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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.[12] 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, and is representative of mid-sized objects under approximately 1000 km that do not appear to have collapsed into fully solid bodies. Its 100-kilometer moon was discovered with the Hubble Space Telescope in 2008.[7][8][13]

Gǃkúnǁʼhòmdímà
2007 UK126 Hubble.png
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
MPC designation(229762) Gǃkúnǁʼhòmdímà
PronunciationEnglish: /ˌɡnhmˈdmə/
Juǀʼhoan: [ᶢᵏǃ͡χʼṹᵑ̊ǁʰòmdímà] (About this soundlisten)
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)
Aphelion107.94 AU
Perihelion37.502 AU
72.722 AU
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
Mean diameter
599–629 km[9]
sphere-equivalent (elliptical fit) 638+24
−12
 km
,[10]
Mass(1.361±0.033)×1020 kg[4]
Mean density
1.04±0.17 g/cm3, based on an effective diameter of 632±34 km[4]
possibly 11.05 h,[11] within 11 to 41 hours[4]
0.150±0.016[9]
0.159+0.007
−0.013
[10]
Temperature50–55 K max.[9]
20.8[3]
3.3[1][5]

Contents

NamesEdit

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,[14] 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 . The moon Gǃòʼé ǃHú is named after Gǃkúnǁʼhòmdímà's horn: gǃòʼé 'oryx', ǃhú 'horn'.[15]

In the Juǀʼhoan language, the 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 /ˈkzə/ (KOH-zə) rather than [ǁʰosa]), resulting in /ˌɡnhmˈdmə/ (GOON-hohm-DEE-mə) and /ˌɡ.ˈh/ or /ˌɡ.ˈk/ (GOH-ay-KOO). Ignoring the usage of click consonants and diacritics, the name is usually written as G!kunll'homdima, with the lateral click "ǁ" replaced with the digraph "ll".[5][12]

OrbitEdit

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 characteristicsEdit

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,[11] 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.[13] 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.[4]

SatelliteEdit

Gǃòʼé ǃHú
Discovery
Discovered byNoll et al.[16]
Discovery date2008
Designations
MPC designation(229762) Gǃkúnǁʼhòmdímà I Gǃòʼé ǃHú
PronunciationEnglish:/ˌɡ.ˈk/
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
≈ 70 km

It has one known satellite, Gǃòʼé ǃHú. It 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 volume, and so is less important than the uncertainties in the primary's diameter.[4]

See alsoEdit

ReferencesEdit

  1. ^ a b c d "229762 (2007 UK126)". Minor Planet Center. Retrieved 25 December 2018.
  2. ^ a b c "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 25 December 2018.
  3. ^ a b Schwamb, M. E.; Brown, M. E.; Rabinowitz, D.; Marsden, B. G. (February 2008). "2007 UK126". Minor Planet Electronic Circular (2008-D38 (2008)). Bibcode:2008MPEC....D...38S. Retrieved 25 December 2018.
  4. ^ a b c d e f g h i j W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D. Ragozzine & H.G. Roe, 'The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)', Icarus [1] doi: 10.1016/j.icarus.2018.12.037,
  5. ^ a b c d e f "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. ^ a b Johnston, Wm. Robert (7 October 2018). "List of Known Trans-Neptunian Objects". Johnston's Archive. Retrieved 25 December 2018.
  8. ^ a b 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. ^ a b c 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.
  10. ^ a b 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. Retrieved 25 December 2018.
  11. ^ a b 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.
  12. ^ a b Minor Planet Center (6 April 2019). "MPC 112429-112436" (PDF). MPC/MPO/MPS Archive. Retrieved 9 April 2019.
  13. ^ a b Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 25 December 2018.
  14. ^ Gǁámígǁàmì is a spiny plant, variously identified, including as Tribulus terrestris 'Devil's-thorn'.
  15. ^ Patrick Dickens (1994) English–Juǀʼhoan Juǀʼhoan–English dictionary, Köppe Verlag.
  16. ^ K.S. Noll, W.M. Grundy, S.D. Benecchi, H.F. Levison & E.A. Barker (2009) 'Discovery of eighteen transneptunian binaries', Bull. Amer. Astron. Soc. 41, 1092 (abstract)


External linksEdit