15094 Polymele is a primitive

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 (celestial body), trojan Libration point orbit, librat ...

from the Greek camp, approximately in diameter. It is a target of the ''Lucy'' mission with a close flyby planned to occur in September 2027. It was discovered on 17 November 1999, by astronomers with the

Catalina Sky Survey Catalina Sky Survey (CSS; obs. code: 703) is an astronomical survey to discover comets and asteroids. It is conducted at the Steward Observatory's Catalina Station, located near Tucson, Arizona, in the United States. CSS focuses on the searc ...

Mount Lemmon Observatory Mount Lemmon Observatory (MLO), also known as the Mount Lemmon Infrared Observatory, is an astronomy, astronomical observatory located on Mount Lemmon in the Santa Catalina Mountains approximately northeast of Tucson, Arizona, Tucson, Arizona (U ...

, Arizona, in the United States. The

P-type asteroid P-type (primitive-type) asteroids have low albedo and a featureless reddish spectrum. It has been suggested that they have a composition of organic-rich silicates, carbon and anhydrous silicates, possibly with water ice in their interior. P-type ...

has a

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 ...

of 5.9 hours and highly flattened shape. It was named after

Polymele In Greek mythology, the name Polymela or Polymele () may refer to the following figures: * Polymele, daughter of Autolycus and one of the possible mothers of Jason by Aeson, King of Iolcus. She was also called Polymede or Polypheme, otherwise ...

from Greek mythology, the wife of Menoetius and the mother of Patroclus. In 2022, it was reported to have a

natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are colloquially referred to as moons, a deriv ...

approximately in diameter.

Orbit and classification

Polymele is a

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

orbiting in the leading Greek camp at Jupiter's

Lagrangian point In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium (mechanics), equilibrium for small-mass objects under the gravity, gravitational influence of two massive orbit, orbiting b ...

, 60 ° ahead of the gas giant's orbit ''(see

Trojans in astronomy In astronomy, a trojan is a small celestial body (mostly asteroids) that shares the orbit of a larger body, remaining in a stable orbit approximately 60° ahead of or behind the main body near one of its Lagrangian points and . Trojans can shar ...

)''. It orbits the Sun at a distance of 4.7–5.7 AU once every 11 years and 9 months (4,289 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 longe ...

of 5.17 AU). Its orbit has 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 0.09 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 13 ° 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 ...

. The asteroid'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 48 years prior to its official discovery observation at Mount Lemmon, with a

precovery In astronomy, precovery (short for pre-discovery recovery) is the process of finding the image of a celestial object in images or photographic plates predating its discovery, typically for the purpose of calculating a more accurate orbit. This ha ...

taken at

Palomar Observatory The Palomar Observatory is an astronomical research observatory in the Palomar Mountains of San Diego County, California, United States. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

in 1951, and published by the ''

Digitized Sky Survey The Digitized Sky Survey (DSS) is a digital data, digitized version of several photography, photographic astronomical surveys of the night sky, produced by the Space Telescope Science Institute between 1983 and 2006. Versions and source materia ...

'' later on.

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 after

, the daughter of

Peleus In Greek mythology, Peleus (; Ancient Greek: Πηλεύς ''Pēleus'') was a hero, king of Phthia, husband of Thetis and the father of their son Achilles. This myth was already known to the hearers of Homer in the late 8th century BC. Biogra ...

from

Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...

. According to the Latin author

Gaius Julius Hyginus Gaius Julius Hyginus (; 64 BC – AD 17) was a Latin author, a pupil of the scholar Alexander Polyhistor, and a freedman of Augustus, and reputed author of the '' Fabulae'' and the '' De astronomia'', although this is disputed. Life and works ...

( 64 BC – AD 17), she is the wife of the Argonaut

Menoetius Menoetius or Menoetes (; ''Menoitios''), meaning ''doomed might'', is a name that refers to three distinct persons from Greek mythology: * Menoetius, a second generation Titan, son of Iapetus and Clymene or Asia, and a brother of Atlas, Pro ...

and the mother of

Patroclus In Greek mythology, Patroclus (generally pronounced ; ) was a Greek hero of the Trojan War and an important character in Homer's ''Iliad''. Born in Opus, Patroclus was the son of the Argonaut Menoetius. When he was a child, he was exiled from ...

