Astronomy:229762 Gǃkúnǁʼhòmdímà

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229762 Gǃkúnǁʼhòmdímà 24px (astrological)
Gǃkúnǁʼhòmdímà and its satellite Gǃòʼé ǃHú, imaged by the Hubble Space Telescope on 2 January 2018
Discovery[1][2][3]
Discovered byM. E. Schwamb
M. E. Brown
D. L. Rabinowitz
Discovery sitePalomar Obs.
Discovery date19 October 2007
Designations
(229762) Gǃkúnǁʼhòmdímà
Pronunciation
Named afterGǃkúnǁʼhòmdímà[4]
(San mythology)
2007 UK126
Minor planet category
Orbital characteristics[5]
Epoch 5 May 2025 (JD 2460800.5)
Uncertainty parameter 1
Observation arc42.52 yr (15,529 d)
Earliest precovery date16 August 1982
|{{{apsis}}}|helion}}111.57 AU (16.691 Tm)
|{{{apsis}}}|helion}}37.600 AU (5.6249 Tm)
74.58 AU (11.157 Tm)
Eccentricity0.4959
Orbital period644.12 yr (235265±9 d)
Mean anomaly348.466°
Mean motion0° 0m 5.509s / day
Inclination23.3389°
Longitude of ascending node131.2214°
|{{{apsis}}}|helion}}23 December 2045
345.856°
Known satellites1 (Gǃòʼé ǃHú)[8]
Physical characteristics
Dimensions658+8
−6 × 658+8
−6 × 588+22
−20 km[9]
Mean diameter634+10
−8 km[9]
Flattening0.105+0.05
−0.04[10]
0.118+0.055
−0.048[10]
Mass(1.361±0.033)×1020 kg[4] (total system mass)
Mean density1.007+0.050
−0.049 g/cm3[9]
Rotation periodpossibly 11.05 h,[11] within 11 to 41 hours[4]
Geometric albedo0.142±0.015[12]
0.150±0.016[13]
Physics50–55 K max.[13]
44.4 K (perihelion)[14]: 11 
Apparent magnitude20.8[3]
Absolute magnitude (H)3.45[2]


229762 Gǃkúnǁʼhòmdímà (provisional designation 2007 UK126) is a large binary trans-Neptunian object and dwarf planet candidate in the scattered disc, located in the outermost region of the Solar System.[17] It was discovered on 19 October 2007 by American astronomers Megan Schwamb, Michael Brown, and David Rabinowitz at the Palomar Observatory in California.[1]

Gǃkúnǁʼhòmdímà measures approximately 600 kilometers (400 miles) in diameter. This medium-sized TNO appears to be representative of a class of mid-sized objects under approximately 1000 km that have not collapsed into fully solid bodies. Its 100-kilometer moon was discovered by Keith Noll, Will Grundy, and colleagues with the Hubble Space Telescope in 2008,[18][7][8][19] and named Gǃòʼé ǃHú.

History

Discovery

Template:Section needs expansion Gǃkúnǁʼhòmdímà was discovered on 19 October 2007 by American astronomers Megan Schwamb, Michael Brown, and David Rabinowitz at the Palomar Observatory in California.[1]

Numbering, naming and provisional designation

When the discovery of Gǃkúnǁʼhòmdímà was announced on 26 February 2008, the Minor Planet Center (MPC) gave the object the provisional designation 2007 UK126, which indicates its discovery date.[3] The MPC later gave it the minor planet catalog number of 229762 on 31 December 2009.[20] The International Astronomical Union's Small Bodies Nomenclature Committee officially named the object Gǃkúnǁʼhòmdímà and its moon Gǃòʼé ǃHú on 6 April 2019.[4][21]

