 A distant view of Arawn (center) fromNew Horizons in November 2015.[n 1] | |
| Discovery[1] | |
|---|---|
| Discovered by | M. J. Irwin A. Żytkow |
| Discovery site | La Palma Obs. |
| Discovery date | 12 May 1994 |
| Designations | |
| (15810) Arawn | |
| Pronunciation | /ˈɑːraʊn/[2] |
Named after | Arawn(Welsh mythology)[1] |
| 1994 JR1 | |
| TNO · plutino[3][4] | |
| Orbital characteristics[5] | |
| Epoch 16 February 2017 (JD 2457800.5) | |
| Uncertainty parameter 2 | |
| Observation arc | 21.91 yr (8,002 days) |
| Aphelion | 44.241AU |
| Perihelion | 34.720 AU |
| 39.480 AU | |
| Eccentricity | 0.1206 |
| 248.07yr (90,609 days) | |
| 30.638° | |
| 0° 0m 14.4s / day | |
| Inclination | 3.8074° |
| 144.69° | |
| 101.89° | |
| Physical characteristics | |
| Dimensions | 133 km (83 mi)[6] 145 km (90 mi)[7] |
| 5.47±0.33 h[8] | |
| 0.04[8] | |
| 7.6[5] | |
15810 Arawn (provisional designation1994 JR1) is atrans-Neptunian object (TNO) from the inner regions of theKuiper belt, approximately 133 kilometres (83 mi) in diameter. It belongs to theplutinos, the most populous class ofresonant TNOs. It was named afterArawn, the ruler of the Otherworld inWelsh mythology, and was discovered on 12 May 1994, by astronomersMichael Irwin andAnna Żytkow with the 2.5-metreIsaac Newton Telescope atRoque de los Muchachos Observatory in the Canary Islands, Spain.[1]
Arawn is unusual in that it has been observed at a much closer distance than most Kuiper belt objects, by theNew Horizons spacecraft, which imaged it from a distance of 111 million km (69 million mi; 0.74 AU) in April 2016; this and its other observations have allowed itsrotation period to be determined.[7][9]
Arawn is moving in a relatively eccentric orbit entirely beyond the orbit ofNeptune. With asemi-major axis of 39.4 AU, it orbits the Sun once every 247 years and 6 months (90,409 days). Its orbit has aperihelion (closest approach to the Sun) of 34.7 AU, anaphelion (farthest distance from the Sun) of 44.1 AU, aneccentricity of 0.12, and aninclination of 4° with respect to theecliptic.[5] It is aplutino, being trapped in a 2:3mean motion resonance with Neptune, similarly to dwarf planetPluto, the largest known plutino.
It measures approximately 133 km (83 mi) in diameter,[6] based on an absolutemagnitude of 7.6, and an estimated albedo of 0.1.[citation needed] Observations by theHubble Space Telescope show that Arawn has a very red surface.[10] In April 2016, itsrotation period of 5.47 hours was determined.[9]
In 2012 Arawn was hypothesized to be in aquasi-satellite 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.[11][12] Measurements made by theNew Horizons probe in 2015 increased the accuracy of calculations of the motion of Arawn.[8] These calculations confirm the general dynamics described in the hypotheses.[13] 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.[8][9][13]
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 andCharon came into existence. It is unlikely to be relatively recent debris that originated in collisions within Pluto's system or a captured object.[11]
Arawn is currently relatively close to Pluto. In 2017 it was only 2.7AU from Pluto.[14] Before486958 Arrokoth was discovered in 2014, Arawn was the best known target for a flyby by theNew Horizons spacecraft after its Pluto flyby in 2015.[15][16]
Arawn was one of the first objects targeted for distant observations byNew Horizons, which were taken on 2 November 2015.[17] More observations were made in April 2016.[7]
On 2 November 2015, Arawn was imaged by the LORRI instrument aboardNew Horizons, and was therefore 1/15 the distance of the previous nearest observation of a Kuiper belt object other than the Pluto–Charon system.[18]
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.[9]
On 15 April 2024, theJames Webb Space Telescope (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.[19]
Arawnocculted a star on 25 August 2022.[20]
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