38628 Huya ( ; provisional designation ) is a binary trans-Neptunian object located in the Kuiper belt, a region of icy objects orbiting beyond Neptune in the outer Solar System. Huya is classified as a plutino, a dynamical class of trans-Neptunian objects with orbits in a 3:2 orbital resonance with Neptune. It was discovered by the Quasar Equatorial Survey Team and was identified by Venezuelan astronomer Ignacio Ferrín in March 2000. It is named after Juyá, the mythological rain god of the Wayuu people native to South America.
Huya's surface is moderately red in color due to the presence of complex organic compounds on its surface. Water ice has been suspected to be also present on its surface, although it has not been directly detected on Huya. Huya is considered to be a mid-sized trans-Neptunian object, with an estimated diameter of about .
Huya has one known natural satellite or moon. The moon is relatively large compared to Huya and is expected to have slowed its rotation, although measurements of Huya's brightness variations have indicated that Huya's rotation may not be synchronous with the moon's orbit.
History Discovery Huya was discovered on 10 March 2000 by a team of astronomers of the Quasar Equatorial Survey Team (QUEST), led by Gustavo Bruzual and Charles Baltay at the Llano del Hato National Astronomical Observatory in Mérida, Venezuela. Huya was first identified by Venezuelan astronomer Ignacio Ferrín during a computer-assisted search through images taken from a six-hour survey of deep-sky objects including quasars and supernovae, using the Llano del Hato National Astronomical Observatory's 1-meter Schmidt telescope on the night of 15 March 2000. At the time of discovery, Huya was located in the constellation of Virgo. The subtle movement of Huya was detected by the QUEST's computer program, which was designed to identify moving objects by superimposing multiple images. The discovery team subsequently analyzed earlier images taken from previous QUEST surveys conducted during the same month in order to verify the orbital motion of Huya.
The discovery of Huya was announced by the Minor Planet Center in a Minor Planet Electronic Circular on 3 June 2000. It was given the provisional designation which indicates its year of discovery, with the first letter further specifying that the discovery took place in the first half of March. The last letter and numbers of its designation indicate that Huya is the 4327th object discovered in the first half of March. At that time, Huya was thought to be one of the largest minor planets in the Solar System due to its apparent magnitude of 20, which is relatively bright for a distant object. Astronomers speculated that Huya could be the second-largest minor planet discovered after , with a diameter around one-fourth the size of the then-planet Pluto. Baltay, leader of the discovery team and chairman of Yale University's Department of Physics, proclaimed that the discovery was significant because it was the largest object discovered in the Kuiper belt since Pluto in 1930. In an interview on their discovery, Baltay asserted:
After the announcement of Huya's discovery, the discovery team found precovery images of Huya taken with the Palomar Observatory's Samuel Oschin telescope on 9 April 1996. These precovery images of Huya from Palomar are the earliest known observations of Huya. The precovery images along with subsequent follow-up observations in 2000 extended Huya's observation arc up to four years, which helped refine Huya's orbit. By 2002, Huya was observed 303 times. This was sufficient to accurately determine its orbit, so it was assigned the minor planet number 38628 on 28 March 2002.
Name This minor planet is named after the mythological figure Huya (Juyá), the rain god of the Wayuu people indigenous to the Guajira Peninsula of northern Venezuela and Colombia. In Wayuu mythology, Juyá is a hunter who controlled the rain and was married to Pulowi, the female figure related to the wind and dry seasons. Juyá is also associated with the winter and lives in the celestial altitudes beyond the sun. The discovery team led by Ferrín particularly chose the name to represent Venezuela's indigenous peoples that lived in the region where Huya was discovered. Ferrín presumed that Huya had experienced multiple impact events during its formation, which he considered analogous to rain, a trait associated with Juyá.
While searching for names, Ferrín and his team had agreed upon a naming scheme based on indigenous names with traits that are associated with the object's characteristics. Among 20 potential names considered by Ferrín's team, they chose the name Juyá, altered to its equivalent phonetic English spelling Huya. The name was later submitted and proposed to the International Astronomical Union (IAU), which then approved the name in 2003. The Minor Planet Center published the naming citation on 1 May 2003. Although the IAU's present naming convention for minor planets requires objects in the orbital class of plutinos (objects in 3:2 orbital resonance with Neptune) to be named after underworld deities, these guidelines had not yet been established when Huya was named.