The name Gǃkúnǁʼhòmdímà is from the Juǀʼhoansi (ǃKung) people of Namibia. In Juǀʼhoan mythology, G!kúnǁ'hòmdímà appears as an aardvark defending her people using gǁámígǁàmì spines,[lower-alpha 1] hail, and her oryx horn.[4] The name is composed of gǃkún 'aardvark', ǁʼhòm mà 'young woman' and the feminine suffix dí. The moon Gǃòʼé ǃHú is named after her horn; it means simply gǃòʼé 'oryx' ǃhú 'horn'.[22]

In the Juǀʼhoan language, the primary and moon names are pronounced ktz and ktz, respectively. Usually, when speaking English, the click consonants in words from Juǀʼhoan and other San languages are simply ignored (much as Xhosa is pronounced /ˈkoʊzə/ (KOH-zə) rather than xho), resulting in /ˌɡuːnhoʊmˈdiːmə/ (GOON-hohm-DEE-mə) for Gǃkúnǁʼhòmdímà and /ˌɡoʊ.eɪˈhuː/ (GOH-ay-HOO) or /ˌɡoʊ.eɪˈkuː/ (GOH-ay-KOO) for Gǃòʼé ǃHú.

ASCII renderings of the names would be ⟨G!kun||'homdima⟩ or ⟨G!kun//'homdima⟩ for the object and ⟨G!o'e !Hu⟩ or ⟨G!o'e!hu⟩ for the moon.[23]

The usage of planetary symbols is now discouraged in astronomy by the International Astronomical Union,[24] so Gǃkúnǁʼhòmdímà never received a symbol in the astronomical literature. There is no standard symbol for Gǃkúnǁʼhòmdímà used by astrologers either. An aardvark's head (16px) has been used.[25]

Orbit and classification

Orbital characteristics and observations

Gǃkúnǁʼhòmdímà orbits the Sun at a distance of 37.5–107.9 AU once every 620 years and 2 months (226,517 days; semi-major axis of 72.72 AU). Its orbit has an eccentricity of 0.48 and an inclination of 23° with respect to the ecliptic.[5]

An eccentricity of 0.48 suggests that it was gravitationally scattered into its current eccentric orbit. It will come to perihelion in February 2046, and mutual occultation events with its satellite will begin in late 2050 and last most of that decade.[4] It has a bright absolute magnitude of 3.45,[2] and has been observed 178 times over 16 oppositions with precovery images back to August 1982.[5]

Classification

Gǃkúnǁʼhòmdímà belongs to the scattered disc.[1] The scattered disc is a population of TNOs that have distant, eccentric, and inclined orbits that come close to Neptune at perihelion.[lower-alpha 2]

Scattered disc objects such as the dwarf planets Eris and Gonggong and the large trans-Neptunian object Chiminigagua, are strongly influenced by Neptune's gravitational perturbations and consequently experience gravitational scattering.[27]: 52 

Both the Minor Planet Center (MPC) and Johnston's Archive classify Gǃkúnǁʼhòmdímà as a scattered disc object.[1][7][8]

Physical characteristics

Size, mass, density and shape

Stellar occultation events indicate that Gǃkúnǁʼhòmdímà has an effective (equivalent-sphere) diameter of 600–670 km, but is not spherical. Due to complications from its non-spherical shape, the rotational period cannot be definitely determined from current light-curve data, which has an amplitude of Δm = 0.03 ± 0.01 mag, but the simplest solution is 11.05 hours.[11] It is almost certainly between that and 41 hours. The system mass is (1.36±0.03)×1020 kg, about 2% that of Earth's moon and a bit more than Saturn's moon Enceladus. The geometric albedo of Gǃkúnǁʼhòmdímà is approximately 0.15, and its bulk density is approximately 1 g/cm3.[4] The satellite Gǃòʼé ǃHú is unlikely to comprise more than 1% or so of the total.

