216 Kleopatra
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Discovery
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| Discovered by | Johann Palisa |
| Discovery date | April 10, 1880 |
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Designations
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| Named after | Cleopatra VII |
| Alternate name(s) | A905 OA, A910 RA |
| Minor planet category |
Main belt |
| Epoch 30 January 2005 (JD 2453400.5) | |
| Aphelion | 3.496 AU (523.049 Gm) |
| Perihelion | 2.089 AU (312.544 Gm) |
| Semi-major axis | 2.793 AU (417.796 Gm) |
| Eccentricity | 0.252 |
| Orbital period | 4.67 a (1704.704 d) |
| Average orbital speed | 17.82 km/s |
| Mean anomaly | 55.259° |
| Inclination | 13.136° |
| Longitude of ascending node | 215.672° |
| Argument of perihelion | 179.099° |
| Satellites | 2 |
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Physical characteristics
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| Dimensions | 217 × 94 × 81 km |
| Mass | 4.64 ± 0.02 × 10^18 kg [1] |
| Mean density | 3.6 |
| Rotation period | 5.385 h |
| Albedo | 0.116 |
| Temperature | unknown |
| Spectral type | M |
| Absolute magnitude (H) | 7.3 |
216 Kleopatra (
/ˌkliːɵˈpætrə/) is a main-belt asteroid. It was discovered by Johann Palisa on April 10, 1880, from Pula. It is named after Cleopatra, the famous queen of Ancient Egypt. It is notable for its peculiar bilobate shape, which has been compared to a dog's bone. It was recently discovered to be a trinary asteroid, having two small moons.
[edit] Physical properties and moons
Kleopatra is a relatively large asteroid, measuring 217 × 94 × 81 km. 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 that has been compared to a dog's bone. This bilobate shape was revealed by adaptive optics on the ESO 3.6 m Telescope at La Silla, run by the European Southern Observatory. By bouncing radar signals off the asteroid, a team of astronomers at the Arecibo radio telescope in Puerto Rico were able to develop a more detailed computer model of its shape, which confirmed the earlier results.
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.[2] The outer and inner satellites are about 5 km and 3 km in diameter, respectively.[3]
In February 2011 they were named Alexhelios (/ˌælɨksˈhiːli.ɵs/, outer) and Cleoselene (/ˌkliːɵsɨˈliːniː/, inner), after Cleopatra's children Alexander Helios and Cleopatra Selene II.[4]
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.[1]
[edit] References
- ^ a b Marchis, Descamps, et al. Icarus, Triplicity and physical characteristics of Asteroid (216) KleopatraFeb. 2011.
- ^ F. Marchis, et al, SETI Institute, UC Berkeley (2008-09-19). "Composite image of (216) Kleopatra observed with the 10m-Keck II telescope". Space.com. http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=081002-seti-dogbone-02.jpg&cap=Composite+image+of+(216)+Kleopatra+observed+with+the+10m-Keck+II+telescope+and+its+adaptive+optics+system+on+September+19+2008+UT.+The+central+dark+circle+shows+the+dog-bone+shape+of+the+primary.+The+arrows+indicate+the+position+of+the+newly+discovered+satellites+with+temporary+names+S/2008+(216)+1+and+S/2008+(216)+2.+Credit:+F.+Marchis,+et+al,+SETI+Institute,+UC+Berkeley. Retrieved 2008-10-02.
- ^ Franck Marchis (Principal Investigator, SETI Institute, UC Berkeley) (2008-09-19). "Two Companions Found Near Dog-Bone Asteroid". SETI Institute. http://www.seti.org/Page.aspx?pid=1182. Retrieved 2009-10-26.
- ^ MPC 73983
- The Asteroid Orbital Elements Database
- Minor Planet Discovery Circumstances
- Asteroid Lightcurve Data File
- Triplicity and physical characteristics of Asteroid (216) Kleopatra
[edit] External links
- Bilobated shape of 216 Kleopatra
- Astronomers Catch Images of Giant Metal Dog Bone Asteroid – NASA article
- An Asteroid for the Dogs
- Orbital simulation from JPL (Java) / Ephemeris
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