 Hubble Space Telescope image of Manwë and Thorondor, taken in 2013 | |
| Discovery[1][2] | |
|---|---|
| Discovered by | M. W. Buie |
| Discovery site | Cerro Tololo Obs. |
| Discovery date | 25 August 2003 |
| Designations | |
| (385446) Manwë | |
| Pronunciation | [ˈmanwɛ] |
Named after | Manwë (fictional character)[2] |
| 2003 QW111 | |
| TNO[1] 4:7 resonance[3] | |
| Orbital characteristics (barycentric)[4] | |
| Epoch 25 February 2023 (JD 2460000.5) | |
| Uncertainty parameter 4[1] | |
| Observation arc | 18.05 yr (6,593 days)[1] |
| Aphelion | 48.667AU |
| Perihelion | 38.758 AU |
| 43.713 AU | |
| Eccentricity | 0.11334 |
| 288.82yr (105,492 d) | |
| 285.002° | |
| 0° 0m 12.285s / day | |
| Inclination | 2.667° |
| 68.494° | |
| 20.173° | |
| Knownsatellites | 1 (Thorondor[θɔˈrɔndɔr]) |
| Physical characteristics | |
| Dimensions | 150 km(volume equivalent for Manwë)[5] 108 km(Thorondor)[6] |
| Mass | 1.41×1018 kg(Manwë)[5] 5×1017 kg(Thorondor) |
Meandensity | ~0.8 g/cm3 |
| 11.8819±0.00005 h(Manwë)[5] 309.3 d(Thorondor)[5] | |
| 27°(relative to ecliptic)[5] 12.5°(relative to orbit)[5] | |
| 0.06(Manwë) 0.09(Thorondor) | |
| B−V =1.07±0.09 V−R =0.61±0.06 R−I =0.61±0.04[6] | |
| 6.57[1] 7.15 (combined)[6] | |
385446 Manwë ([ˈmanwɛ]), or(385446) Manwë–Thorondor ([θɔˈrɔndɔr], provisional designation2003 QW111), is a binaryresonantKuiper belt object in a 4:7 mean-motion resonance withNeptune.[7] It was discovered on 25 August 2003, by American astronomerMarc Buie atCerro Tololo Observatory in northern Chile.[2] A study of Manwë'slight curve in 2019 suggests that it may be acontact binary object.[5]
Manwë was discovered on 25 August 2003 byM. W. Buie at Cerro Tololo as a part of theDeep Ecliptic Survey.[1] The object was named afterManwë, the fictional king of theValar inJ. R. R. Tolkien'sMiddle-earthlegendarium. Manwë is foremost among the great spirits who rule the world, and takes special responsibility for the air and winds.Thorondor is the Lord of Eagles in the First Age in Tolkien's writing.[1]
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.[6] 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.[6] At least one other Kuiper belt object,55637 Uni, has been found with a density of less than 1 g/cm3, which implies an object made mostly of ice with a low rock fraction and high porosity.[8]
Manwë orbits theSun at an average distance of about 43.7 AU (6.54×109 km), taking 289 years to complete a full orbit.[4] Manwë has a loworbital inclination of 2.7 degrees. Its orbit is elongated, with anorbital eccentricity of 0.11. Due to its eccentric orbit, Manwë's distance from the Sun varies over the course of its orbit, approaching 38.8 AU atperihelion and 48.7 AU ataphelion.[4] Manwë is in a 4:7mean-motion orbital resonance with Neptune, meaning Manwë completes 4 orbits for every 7 orbits completed by Neptune.[3]
Being part of a binary system, Manwë has one knowncompanion namedThorondor, formally designated(385446) Manwë I. It is estimated to be about two-thirds the size of the primary, approximately 108 km (67 mi) for a volume equivalent diameter.[5] The rotation period of Thorondor is uncertain, though a best-fit model suggests a very slow rotation period of 309.3 days.[5] Thorondor's rotation is expected to bechaotic likePluto's smaller moons, as a result of gravitationaltorquing by Manwë over the course of their eccentric mutual orbit.[5] Thorondor'slight curve has considerable photometric variability, with an amplitude of 0.55 magnitudes.[5] This implies that Thorondor could have a very flattened shape, akin to the larger lobe of thecontact binary Kuiper belt object486958 Arrokoth.[5] Assuming a ellipsoid shape for Thorondor, a best-fit model for its shape suggests theaspect ratios ofa/c = 7.33 andb/c = 6.67.[5]
The satellite's orbit has the following parameters: semi-major-axis,6674 ± 41 km; period,110.176 ± 0.018 days; eccentricity,0.5632 ± 0.0070; and inclination,25.58 ± 0.23°. The total system mass is about 1.94 × 1018 kg.[6]
Manwë and Thorondor were expected to go through a period of mutual occultations and transits from 2014–2018, where one object crosses in front of the other as seen from Earth.Pluto andCharon went through asimilar series of mutual events from 1985–1990. Observations of these events could allow for better estimates of the radii of the two objects and their densities, as well as possibly determining their shapes and mapping surface color and albedo features. The first event, an inferior occultation, was predicted for 2014 July 16, and they continue until 2018 October 25.[6][9]
The actual observations revealed none of the four predicted occultations, likely due to error measuring orbital period of Thorondor, although photometry data gathered during the observation campaign determined that Manwë is a highly bilobate contact binary, potentially surrounded by rapidly orbitingmoonlets besides Thorondor.[5]
On 18 September 2024, Manwëocculted themagnitude 14.6 starUCAC4 445-000300. The star may have dimmed for no more than 8.1 seconds during the event, which was observable in a path extending fromJapan to Asia and Africa, and ending atGabon inCentral Africa.[10]
The Manwë–Thorondor system has been researched for exploration, with the fastest trajectory launching on 9 April 2032, performinggravity assists atJupiter and Neptune in 2033 and 2039 respectively, and arriving in March 2042 after only 10 years. Manwë would be 41 AU from the Sun at the time, and the spacecraft would have a flyby velocity of20.1 km/s.[11]
