216 Kleopatra

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216 Kleopatra
Kleopatra moons - eso2113e.jpg
Kleopatra and its two moons imaged by VLT-SPHERE in 2017
Discovery [1]
Discovered by J. Palisa
Discovery site Pola Obs.
Discovery date10 April 1880
(216) Kleopatra
Pronunciation /ˌkliəˈpætrə/ [2]
Named after
Cleopatra (Egyptian queen) [3]
A905 OA ·A910 RA
main-belt [1] [4]  ·(central) [5]
background [6]
Adjectives Kleopatrian, Kleopatrean
Orbital characteristics [4]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc 137.60 yr (50,259 d)
Aphelion 3.4951 AU
Perihelion 2.0931 AU
2.7941 AU
Eccentricity 0.2509
4.67 yr (1,706 d)
0° 12m 39.6s / day
Inclination 13.113°
Known satellites 2 (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]
0.1164±0.004 [10]
0.170 [12]
0.149±0.005 [9]
0.1111±0.0336 [13]
0.1068 [14]
0.200±0.028 [8]
M (Tholen) [4]  · X e (SMASS) [4]
M [13] [15]
B–V = 0.713 [4]
U–B = 0.238 [4]
7.30 [4] [8] [10] [9] [13]
7.35±0.02 [5] [14] [16]  ·7.45 [12]

    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. [5] It was named after Cleopatra, the famous Egyptian queen. Two small minor-planet moons were discovered in 2008, and later named Alexhelios and Cleoselene.


    Orbit and classification

    Kleopatra is a non-family asteroid from the main belt's background population. [6] 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. [4] 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]

    216 Kleopatra-orbit.png

    Physical characteristics

    3D model of Kleopatra from radar observation (animation) Kleopatra.jpg
    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 also

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