253) 2001 XU10 2001 704 LINEAR15.23 km APO 1.7540.43942.00.9832.5240.02934 MPC  · JPL  · catalog
(53319) 1999 JM8 1999 704 LINEAR15.27 km APO 2.7260.64113.80.9784.4740.02346likely largest PHO MPC  · JPL  · catalog
1981 Midas 1973 675 C. T. Kowal15.22 km APO 1.7760.65039.80.6212.9310.00449 MPC  · JPL  · catalog
2201 Oljato 1947 690 H. L. Giclas15.252.1 km APO 2.1750.7132.50.6243.7260.00305 MPC  · JPL  · catalog
(90075) 2002 VU94 2002 644 NEAT15.32.2 km APO 2.1340.5768.90.9043.3630.03010 MPC  · JPL  · catalog
4179 Toutatis 1989 010 C. Pollas15.302.5 km APO 2.5360.6290.40.9404.1320.00615 MPC  · JPL  · catalog
(159857) 2004 LJ1 2004 704 LINEAR15.43 km APO 2.2640.59323.10.9203.6070.01682 MPC  · JPL  · catalog
(85713) 1998 SS49 1998 704 LINEAR15.63.5 km APO 1.9240.63910.80.6943.1540.00234 MPC  · JPL  · catalog
4486 Mithra 1987 071 E. W. Elst
V. G. Shkodrov
15.62 km APO 2.2000.6633.00.7423.6580.04626 MPC  · JPL  · catalog
1620 Geographos 1951 675 A. G. Wilson
R. Minkowski
15.602.5 km APO 1.2450.33513.30.8281.6630.03007 MPC  · JPL  · catalog
(415029) 2011 UL21 2011 703 CSS15.72.5 km APO 2.1220.65334.90.7363.5090.01925 MPC  · JPL  · catalog
(242216) 2003 RN10 2003 699 LONEOS15.72.5 km AMO 2.2310.54139.61.0243.4380.00956 MPC  · JPL  · catalog
12923 Zephyr 1999 699 LONEOS15.82 km APO 1.9620.4925.30.9962.9270.02115 MPC  · JPL  · catalog
(52768) 1998 OR2 1998 566 NEAT15.82 km APO 2.3800.5735.91.0173.7430.01573 MPC  · JPL  · catalog

Statistics

Below is a list of the largest PHAs (based on absolute magnitude H) discovered in a given year. [21] Historical data of the cumulative number of discovered PHA since 1999 are displayed in the bar charts—one for the total number and the other for objects larger than one kilometer. [5]

Brightest PHA discoveries of each calendar year since 1989 [21]
NumberNameYear (H) Refs
4179 Toutatis 198915.3 MPC  · JPL  · catalog
4953 1990 MU 199014.1 MPC  · JPL  · catalog
7341 1991 VK 199116.7 MPC  · JPL  · catalog
5604 1992 FE 199216.4 MPC  · JPL  · catalog
39572 1993 DQ1 199316.4 MPC  · JPL  · catalog
136618 1994 CN2 199416.6 MPC  · JPL  · catalog
243566 1995 SA 199517.3 MPC  · JPL  · catalog
8566 1996 EN 199616.5 MPC  · JPL  · catalog
35396 1997 XF11 199716.9 MPC  · JPL  · catalog
16960 1998 QS52 199814.3 MPC  · JPL  · catalog
137427 1999 TF211 199915.0 MPC  · JPL  · catalog
23187 2000 PN9 200016.1 MPC  · JPL  · catalog
111253 2001 XU10 200114.9 MPC  · JPL  · catalog
89830 2002 CE 200214.7 MPC  · JPL  · catalog
242216 2003 RN10 200315.7 MPC  · JPL  · catalog
242450 2004 QY2 200414.7 MPC  · JPL  · catalog
308242 2005 GO21 200516.4 MPC  · JPL  · catalog
374851 2006 VV2 200616.8 MPC  · JPL  · catalog
214869 2007 PA8 200716.2 MPC  · JPL  · catalog
294739 2008 CM 200817.1 MPC  · JPL  · catalog
369264 2009 MS 200916.0 MPC  · JPL  · catalog
381906 2010 CL19 201017.8 MPC  · JPL  · catalog
415029 2011 UL21 201115.7 MPC  · JPL  · catalog
482467 2012 LK9 201217.8 MPC  · JPL  · catalog
507716 2013 UP8 201316.5 MPC  · JPL  · catalog
533671 2014 LJ21 201416.0 MPC  · JPL  · catalog
2015 HY116 201517.5 MPC  · JPL  ·
2016 CB194 201617.6 MPC  · JPL  ·
2017 CH1 201717.9 MPC  · JPL  ·
2018 XV5 201817.5 MPC  · JPL  ·
2019 CE4 201918.0 MPC  · JPL  ·
2020 SL1 202017.4 MPC  · JPL  ·
50
100
150
200
prev.
1999
2001
2003
2005
2007
2009
2011
2013
2015
2017
2019
PHA-KM: potentially hazardous asteroids larger than 1 kilometer since 1999 – Cumulative number of discovered PHA by end of year (first of December). As of September 2020, there are 157 known PHAs larger than one kilometer. [5]
500
1,000
1,500
2,000
2,500
3,000
prev.
1999
2001
2003
2005
2007
2009
2011
2013
2015
2017
2019
PHA: total number of potentially hazardous asteroids since 1999 – Cumulative number of all discovered PHA by end of year (first of December). As of September 2020, there are 2115 PHAs. [5]

