229762 Gǃkúnǁʼhòmdímà

229762 Gǃkúnǁʼhòmdímà, provisional designation 2007 UK126, is a trans-Neptunian object and binary system from the extended scattered disc, located in the outermost region of the Solar System.[13] It was discovered on 19 October 2007 by American astronomers Megan Schwamb, Michael Brown, and David Rabinowitz at the Palomar Observatory in California[1] and 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,[14][7][8][15] and named Gǃòʼé ǃHú.

Gǃkúnǁʼhòmdímà
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
PronunciationEnglish: /ˌɡuːnhoʊmˈdiːmə/
Juǀʼhoan: [ᶢᵏǃ͡χʼṹᵑ̊ǁʰòmdímà] (listen)
Named after
Gǃkúnǁʼhòmdímà [4]
(San mythology)
2007 UK126
TNO [5] · Scat-ext [6]
SDO [2][7] · distant [1]
Orbital characteristics [5]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 2
Observation arc36.16 yr (13,209 d)
Earliest precovery date1982
Aphelion108.058 AU (16.1652 Tm)
Perihelion37.5449328 AU (5.61664200 Tm)
72.8013046 AU (10.89092015 Tm)
Eccentricity0.4843
620.17 yr (226,517 d)
344.21°
0° 0m 5.76s / day
Inclination23.378°
131.09°
346.88°
Known satellites1[8]
Physical characteristics
Dimensions678.0±11 × 611.4±18 km occultation[9]
Mean diameter
642±28[9]
599–629 km[10]
638+24
−12 km sphere-equivalent (elliptical fit)[11]
Flattening0.105+0.05
−0.04[11]
0.118+0.055
−0.048[11]
Mass(1.361±0.033)×1020 kg[4](total system mass)
Mean density
1.04±0.17 g/cm3, based on an effective diameter of 632±34 km[4]
possibly 11.05 h,[12] within 11 to 41 hours[4]
0.142±0.015[9]
0.150±0.016[10]
0.159+0.007
−0.013[11]
Temperature50–55 K max.[10]
20.8[3]
HV= 3.69 ± 0.04;
HR= 3.07 ± 0.04[10]

    Names

    The name Gǃkúnǁʼhòmdímà is from the Juǀʼhoansi (ǃKung) people of Namibia. Gǃkúnǁʼhòmdímà is the beautiful aardvark girl of Juǀʼhoan mythology, who sometimes appears in the stories of other San peoples as a python girl or elephant girl; she defends her people and punishes wrongdoers using gǁámígǁàmì spines,[16] a rain-cloud full of hail, and her magical oryx horn.[4] The name "Gǃkúnǁʼhòmdímà" derives from gǃkún 'aardvark', ǁʼhòm mà 'young woman' and the feminine suffix dí. The moon Gǃòʼé ǃHú is named after her horn: it means simply 'oryx' (gǃòʼé) 'horn' (ǃhú).[17]

    In the Juǀʼhoan language, the planet and moon names are pronounced [ᶢᵏǃ͡χʼṹ ᵑ̊ǁʰòmdí mà] (listen) and [ᶢǃòˀé ǃʰú] (listen), 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 [ǁʰosa]), resulting in /ˌɡuːnhoʊmˈdiːmə/ (GOON-hohm-DEE-mə) and /ˌɡoʊ.eɪˈhuː/ (GOH-ay-HOO) or /ˌɡoʊ.eɪˈkuː/ (GOH-ay-KOO).

    ASCII renderings of the names would be ⟨G!kun||'homdima⟩ (or ⟨G!kun//'homdima⟩) for the primary and ⟨G!o'e !Hu⟩ or ⟨G!o'e!hu⟩ for the secondary.[18]

    Orbit

    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 July 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 3.7,[2] and has been observed 178 times over 16 oppositions with precovery images back to 1982.[5]

    Physical characteristics

    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,[12] but the simplest solution is 11.05 hours. 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 moon is unlikely to comprise more than 1% or so of the total. Its geometric albedo is approximately 0.15, and its density approximately 1.[4]

    As of June 2018, Mike Brown lists it as highly likely to be a dwarf planet, due to its size.[15] However, Grundy et al. propose that the low density and albedo, combined with the fact that TNOs both larger and smaller – including comets – have a substantial fraction of rock in their composition, indicate that it and similar objects such as 174567 Varda and 120347 Salacia (in the size range of 400–1000 km, with albedos less than ≈0.2 and densities of ≈1.2 g/cm3 or less) may retain a degree of porosity in their physical structure, having never collapsed and possibly differentiated into planetary bodies like higher density or higher albedo (and presumably resurfaced) 90482 Orcus and 50000 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]

