2001 QW322
Ultrawide binary Kuiper belt object

2001 QW322
2001 QW322 imaged by the Canada–France–Hawaii Telescope on 24 August 2001
Discovery
Discovered byCanada–France Ecliptic Plane Survey[1][2]
Discovery siteMauna Kea Obs.
Discovery date24 August 2001[5]
Designations
2001 QW322
Orbital characteristics (barycentric)[8]
Epoch 21 November 2025 (JD 2461000.5)
Uncertainty parameter 4
Observation arc22.11 yr (8,076 days)
Earliest precovery date27 July 2001[5]
Aphelion45.052 AU
Perihelion42.922 AU
43.987 AU
Eccentricity0.0242
291.54 yr (106,486 d)
134.122°
0° 0m 12.171s / day
Inclination4.8095°
124.690°
74.789°
Known satellites1
Physical characteristics
128+2
−4 km (primary)[9][10]: 14 
Mass2.150+0.144
−0.223×1018 kg (system)[a]
Mean density
1±0.2 g/cm3[1]
0.093+0.010
−0.006[10]: 14 
  • 7.51 (primary)[10]: 3 
  • 7.7 (JPL)[6]

2001 QW322 is an extremely wide binary system of Kuiper belt objects discovered by John J. Kavelaars, Jean-Marc Petit, Brett Gladman, and Matthew Holman on 24 August 2001. Located beyond Neptune, the binary system comprises two identical components, each about 128 km (80 mi) in diameter, orbiting around their mutual barycenter with an extremely long orbital period of 17 years. The components have an average separation of 101,500 km (63,100 mi), making 2001 QW322 the widest binary minor planet known as of 2023[update].[11] The immense separation between components means that the binary system is weakly bound by gravity, which makes it prone to disruption by collisions or gravitational perturbations by close-passing Kuiper belt objects within the next one billion years.[1][12]

The 2001 QW322 system is a member of the "cold" classical population of the Kuiper belt, because it follows a nearly circular and low-inclination orbit around the Sun. This implies that it has not been significantly disturbed by Neptune's gravitational influence.[13][12] Both components of the 2001 QW322 system exhibit less red ("blue") colors compared to most cold classical Kuiper belt objects, which has been proposed to be an indication of early, high-temperature formation at its current location in the protosolar disk, before red substances like methanol and hydrocarbons began forming.[13]

Discovery

The Canada–France–Hawaii Telescope's discovery images of 2001 QW322 show two distinctly separated components moving together with respect to background stars.

2001 QW322 was discovered by astronomers of the Canada–France Ecliptic Plane Survey (CFEPS),[1][2] which included John J. Kavelaars, Jean-Marc Petit, Brett Gladman, and Matthew Holman.[3][4] The discovery took place on 24 August 2001, during a search for moons of Uranus using the Canada–France–Hawaii Telescope at Mauna Kea Observatory in Hawaii.[14][1] The discovery images, which were taken by Kavelaars and analyzed by Petit, revealed that 2001 QW322 is a binary system consisting of two identical components moving together.[3] The components had an angular separation of 4 arcseconds from each other, which translated to an apparent physical separation of 125,000 km (78,000 mi)—far larger than any other binary Solar System object known at the time.[3][1]

The discoverers immediately recognized the exceptionally wide binary nature of 2001 QW322 and thus begun a multi-year observing campaign using various large telescopes to determine the binary system's mutual and heliocentric orbit.[14][2][b] The discovery of the 2001 QW322 binary system was announced in circulars issued by the Minor Planet Center and Central Bureau for Astronomical Telegrams on 9 November 2001.[3][4] The heliocentric orbit of 2001 QW322 became determined by 2003, while the mutual orbit became determined by late 2007 and announced in October 2008.[14][15]

Heliocentric orbit

Orbit of 2001 QW322 around the Sun, including the orbits of other planets

The 2001 QW322 system orbits the Sun at an average distance (semi-major axis) of 44.0 AU (6.58 billion km; 4.09 billion mi), taking 291.5 years to complete one heliocentric orbit.[8][c] It is located in the classical region of the Kuiper belt between 42 and 47 AU from the Sun,[10] beyond the orbit of Neptune where many other icy objects like Pluto can be found.[15] Because 2001 QW322 shares its orbit with many other objects in the Kuiper belt, close encounters between these objects are common.[12]: 2 

