229762 Gǃkúnǁʼhòmdímà

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229762 Gǃkúnǁʼhòmdímà
File:2007 UK126 Hubble (crop).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
(229762) Gǃkúnǁʼhòmdímà
Pronunciation
Named after
Gǃkúnǁʼhòmdímà[4]
(San mythology)
2007 UK126
SymbolFile:Gǃkunǁʼhomdima symbol (bold).svg (astrological)
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
Aphelion111.57 AU (16.691 Tm)
Perihelion37.600 AU (5.6249 Tm)
74.58 AU (11.157 Tm)
Eccentricity0.4959
644.12 yr (235265±9 d)
348.466°
0° 0m 5.509s / day
Inclination23.3389°
131.2214°
23 December 2045
345.856°
Known satellites1 (Gǃòʼé ǃHú)[8]
Physical characteristics
Dimensions678.0±11 × 611.4±18 km occultation[9]
642±28 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 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]
0.142±0.015[9]
0.150±0.016[12]
Temperature50–55 K max.[12]
20.8[3]
3.45

229762 Gǃkúnǁʼhòmdímà (provisional designation 2007 UK126) is a large binary trans-Neptunian object in the scattered disc, located in the outermost region of the Solar System.[16] 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,[17][7][8][18] and named Gǃòʼé ǃHú.

Names

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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.[19] The International Astronomical Union's Small Bodies Nomenclature Committee officially named the object Gǃkúnǁʼhòmdímà and its moon Gǃòʼé ǃHú on 6 April 2019.[4][20]

The name Gǃkúnǁʼhòmdímà is from the Juǀʼhoansi (ǃKung) people of Namibia. In Juǀʼhoan mythology, G!kún||'hòmdímà appears as an aardvark defending her people using gǁámígǁàmì spines,[a] 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'.[21]

In the Juǀʼhoan language, the primary and moon names are pronounced [ᶢᵏǃ͡χʼṹ ᵑ̊ǁʰòmdí mà] <phonos file="Gǃkunǁ'homdima.ogg"></phonos> and [ᶢǃòˀé ǃʰú] Audio file "Gǃo'e ǃHu.ogg" not found, 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) 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.[22]

The usage of planetary symbols is now discouraged in astronomy, 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 (File:Gǃkunǁʼhomdima symbol.svg) has been used.[23]

Orbit

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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] It is a scattered-disc object.[1]

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

Physical characteristics

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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.

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 such as Gǃkúnǁʼhòmdímà and 174567 Varda (in the size range of 400–1000 km, with albedos less than ≈0.2 and densities of ≈1.2 g/cm3 or less) 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) 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]

Surface

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In visible light, the surface of Gǃkúnǁʼhòmdímà appears moderately red (color class IR or RR) with a geometric albedo of about 0.15.[12]: 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.[12]: 3  Because of this, Gǃkúnǁʼhòmdímà does not neatly fall within these four categories of TNO colors.[12]: 3  Rather, it shares its outlying colors with some TNOs, namely (26375) 1999 DE9 and 145452 Ritona.[15]: 5 

Near-infrared spectroscopy by the James Webb Space Telescope (JWST) has shown that Gǃkúnǁʼhòmdímà's surface is composed of water ice, carbon dioxide (CO
2) ice, carbon monoxide (CO) ice, and various organic compounds (tholins).[13]: 234 [14]: 11  This composition is shared among CO
2-type (aka "double-dip") TNOs,[b] which are commonly found on dynamically excited orbits such as those in the scattered disc (where Gǃkúnǁʼhòmdíma resides).[13]: 234, 236 

Satellite

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Gǃòʼé ǃHú
Discovery
Discovered byNoll et al.[17]
Discovery date2008
Designations
Designation
(229762) Gǃkúnǁʼhòmdímà I
PronunciationEnglish:/ˌɡoʊ.eɪˈkuː/
Juǀʼhoan: [ᶢǃòˀéᵏǃʰú] Audio file "Gǃo'e ǃHu.ogg" not found
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
142±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

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  • 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

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  1. ^ Gǁámígǁàmì is a spiny plant, variously identified, including as Tribulus terrestris 'Devil's-thorn'.
  2. ^ The "double-dip" TNO spectral type were later renamed to the "CO
    2    -type" in 2025.[24]

References

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  1. ^ a b c d Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  2. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  3. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  4. ^ a b c d e f g h i j k l m n o p q Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  5. ^ a b c d Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  6. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  7. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  8. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  9. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  10. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  11. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  12. ^ a b c d e f Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  13. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  14. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  15. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  16. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  17. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  18. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  19. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  20. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  21. ^ Patrick Dickens: English–Juǀʼhoan – Juǀʼhoan–English dictionary, Rüdiger Köppe Verlag, Köln 1994, Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value)..
  22. ^ Minor Planet Names: Alphabetical List
  23. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  24. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).


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