Unlikely dwarf planet

Grundy et al. propose that the low density and albedo of Gǃkúnǁʼhòmdímà, combined with the fact that TNOs both larger and smaller – including comets – have a substantial fraction of rock in their composition, indicate that objects in the size range of 400–1000 km, such as Gǃkúnǁʼhòmdímà and 55637 Uni, retain a degree of porosity in their physical structure, having never collapsed and differentiated into planetary bodies like higher density or higher albedo (and thus presumably resurfaced) Orcus and Quaoar, or at best are only partially differentiated; such objects would never have been in hydrostatic equilibrium and would not be dwarf planets at present.[4]

Surface and spectra

In visible light, the surface of Gǃkúnǁʼhòmdímà appears moderately red (color class IR or RR) with a geometric albedo of about 0.15.[13]: 1, 3  In near-infrared, however, its reflectance drops at longer wavelengths—a characteristic more typical of bluer TNOs (color class BB or BR) than moderately red ones.[13]: 3  Because of this, Gǃkúnǁʼhòmdímà does not neatly fall within these four categories of TNO colors.[13]: 3  Rather, it shares its outlying colors with some TNOs, namely (26375) 1999 DE9 and 145452 Ritona.[16]: 5 

Near-infrared spectroscopy by the James Webb Space Telescope (JWST) has shown that Gǃkúnǁʼhòmdímà's surface is composed of water ice, carbon dioxide (CO2) ice, carbon monoxide (CO) ice, and various organic compounds (tholins).[15]: 234 [14]: 11  This composition is shared among CO2-type (aka "double-dip") TNOs,[lower-alpha 3] which are commonly found on dynamically excited orbits such as those in the scattered disc (where Gǃkúnǁʼhòmdíma resides).[15]: 234, 236 

Satellite

Gǃòʼé ǃHú
Discovery
Discovered byNoll et al.[18]
Discovery date2008
Designations
Designation
(229762) Gǃkúnǁʼhòmdímà I
PronunciationEnglish:/ˌɡoʊ.eɪˈkuː/
Juǀʼhoan: ktz
Orbital characteristics[4]
6000±12 km
Eccentricity0.0236±0.0066
Orbital period11.31473±0.00016 d (prograde)
Inclination43.75°±0.38° (to J2000 equatorial frame)
Physical characteristics
Mean diameter142±8 km[4]
Spectral type
V–I = 1.803±0.084[4]


Gǃkúnǁʼhòmdímà has one known satellite, Gǃòʼé ǃHú, which is one of the reddest known TNOs.[4] Size and mass can only be inferred. The magnitude difference between the two is 3.24±0.04 mag. This would correspond to a difference in diameter by a factor of 4.45±0.08, assuming the same albedo.[4] Red satellites often have lower albedos than their primaries, though it is not known if that is the case with this moon. Such uncertainties do not affect density calculations of Gǃkúnǁʼhòmdímà, as Gǃòʼé ǃHú has only about 1% the total volume, and therefore is less important than the uncertainties in Gǃkúnǁʼhòmdímà's diameter.[4]

See also

  • 55637 Uni – mid-sized Kuiper belt object with a moon and a very low density of 0.82 g/cm3, similar to Gǃkúnǁʼhòmdímà[4]
  • 532037 Chiminigagua – large scattered disc object (≈740 km diameter) with a moon

