385446 Manwë
Binary resonant Kuiper belt object in 4:7 resonance with Neptune.
385446 Manwë, also known as (385446) Manwë–Thorondor, is a binary object in the Kuiper belt that orbits in a 4:7 resonance with Neptune. Its provisional designation is 2003 QW111. American astronomer Marc Buie discovered it on 25 August 2003 at the Cerro Tololo Observatory in Chile. A 2019 analysis of its light curve indicates it might be a contact binary.
The object was named for Manwë, the king of the Valar in J. R. R. Tolkien's legendarium, who rules the world and governs the air and winds. Its satellite is named for Thorondor, the Lord of Eagles in Tolkien's First Age.
Manwë shows strong and irregular brightness variations, meaning its two components are not tidally locked. Both Manwë and Thorondor have very red surfaces. The composition is unknown, but it is probably mostly ice, since the nominal density (though highly uncertain) is less than that of water. Another Kuiper belt object, 55637 Uni, also has a density below 1 g/cm³, suggesting an icy body with low rock content and high porosity.
Manwë orbits the Sun at an average distance of about 43.7 AU, taking 289 years per orbit. Its orbit has a low inclination of 2.7 degrees and an eccentricity of 0.11, so its distance ranges from 38.8 AU at perihelion to 48.7 AU at aphelion. It is locked in a 4:7 mean-motion resonance with Neptune, completing four orbits for every seven of Neptune's.
The system has one known satellite, Thorondor (formally (385446) Manwë I). It is about two-thirds the size of the primary, with a volume-equivalent diameter of roughly 108 km. Its rotation period is uncertain, but a best-fit model gives a very slow 309.3 days. Thorondor's rotation is likely chaotic, similar to Pluto's smaller moons, due to gravitational torques from Manwë during their eccentric mutual orbit. Its light curve varies by 0.55 magnitudes, suggesting a very flattened shape, like the larger lobe of the contact binary Arrokoth. If Thorondor is an ellipsoid, a best-fit model gives aspect ratios of a/c = 7.33 and b/c = 6.67.
The satellite's orbit has a semi-major axis of 6674 ± 41 km, a period of 110.176 ± 0.018 days, an eccentricity of 0.5632 ± 0.0070, and an inclination of 25.58° ± 0.23°. The total system mass is about 1.94 × 10¹⁸ kg.
From 2014 to 2018, Manwë and Thorondor were expected to undergo mutual occultations and transits, similar to Pluto and Charon from 1985 to 1990.
Quick Facts
- Minorplanet
- yes
- Background
- #C2E0FF
- Discoverer
- M. W. Buie
- Discovery Site
- Cerro Tololo Obs.
- Discovered
- 25 August 2003
- Mpc Name
- (385446) Manwë
- Pronounced
- qya · ˈmanwɛ
- Named After
- Manwë / (fictional character)
- Mp Category
- TNO / 4:7 resonance
- Epoch
- 25 February 2023 (JD 2460000.5)
- Uncertainty
- 4
- Observation Arc
- 18.05 yr (6,593 days)
Facts from the source article.
Lore & Background
Manwë was discovered on 25 August 2003 by M. W. Buie at Cerro Tololo as part of the Deep Ecliptic Survey. The object was named after Manwë, the fictional king of the Valar in J. R. R. Tolkien's Middle-earth legendarium, who is foremost among the great spirits and takes responsibility for air and winds. Its satellite Thorondor is named after the Lord of Eagles in the First Age of Tolkien's writing. Manwë has significant and irregular photometric variability, demonstrating that its components are not tidally locked. The surfaces of Manwë and Thorondor appear to be very red. The composition of Manwë is unknown but likely to be mostly ice, because the nominal density (with large uncertainty) is less than that of water. At least one other Kuiper belt object, 55637 Uni, has been found with a density of less than 1 g/cm³, implying an object made mostly of ice with low rock fraction and high porosity.
Reader's Guide
The Manwë–Thorondor system is notable as a binary resonant Kuiper belt object, with Manwë in a 4:7 mean-motion resonance with Neptune. Its satellite Thorondor is about two-thirds the size of the primary, with an estimated volume equivalent diameter of 108 km. The system's total mass is about 1.94 × 10^18 kg. A 2019 light-curve study suggests Manwë may be a contact binary object. The satellite's orbit is highly eccentric (0.5632) and inclined (25.58°), with a period of 110.176 days. Thorondor's rotation is expected to be chaotic, similar to Pluto's smaller moons, due to gravitational torquing by Manwë. Its light curve shows considerable variability, implying a very flattened shape, possibly akin to the larger lobe of the contact binary Arrokoth. Mutual occultations and transits were predicted from 2014 to 2018, but none of the four predicted events were observed, likely due to error in measuring Thorondor's orbital period. However, photometry from the campaign determined that Manwë is a highly bilobate contact binary. The system has been researched for exploration, with a proposed trajectory launching on 9 April 2032, using gravity assists at Jupiter and Neptune, arriving in March 2042 after 10 years, when Manwë would be 41 AU from the Sun.
Did You Know?
- Manwë was discovered on 25 August 2003 by Marc Buie at Cerro Tololo Observatory in Chile.
- Manwë is in a 4:7 mean-motion orbital resonance with Neptune.
More in Trans-Neptunian Objects 1-24
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