The heliocentric orbit of the 2001 QW322 system is nearly circular with a low orbital eccentricity of 0.024, so its distance from the Sun does not vary significantly throughout its orbit.[8] It comes as close as 42.9 AU to the Sun at perihelion to as far as 45.1 AU from the Sun at aphelion,[8] and does not come closer than 12.6 AU from Neptune.[d] Its heliocentric orbit is slightly tilted with a low orbital inclination of 4.8° with respect to the ecliptic.[8]

The low-inclination and low-eccentricity orbit of 2001 QW322 makes it a member of the "cold" classical Kuiper belt objects (KBOs), which are so named because they have distinctly less excited (dynamically "cold") orbits.[10]: 2–3 [e] The cold classical KBOs do not come close enough to Neptune to experience significant perturbations by the planet's gravity, so their orbits can remain stable for a long period of time.[12]: 2  Wide and fragile binary systems like 2001 QW322 have been observed to occur more frequently in the cold classical KBO population, which suggests that the population was not greatly disturbed in the past few billion years.[13]: 1–2 [12]: 2 

Binary system

2001 QW322 ("A"/"southern")
Discovery
Discovered byCanada–France Ecliptic Plane Survey[1][2]
Discovery siteMauna Kea Obs.
Discovery date24 August 2001
Orbital characteristics[10]: 7 
Epoch 27 July 2001 10:04:48 UTC
(JD 2452117.92)
  • 101500+3800
    −1400     km     (mutual separation; wrt primary)
  • (22.22%+1.33%
    −0.61%     of system Hill radius)
Eccentricity0.46+0.02
−0.01
17.01+1.55
−0.69 yr
3 km/h (0.83 m/s)[17]
158°+19°
−10°
Inclination
243°+3°
−4°
  • 257°+5°
    −10°     (wrt ecliptic)
  • 248°+6°
    −10°     (wrt heliocentric orbit)
Satellite of2001 QW322
Physical characteristics
126+3
−5 km[9]
Mean density
1±0.2 g/cm3 (assumed same as primary)[1]
Albedo0.093±0.008 (assumed same as primary)[9]
7.54±0.05[f]

Nomenclature

2001 QW322 is the minor planet provisional designation of the whole binary system, given by the Minor Planet Center (MPC) as a shorthand for its discovery date.[4][18] Because the components of the 2001 QW322 system are identical in brightness and size, they could only be reliably distinguished by their relative positions in the sky.[1][10]: 9  The MPC and a 2008 study led by Jean-Marc Petit has labeled the southern component "A" and the northern component "B",[4][1] whereas a 2011 study led by Alex H. Parker has arbitrarily labeled the northern component as "primary" and the southern component as "secondary".[10]: 9 

The MPC may give a permanent minor planet number to 2001 QW322 once its heliocentric orbit is well determined with multiple years of observations, which would make it eligible for formal naming.[19][g] According to naming guidelines by the International Astronomical Union's Working Group for Small Bodies Nomenclature, trans-Neptunian objects must be given a mythological name, though in the case of classical KBOs like 2001 QW322, names related to creation myths are preferred.[20]: 8  John J. Kavelaars, one of the discoverers, has nicknamed 2001 QW322 "Antipholus and Antipholus" (after the twin brothers from William Shakespeare's play The Comedy of Errors) in a 2011 news release on the CFEPS website.[2]

Physical characteristics

The components of the 2001 QW322 system are virtually identical in brightness, with the northern "primary" (B) being 0.03 magnitudes brighter than the southern "secondary" (A) on average.[h] If both components share the same albedo, then their identical brightnesses imply identical sizes.[1] The albedo of 2001 QW322 is inferred to be 0.093+0.010
−0.006, which suggests a diameter of approximately 128 km (80 mi) for the northern "primary" component.[10]: 14  A calculation by Johnston's Archive finds a marginally smaller diameter of 126+3
−5 km for the southern "secondary" component based on its slightly dimmer brightness, although it is still identical to the primary component's diameter within error bounds.[9] Both components are assumed to be made of water ice and rock, with identical masses and densities within the range of 0.8 to 1.2 g/cm3.[1] The total mass of the 2001 QW322 system, which was determined from their mutual orbit, is 2.150+0.144
−0.223×1018 kg.[10]: 7 