Notes

  1. ↑ Gǁámígǁàmì is a spiny plant, variously identified, including as Tribulus terrestris 'Devil's-thorn'.
  2. ↑ Neptune's orbit is at 30 AU[26]
  3. ↑ The "double-dip" TNO spectral type were later renamed to the "CO2-type" in 2025.[28]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 "(229762) Gǃkúnǁʼhòmdímà = 2007 UK126". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?object_id=229762. 
  2. ↑ 2.0 2.1 2.2 2.3 "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. https://www.minorplanetcenter.net/iau/lists/t_centaurs.html. 
  3. ↑ 3.0 3.1 3.2 Schwamb, M. E.; Brown, M. E.; Rabinowitz, D.; Marsden, B. G. (February 2008). "2007 UK126". Minor Planet Electronic Circular 2008-D38 (2008-D38 (2008)). Bibcode: 2008MPEC....D...38S. https://minorplanetcenter.net//mpec/K08/K08D38.html. Retrieved 25 December 2018. 
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 Grundy, W. M.; Noll, K. S.; Buie, M. W.; Benecchi, S. D.; Ragozzine, D.; Roe, H. G. (December 2019). "The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)". Icarus 334: 30–38. doi:10.1016/j.icarus.2018.12.037. Bibcode: 2019Icar..334...30G. http://www2.lowell.edu/users/grundy/abstracts/preprints/2019.G-G.pdf. 
  5. ↑ 5.0 5.1 5.2 5.3 "JPL Small-Body Database Browser: 229762 G!kunll'homdima (2007 UK126)". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2229762. 
  6. ↑ Marc W. Buie (8 May 2012). "Orbit Fit and Astrometric record for 229762". SwRI (Space Science Department). http://www.boulder.swri.edu/~buie/kbo/astrom/229762.html. 
  7. ↑ 7.0 7.1 7.2 Johnston, Wm. Robert (7 October 2018). "List of Known Trans-Neptunian Objects". Johnston's Archive. http://www.johnstonsarchive.net/astro/tnoslist.html. 
  8. ↑ 8.0 8.1 8.2 Johnston, Wm. Robert (20 September 2014). "Asteroids with Satellites Database – (229762) Gǃkunǁʼhomdima and GǃoʼeǃHu". Johnston's Archive. http://www.johnstonsarchive.net/astro/astmoons/am-229762.html. 
  9. ↑ 9.0 9.1 9.2 Proudfoot, Benjamin; Grundy, Will; Rommel, Flavia Luane; Fernández-Valenzuela, Estela; Ragozzine, Darin (2026-05-27). "Triaxial shapes and densities of G!kún||'hòmdímà, Haumea, and Varda from stellar occultations". The Planetary Science Journal. 
  10. ↑ 10.0 10.1 Benedetti-Rossi, G.; Sicardy, B.; Buie, M. W.; Ortiz, J. L.; Vieira-Martins, R.; Keller, J. M. et al. (December 2016). "Results from the 2014 November 15th Multi-chord Stellar Occultation by the TNO (229762) 2007 UK126". The Astronomical Journal 152 (6): 11. doi:10.3847/0004-6256/152/6/156. Bibcode: 2016AJ....152..156B. 
  11. ↑ 11.0 11.1 Thirouin, A.; Noll, K. S.; Ortiz, J. L.; Morales, N. (1 September 2014). "Rotational properties of the binary and non-binary populations in the trans-Neptunian belt" (in en). Astronomy & Astrophysics 569: A3. doi:10.1051/0004-6361/201423567. Bibcode: 2014A&A...569A...3T. 
  12. ↑ Ortiz, Sicardy, Camargo & Braga-Ribas (2019). "Stellar Occultations by Transneptunian Objects: From Predictions to Observations and Prospects for the Future". in Prialnik, Barucci & Young. The Transneptunian Solar System. Elsevier. 
  13. ↑ 13.0 13.1 13.2 13.3 13.4 13.5 Schindler, K.Expression error: Unrecognized word "etal". (April 2017). "Results from a triple chord stellar occultation and far-infrared photometry of the trans-Neptunian object (229762) 2007 UK126". Astronomy and Astrophysics 600: 16. doi:10.1051/0004-6361/201628620. Bibcode: 2017A&A...600A..12S. https://www.aanda.org/articles/aa/pdf/2017/04/aa28620-16.pdf. Retrieved 25 December 2018. 