See also

Notes

  1. An object's calculated mean-diameter is only a rough estimate. It is inferred from the object's varying brightness—observed and measured at various times—and the assumed, yet often unknown reflectivity of its surface. NASA's Asteroid Size Estimator is a tool for a generic absolute magnitude-to-diameter conversion for an assumed geometric albedo.

Related Research Articles

Near-Earth object Small Solar System body whose orbit brings it close to the Earth

A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets.

(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.

Sentry (monitoring system) JPL program to monitor the Minor Planet Centers catalog for Earth impacts

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; a prediction of where it will not be.

Minimum orbit intersection distance Measure of close approach or collision risk in astronomy

Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. 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.

(153814) 2001 WN5 is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group.

(410777) 2009 FD

(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.

(242450) 2004 QY2 (prov. designation:2004 QY2) is an asteroid on an eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 3 kilometers (2 miles) in diameter. It was discovered on 20 August 2004 by the Siding Spring Survey at an apparent magnitude of 16.5 using the 0.5-metre (20 in) Uppsala Southern Schmidt Telescope. It is one of the largest potentially hazardous asteroids known to exist.

(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.

(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.

2011 EO40 is an asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. It is a possible candidate for the parent body of the Chelyabinsk superbolide.

<span class="nowrap">2013 YP<sub>139</sub></span>

2013 YP139 is a dark sub-kilometer asteroid on a highly eccentric orbit, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 400 meters (1,300 feet) in diameter.

2012 UE34 is a sub-kilometer asteroid, classified as a near-Earth object of the Apollo group, approximately 70 meters (230 feet) in diameter. It was first observed on 18 October 2012, by Pan-STARRS at Haleakala Observatory on the island of Maui, Hawaii, in the United States. The object was removed from the Sentry Risk Table on 29 December 2013. On 8 April 2041 it will pass Earth at a nominal distance of 0.29 LD (0.0007329 AU). Due to its presumed small size, it does not qualify as a potentially hazardous asteroid, despite its low Earth MOID.

(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.

(163243) 2002 FB3, provisional designation 2002 FB3, is a stony asteroid on an eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Athen group, approximately 1.6 kilometers (1 mile) in diameter. It was discovered on 18 March 2002, by astronomers with the Lincoln Near-Earth Asteroid Research at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. The Q-type asteroid has a rotation period of 6.2 hours.

(164121) 2003 YT1, provisional designation 2003 YT1, is a bright asteroid and synchronous binary system on a highly eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 2 kilometers (1.2 miles) in diameter. It was discovered on 18 December 2003, by astronomers with the Catalina Sky Survey at the Catalina Station near Tucson, Arizona, in the United States. The V-type asteroid has a short rotation period of 2.3 hours. Its 210-meter sized minor-planet moon was discovered at Arecibo Observatory in May 2004.

(85182) 1991 AQ, provisional designation 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.

