is a

Neptune trojan Neptune trojans are bodies that orbit the Sun near one of the stable Lagrangian points of Neptune, similar to the Trojan (astronomy), trojans of other planets. They therefore have approximately the same orbital period as Neptune and follow rough ...

first observed on 7 June 2008 by American astronomers

Scott Sheppard Scott Sander Sheppard (born 1977) is an American astronomer and a discoverer of numerous moons, comets and minor planets in the outer Solar System. He is an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institution for Scie ...

and Chad Trujillo using the

Subaru Telescope is the telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades. It had the largest monolithic primary mirror in the wo ...

Mauna Kea Observatories The Mauna Kea Observatories (MKO) are a group of independent astronomical research facilities and large telescope observatories that are located at the summit of Mauna Kea on the Big Island of Hawaiʻi, United States. The facilities are located ...

on Hawaii, United States. It was the first object found in Neptune's trailing

Lagrangian point In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of th ...

and measures approximately 100 kilometers in diameter.

Orbit and classification

Neptune trojans are

resonant trans-Neptunian object In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object (TNO) in mean-motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune, e.g. 1:2, 2 ...

s in a 1:1 mean-motion orbital resonance with Neptune. These

trojans Trojan or Trojans may refer to: * Of or from the ancient city of Troy * Trojan language, the language of the historical Trojans Arts and entertainment Music * ''Les Troyens'' ('The Trojans'), an opera by Berlioz, premiered part 1863, part 1890 ...

have 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 long ...

and an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

very similar to Neptune's (30.10 AU; 164.8 years). belongs to the trailing 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 an eccentricity of 0.08 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 Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

of 27.4 ° with respect to the ecliptic. This object has the second highest inclination of any known Neptune trojan after , which has 29.3°.

Search for Neptune trojans

The search for 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. was found in a location where background stars are obscured by a

dust cloud Fugitive dust is an environmental air quality term for very small particles suspended in the air, primarily mineral dust that is sourced from the soil of Earth's pedosphere. A significant volume of fugitive dust that is visible from a distance i ...

. The discovery of one Neptune trojan in a searched area of 19 square degrees suggests that there may be 150 Neptune trojans with a diameter greater than ~80 km (24th magnitude), similar to the estimate of such objects in Neptune's swarm.

New Horizons probe

was not close enough for investigation by the ''

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

'' spacecraft when it crossed Neptune's region en route to

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 S ...

in 2013–2014, but its discovery showed that other, more accessible Neptune trojans could potentially have been found before that time. was 2 AU from Pluto in 1997.2008 LC18 at JPL Horizons
Change "Observer Location" to @Pluto crossed the

ecliptic plane The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...

in 2011. , it is 33 AU from Neptune.

Physical characteristics

The discoverers estimate that the body has a mean-diameter of 100 kilometers based on a magnitude of 23.2. Based on a generic magnitude-to-diameter conversion, it measures approximately 98 kilometers in diameter using an

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

of 8.2 with an assumed

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

of 0.10.

Numbering and naming

Due to its orbital uncertainty, this

minor planet According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...

has not been numbered and its official discoverers have not been determined. If named, it will follow the naming scheme already established with

385571 Otrera 385571 Otrera, provisional designation , is a Neptune trojan leading Neptune's orbit in the outer Solar System. It was discovered by American astronomers Scott Sheppard and Chad Trujillo at Las Campanas Observatory on 16 October 2004. It measures ...

, which is to name these objects after figures related to the

Amazons In Greek mythology, the Amazons (Ancient Greek: Ἀμαζόνες ''Amazónes'', singular Ἀμαζών ''Amazōn'', via Latin ''Amāzon, -ŏnis'') are portrayed in a number of ancient epic poems and legends, such as the Labours of Hercules, ...

, an all-female warrior tribe that fought in the

Trojan War In Greek mythology, the Trojan War was waged against the city of Troy by the Achaeans (Greeks) after Paris of Troy took Helen from her husband Menelaus, king of Sparta. The war is one of the most important events in Greek mythology and has ...

on the side of the Trojans against the Greek.

References

External links

AstDys-2
about * * * {{DEFAULTSORT:2008 LC18 # Minor planet object articles (unnumbered) # # # 20080607