Observations of 2001 QW322 in different visible light filters have shown that both components share identical colors, implying they have similar surfaces and therefore similar albedos.[1][2] The components have a spectral slope of (−2.2±3.3)%/100 nm, indicating they are less red ("blue") compared to most cold classical KBOs.[21][1] The "blue" color of 2001 QW322's components suggests they have exposed ice surfaces.[2] Blue cold classical KBOs like 2001 QW322 have been observed to occur more frequently as binary systems than as single objects; astronomers have termed these systems "blue binaries".[21][13]

The components of the 2001 QW322 system have been reported to vary in brightness during observations from 2002 to 2007, with the southern component (A) varying up to 0.45 magnitudes and the northern component (B) varying up to 0.35 magnitudes.[1] The components' brightness variations may be caused by both phase angle effects and the rotation of a non-spherical shape, although the photometric precision of these observations was insufficient to determine a rotation period for either component.[1]

Mutual orbit

Since the components of 2001 QW322 have presumably identical masses, the binary system's barycenter lies between them.[1] The components are separated by an average distance of approximately 101,500 km (63,100 mi),[10]: 7  which is roughly equivalent to one-fourth of the distance between Earth and the Moon,[i] or about 22% of the binary system's Hill radius (extent of the system's gravitational influence).[10]: 9  The 2001 QW322 system has the widest separation of components of any known binary minor planet as of 2023[update].[11] Due to their immense separation, the components are weakly bound together by each other's gravity, which makes them prone to perturbations by close-passing KBOs and the Kozai effect.[10][12]

The components follow extremely slow, elliptical orbits around their system barycenter, taking 17 years to complete one mutual orbit.[10]: 7  The components move at an average orbital speed of approximately 3 km/h (0.83 m/s; 1.9 mph), comparable to the walking speed of a human.[17] Their mutual orbit has an average eccentricity of 0.41, though the Kozai effect can make it vary between 0.342 and 0.477.[10]: 9  At periapsis of their mutual orbit, the components can come as close as 54,700+4,100
−2,600 km (34,000+2,500
−1,600 mi) from each other, although orbital variations by the Kozai effect can make their periapsis separation as small as 53,100+2,300
−1,900 km (33,000+1,400
−1,200 mi).[j] The mutual orbit of the 2001 QW322 system is retrograde with respect to the ecliptic and its heliocentric orbit; its orbital inclination with respect to these reference planes are 150.7° and 152.7°, respectively.[23][10]: 7 

