 | |
| Discovery [1] | |
|---|---|
| Discovered by | J. Palisa |
| Discovery site | Pola Obs. |
| Discovery date | 10 April 1880 |
| Designations | |
| (216) Kleopatra | |
| Pronunciation | /ˌkliəˈpætrə/[2] |
Named after | Cleopatra(Egyptian queen)[3] |
| A880 GB · 1905 OA 1910 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 | 137.60yr (50,259 d) |
| Aphelion | 3.4951AU |
| Perihelion | 2.0931 AU |
| 2.7941 AU | |
| Eccentricity | 0.2509 |
| 4.67 yr (1,706 d) | |
| 346.24° | |
| 0° 12m 39.6s / day | |
| Inclination | 13.113° |
| 215.36° | |
| 180.11° | |
| Knownsatellites | 2 (Alexhelios · Cleoselene) |
| Physical characteristics | |
| Dimensions | (276 × 94 × 78) ± 15% km[7] |
| 118±2 km[8] 122±30 km[7] 103±4 km[9] 121.6±1.6 km[10] 135±2 km[11] | |
| Flattening | 0.82[a] |
| Mass | (3.0±0.3)×1018 kg[8] (2.97±0.02)×1018 kg[12][7] |
Meandensity | 3.45±0.41 g/cm3[8] ca.4.5 g/cm3 (most likely between3.6±0.4 g/cm3 for D = 135 km and5.4±0.4 g/cm3 for D = 109 km)[7] |
| 5.385280±0.000001 h[7] | |
| 0.152 (calculated)[8] 0.1164±0.004[11][4] 0.170[13] 0.149±0.005[10] 0.1111±0.0336[14] 0.1068[15] 0.200±0.028[9] | |
| M(Tholen)[4] · Xe(SMASS)[4] M [14][16] B–V = 0.713[4] U–B = 0.238[4] | |
| 7.30[9][11][10][14] 7.09[4] 7.35±0.02[5][15][17] 7.45[13] | |
216 Kleopatra is a largeM-typeasteroid with amean diameter of 120 kilometers (75 miles) and is noted for its elongate bone or dumbbell shape.[18][19][7][20] It was discovered on 10 April 1880 by Austrian astronomerJohann Palisa at the Austrian NavalPola Observatory, in what is nowPula, Croatia, and was named afterCleopatra, the famous Egyptian queen.[1] It has two smallminor-planet moons which were discovered in 2008 and later namedAlexhelios andCleoselene.
Kleopatra is a non-family asteroid from the main belt'sbackground population.[6] It orbits the Sun in thecentral 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 aneccentricity of 0.25 and aninclination of 13° with respect to theecliptic.[4] The body'sobservation arc begins at Leipzig Observatory (534) on 20 April 1880, ten days after its official discovery observation at Pola Observatory.[1]
Kleopatra is a relatively large asteroid, with a mean (volume-equivalent) diameter of120±2 km[7][20] and an unusually elongated shape.
The initial mapping of its elongated shape was indicated by stellar occultation observations from eight distinct locations on 19 January 1991.[21] Subsequent observations with theESO 3.6 m Telescope atLa Silla, run by theEuropean Southern Observatory, were interpreted to show a double source with two distinct lobes of similar size.[22] These results were disputed when radar observations at theArecibo 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.[18] Later models suggested that Kleopatra was more elongate and the most recent models usingradar delay-Doppler imaging,adaptive optics, andstellar occultations provide dimensions of 267 × 61 × 48 km.[23][7][20]
In 1988 a search for satellites or dust orbiting this asteroid was performed using theUH88 telescope at theMauna Kea Observatories, but the effort was fruitless.[24] In September 2008,Franck Marchis and his collaborators announced that by using theKeck Observatory'sadaptive optics system, they had discovered twomoons orbiting Kleopatra.[25] In February 2011, theminor-planet moons were named Alexhelios/ˌæləksˈhiːliɒs/ (outer) and Cleoselene/ˌkliːoʊsəˈliːniː/ (inner), after Cleopatra's childrenAlexander Helios andCleopatra Selene II.[1] The outer and inner satellites are about 8.9 ± 1.6 and 6.9 ± 1.6 km in diameter, with periods of 2.7 and 1.8 days, respectively.[26]
The presence of two moons provides a way to estimate Kleopatra's mass, although its irregular shape makes the orbital modeling a challenge.[26] The most recent adaptive-optics observations and modeling provides a mass of Kleopatra of(1.49±0.16)×10−12 M⊙, or(2.97±0.32)×1018 kg, which is significantly lower than previously thought.[12] When combined with the best volume estimate for Kleopatra, this indicates a bulk density of3.38±0.50 g/cm3.[20]
These recent bulk density results call into question the canonical view of Kleopatra as a pure metallic object.[18] Kleopatra's radar albedo suggests a high metal content in the southern hemisphere, but is similar to the more common S- and C-class asteroids along the equator.[7] One way to reconcile these observations is to hypothesize that Kleopatra is arubble-pile asteroid with significant porosity in dynamic equilibrium.[20]
One possible origin that explains Kleopatra's shape, rotation, and moons is that it was created by 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 acontact binary – if it were spinning much faster, the two lobes would separate from each other, making a true binary system.[12][20]
