469705 ǂKá̦gára
A binary Kuiper belt object with mutual occultation events.
469705 ǂKá̦gára, originally labeled 2005 EF298, is a binary system in the core Kuiper belt, a region at the solar system’s outer edge. American astronomer Marc Buie spotted it on March 11, 2005, using the Kitt Peak Observatory in Arizona. The system’s primary body is roughly 140 kilometers across, while its companion, ǃHãunu, spans about 120 kilometers and was detected by the Hubble Space Telescope in 2009. From Earth’s perspective, the two objects are currently undergoing mutual occultation and eclipsing events, where one blocks or casts a shadow on the other.
The names come from ǀXam mythology of South Africa. ǂKá̦gára (also written ǂKaʻgara) and his brother-in-law ǃHãunu fought an epic battle in the east, wielding thunder and lightning that created mountainous clouds and rain. The conflict started when ǂKá̦gára sent his younger sister—ǃHãunu’s wife—back to their parents. The International Astronomical Union’s Working Group on Small Body Nomenclature approved these names on June 16, 2021.
ǂKá̦gára is a cold classical Kuiper belt object. It circles the Sun at 44 AU, completing one orbit every 290 years, with an eccentricity of 0.09 and an inclination of 3 degrees relative to the ecliptic. If the two bodies are spheres of equal density, mutual occultations began in 2015 and will continue until 2035. When ǂKá̦gára passes in front of ǃHãunu, events can last up to 8 hours; when ǃHãunu passes in front of ǂKá̦gára, they may last up to two days, but these longer events are expected only from 2022 to 2027.
Tight binary systems like this one, where the satellite’s semimajor axis is less than about 5% of its Hill radius, tend to have prograde orbits. Grundy et al. suggest this could indicate formation via gravitational collapse of local density enhancements, such as those caused by the streaming instability—the same mechanism proposed for the only visited planetesimal, 486958 Arrokoth.
ǂKá̦gára’s sole known satellite is ǃHãunu. The magnitude difference between them is 0.59 mag, implying a 13% difference in diameter if both have the same albedo. The system’s total mass is (2.18±0.12)×10¹⁸ kg, equivalent to a single sphere 174+27−32 km in diameter, yielding a density of 1.1+0.9−0.4 g/cm³. This density range doesn’t strongly constrain composition, as it covers both small, porous bodies and larger, collapsed ones.
Quick Facts
- Minorplanet
- yes
- Background
- #C2E0FF
- Discoverer
- Marc Buie
- Discovery Site
- Kitt Peak Observatory
- Discovered
- 11 March 2005
- Mpc Name
- (469705) ǂKá̦gára
- Named After
- ǂKá̦gára (ǀXam mythology)
- Mp Category
- Cold classical KBO
- Epoch
- (JD 2460800.5)
- Uncertainty
- 2
- Observation Arc
- 19.91 yr (7271 d)
- Aphelion
- 47.884 AU
Facts from the source article.
Lore & Background
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 fought over ǂKá̦gára returning his younger sister, ǃHãunu's wife, to their parents. The names were approved and an official naming citation was published on 16 June 2021 by the International Astronomical Union's Working Group on Small Body Nomenclature.
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 degrees with respect to the ecliptic. 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.
Prograde orbits dominate tight binary systems such as 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', which has been suggested as the formative mechanism of the only visited planetesimal, 486958 Arrokoth.
Reader's Guide
The ǂKá̦gára–ǃHãunu system is significant as a rare example of a binary trans-Neptunian object undergoing mutual occultation and eclipsing events observable from Earth. These events, which began in 2015 and are expected to continue until 2035, allow precise measurement of the bodies' sizes, orbits, and densities. The system's mass is (2.18±0.12)×10^18 kg, with a density of 1.1+0.9−0.4 g/cm³, which does not particularly constrain composition, as error bars cover densities of both small porous bodies and larger collapsed bodies. The magnitude difference between the two bodies is 0.59 mag, corresponding to a 13% difference in diameter if albedos are equal. The system's prograde orbit and tight configuration (satellite semimajor axis less than about 5% of its Hill radius) support the hypothesis that such binaries form via gravitational collapse of local density enhancements, as suggested for Arrokoth. The naming after ǀXam mythology adds cultural significance, linking the object to the epic battle between ǂKá̦gára and ǃHãunu.
Did You Know?
- The primary body measures around 140 kilometers in diameter, and its companion ǃHãunu is about 120 kilometers across.
- The names come from ǀXam mythology, where ǂKá̦gára and his brother-in-law ǃHãunu fought an epic battle using thunder and lightning.
- The system's density is 1.1+0.9−0.4 g/cm³, which does not particularly constrain the composition of the bodies.
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