Origin

See also

Notes

  1. ^ The system mass of 2.150+0.144
    −0.223    ×1018 kg     is the total mass of the 2001 QW322 binary system, including both primary and secondary components.[10]
  2. ^ "Mutual" refers to the two components of the 2001 QW322, while "heliocentric" refers to around the Sun.
  3. ^ These orbital elements are expressed in terms of the Solar System Barycenter (SSB) as the frame of reference.[8] Due to planetary perturbations, the Sun revolves around the SSB at non-negligible distances, so heliocentric-frame orbital elements and distances can vary in short timescales as shown in JPL-Horizons.[16]
  4. ^ The Minor Planet Center calculates a minimum orbit intersection distance of 12.67 AU between 2001 QW322 and Neptune.[5]
  5. ^ "Cold" does not refer to an object's temperature, but the dynamics of its orbit. Highly perturbed or excited orbits are dynamically "hot" whereas less perturbed orbits are dynamically "cold".[10]: 2–3 
  6. ^ Parker et al. (2011) find an absolute magnitude (H) of 7.51 for the primary component and a magnitude difference of 0.03±0.05 between the primary and secondary (with the secondary being fainter).[10]: 3  The secondary component's absolute magnitude can be obtained by adding the magnitude difference to the primary component's absolute magnitude.
  7. ^ As of 2026[update], the MPC and the Jet Propulsion Laboratory's Small-Body Database estimate the uncertainty of 2001 QW322's heliocentric orbit with an uncertainty parameter of 4.[6][5]
  8. ^ Petit's 2008 study found an average magnitude difference of (mB – mA) = −0.03±0.02 between the northern "primary" (B) and southern "secondary" (A) components (suggesting the northern "primary" component B is brighter; lower magnitude value means brighter),[1] whereas Parker's 2011 study found an average magnitude difference of (mA – mB) = +0.03±0.05 between the southern "secondary" (A) and northern "primary" (B) components (suggesting the northern "primary" component B is brighter).[10]: 3 
  9. ^ The Earth–Moon distance is 384,400 km (238,900 mi).[22] One-fourth of the Earth–Moon distance is 96,000 km (60,000 mi), which is 5,500 km (3,400 mi) off from 2001 QW322's average separation of 101,500 km (63,100 mi). The Gemini Observatory and Canada–France Ecliptic Plane Survey has claimed in 2008 and 2011 that 2001 QW322's average separation is approximately equivalent to one-third of the Earth–Moon distance (128,333 km or 79,742 mi), but this comparison is outdated as it uses an earlier estimate of 2001 QW322's average separation (125,000 km or 78,000 mi).[15][2]
  10. ^ Parker et al. (2011) give 2001 QW322's periapsis separation distance in terms of "primary radii", or multiples of the primary component's radius. The "derived" periapsis separation of 2001 QW322 is 855+64
    −40     primary radii, while the minimum periapsis separation due to the Kozai effect is 830+36
    −29     primary radii.[10]: 7–8  The radius of the 2001 QW322 primary is 64 km (40 mi), according to Parker et al. (2011).[10]: 14 