    Satellite
    Gǃòʼé ǃHú
    Discovery
    Discovered byNoll et al.[14]
    Discovery date2008
    Designations
    Designation
    		(229762) Gǃkúnǁʼhòmdímà I Gǃòʼé ǃHú
    PronunciationEnglish:/ˌɡoʊ.eɪˈkuː/
    Juǀʼhoan: [ᶢǃòˀéǃʰú] (listen)
    Orbital characteristics[4]
    6035±48 km
    Eccentricity0.0236±0.0066
    11.31473±0.00016 d (prograde)
    Inclination43.75°±0.38° (to J2000 equatorial frame)
    Physical characteristics
    Equatorial radius
    		71±4 km[4]

    Gǃkúnǁʼhòmdímà has one known satellite, Gǃòʼé ǃHú, which is one of the reddest known TNOs. Size and mass can only be inferred. The magnitude difference between the two is 3.242±0.039 mag. This would correspond to a difference in diameter of a factor of 4.45±0.08, assuming the same albedo. Red satellites often have lower albedos than their primaries, but that may not be the case with this moon. Such uncertainties do not affect density calculations as the moon has only about 1% the total volume, and so is less important than the uncertainties in the primary's diameter.[4]

    See also

    References
    1. "229762 (2007 UK126)". Minor Planet Center. Retrieved 25 December 2018.
    2. "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 25 December 2018.
    3. 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. Retrieved 25 December 2018.
    4. Grundy, W.M.; Noll, K.S.; Buie, M.W.; Benecchi, S.D.; Ragozzine, D.; Roe, H.G. (December 2018). "The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)" (PDF). Icarus. 334: 30–38. doi:10.1016/j.icarus.2018.12.037. Archived from the original on 7 April 2019. Retrieved 12 August 2019.
    5. "JPL Small-Body Database Browser: 229762 G!kunll'homdima (2007 UK126)" (2018-10-15 last obs.). Jet Propulsion Laboratory. Retrieved 25 December 2018.
    6. Marc W. Buie (8 May 2012). "Orbit Fit and Astrometric record for 229762". SwRI (Space Science Department). Retrieved 7 May 2012.
    7. Johnston, Wm. Robert (7 October 2018). "List of Known Trans-Neptunian Objects". Johnston's Archive. Retrieved 25 December 2018.
    8. Johnston, Wm. Robert (20 September 2014). "Asteroids with Satellites Database – (229762) G!kunll'homdima and G!o'e!Hu". Johnston's Archive. Retrieved 25 December 2018.
    9. Ortiz, Sicardy, Camargo & Braga-Ribas (2019). "Stellar Occultations by Transneptunian Objects: From Predictions to Observations and Prospects for the Future". In Prialnik, Barucci & Young (ed.). The Transneptunian Solar System. Elsevier. arXiv:1905.04335.CS1 maint: multiple names: authors list (link)
    10. Schindler, K.; Wolf, J.; Bardecker, J.; Olsen, A.; Müller, T.; Kiss, C.; et al. (April 2017). "Results from a triple chord stellar occultation and far-infrared photometry of the trans-Neptunian object (229762) 2007 UK126" (PDF). Astronomy and Astrophysics. 600: 16. arXiv:1611.02798. Bibcode:2017A&A...600A..12S. doi:10.1051/0004-6361/201628620. Retrieved 25 December 2018.
    11. 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. arXiv:1608.01030. Bibcode:2016AJ....152..156B. doi:10.3847/0004-6256/152/6/156.
    12. 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". Astronomy & Astrophysics. 569: A3. arXiv:1407.1214. Bibcode:2014A&A...569A...3T. doi:10.1051/0004-6361/201423567.
    13. Minor Planet Center (6 April 2019). "MPC 112429-112436" (PDF). MPC/MPO/MPS Archive. Retrieved 9 April 2019.
    14. 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.
    15. Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 25 December 2018.
    16. Gǁámígǁàmì is a spiny plant, variously identified, including as Tribulus terrestris 'Devil's-thorn'.
    17. Patrick Dickens: English–Juǀʼhoan – Juǀʼhoan–English dictionary, Rüdiger Köppe Verlag, Köln 1994, ISBN 978-3-89645-868-1.
    18. Minor Planet Names: Alphabetical List


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