229762 Gǃkúnǁʼhòmdímà

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229762 Gǃkúnǁʼhòmdímà
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 by M. E. Schwamb
M. E. Brown
D. L. Rabinowitz
Discovery site Palomar Obs.
Discovery date19 October 2007
Designations
(229762) Gǃkúnǁʼhòmdímà
Pronunciation
Named after
Gǃkúnǁʼhòmdímà [4]
(San mythology)
2007 UK126
Orbital characteristics [5]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 2
Observation arc 36.16 yr (13,209 d)
Earliest precovery date1982
Aphelion 108.058 AU (16.1652 Tm)
Perihelion 37.5449328 AU (5.61664200 Tm)
72.8013046 AU (10.89092015 Tm)
Eccentricity 0.4843
620.17 yr (226,517 d)
344.21°
0° 0m 5.76s / day
Inclination 23.378°
131.09°
≈ 24 February 2046 [8]
±1 days
346.88°
Known satellites 1 (Gǃòʼé ǃHú) [9]
Physical characteristics
Dimensions678.0±11 × 611.4±18 km occultation [10]
Mean diameter
642±28 [10]
599–629  km [11]
638+24
−12
 km
sphere-equivalent (elliptical fit) [12]
Flattening 0.105+0.05
−0.04
[12]
0.118+0.055
−0.048
[12]
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, [13] within 11 to 41 hours [4]
0.142±0.015 [10]
0.150±0.016 [11]
0.159+0.007
−0.013
[12]
Temperature 50–55 K max. [11]
V–R=0.62±0.05 [14]
V–I=1.028±0.027 [4]
20.8 [3]
HV=3.69±0.04;
HR=3.07±0.04 [11]

    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. [15] 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, [16] [7] [9] [17] and named Gǃòʼé ǃHú.

    Contents

    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, [18] 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 her horn: it means simply 'oryx' (gǃòʼé) 'horn' (ǃhú). [19]

    In the Juǀʼhoan language, the planetoid and moon names are pronounced [ᶢᵏǃ͡χʼṹ ᵑ̊ǁʰòmdí mà] ( Loudspeaker.svg listen ) and [ᶢǃòˀé ǃʰú] ( Loudspeaker.svg 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/ (GOH-ay-HOO) or /ˌɡ.ˈk/ (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. [20]

    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 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 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, [13] 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 geometric albedo of Gǃkúnǁʼhòmdímà is approximately 0.15, and its bulk density 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 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]

    Gǃkúnǁʼhòmdímà exhibits an unusual disparity of visible and near-infrared colors: it appears reddish at visible wavelengths (V–R=0.62) while it appears bluer in the near-infrared (V–I=1.09). Hence, it does not fall within the four proposed taxonomic classes for TNO colors. Two other TNOs, namely (26375) 1999 DE9 and (145452) 2005 RN43 , exhibit this same color behavior, implying an additional color group among TNOs. [14]

    Satellite

    Gǃòʼé ǃHú
    Discovery
    Discovered by Noll et al. [16]
    Discovery date2008
    Designations
    Designation
    (229762) Gǃkúnǁʼhòmdímà I Gǃòʼé ǃHú
    PronunciationEnglish: /ˌɡ.ˈk/
    Juǀʼhoan: [ᶢǃòˀéᵏǃʰú] ( Loudspeaker.svg listen )
    Orbital characteristics [4]
    6035±48 km
    Eccentricity 0.0236±0.0066
    11.31473±0.00016 d (prograde)
    Inclination 43.75°±0.38° (to J2000 equatorial frame)
    Physical characteristics
    Mean radius
    71±4 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. 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

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