|Discovered by||M. W. Buie|
|Discovery site||Cerro Tololo Obs.|
|Discovery date||25 August 2003|
|MPC designation||(385446) Manwë|
4:7 resonance 
|Orbital characteristics |
|Epoch 16 February 2017 (JD 2457800.5)|
|Uncertainty parameter 0|
|Observation arc||23.23 yr (8,485 days)|
|3.83 yr (1,399 days)|
|0° 15m 26.28s / day|
|Known satellites||1 (diam. 33–53 km)|
|Mass||1.941 ± 0.036 × 1018 kg|
|B−V = ±0.091.07
V−R = ±0.060.61
R−I = ±0.040.61
385446 Manwë ([ˈmanwe]) is a binary resonant Kuiper belt object in a 4:7 mean-motion resonance with Neptune. It was discovered on 25 August 2003, by American astronomer Marc Buie at Cerro Tololo Observatory in northern Chile.
The secondary, Thorondor, formally (385446) Manwë I Thorondor, is estimated to be about half the size of the primary, 33–53 km vs. 58–92 km. The light curve has considerable photometric variability, with the relative magnitude of the two objects measured variously from 0.6–2.1 over the course of a few years.
Discovery and naming
Manwë was discovered on 25 August 2003 by M. W. Buie at Cerro Tololo as a 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. Manwë is foremost among the great spirits who rule the world. Manwë takes special responsibility for the air and winds. Thorondor is the Lord of Eagles in the First Age in Tolkien's writing.
Manwë has one known satellite, Thorondor. 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.
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) 2002 UX25, 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.
Manwë and Thorondor are predicted to be going 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 and Charon went through a similar series of mutual events from 1985–1990. Observations of these events will 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, is predicted for 2014 July 16, and they continue until 2018 October 25.[needs update]
- "JPL Small-Body Database Browser: 385446 Manwe (2003 QW111)" (2013-11-20 last obs.). Jet Propulsion Laboratory. Retrieved 16 March 2017.
- "385446 Manwe (2003 QW111)". Minor Planet Center. Retrieved 16 March 2017.
- Marc W. Buie. "Orbit Fit and Astrometric record for 385446". SwRI (Space Science Department). Retrieved 2014-04-23.
- Grundy, W.M.; Benecchi, S.D.; Porter, S.B.; Noll, K.S. (2014). "The Orbit of Transneptunian Binary Manwë and Thorondor and their Upcoming Mutual Events". Icarus. 237: 1–8. arXiv: . Bibcode:2014Icar..237....1G. doi:10.1016/j.icarus.2014.04.021.
- Johnston's Archive on (385446) Manwë Retrieved 2014-04-23
- Brown, M. E. (2013). "The density of mid-sized Kuiper belt object 2002 UX25 and the formation of the dwarf planets". The Astrophysical Journal Letters. 778 (2): L34. arXiv: . Bibcode:2013ApJ...778L..34B. doi:10.1088/2041-8205/778/2/l34.
- Manwë—Thorondor Mutual Events