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| Discovery [1] | |
|---|---|
| Discovered by | Robert Luther |
| Discovery date | 1 October 1866 |
| Designations | |
| (90) Antiope | |
| Pronunciation | /ænˈtaɪəpiː/[1] |
| 1952 BK2[2] | |
| Main belt[2] (Themis family) | |
| Adjectives | Antiopean |
| Orbital characteristics[2] | |
| Epoch 23 July 2010 (JD 2455400.5) | |
| Aphelion | 3.6494 AU |
| Perihelion | 2.6606 AU |
| 3.1550AU | |
| Eccentricity | 0.15670 |
| 2046.9 d (5.60yr) | |
Averageorbital speed | 16.66 km/s |
| 304.12° | |
| Inclination | 2.2195° |
| 70.21° | |
| 242.96° | |
| Physical characteristics | |
| Dimensions | 93.0×87.0×83.6 km[3] 87.8 ± 1.0 km[3] |
| Mass | 8.3×1017 kg (whole system)[4] ~ 4.1−4.2×1017 kg (components) |
Meandensity | 1.25 ± 0.05 g/cm3 (each)[5] |
| 0.687 d (16.50 h)[6] (synchronous) | |
| 0.060[7] | |
| C[8] | |
| 8.27 (together)[2] 9.02 (each component) | |
 | |
| Discovery[9] | |
|---|---|
| Discovered by | W. J. Merline,L. M. Close, J. C. Shelton,C. Dumas, F. Menard,C. R. Chapman, andD. C. Slater |
| Discovery date | 10 August 2000[10] |
| Designations | |
| Main belt (Themis family) | |
| Orbital characteristics[4] | |
| 171 ± 1 km | |
| Eccentricity | <0.006 |
| 0.687713 ± 0.00004 d (16.5051 ± 0.0001 h) | |
Averageorbital speed | 18.0 m/s |
| Satellite of | Binary with 90 Antiope |
| Physical characteristics | |
| Dimensions | 89.4×82.8×79.6 km[3] |
| 83.8 ± 1.0 km[3] | |
| Mass | ~ 8.1−8.5×1017 kg[5] |
Equatorialescape velocity | variable; ~ 35−40 m/s |
| 0.687 d (16.50 h)[6] (synchronous) | |
| 9.02 | |
90 Antiope is adouble asteroid in the outerasteroid belt. It was discovered on 1 October 1866, byRobert Luther. In 2000, it was found to consist of two almost-equally-sized bodies orbiting each other. At average diameters of about 88 km and 84 km, both components are among the 500 largestasteroids. Antiope is a member of theThemis family of asteroids that share similarorbital elements.[11]
The asteroid's proper name comes fromGreek mythology, but it is unclear whether it refers toAntiope the Amazon orAntiope the mother of Amphion and Zethus.[12]
Since the discovery of Antiope's binary nature, the name "Antiope" technically refers to the slightly larger of the two components. The smaller component is sometimes referred to under the (unofficial) designationS/2000 (90) 1.[13] However, the name "Antiope" is also used to refer to the binary system as a whole.[where?]
The most remarkable feature of Antiope is that it consists of two components of almost equal size (the difference in mass is less than 2.5%[14]), making it a truly"double" asteroid. Its binary nature was discovered on 10 August 2000 by a group of astronomers usingadaptive optics at theKeck Telescope onMauna Kea.[9] Before this,IRAS observations had suggested that the asteroid was 120 km in diameter.[2]
Antiope orbits in the outer third of the core region of theasteroid belt, and is a member of theThemis family.[15]
Since each component is about 86±1 km across, with their centers separated by only about 171 kilometers,[4] the gap separating the two halves is about the same as the diameter of each component. As a result, the two bodies orbit around the commoncenter of mass which lies in the space between them. The orbital period is approximately 16.50 hours, and the eccentricity below 0.006.[4] Every several years, a period of mutual occultations occurs when the asteroid is viewed from Earth.[6] UsingKepler'sthird law, the mass and density of the components can be derived from the orbital period and component sizes.
The axis of the mutual orbit of the two components points towardsecliptic coordinates (β, λ) = (200°, 38°)[5] with 2 degrees uncertainty.[5] This is tilted about 63° to the circumsolar orbit of the system.
Antiope itself has an average diameter of about 88 km, while its companion has an average diameter of 84 km. Like most bodies in this region, the components of the Antiope system are of the darkC spectral type, indicating acarbonaceous composition. The lowdensity (1.3±0.2 g/cm3) of its components (see below) suggests a significantporosity (>30%), indicatingrubble-pile asteroids composed of debris that accumulated in the aftermath of a previous asteroid collision, possibly the one that formed the Themis family.[citation needed]
Complementary observations usingadaptive optic observations on 8–10 m class telescopes and mutual events photometric lightcurve over several months have served as input quantities for a derivation of a whole set of other physical parameters (shapes of the components, surface scattering, bulk density, and internal properties). The shape model is consistent with slightly non-spherical components, having a size ratio of 0.95 (with an average radius of 42.9 km), and exhibiting equilibrium figures for homogeneous rotating bodies. A comparison with grazing occultation event lightcurves taken in 2003 suggests that the real shape of the components do not depart much fromRoche equilibrium figures (by more than 10%).[citation needed]
Observations from theVLT-UT4 telescope equipped with anadaptive optics system in 2007 andlightcurve data analysis suggest that one of the components appears to have a 68 km bowl-shaped impact crater that may be the result of a violent collision that brokeproto-Antiope into two equisized bodies.[16] The impactor is calculated to have been more than 17 km in diameter.[17] The crater can not be resolved using theW.M. Keck II telescope.
The two parts of the Antiope have very similar spectra. This implies they may have a common origin, such as being formed from the breakup of a larger rubble-pile asteroid, but other formation scenarios cannot be ruled out.[18]
There have been 9 occultations observed since 1988,[19] many of which aremultichord occultations.
The best is the 19 July 2011 event observed from 57 stations spread out along the western USA coast where 46 stations recorded positive occultations and 11 stations observed misses. However many of the misses were important to clearly separate the two components of 90 Antiope. Many planned stations were unfortunately clouded. Many stations were so-called Mighty-Mini or Mighty-Maxi, consisting of a binocular objective (homemade using binoculars + hacksaw + plumbing fittings) with a video camera and Video Time Inserter (VTI), and were pre-pointed and left to run unattended, thereby allowing one observer to deploy many stations.
The crater mentioned above was confirmed by this occultation.[20][21]
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