2016 NL56 (also written 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.

2017 QC36 is a near-Earth object and a potentially hazardous asteroid of the Aten group, It measures approximately 200 meters (660 feet) in diameter and was briefly observed by the Wide-field Infrared Survey Explorer on 18 August 2017 before it became a lost asteroid on the following day. It was later recovered in 2021 from archival Pan-STARRS and Cerro Tololo observations.

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.

References

  1. 1 2 Task Force on potentially hazardous Near Earth Objects (September 2000). "Report of the Task Force on potentially hazardous Near Earth Objects" (PDF). Archived from the original (PDF) on 10 December 2016. Retrieved 22 January 2018.Cite journal requires |journal= (help)
  2. 1 2 3 "NEO Basics – Potentially Hazardous Asteroids (PHAs)". CNEOS NASA/JPL. Retrieved 16 January 2020.
  3. (32 Sentry risk-listed PHAs / 2173 PHAs) = 1.5%
  4. 1 2 "Sentry Risk Table" . Retrieved 2019-08-15. (Click "Use Unconstrained Settings" AND select "H<=22" for list of PHAs)
  5. 1 2 3 4 5 6 "Discovery Statistics – Cumulative Totals". CNEOS NASA/JPL. 7 January 2020. Retrieved 16 January 2020.
  6. "Unusual Minor Planets – Overview". Minor Planet Center. Retrieved 16 January 2020.
  7. "JPL Small-Body Database Search Engine: PHAs and orbital class (APO)". JPL Solar System Dynamics. Retrieved 16 January 2020.
  8. "JPL Small-Body Database Search Engine: PHAs and orbital class (ATE)". JPL Solar System Dynamics. Retrieved 16 January 2020.
  9. 1 2 3 "List of the Potentially Hazardous Asteroids (PHAs)". Minor Planet Center. Retrieved 16 January 2018.
  10. McFall-Johnsen, Morgan; Woodward, Aylin (12 May 2021). "A NASA simulation revealed that 6 months' warning isn't enough to stop an asteroid from hitting Earth. We'd need 5 to 10 years". Business Insider . Retrieved 14 May 2021.
  11. Bartels, Meghan (1 May 2021). "How did you spend your week? NASA pretended to crash an asteroid into Earth". Space.com . Retrieved 14 May 2021.
  12. Chodas, Paul; Khudikyan, Shakeh; Chamberlin, Alan (30 April 2021). "Planetary Defense Conference Exercise - 2021 Planetary Defense Conference (virtually) in Vienna, Austria, April 26–April 30, 2021". NASA . Retrieved 14 May 2021.
  13. 1 2 "NASA news – NASA Survey Counts Potentially Hazardous Asteroids". NASA/JPL. 16 May 2012. Retrieved 22 January 2018.
  14. Will Ferguson (22 January 2013). "Asteroid Hunter Gives an Update on the Threat of Near-Earth Objects". Scientific American . Retrieved 2013-01-23.
  15. Chang, Kenneth (23 May 2016). "How Big Are Those Killer Asteroids? A Critic Says NASA Doesn't Know". New York Times . Retrieved 24 May 2016.
  16. Myhrvold, Nathan (23 May 2016). "Asteroid thermal modeling in the presence of reflected sunlight with an application to WISE/NEOWISE observational data". arXiv: 1605.06490v2 [astro-ph.EP].
  17. Billings, Lee (27 May 2016). "For Asteroid-Hunting Astronomers, Nathan Myhrvold Says the Sky Is Falling". Scientific American . Retrieved 28 May 2016.
  18. NASA Administrator (25 May 2016). "NASA Response to Recent Paper on NEOWISE Asteroid Size Results". NASA . Retrieved 29 May 2016.
  19. Myhrvold, Nathan (2018). "An empirical examination of WISE/NEOWISE asteroid analysis and results". Icarus . 314: 64–97. Bibcode:2018Icar..314...64M. doi: 10.1016/j.icarus.2018.05.004 .
  20. Chang, Kenneth (14 June 2018). "Asteroids and Adversaries: Challenging What NASA Knows About Space Rocks - Two years ago, NASA dismissed and mocked an amateur's criticisms of its asteroids database. Now Nathan Myhrvold is back, and his papers have passed peer review". The New York Times . Retrieved 14 June 2018.
  21. 1 2 "JPL Small-Body Database Search Engine: PHAs and H < 18 (mag)". JPL Solar System Dynamics. Retrieved 2012-06-13.

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