216 Kleopatra

216 Kleopatra is a metallic, ham-bone-shaped asteroid and trinary system orbiting in the central region of the asteroid belt, with a mean diameter of 120 kilometers (75 miles). It was discovered on 10 April 1880, by Austrian astronomer Johann Palisa at the Austrian Naval Pola Observatory, in what is now Pula, Croatia.[1] The M-type asteroid has a shorter than average rotation period of 5.4 hours.[4] It was named after Cleopatra, the famous Egyptian queen. Two small minor-planet moons were discovered in 2008, and later named Alexhelios and Cleoselene.

216 Kleopatra
Kleopatra moons - eso2113e.jpg
Kleopatra and its two moons imaged by VLT-SPHERE in 2017
Discovery [1]
Discovered byJ. Palisa
Discovery sitePola Obs.
Discovery date10 April 1880
(216) Kleopatra
Named after
Cleopatra (Egyptian queen)[2]
A905 OA · A910 RA
main-belt[1][3] · (central)[4]
AdjectivesKleopatrian, Kleopatrean
Orbital characteristics[3]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc137.60 yr (50,259 d)
Aphelion3.4951 AU
Perihelion2.0931 AU
2.7941 AU
4.67 yr (1,706 d)
0° 12m 39.6s / day
Known satellites2 (Alexhelios · Cleoselene)
Physical characteristics
Dimensions(276 × 94 × 78) ± 15% km[7]
Mean diameter
122±30 km[7]
103±4 km[8]
121.6±1.6 km[9]
135±2 km[10]
Mass(2.97±0.02)×1018 kg[11][7]
Mean density
ca. 4.5 g/cm3 (most likely between 3.6±0.4 g/cm3 for D = 135 km and 5.4±0.4 g/cm3 for D = 109 km)[7]
5.385280±0.000001 h[7]
M (Tholen)[3] · Xe (SMASS)[3]
B–V = 0.713[3]
U–B = 0.238[3]
7.35±0.02[4][14][16] · 7.45[12]

Orbit and classificationEdit

Kleopatra is a non-family asteroid from the main belt's background population.[5] It orbits the Sun in the central asteroid belt at a distance of 2.1–3.5 AU once every 4 years and 8 months (1,706 days; semi-major axis of 2.79 AU). Its orbit has an eccentricity of 0.25 and an inclination of 13° with respect to the ecliptic.[3] The body's observation arc begins at Leipzig Observatory (534) on 20 April 1880, ten days after to its official discovery observation at Pola Observatory.[1]


Physical characteristicsEdit

3D model of Kleopatra from radar observation (animation)

Kleopatra is a relatively large asteroid, measuring 217 × 94 × 81 km.[17] Calculations from its radar albedo and the orbits of its moons show it to be a rubble pile, a loose amalgam of metal, rock, and 30–50% empty space by volume, likely due to a disruptive impact prior to the impact that created its moons.

Kleopatra has an unusual shape. The initial mapping of its elongated shape was indicated by stellar occultation observations from eight distinct locations on 19 January 1991.[18] Subsequent observations with the ESO 3.6 m Telescope at La Silla, run by the European Southern Observatory, were interpreted to show a double source with two distinct lobes of similar size.[19] These results were disputed when radar observations at the Arecibo Observatory showed that the two lobes of the asteroid are connected, resembling the shape of a ham-bone. The radar observations provided a detailed shape model that appeared on the cover of Science Magazine.[17]

Adaptive-optics observations of 216 Kleopatra have allowed detailed modelling of this triple asteroid by Broz et al in 2021.[20] The model indicates a mass of Kleopatra of (1.49 ± 0.16) × 10−12 M⊙ or 2.97 × 10^18 kg, which is significantly lower than previously thought. Orbital periods of the two satellites are estimated as 1.8 and 2.7 days; their diameters are estimated as 6.9 and 8.9 kilometers. Orbital evolution of the satellites around such an extremely irregular body is to be expected.

The unique nature of the Kleopatra system makes it an object of intense ongoing study. ([21] and [22])


In 1988 a search for satellites or dust orbiting this asteroid was performed using the UH88 telescope at the Mauna Kea Observatories, but the effort came up empty.[23] In September 2008, Franck Marchis and his collaborators announced that by using the Keck Observatory's adaptive optics system, they had discovered two moons orbiting Kleopatra.[24] The outer and inner satellites are about 8.9 ± 1.6 and 6.9 ± 1.6 km in diameter, with periods of 2.32 ± 0.02 and 1.24 ± 0.02 days, respectively.[25][26]

In February 2011, the minor-planet moons were named Alexhelios /ˌælɪksˈhliɒs/ (outer) and Cleoselene /ˌklsɪˈln/ (inner), after Cleopatra's children Alexander Helios and Cleopatra Selene II.[1]


It is believed that Kleopatra's shape, rotation, and moons are due to an oblique impact perhaps 100 million years ago. The increased rotation would have elongated the asteroid and caused Alexhelios to split off. Cleoselene may have split off later, around 10 million years ago. Kleopatra is a contact binary – if it were spinning much faster, the two lobes would separate from each other, making a true binary system.[11]

