Heracles orbits the Sun in the inner 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.[1] The first precovery was taken at Palomar during the Digitized Sky Survey in 1953, extending the body's observation arc by 38 years prior to its official discovery observation.[3]
A large number of rotational lightcurves of Heracles were obtained from photometric observations between 2006 and 2016. Lightcurve data gives a rotation period between 2.7051 and 2.7065 hours with a brightness variation of 0.05 to 0.20 magnitude (U=3/3/3/3/3-).[5][11][15][16][a]
Diameters
According to the surveys carried out by the Spitzer Space Telescope, 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.[8][9][10][13] 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.[11][12]
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 in Puerto Rico, following months of intensive photometric lightcurve observations (see above). It was designated S/2011 (5143) 1.
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 3.6±1.2 and 0.6±0.3 kilometer, respectively.[6][7][11]
Follow-up observations in 2016 confirmed an orbital period of 17 hours for the asteroid moon.[25]
^ abWarner (2017c): lightcurve plot of (5143) Heracles, with a rotation period 2.704±0.002 hours and a brightness amplitude of 0.15 mag (Quality Code of 2; 133 points). Observations from 12 to 17 September 2016, at CS3-Palmer Divide Station. Summary figures at Collaborative Asteroid Lightcurve Link (CALL)
^ abcdPravec, Petr; Harris, Alan W.; Kusnirák, Peter; Galád, Adrián; Hornoch, Kamil (September 2012). "Absolute magnitudes of asteroids and a revision of asteroid albedo estimates from WISE thermal observations". Icarus. 221 (1): 365–387. Bibcode:2012Icar..221..365P. doi:10.1016/j.icarus.2012.07.026.
^ abcPolishook, David (July 2012). "Lightcurves and Spin Periods of Near-Earth Asteroids, The Wise Observatory, 2005 - 2010". The Minor Planet Bulletin. 39 (3): 187–192. Bibcode:2012MPBu...39..187P. ISSN1052-8091.
^Linder, Tyler R.; Sampson, Ryan; Holmes, Robert (January 2013). "Astronomical Research Institute Photometric Results". The Minor Planet Bulletin. 40 (1): 4–6. Bibcode:2013MPBu...40....4L. ISSN1052-8091.