2148 Epeios is a mid-sized

Jupiter trojan The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange poin ...

from the

Greek camp This is a list of Jupiter trojans that lie in the Greek camp, an elongated curved region around the leading Lagrangian point (), 60 ° ahead of Jupiter in its orbit. All the asteroids at Jupiter's point have names corresponding to participants ...

, approximately in diameter. It was discovered on 24 October 1976, by Danish astronomer

Richard Martin West Richard Martin West (born 1941) is a Danish astronomer and discoverer of astronomical objects with a long career at the European Southern Observatory (ESO) and at the International Astronomical Union (IAU). He discovered numerous comets, includi ...

ESO The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based ast ...

's La Silla Observatory in northern Chile. The dark Jovian

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

is the principal body of the proposed Epeios family and was named after Epeius from Greek mythology.

Orbit and classification

''Epeios'' is a

in a 1:1 orbital resonance with Jupiter. It is located in the leading

at the Gas Giant's

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 ...

, 60 ° ahead on its orbit . It orbits the Sun at a distance of 4.9–5.5 AU once every 11 years and 11 months (4,350 days;

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 ...

of 5.22 AU). Its orbit has an eccentricity of 0.06 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 9 ° with respect to the ecliptic. The body's

observation arc In observational astronomy, the observation arc (or arc length) of a Solar System body is the time period between its earliest and latest observations, used for tracing the body's path. It is usually given in days or years. The term is mostly use ...

begins with its official discovery observation at La Silla in October 1976.

Epeios family

Fernando Roig and

Ricardo Gil-Hutton This is a list of minor-planet discoverers credited by the Minor Planet Center with the discovery of one or several minor planets (such as near-Earth and main-belt asteroids, Jupiter trojans and distant objects). , the discovery of 612,011 numb ...

identified ''Epeios'' as the principal body of a small Jovian

asteroid family An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An a ...

, using the hierarchical clustering method (HCM), which looks for groupings of neighboring asteroids based on the smallest distances between them in the

proper orbital element __NOTOC__ The proper orbital elements or proper elements of an orbit are constants of motion of an object in space that remain practically unchanged over an astronomically long timescale. The term is usually used to describe the three quantitie ...

space. According to the astronomers, the Epeios family belongs to the larger

Menelaus clan 1647 Menelaus is a mid-sized Jupiter trojan from the Greek camp, approximately in diameter. It was discovered on 23 June 1957 by American astronomer Seth Nicholson at the Palomar Observatory in California, and later named after the Spartan King ...

, an aggregation of Jupiter trojans which is composed of several families, similar to the Flora family in the inner asteroid belt. However this family is not included in

David Nesvorný David (; , "beloved one") (traditional spelling), , ''Dāwūd''; grc-koi, Δαυΐδ, Dauíd; la, Davidus, David; gez , ዳዊት, ''Dawit''; xcl, Դաւիթ, ''Dawitʿ''; cu, Давíдъ, ''Davidŭ''; possibly meaning "beloved one". w ...

HCM-analysis from 2014. Instead, ''Epeios'' is listed as a non-family asteroid of the Jovian background population on the Asteroids Dynamic Site (AstDyS) which based on another analysis by Milani and Knežević.

Naming

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 ...

was named from

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical co ...

after the Greek warrior Epeius, leader of the contingent from

Phocis Phocis ( el, Φωκίδα ; grc, Φωκίς) is one of the regional units of Greece. It is part of the administrative region of Central Greece. It stretches from the western mountainsides of Parnassus on the east to the mountain range of Vardo ...

during 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 ...

. Epeius also built the wooden

Trojan Horse The Trojan Horse was a wooden horse said to have been used by the Greeks during the Trojan War to enter the city of Troy and win the war. The Trojan Horse is not mentioned in Homer's ''Iliad'', with the poem ending before the war is concluded, ...

. He then chose the other 29 soldiers who would accompany him inside. The official was published by the

Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function ...

on 1 July 1979 ().

Physical characteristics

Rotation period

As of 2018, no rotational lightcurve of ''Epeios'' has been obtained from photometric observations. The body's

rotation period The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the ...

, pole and shape remain unknown.

Diameter and albedo

According to the survey carried out by the NEOWISE mission of NASA's

Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 2011, ...

, ''Epeios'' measures 37.98 kilometers in diameter and its surface has an albedo of 0.064.

References

External links

Dictionary of Minor Planet Names
Google books

– Minor Planet Center
Asteroid 2148 Epeios
at the Small Bodies Data Ferret * * {{DEFAULTSORT:Epeios 002148 Discoveries by Richard Martin West Named minor planets 19761024