See alsoEdit


  1. ^ a b c d e "216 Kleopatra". Minor Planet Center. Retrieved 22 April 2017.
  2. ^ Schmadel, Lutz D. (2007). "(216) Kleopatra". Dictionary of Minor Planet Names – (216) Kleopatra. Springer Berlin Heidelberg. p. 34. doi:10.1007/978-3-540-29925-7_217. ISBN 978-3-540-00238-3.
  3. ^ a b c d e f g h "JPL Small-Body Database Browser: 216 Kleopatra" (2016-09-20 last obs.). Jet Propulsion Laboratory. Archived from the original on 23 April 2017. Retrieved 22 April 2017.
  4. ^ a b c "LCDB Data for (216) Kleopatra". Asteroid Lightcurve Database (LCDB). Retrieved 22 April 2017.
  5. ^ a b "Asteroid 216 Kleopatra". Small Bodies Data Ferret. Retrieved 24 October 2019.
  6. ^ "Cleopatra". Lexico UK Dictionary. Oxford University Press.
  7. ^ a b c d e Shepard et. al (2018) A revised shape model of asteroid (216) Kleopatra, Icarus 311, 197-209
  8. ^ a b c Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Nugent, C.; et al. (November 2012). "Preliminary Analysis of WISE/NEOWISE 3-Band Cryogenic and Post-cryogenic Observations of Main Belt Asteroids". The Astrophysical Journal Letters. 759 (1): 5. arXiv:1209.5794. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8. Retrieved 22 April 2017.
  9. ^ a b c Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117.
  10. ^ a b c Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 22 October 2019.
  11. ^ a b Descamps, P.; Marchis, F.; Berthier, J.; Emery, J. P.; Duchê; ne, G.; et al. (February 2011). "Triplicity and physical characteristics of Asteroid (216) Kleopatra". Icarus. 211 (2): 1022–1033. arXiv:1011.5263. Bibcode:2011Icar..211.1022D. doi:10.1016/j.icarus.2010.11.016.
  12. ^ a b Shevchenko, Vasilij G.; Tedesco, Edward F. (September 2006). "Asteroid albedos deduced from stellar occultations". Icarus. 184 (1): 211–220. Bibcode:2006Icar..184..211S. doi:10.1016/j.icarus.2006.04.006. Retrieved 22 April 2017.
  13. ^ a b c Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90.
  14. ^ a b Pravec, 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. Retrieved 22 April 2017.
  15. ^ Belskaya, I. N.; Fornasier, S.; Tozzi, G. P.; Gil-Hutton, R.; Cellino, A.; Antonyuk, K.; et al. (March 2017). "Refining the asteroid taxonomy by polarimetric observations". Icarus. 284: 30–42. Bibcode:2017Icar..284...30B. doi:10.1016/j.icarus.2016.11.003. Retrieved 22 April 2017.
  16. ^ Harris, A. W.; Young, J. W. (October 1989). "Asteroid lightcurve observations from 1979-1981". Icarus. 81 (2): 314–364. Bibcode:1989Icar...81..314H. doi:10.1016/0019-1035(89)90056-0. ISSN 0019-1035. Retrieved 22 April 2017.
  17. ^ a b Ostro, Steven J.; Hudson, R. Scott; Nolan, Michael C.; Margot, Jean-Luc; Scheeres, Daniel J.; Campbell, Donald B.; et al. (May 2000). "Radar Observations of Asteroid 216 Kleopatra". Science. 288 (5467): 836–839. Bibcode:2000Sci...288..836O. doi:10.1126/science.288.5467.836. PMID 10797000. Retrieved 21 March 2018.
  18. ^ David W. Dunham, Sichao (1991). "The sizes and shapes of (4) Vesta, (216) Kleopatra and (381) Myrrha from observations of occultations during January 1991". International Conference on Asteroids, Comets, Meteors 1991. Retrieved 13 October 2021.
  19. ^ Marchis, F. (13 November 1999). "(216) Kleopatra". Central Bureau for Astronomical Telegrams. Retrieved 21 March 2018.
  20. ^ M. Broz, B. Yang (September 2021). "An advanced multipole model for (216) Kleopatra triple system". Astronomy & Astrophysics. Retrieved 13 October 2021.
  21. ^ F. Marchis, B. Yang (September 2021). "(216) Kleopatra, a low density critically rotating M-type asteroid". Astronomy & Astrophysics. Retrieved 13 October 2021.
  22. ^ Dickinson, David (September 2021). "Here's Our Best View Yet of Asteroid Kleopatra". UniverseToday.com. Retrieved 13 October 2021.
  23. ^ Gradie, J.; Flynn, L. (March 1988). "A Search for Satellites and Dust Belts Around Asteroids: Negative Results". Abstracts of the Lunar and Planetary Science Conference. 19: 405–406. Bibcode:1988LPI....19..405G. Retrieved 21 March 2018.
  24. ^ Marchis, Franck (2 October 2008). "Two Companions Found Near Dog-bone Asteroid". Space.com. Retrieved 20 March 2018.
  25. ^ Lakdawalla, Emily (23 February 2011). "A dog-bone-shaped asteroid's two moons: Kleopatra, Cleoselene, and Alexhelios". Planetary Society blogs. The Planetary Society. Retrieved 28 August 2018.
  26. ^ Hirabayashi, M.; Scheeres, D. J. (2013). "Analysis of asteroid (216) Kleopatra using dynamical and structural constraints". The Astrophysical Journal. 780 (2): 160. arXiv:1312.4976. Bibcode:2014ApJ...780..160H. doi:10.1088/0004-637X/780/2/160.

External linksEdit