References

  1. ^ a b c d e f g h i j k l m n o p q r Petit, J.-M.; Kavelaars, J. J.; Gladman, B. J.; Margot, J.-L.; Nicholson, P. D.; Jones, R. L.; et al. (October 2008). "The Extreme Kuiper Belt Binary 2001 QW322" (PDF). Science. 322 (5900): 432–434. Bibcode:2008Sci...322..432P. doi:10.1126/science.1163148. PMID 18927391. S2CID 206515135.
  2. ^ a b c d e f g h Kavelaars, JJ (9 August 2011). "2001 QW322: Antipholus and Antipholus". Canada-France Ecliptic Plane Survey. Archived from the original on 23 October 2021. Retrieved 16 January 2026.
  3. ^ a b c d e f Kavelaars, J. J.; Petit, J.-M.; Gladman, B.; Holman, M. (9 October 2003). Green, Daniel W. E. (ed.). "IAUC 7749: 2001 QW_322; U Sco; 1RXS J232953.9+062814". IAU Circular (7749). Central Bureau of Astronomical Telegrams: 1. Bibcode:2001IAUC.7749....1K. Retrieved 13 January 2026.
  4. ^ a b c d e f "MPEC 2001-V34 : 2001 QW322". Minor Planet Electronic Circular. 2001-V34. Minor Planet Center. 9 November 2001. Bibcode:2001MPEC....V...34K. Retrieved 13 January 2026.
  5. ^ a b c d e "2001 QW322". Minor Planet Center. Retrieved 13 January 2026.
  6. ^ a b c "JPL Small-Body Database Lookup: (2001 QW322)" (2023-09-06 last obs.). Jet Propulsion Laboratory. Retrieved 13 January 2026.
  7. ^ Marc W. Buie. "Orbit Fit and Astrometric record for 01QW322". SwRI (Space Science Department). Retrieved 17 February 2018.
  8. ^ a b c d e f "JPL Horizons On-Line Ephemeris for 2001 QW322 (system barycenter) at epoch JD 2461000.5". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 13 January 2026. Solution using the Solar System Barycenter. Ephemeris Type: Elements and Center: @0)
  9. ^ a b c d Johnston, Wm. Robert (20 September 2014). "Asteroids with Satellites Database – 2001 QW322". Johnston's Archive. Retrieved 8 September 2020.
  10. ^ a b c d e f g h i j k l m n o p q r s t u v Parker, Alex H.; Kavelaars, J. J.; Petit, Jean-Marc; Jones, Lynne; Gladman, Brett; Parker, Joel; et al. (December 2011). "Characterization of Seven Ultra-wide Trans-Neptunian Binaries". The Astrophysical Journal. 743 (1): 1. arXiv:1108.2505. Bibcode:2011ApJ...743....1P. doi:10.1088/0004-637X/743/1/1.
  11. ^ a b Campbell, Hunter (August 2023). Evolution and Stability of Ultra-Wide Trans-Neptunian Binaries (PhD thesis). The University of Oklahoma. hdl:11244/338756. Archived from the original on 14 January 2026.
  12. ^ a b c d e f Campbell, Hunter M.; Stone, Lukas R.; Kaib, Nathan A. (January 2023). "Close Trans-Neptunian Object Passages as a Driver of the Origin and Evolution of Ultrawide Kuiper Belt Binaries". The Astronomical Journal. 165 (1): 19. arXiv:2211.06383. Bibcode:2023AJ....165...19C. doi:10.3847/1538-3881/aca08e.
  13. ^ a b c d Nesvorný, David; Vokrouhlický, David; Fraser, Wesley C. (March 2022). "Dynamical Implantation of Blue Binaries in the Cold Classical Kuiper Belt". The Astronomical Journal. 163 (3): 137. arXiv:2201.02747. Bibcode:2022AJ....163..137N. doi:10.3847/1538-3881/ac4bc9.
  14. ^ a b c Petit, J.-M.; Kavelaars, J. J.; Gladman, B. J.; Margot, J.-L.; Nicholson, P. D.; Jones, R. L.; et al. (July 2008). The Extreme Kuiper Belt Binary 2001 QW322 (PDF). Asteroids, Comets, Meteors. Baltimore, Maryland: Lunar and Planetary Institute. p. 8354. Bibcode:2008LPICo1405.8354P.
  15. ^ a b c "A Highly-split Kuiper Belt Pair". International Gemini Observatory. 28 October 2008. Archived from the original on 9 December 2024. Retrieved 15 January 2026.
  16. ^ "JPL Horizons On-Line Ephemeris for 2001 QW322 (system barycenter) at epochs JD 2460800.5–2461000.5". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 13 January 2026. Solution using the Sun. Ephemeris Type: Elements and Center: @sun)
  17. ^ a b Courtland, Rachel (16 October 2008). "Kuiper belt pair sets record for long-distance relationship". New Scientist. Archived from the original on 5 March 2023. Retrieved 15 January 2026.
  18. ^ "New- And Old-Style Minor Planet Designations". Minor Planet Center. Retrieved 14 January 2026.
  19. ^ "How Are Minor Planets Named?". Minor Planet Center. Retrieved 14 January 2026.
  20. ^ "Rules and Guidelines for Naming Non-Cometary Small Solar-System Bodies" (PDF). IAU Working Group for Small Bodies Nomenclature. 22 February 2025. Retrieved 13 January 2026.
  21. ^ a b Fraser, Wesley C.; Benecchi, Susan D.; Kavelaars, J. J.; Marsset, Michaël; Pike, Rosemary E.; Bannister, Michele T.; et al. (June 2021). "Col-OSSOS: The Distinct Color Distribution of Single and Binary Cold Classical KBOs". The Planetary Science Journal. 2 (3): 90. arXiv:2104.00028. Bibcode:2021PSJ.....2...90F. doi:10.3847/PSJ/abf04a.
  22. ^ Barry, Caela (17 December 2025). "Moon Facts". NASA. Retrieved 15 January 2026.
  23. ^ "Trans-Neptunian Binaries and the History of the Outer Solar System". International Gemini Observatory. 22 August 2011. Archived from the original on 13 February 2025. Retrieved 16 January 2026.
Wikimedia Commons has media related to 2001 QW322.
  • The Extreme Kuiper Belt Binary 2001 QW322, Isaac Newton Group of Telescopes, 13 December 2010
  • Trans-Neptunian Binaries and the History of the Outer Solar System, Gemini Observatory, 22 August 2011
  • A Highly-split Kuiper Belt Pair, Gemini Observatory, 28 October 2008
  • Kuiper belt pair sets record for long-distance relationship, New Scientist, 16 October 2008
  • 2001 QW322 at the JPL Small-Body Database
    • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters
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