Orbit
Huya is a trans-Neptunian object (TNO) in a 2:3 mean-motion orbital resonance with Neptune, meaning that Huya completes two orbits around the Sun for every three orbits completed by Neptune. Due to its 2:3 orbital resonance with Neptune, Huya is classified as a plutino, a dynamical class of objects with orbits similar to that of Pluto. Huya orbits the Sun at an average distance of , taking 247 years to complete a full orbit. Huya's orbit is inclined to the ecliptic by 15.5 degrees, slightly less than Pluto's orbital inclination of 17 degrees. It has an elongated orbit with an orbital eccentricity of 0.28. Due to its eccentric orbit, its distance from the Sun varies over the course of its orbit, ranging from 28.5 AU at perihelion (closest distance) to 50.3 AU at aphelion (farthest distance). Like Pluto, Huya's orbital resonance prevents close approaches to Neptune. The minimum orbit intersection distance (MOID) between Huya and Neptune is approximately 1.4 AU, but due to the resonance, the two never come closer than 17 AU of each other.
Huya passed perihelion in December 2014, and is now moving away from the Sun, approaching aphelion by 2139. , Huya is approximately 28.8 AU from the Sun, located in the direction of the constellation Ophiuchus. Simulations by the Deep Ecliptic Survey (DES) show that Huya can acquire a perihelion distance (qmin) as small as 27.27 AU over the next 10 million years.
Observability
The Huya system's current apparent magnitude, the brightness as seen from Earth, is about 20. Huya comes to opposition every June, when it appears brightest from Earth. As Huya's phase angle approaches zero during opposition, its brightness increases gradually, which indicates it has a low geometric albedo. Huya's low albedo has since been confirmed with measurements of Huya's diameter via thermal emission and occultation observations. Huya's brightness behavior at opposition, or opposition surge, was first studied in 2001; it is the first trans-Neptunian object other than Pluto to have its opposition surge studied. Huya appeared to display very little variability in brightness, with an estimated light curve amplitude of less than 0.097 magnitudes.
Occultations Stellar occultations by Huya occur when it passes in front of a star and blocks out its light, causing the star to dim for several seconds until Huya emerges. Observing stellar occultations by Huya can provide accurate measurements for its position, shape, and size. The first successful detection of a stellar occultation by Huya took place on 18 March 2019. The observing occultations for this occultation were favorable as the occulted star was bright (apparent magnitude 11) and the event was observable at central Europe and west Asia, where there were already many telescopes operated by amateur and professional astronomers. A total of 49 telescopes attempted to observe the occultation, with 21 positive detections reported from Romania, Turkey, and Israel. No signs of a possible atmosphere or rings were detected during the occultation, placing an upper limit surface atmospheric pressure of 10 nanobars, an upper limit ring opacity of 2.7%, and an upper limit ring width of . The moon of Huya was not detected in the occultation.
Additional stellar occultations by the Huya system were observed on 28 March 2021, 17 February 2023, and 24 June 2023. In all three events, the moon of Huya was detected, allowing for the determination of its orbit around Huya. Only one telescope detected the occultation in March 2021 and February 2023, whereas in June 2023 twelve out of the 30 participating telescopes detected the occultation. None of these occultation observations revealed any rings within from Huya.
Physical characteristics + History of diameter estimates for HuyaYear ofpublicationHuya + moondiameter (km)Huyadiameter (km)MethodRefs2001assumed albedo2004thermal2008thermal2012thermal2012thermal2013thermal2017thermal2022occultation2025occultation
Diameter and shape Results from the March 2019 and June 2023 occultations show that Huya has a flattened shape resembling an ellipse, with an equatorial diameter of . It is not known for certain whether Huya's true shape is an oblate spheroid or a triaxial ellipsoid; slight variations in Huya's shape between the 2019 and 2023 occultations could indicate rotation of a triaxial shape, although these could also be caused by measurement errors or topographic features on Huya. Huya's brightness does not fluctuate enough to suggest a triaxial shape, which leads researchers to conclude that Huya's shape is more likely an oblate spheroid. If Huya has an oblate spheroid shape and its equator lies in the same plane as the orbit of its moon, then Huya's polar diameter would be , about 14% shorter than its equatorial diameter. These oblate spheroid dimensions correspond to a volume-equivalent diameter of . For comparison, Huya is about the size of Saturn's smallest round moon Mimas () and Neptune's largest non-spherical moon Proteus ().
The diameter of Huya from occultations agrees with 2013 estimates of Huya's diameter from its infrared thermal emission. Before 2013, Huya was thought to be larger because its moon was not known at the time; the moon adds to Huya's overall brightness in visible light and infrared, thus making it seem brighter and larger than it actually is. Even earlier estimates of Huya's diameter proposed around the time of its discovery placed it at around , or one-fourth the diameter of Pluto. These initial diameter estimates led some astronomers to suspect that Huya could be a possible dwarf planet whose shape is rounded by its own gravity, but later estimates have since disproven this.
Mass and density
Since the orbit of Huya's moon is known, the mass and density of Huya can be determined via Kepler's third law. The total mass of Huya and its moon is . If Huya and its moon both have spheroidal shapes with equal densities, then the bulk density of both objects in the Huya system is . Comparing the density of the Huya system to other binary TNOs with known densities agrees with the observation that densities of TNOs are correlated with their diameter.