, who participated in the

Trojan War The Trojan War was a legendary conflict in Greek mythology that took place around the twelfth or thirteenth century BC. The war was waged by the Achaeans (Homer), Achaeans (Ancient Greece, Greeks) against the city of Troy after Paris (mytho ...

. Polymele is also known as "

Philomela Philomela () or Philomel (; , ; ) is a minor figure in Greek mythology who is frequently invoked as a direct and figurative symbol in literary and artistic works in the Western canon. Family Philomela was the younger of two daughters of P ...

"; that name was previously used for the asteroid 196 Philomela. The approved naming citation 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. Funct ...

on 22 February 2016 ().

Physical characteristics

Polymele has been characterized as a primitive

by the investigators of the ''Lucy'' mission. P-type asteroids are known for their low

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

. It has a V–I color index of 0.799, which is lower than that for most larger Jupiter trojans ''(see table below)''.

Size, shape, and albedo

According to the survey carried out by the

NEOWISE Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and MIDEX-6) was a NASA infrared astronomy space telescope in the Explorers Program launched in December 2009.. . WISE discovered thousands of minor planets and nu ...

mission of NASA's

Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, List of observatory codes, observatory code C51, Explorer 92 and MIDEX-6) was a NASA infrared astronomy Space observatory, space telescope in the Explorers Program launched in December 2009.. . WISE L ...

, Polymele measures 21.075 kilometers in diameter and its surface has an

of 0.091, while in 2018,

Marc Buie Marc William Buie (; born September 17, 1958) is an American astronomer and prolific discoverer of minor planets who works at the Southwest Research Institute in Boulder, Colorado in the Space Science Department. Formerly he worked at the Lowel ...

published an albedo of 0.073 and an absolute magnitude of 11.691 in the S- and/or R band. The ''Collaborative Asteroid Lightcurve Link'' assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a larger diameter of 26.64 kilometers based on an absolute magnitude of 11.6. On 27 March 2022, multiple astronomers observed a

stellar occultation Stellar means anything related to one or more stars (''stella''). The term may also refer to: Arts, entertainment, and media * Stellar (magazine), ''Stellar'' (magazine), an Irish lifestyle and fashion magazine * Stellar Loussier, a character fro ...

by Polymele, which revealed an apparently elongated projected shape with projected dimensions of . Additional occultation observations of Polymele from 2020 to 2023 revealed that Polymele's true shape is a highly flattened disk with dimensions , similar to the large flat lobe of the

Kuiper belt object 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 ...

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 ...

. This unusual flattened shape of Polymele implies that it had retained its original shape from when it formed by accretion.

Rotation

In March 2016, a rotational

lightcurve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

of Polymele was obtained from photometric observations by

and colleagues. Lightcurve analysis gave a

of hours with a small brightness amplitude of

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 ...

(), which indicates the body is being viewed pole-on. Previously, the ''Lucy'' mission team published spin rates of 6.1 and 4 hours, respectively. In a 2021 paper, the Lucy team published a rotation period of hours, implying that the previous period may have been an alias. The resolved observation of Polymele's shape in multiple occultation events allowed the ''Lucy'' team to determine the orientation of Polymele's rotational pole. Polymele's rotational north pole points toward

ecliptic latitude In astronomy, the ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small So ...

–80.9°, which corresponds to an

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbita ...

of 170.9° with respect to the

, making Polymele a retrograde rotator.

Satellite

Following observations of an occultation on 26 March 2022, the ''Lucy'' mission team reported the discovery of a

around Polymele. The satellite is a smaller asteroid about in diameter, orbiting nearly in the equatorial plane of Polymele at a distance of . Assuming Polymele has a density of , the satellite should have an orbital period between 14.4 and 16.6 days. It will not be assigned a formal name until further observations determine its orbit. The ''Lucy'' team refers to the companion by the temporary informal name "Shaun," after Aardman Animations' animated sheep. The satellite was detected again in an occultation on 4 February 2023, in the largest organized occultation expedition in history. Nearly 200 astronomers across two continents participated in the campaign.

Exploration

''Lucy'' mission target

Polymele is planned to be visited by the ''Lucy'' spacecraft which launched in 2021. The flyby is scheduled for 15 September 2027, and will approach the asteroid to a distance of at a relative velocity of .

References

External links

Asteroid Lightcurve Database (LCDB)
query form

)
Dictionary of Minor Planet Names
Google books

– Minor Planet Center * * {{DEFAULTSORT:Polymele 015094 015094 Named minor planets 015094 19991117