15810 Arawn ( provisional designation ) is a

trans-Neptunian object A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has an orbital semi-major axis of 30.1 astronomical units (AU). ...

(TNO) from the inner regions of the

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 ...

, approximately in diameter. It belongs to the

plutino In astronomy, the plutinos are a dynamical group of trans-Neptunian objects that orbit in 2:3 mean-motion resonance with Neptune. This means that for every two orbits a plutino makes, Neptune orbits three times. The dwarf planet Pluto is the la ...

s, the most populous class of resonant TNOs. It was named after Arawn, the ruler of the Otherworld in

Welsh mythology Welsh mythology (also commonly known as ''Y Chwedlau'', meaning "The Legends") consists of both folk traditions developed in Wales, and traditions developed by the Celtic Britons elsewhere before the end of the first millennium. As in most of t ...

, and was discovered on 12 May 1994, by astronomers Michael Irwin and Anna Żytkow with the 2.5-metre

Isaac Newton Telescope The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope run by the Isaac Newton Group of Telescopes at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984. Originally the INT was situated at He ...

Roque de los Muchachos Observatory Roque de los Muchachos Observatory (, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands, Spain. The observatory site is operated by the Instituto de Astrofísica de Can ...

in the Canary Islands, Spain. Arawn is unusual in that it has been observed at a much closer distance than most Kuiper belt objects, by the ''

New Horizons ''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institut ...

'' spacecraft, which imaged it from a distance of in April 2016; this and its other observations have allowed its

rotation period In astronomy, the rotation period or spin period of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the '' sidereal rotation period'' (or ''sidereal day''), i.e., the time that the objec ...

to be determined.

Orbit and physical properties

Arawn is moving in a relatively eccentric orbit entirely beyond the orbit of

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 ...

. With a

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the longe ...

of 39.4 AU, it orbits the Sun once every 247 years and 6 months (90,409 days). Its orbit has a

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 ...

(closest approach to the Sun) of 34.7 AU, an

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 ...

(farthest distance from the Sun) of 44.1 AU, an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.12, and an

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 Eart ...

of 4 ° with respect to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

. It is a

, being trapped in a 2:3

mean motion resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relations ...

with Neptune, similarly to dwarf planet

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 ...

, the largest known plutino. It measures approximately in diameter, based on an absolute

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 ...

of 7.6, and an estimated albedo of 0.1. Observations by the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

show that Arawn has a very red surface. In April 2016, its

of 5.47 hours was determined.

Quasi-satellite dynamical state and orbital evolution

In 2012 Arawn was hypothesized to be in a

quasi-satellite A quasi-satellite is an object in a specific type of co-orbital configuration (1:1 orbital resonance) with a planet (or dwarf planet) where the object stays close to that planet over many orbital periods. A quasi-satellite's orbit around the Sun ...

loop around Pluto, as part of a recurring pattern, becoming a Plutonian quasi-satellite every 2 Myr and remaining in that phase for nearly 350,000 years. Measurements made by the ''

'' probe in 2015 increased the accuracy of calculations of the motion of Arawn. These calculations confirm the general dynamics described in the hypotheses. However, whether this motion means that Arawn should be classified as a quasi-satellite of Pluto remains debated, because Arawn's orbit is primarily controlled by Neptune with only occasional smaller perturbations caused by Pluto.

Origin

Arawn is moving in a very stable orbit, likely as stable as Pluto's. This suggests that it might be a primordial plutino formed around the same time Pluto itself 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 ...

came into existence. It is unlikely to be relatively recent debris that originated in collisions within Pluto's system or a captured object.

Observation

Arawn is currently relatively close to Pluto. In 2017 it was only 2.7 AU from Pluto. Before

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 ...

was discovered in 2014, Arawn was the best known target for a flyby by the ''

'' spacecraft after its Pluto flyby in 2015. Arawn was one of the first objects targeted for distant observations by ''New Horizons'', which were taken on 2 November 2015. More observations were made in April 2016. On 2 November 2015, Arawn was imaged by the LORRI instrument aboard ''New Horizons'', and was therefore 1/15 the distance of the previous nearest observation of a Kuiper belt object other than the Pluto–Charon system. Between 7–8 April 2016, ''New Horizons'' imaged Arawn from a new record distance of about 111 million kilometres, using the LORRI instrument. The new images allowed the science team at Southwest Research Institute (SwRI) in Boulder, Colorado, to further pinpoint the location of Arawn to within 1000 kilometers. The new data also enabled calculation that its rotation period is about 5.47 hours. On 15 April 2024, the ''

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

'' (JWST) conducted an observation of the Kuiper Belt object Arawn for a duration of 1 minute and 4 seconds using its NIRCam instrument in Moving Target mode with published findings expected at a later date. File:PIA205891994 JR1newhorizons.gif, April 2016 observations of Arawn by ''New Horizons'' File:New Horizons KEM Trajectory.png, Trajectory of ''New Horizons'' and other nearby Kuiper belt objects, with as Arawn. File:1994_JR1_orbit_2015.png, Orbit of Arawn near Pluto Arawn

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 ...

a star on 25 August 2022.

References

Notes

External links

Asteroid Lightcurve Database (LCDB)
query form

)
Dictionary of Minor Planet Names
Google books

– Observatoire de Genève, Raoul Behrend

– Minor Planet Center * {{DEFAULTSORT:Arawn 015810 Discoveries by Anna N. Żytkow Discoveries by Michael J. Irwin Named minor planets New Horizons 19940512