385446 Manwë (), or (385446) Manwë–Thorondor (), is a binary

resonant Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...

Kuiper belt The Kuiper belt ( ) is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...

object in a 4:7 mean-motion resonance with

Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...

. It was discovered on 25 August 2003, by American astronomer

Marc Buie Marc William Buie (; born September 17, 1958) is an American astronomer and prolific discoverer of minor planets who works at the Southwest Research Institute in Boulder, Colorado in the Space Science Department. Formerly he worked at the Lowel ...

at Cerro Tololo Observatory in northern Chile. A study of Manwë's

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

in 2019 suggests that it may be a

contact binary In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontac ...

object.

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 Deep Ecliptic Survey (DES) is a project to find Kuiper belt objects (KBOs), using the facilities of the National Optical Astronomy Observatory (NOAO). The principal investigator is Robert L. Millis. Since 1998 through the end of 2003, the s ...

. The object was named after Manwë, the fictional king of the

Valar The Valar (; singular Vala) are characters in J. R. R. Tolkien's Middle-earth writings. They are "angelic powers" or "gods" subordinate to the one God ( Eru Ilúvatar). The '' Ainulindalë'' describes how some of the Ainur choose to enter the ...

J. R. R. Tolkien John Ronald Reuel Tolkien (, 3 January 1892 – 2 September 1973) was an English writer and philologist. He was the author of the high fantasy works ''The Hobbit'' and ''The Lord of the Rings''. From 1925 to 1945, Tolkien was the Rawlinson ...

Middle-earth Middle-earth is the Setting (narrative), setting of much of the English writer J. R. R. Tolkien's fantasy. The term is equivalent to the ''Midgard, Miðgarðr'' of Norse mythology and ''Middangeard'' in Old English works, including ''Beowulf'' ...

legendarium Tolkien's legendarium is the body of J. R. R. Tolkien's mythopoeic writing, unpublished in his lifetime, that forms the background to his ''The Lord of the Rings'', and which his son Christopher summarized in his compilation of ''The Silmari ...

. 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.

Physical properties

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, , 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.

Orbit

Manwë orbits the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

at an average distance of about , taking 289 years to complete a full orbit. Manwë has a low

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

of 2.7 degrees. Its orbit is elongated, with an

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...

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 at

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

and 48.7 AU at

aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

. Manwë is in a 4:7 mean-motion orbital resonance with Neptune, meaning Manwë completes 4 orbits for every 7 orbits completed by Neptune.

Satellite

Physical characteristics

Being part of a binary system, Manwë has one known companion named Thorondor, formally designated (385446) Manwë I. It is estimated to be about two-thirds the size of the primary, approximately for a volume equivalent diameter. The rotation period of Thorondor is uncertain, though a best-fit model suggests a very slow rotation period of 309.3 days. Thorondor's rotation is expected to be chaotic like Pluto's smaller moons, as a result of gravitational

torquing In the field of solid mechanics, torsion is the twisting of an object due to an applied torque. Torsion could be defined as strain or angular deformation, and is measured by the angle a chosen section is rotated from its equilibrium position. Th ...

by Manwë over the course of their eccentric mutual orbit. Thorondor's

has considerable photometric variability, with an amplitude of 0.55 magnitudes. This implies that Thorondor could have a very flattened shape, akin to the larger lobe of the

Kuiper belt object

486958 Arrokoth 486958 Arrokoth (Provisional designation in astronomy, provisional designation ; formerly nicknamed Ultima Thule) is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive List of minor planet ...

. Assuming a ellipsoid shape for Thorondor, a best-fit model for its shape suggests the

aspect ratio The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...

s of ''a''/''c'' = 7.33 and ''b''/''c'' = 6.67.

Orbit

The satellite's orbit has the following parameters: semi-major-axis, ; period, ; eccentricity, ; and inclination, The total system mass is about 1.94 kg.

Mutual events

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 Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

and

Charon In Greek mythology, Charon or Kharon ( ; ) is a psychopomp, the ferryman of the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the worlds of the living and ...

went through a similar 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. 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 orbiting

moonlet A moonlet, minor moon, minor natural satellite, or minor satellite is a particularly small natural satellite orbiting a planet, dwarf planet, or other minor planet. Up until 1995, moonlets were only hypothetical components of Saturn's F-ring ...

s besides Thorondor.

Stellar occultation

On 18 September 2024, Manwë

occulted An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...

the

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

14.6 star . The star may have dimmed for no more than 8.1 seconds during the event, which was observable in a path extending from

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

to Asia and Africa, and ending at

Gabon Gabon ( ; ), officially the Gabonese Republic (), is a country on the Atlantic coast of Central Africa, on the equator, bordered by Equatorial Guinea to the northwest, Cameroon to the north, the Republic of the Congo to the east and south, and ...

Central Africa Central Africa (French language, French: ''Afrique centrale''; Spanish language, Spanish: ''África central''; Portuguese language, Portuguese: ''África Central'') is a subregion of the African continent comprising various countries accordin ...

Exploration

The Manwë-Thorondor system has been researched for exploration, with the fastest trajectory launching on 9 April 2032, performing gravity assists at

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

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 of .

References

External links

* * {{DEFAULTSORT:Manwe 385446 Discoveries by Marc Buie Named minor planets Binary trans-Neptunian objects 20030825 385446