229762 Gǃkúnǁʼhòmdímà

229762 Gǃkúnǁʼhòmdímà

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 date	19 October 2007
Designations
MPC designation	(229762) Gǃkúnǁʼhòmdímà
Pronunciation	English: /ˌɡuːnhoʊmˈdiːmə/ Juǀʼhoan: [ᶢᵏǃ͡χʼṹᵑ̊ǁʰòmdímà] ⓘ
Named after	Gǃkúnǁʼhòmdímà[4] (San mythology)
Alternative designations	2007 UK126
Minor planet category	TNO[5] Scat-ext[6] SDO[2][7] distant[1]
Symbol	(astrological)
Orbital characteristics[5]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 2 · 3[1]
Observation arc	36.16 yr (13,209 d)
Earliest precovery date	16 August 1982[1]
Aphelion	108.058 AU (16.1652 Tm)
Perihelion	37.5449328 AU (5.61664200 Tm)
Semi-major axis	72.8013046 AU (10.89092015 Tm)
Eccentricity	0.4843
Orbital period (sidereal)	620.17 yr (226,517 d)
Mean anomaly	344.21°
Mean motion	0° 0m 5.76s / day
Inclination	23.378°
Longitude of ascending node	131.09°
Time of perihelion	≈ 24 February 2046[8] ±1 days
Argument of perihelion	346.88°
Known satellites	1 (Gǃòʼé ǃHú)[9]
Physical characteristics
Dimensions	678.0±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]
Synodic rotation period	possibly 11.05 h,[13] within 11 to 41 hours[4]
Geometric albedo	0.142±0.015[10] 0.150±0.016[11] 0.159+0.007 −0.013[12]
Temperature	50–55 K max.[11]
Spectral type	V–R=0.62±0.05[14] V–I=1.028±0.027[4]
Apparent magnitude	20.8[3]
Absolute magnitude (H)	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.

Names[edit]

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 dí. 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] ^ⓘ and [ᶢǃòˀé ǃʰú] ^ⓘ, 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.^[20]

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 () has been used.^[21]

Orbit[edit]

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[edit]

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.^[13] 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]

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[edit]

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[edit]

• Palomar Distant Solar System Survey (PDSSS)

References[edit]

External links[edit]

• Gǃkúnǁʼhòmdímà and Gǃòʼé ǃhú, Will Grundy, Lowell Observatory (Last updated: 24 Dec 2018)
• 2007 UK126 Precovery Images
• 3rd largest scattered disk object discovered (Yahoo Groups)
• 2007 UK126 Minor planet designation number
• 229762 Gǃkúnǁʼhòmdímà at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 229762 Gǃkúnǁʼhòmdímà at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters