5143 Heracles( provisional designation ) is a highly eccentric, rare-type

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. ...

and synchronous binary system, classified as near-Earth object of the

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, approximately 4.8 kilometers in diameter. The asteroid was discovered on 7 November 1991, by American astronomer Carolyn Shoemaker at

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

in California, United States. It is named for the Greek divine hero Heracles. It has an Earth minimum orbit intersection distance of and is associated with the Beta Taurids daytime meteor shower.

Classification and orbit

Heracles orbits the Sun in the

inner Interior may refer to: Arts and media * ''Interior'' (Degas) (also known as ''The Rape''), painting by Edgar Degas * ''Interior'' (play), 1895 play by Belgian playwright Maurice Maeterlinck * ''The Interior'' (novel), by Lisa See * Interior de ...

main-belt at a distance of 0.4–3.2 AU once every 2 years and 6 months (907 days). Its orbit has an eccentricity of 0.77 and an inclination of 9 ° with respect to the ecliptic. The first

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

was taken at Palomar during the ''

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

'' in 1953, extending the body's observation arc by 38 years prior to its official discovery observation. Due to its high eccentricity, Heracles is also a

Mercury-grazer A Mercury crosser is an asteroid whose orbit crosses that of Mercury. The Mercury crossers proper have aphelia outside Mercury's (0.4667 AU) and perihelia inside Mercury's (0.3075 AU), whereas those listed here as outer grazers have perihelia wit ...

and a Mars-crosser. It has a minimum orbital intersection distance with Earth of which corresponds to 22.8 lunar distances.

Physical characteristics

Spectral type

In the SMASS taxonomy, Heracles is a rare

O-type asteroid The rare O-type asteroids have spectra similar to the unusual asteroid 3628 Boznemcová, which is the best asteroid match to the spectra of L6 and LL6 ordinary chondrite meteorites. Their spectra have a deep absorption feature longward of 0.75 μm ...

, which have spectra similar to those of stony chondritic meteorites of the L6 and LL6 type. However, it has also been characterized as a carbonaceous C-type, as well as a stony Sk and

Q-type asteroid Q-type asteroids are relatively uncommon inner-belt asteroids with a strong, broad 1 micrometre olivine and pyroxene feature, and a spectral slope that indicates the presence of metal. There are absorption features shortwards and longwards of 0. ...

Lightcurves

A large number of rotational lightcurves of Heracles were obtained from photometric observations between 2006 and 2016. Lightcurve data gives a

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 ...

between 2.7051 and 2.7065 hours with a brightness variation of 0.05 to 0.20 magnitude ().

Diameters

According to the surveys carried out by the

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, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, the asteroid measures between 3.26 and 4.843 kilometers in diameter, and its surface has an albedo between 0.20 and 0.24. The ''Collaborative Asteroid Lightcurve Link'' adopts the results from Petr Pravec's revised WISE data, that is, an albedo of 0.1481 and a diameter of 4.83 kilometers with an absolute magnitude of 14.27.

Binary system

On 12 July 2012, it was announced that Heracles is an assumed synchronous binary asteroid with a minor-planet moon orbiting its primary in a retrograde motion approximately every 16 hours. The companion was discovered in December 2011, by a team of astronomers using radar observations from

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

in Puerto Rico, following months of intensive photometric lightcurve observations ''(see above)''. It was designated . The satellite received the nickname Omphale, after the wife of Heracles who birth to his children. A longer orbital period of 40–57 hours cannot be excluded, which would then no longer be a synchronous system. Estimated diameters for Heracles and its moon are and kilometer, respectively. Follow-up observations in 2016 confirmed an orbital period of 17 hours for the asteroid moon.

Naming

This minor planet was named after Heracles, the divine gatekeeper of Mount Olympus and one of the greatest heroes in Greek mythology, known for his strength and his '' Twelve Labors''. Heracles is the son of Zeus and Alcmena, after whom the asteroids and were named. In the Roman adaptation, Heracles is known as Hercules. 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. Function ...

on 14 July 1992 ().