  14. ↑ 14.0 14.1 14.2 Brunetto, R.Expression error: Unrecognized word "etal". (March 2025). "Spectral Diversity of DiSCo's TNOs Revealed by JWST: Early Sculpting and Late Irradiation". The Astrophysical Journal Letters 982 (1): L8. doi:10.3847/2041-8213/adb977. Bibcode: 2025ApJ...982L...8B. 
  15. ↑ 15.0 15.1 15.2 Pinilla-Alonso, Noemí et al. (December 2024). "A JWST/DiSCo-TNOs portrait of the primordial Solar System through its trans-Neptunian objects". Nature Astronomy 9 (2): 230–244. doi:10.1038/s41550-024-02433-2. Bibcode: 2025NatAs...9..230P. 
  16. ↑ 16.0 16.1 Perna, D.Expression error: Unrecognized word "etal". (February 2010). "Colors and taxonomy of Centaurs and trans-Neptunian objects". Astronomy and Astrophysics 510: A53. doi:10.1051/0004-6361/200913654. Bibcode: 2010A&A...510A..53P. https://www.aanda.org/articles/aa/pdf/2010/02/aa13654-09.pdf. 
  17. ↑ Minor Planet Center (6 April 2019). "MPC 112429-112436". MPC/MPO/MPS Archive. https://www.minorplanetcenter.net/iau/ECS/MPCArchive/2019/MPC_20190406.pdf. 
  18. ↑ 18.0 18.1 Noll, Keith S.; Grundy, W. M.; Benecchi, S. D.; Levison, H. F.; Barker, E. A. (2009). "Discovery of Eighteen Transneptunian Binaries". Bulletin of the American Astronomical Society 41: 1092. Bibcode: 2009DPS....41.4707N. 
  19. ↑ Brown, Michael E.. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. http://web.gps.caltech.edu/~mbrown/dps.html. 
  20. ↑ "M.P.C. 67989". Minor Planet Circulars (Minor Planet Center) (114692): 95. 31 December 2009. https://www.minorplanetcenter.net/iau/ECS/MPCArchive/2009/MPC_20091231.pdf#page=95. Retrieved 14 August 2025. 
  21. ↑ "M.P.C. 112430". Minor Planet Circulars (Minor Planet Center) (112430): 2. 16 April 2019. https://minorplanetcenter.net/iau/ECS/MPCArchive/2019/MPC_20190406.pdf#page=2. Retrieved 14 August 2025. 
  22. ↑ Patrick Dickens: English–Juǀʼhoan – Juǀʼhoan–English dictionary, Rüdiger Köppe Verlag, Köln 1994, ISBN 978-3-89645-868-1.
  23. ↑ Minor Planet Names: Alphabetical List
  24. ↑ The IAU Style Manual. 1989. p. 27. http://www.iau.org/static/publications/stylemanual1989.pdf. 
  25. ↑ Miller, Kirk (26 October 2021). "Unicode request for dwarf-planet symbols". https://www.unicode.org/L2/L2021/21224-dwarf-planet-syms.pdf. 
  26. ↑ Yeomans, Donald K.. "HORIZONS Web-Interface for Neptune Barycenter (Major Body=8)". JPL Horizons On-Line Ephemeris System. https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%278%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%272000-01-01%27&STOP_TIME=%272000-01-02%27&STEP_SIZE=%27200%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27. —Select "Ephemeris Type: Orbital Elements", "Time Span: 2000-01-01 12:00 to 2000-01-02". ("Target Body: Neptune Barycenter" and "Center: Solar System Barycenter (@0)".)
  27. ↑ Gladman, Brett; Marsden, Brian G.; VanLaerhoven, Christa (2008). "Nomenclature in the Outer Solar System". The Solar System Beyond Neptune. University of Arizona Press. pp. 43–57. ISBN 9780816527557. Bibcode: 2008ssbn.book...43G. https://www.lpi.usra.edu/books/ssbn2008/7002.pdf. 
  28. ↑ Holler, Bryan J. et al. (September 2025). "A Descriptive Taxonomic Nomenclature for Intermediate-sized Trans-Neptunian Object Spectra". Research Notes of the American Astronomical Society 9 (9): 241. doi:10.3847/2515-5172/ae03a2. Bibcode: 2025RNAAS...9..241H. 




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