216 Kleopatra

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216 Kleopatra
Kleopatra.jpg
(Animation)
Discovery
Discovered by Johann Palisa
Discovery date April 10, 1880
Designations
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
55.259°
Inclination 13.136°
215.672°
179.099°
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)
7.35[4]

216 Kleopatra /ˌklˈpætrə/ is an asteroid orbiting in the asteroid belt. It was discovered by Austrian astronomer Johann Palisa on April 10, 1880, from Pula.[5] 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 properties and moons

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.[6] 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.[7] 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.[8] The outer and inner satellites are about 5 km and 3 km in diameter, respectively.[9]

In February 2011 the moons were named Alexhelios (/ˌælksˈhli.s/, outer) and Cleoselene (/ˌklsˈln/, inner), after Cleopatra's children Alexander Helios and Cleopatra Selene II.[10]

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]

References

  1. 1.0 1.1 1.2 Lua error in package.lua at line 80: module 'strict' not found.
  2. 2.0 2.1 Marchis, Descamps, et al. Icarus, Triplicity and physical characteristics of Asteroid (216) KleopatraFeb. 2011.
  3. Lua error in package.lua at line 80: module 'strict' not found. See Table 1.
  4. 4.0 4.1 4.2 Lua error in package.lua at line 80: module 'strict' not found. See Table 4.
  5. Lua error in package.lua at line 80: module 'strict' not found.
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  10. MPC 73983

External links