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469705 ǂKá̦gára, provisional designation 2005 EF₂₉₈, is a trans-Neptunian object and binary system of the core Kuiper belt, located in the outermost region of the Solar System. It was discovered on 11 March 2005 by American astronomer Marc Buie at the Kitt Peak Observatory in Arizona.[1] The primary body measures perhaps 140 kilometers (90 miles) in diameter. Its ≈120-kilometer (75-mile) companion ǃHãunu was discovered with the Hubble Space Telescope in 2009. The ǂKá̦gára–ǃHãunu system is currently undergoing mutual occultation and eclipsing events in which one body casts its shadow upon or obstructs the view of the other.

469705 ǂKá̦gára

Stacked Hubble Space Telescope images of ǂKá̦gára and ǃHãunu
Discovery [1]
Discovered by	Marc Buie
Discovery site	Kitt Peak Obs.
Discovery date	11 March 2005
Designations
MPC designation	(469705) ǂKá̦gára
Pronunciation	English: /ˈkɑːʔɡɑːrə/ ǀXam: [ǂ͡káˤɡáɾa] (listen)
Named after	ǂKá̦gára (San mythology)[2]
Alternative designations	2005 EF298
Minor planet category	Cold classical KBO[2]
Orbital characteristics[3][1]
Epoch (JD 2458600.5)
Uncertainty parameter 3
Observation arc	10.10 yr (3688 d)
Aphelion	44.058 AU
Perihelion	40.013 AU
Semi-major axis	44.081 AU
Eccentricity	0.085
Orbital period (sidereal)	292.45 yr (106744.25 d)
Mean anomaly	118.059°
Mean motion	0.00337 0° 0m 0s / day
Inclination	1.60°
Longitude of ascending node	118.059°
Argument of perihelion	77.966°
Known satellites	1[4]
Physical characteristics
Mean diameter	138+21 −25 km, assuming same albedo as ǃHãunu
Mass	(1.29±0.07)×1018 kg, assuming same density and albedo as ǃHãunu
Mean density	1.1+0.9 −0.4 g/cm3, assuming equal compositions of the bodies
Absolute magnitude (H)	HV = 6.2±0.5

Names

The names ǂKá̦gára and ǃHãunu are from the mythology of the ǀXam people of South Africa. ǂKá̦gára (also rendered ǂKaʻgara) and his brother-in-law ǃHãunu fought an epic battle in the east using thunder and lightning, producing mountainous clouds and rain. The conflict was over ǂKá̦gára's returning his younger sister, ǃHãunu's wife, to their parents.[2][5] The names were approved and an official naming citation was published on 16 June 2021, by the IAU's Working Group on Small Body Nomenclature.[6]

In the ǀXam language, the names are thought to have been pronounced [ǂ͡káˤɡáɾa] (listen)[Note 1] and [ᵑ̊ǃʰəunu] (listen),[Note 2] respectively.[7] The initial letters ǂK and !H (and indeed the letter ǀX in 'ǀXam') represent some of the many click consonants that characterize ǀXam and other San languages. The diacritic under or after the first 'a' in ǂKá̦gára/ǂKaʻgara indicates that it is a pharyngealized vowel, which are also characteristic of San languages. Usually, when speaking English, the click consonants in words from ǀXam and other San languages are simply ignored (much as Xhosa is pronounced /ˈkoʊzə/ (KOH-zə) rather than [ǁʰosa]), resulting in /ˈkɑːʔɡɑːrə/ (KAHʼ-gar-ə) and /ˈhaʊnuː/ (HOW-noo). ASCII approximations of the names are =Ka'gara (or =Kagara, #Kagara, etc.) and !Haunu.

Orbit and occultations

ǂKá̦gára is a cold classical Kuiper belt object. It orbits the Sun at a distance of 44 AU once every 290 years. Its orbit has an eccentricity of 0.09 and an inclination of 3° with respect to the ecliptic.[3]

If the two bodies are spheres with equal density, then mutual occultation events between ǂKá̦gára and its satellite ǃHãunu should have begun in 2015 and should continue until 2035. When ǂKá̦gára passes in front of ǃHãunu, events may last as long as 8 hours, but when ǃHãunu passes in front of ǂKá̦gára, they are expected to last as long as 2 days. These latter events are only expected to occur from 2022 to 2027.[2]

Formation

Prograde orbits dominate tight binary systems such as 469705 ǂKá̦gára, those with satellite semimajor axes less than about 5% of their Hill radii. Grundy et al. suggest that this could be "the signature of planetesimal formation through gravitational collapse of local density enhancements such as caused by the streaming instability",[2] which has been suggested as the formative mechanism of the only visited planetesimal, 486958 Arrokoth.

Satellite, size and mass

ǃHãunu

Discovery
Discovery date	2009
Designations
Pronunciation	English: /ˈhaʊnuː/ ǀXam: [ᵑ̊ǃʰəunu] (listen)
Named after	ǃHãunu (San mythology)[2]
Alternative names	ǂKá̦gára I S/2009 (2005 EF298) 1
Orbital characteristics[2][8][4]
Semi-major axis	7670±140 km
Eccentricity	0.694±0.013
Orbital period (sidereal)	128.107±0.027 d (prograde)
Inclination	33.33°±0.41° ref'd to J2000 equatorial frame 11.17°±0.41° to heliocentric orbit
Physical characteristics
Mean diameter	122+16 −19 km, assuming same albedo as ǂKá̦gára
Mass	(0.89±0.05)×1018 kg, assuming same density and albedo as ǂKá̦gára
Apparent magnitude	ΔH = 0.59

469705 ǂKá̦gára has one known satellite, ǃHãunu. The magnitude difference between ǂKá̦gára and ǃHãunu is 0.59 mag. This corresponds to a difference in diameter of 13%, if the two bodies have the same albedo.[2]

The system mass is (2.18±0.12)×10¹⁸ kg, and, given the albedo, the bodies are equivalent to a single sphere of diameter 174+27
−32 km. This corresponds to a density of 1.1+0.9
−0.4 g/cm³. This does not particularly constrain the composition of the bodies, as the error bars cover the densities of both small, porous bodies and larger, collapsed bodies. (See 229762 Gǃkúnǁʼhòmdímà for discussion.) Assuming the two bodies have the same albedo and density, their masses are (1.29±0.07)×10¹⁸ kg and (0.89±0.05)×10¹⁸ kg, and their diameters are 138+21
−25 km and 122+16
−19 km.[2]

Notes

References

External links

• Asteroids with Satellites, Johnston's Archive
• List of Known Trans-Neptunian Objects, Johnston's Archive
• List of Transneptunian Objects, Minor Planet Center
• 469705 ǂKá̦gára at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters
• 469705 ǂKá̦gára at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info

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