| Discovery[1][2] | |
|---|---|
| Discovered by | |
| Discovery site | Mauna Kea Obs. |
| Discovery date | 7 June 2008 |
| Designations | |
| 2008 LC18 | |
| Orbital characteristics[1] | |
| Epoch 4 September 2017 (JD 2458000.5) | |
| Uncertainty parameter 5 | |
| Observation arc | 4.12 yr (1,506 days) |
| Aphelion | 32.445 AU |
| Perihelion | 27.667 AU |
| 30.056 AU | |
| Eccentricity | 0.0795 |
| 164.78 yr (60,186 days) | |
| 185.24° | |
| 0° 0m 21.6s / day | |
| Inclination | 27.496° |
| 88.493° | |
| 6.7420° | |
| Physical characteristics | |
| Dimensions | |
| 23.2[5][6] | |
| 8.2[1] | |
2008 LC18 is aNeptune trojan first observed on 7 June 2008 by American astronomersScott Sheppard andChad Trujillo using theSubaru Telescope atMauna Kea Observatories on Hawaii, United States.[6] It was the first object found in Neptune's trailingL5Lagrangian point and measures approximately 100 kilometers in diameter.[5]
Neptune trojans areresonant trans-Neptunian objects in a1:1 mean-motionorbital resonance with Neptune. Thesetrojans have asemi-major axis and anorbital period very similar to Neptune's (30.10 AU; 164.8 years).
2008 LC18 belongs to the trailingL5 group, which follow 60° behind Neptune's orbit. It orbits the Sun with a semi-major axis of 30.056 AU at a distance of 27.7–32.4 AU once every 164 years and 9 months (60,186 days). Its orbit has aneccentricity of 0.08 and aninclination of 27.4° with respect to theecliptic.[1] This object has the second highest inclination of any known Neptune trojan after2011 HM102, which has 29.3°.[3]
The search for L5 trojans of Neptune has been impeded by the fact that this region of space is currently along the line of sight to the center of the Milky Way, an area of the sky crowded with stars.2008 LC18 was found in a location where background stars are obscured by adust cloud.[6][5] The discovery of one Neptune L5 trojan in a searched area of 19 square degrees suggests that there may be 150 Neptune L5 trojans with a diameter greater than ~80 km (24th magnitude), similar to the estimate of such objects in Neptune'sL4 swarm.[6]
2008 LC18 was not close enough for investigation by theNew Horizons spacecraft when it crossed Neptune'sL5 region en route toPluto in 2013–2014, but its discovery showed that other, more accessible Neptune trojans could potentially have been found before that time.[7]2008 LC18 was 2 AU from Pluto in 1997.[8]2008 LC18 crossed theecliptic plane in 2011. As of 2016[update], it is 33 AU from Neptune.
The discoverers estimate that the body has a mean-diameter of 100 kilometers based on amagnitude of 23.2.[5][6] Based on a generic magnitude-to-diameter conversion, it measures approximately 98 kilometers in diameter using anabsolute magnitude of 8.2 with an assumedalbedo of 0.10.[4]
Due to itsorbital uncertainty, thisminor planet has not been numbered and its officialdiscoverers have not been determined.[1][2] If named, it will follow the naming scheme already established with385571 Otrera, which is to name these objects after figures related to theAmazons, an all-female warrior tribe that fought in theTrojan War on the side of the Trojans against the Greek.[9]
