216 Kleopatra

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216 Kleopatra
Discovered by Johann Palisa
Discovery date April 10, 1880
Named after
Cleopatra VII
A905 OA, A910 RA
Main belt
Orbital characteristics
Epoch 30 January 2005 (JD 2453400.5)
Aphelion 3.496 AU (523.049 Gm)
Perihelion 2.089 AU (312.544 Gm)
2.793 AU (417.796 Gm)
Eccentricity 0.252
4.67 a (1704.704 d)
17.82 km/s
Inclination 13.136°
Known satellites 2
Physical characteristics
Dimensions 217 × 94 × 81 km [1]
Mass 4.64 ± 0.02 × 10^18 kg [2]
Mean density
4.27 ± 0.86[3] g/cm3
5.385 h
Albedo 0.1068 ± 0.0370[4]
Spectral type
M[4] (Tholen)

216 Kleopatra (/ˌkləˈpætrə, -ˈpɑː-, -ˈp-/[5]) is an asteroid orbiting in the asteroid belt. It was discovered by Austrian astronomer Johann Palisa on April 10, 1880, from Pula.[6] It is named after Cleopatra, the famous queen of Ancient Egypt. The asteroid is notable for its peculiar shape that resembles that of a ham-bone. In 2008, it was discovered to be a ternary asteroid, having two small moons.

Physical characteristics[edit]

Kleopatra is a relatively large asteroid, measuring 217 × 94 × 81 km.[1] 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. Initial 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.[7] 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.[1]


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.[8] 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.[9] The outer and inner satellites are about 5 km and 3 km in diameter, respectively.[10]

In February 2011 the moons were named Alexhelios (/ˌælksˈhlis/, outer) and Cleoselene (/ˌklsˈln/, inner), after Cleopatra's children Alexander Helios and Cleopatra Selene II.[11]


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.[2]


  1. ^ a b c Ostro, S. J.; et al. (2000). "Radar Observations of Asteroid 216 Kleopatra". Science. 288 (5467): 836–839. Bibcode:2000Sci...288..836O. doi:10.1126/science.288.5467.836. ISSN 0036-8075. PMID 10797000. 
  2. ^ a b Marchis, Descamps, et al. Icarus, Triplicity and physical characteristics of Asteroid (216) KleopatraFeb. 2011.
  3. ^ Carry, B. (December 2012), "Density of asteroids", Planetary and Space Science, 73, pp. 98–118, arXiv:1203.4336Freely accessible, Bibcode:2012P&SS...73...98C, doi:10.1016/j.pss.2012.03.009.  See Table 1.
  4. ^ a b c Pravec, P.; et al. (May 2012), "Absolute Magnitudes of Asteroids and a Revision of Asteroid Albedo Estimates from WISE Thermal Observations", Asteroids, Comets, Meteors 2012, Proceedings of the conference held May 16–20, 2012 in Niigata, Japan (1667), Bibcode:2012LPICo1667.6089P.  See Table 4.
  5. ^ "Kleopatra". Dictionary.com Unabridged. Random House. Retrieved 2016-01-23. 
  6. ^ "Numbered Minor Planets 1–5000", Discovery Circumstances, IAU Minor Planet center, retrieved 2013-04-07. 
  7. ^ Marchis, F; et al. (1999), (216) Kleopatra (7308), Central Bureau for Astronomical Telegrams, retrieved 2013-08-27 
  8. ^ 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, pp. 405–406, Bibcode:1988LPI....19..405G. 
  9. ^ F. Marchis; SETI Institute, UC Berkeley; et al. (2008-09-18). "Composite image of (216) Kleopatra observed with the 10m-Keck II telescope". Space.com. Retrieved 2008-10-02. 
  10. ^ Franck Marchis (Principal Investigator, SETI Institute, UC Berkeley). "Two Companions Found Near Dog-Bone Asteroid". SETI Institute. Retrieved 2009-10-26. 
  11. ^ MPC 73983

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