Adaptive optics image of Antiope
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Discovery [1] and designation
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| Discovered by | Robert Luther | |||||||||
| Discovery date | October 1, 1866 | |||||||||
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Designations
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| Alternate name[note 1] | 1952 BK2 [2] | |||||||||
| Minor planet category |
Main belt (Themis family) |
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| Epoch August 18, 2005 (JD 2453600.5) |
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| Aphelion | 545.753 Gm 3.648 AU |
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| Perihelion | 398.502 Gm 2.664 AU |
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| Semi-major axis | 472.128 Gm 3.156 AU |
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| Eccentricity | 0.156 | |||||||||
| Orbital period | 2047.856 d (5.61 a) | |||||||||
| Average orbital speed | 16.66 km/s | |||||||||
| Mean anomaly | 348.378° | |||||||||
| Inclination | 2.220° | |||||||||
| Longitude of ascending node | 70.235° | |||||||||
| Argument of perihelion | 242.480° | |||||||||
| Dimensions | 93.0×87.0×83.6 km | |||||||||
| Mass | 8.3×1017 kg (whole system)[1] ~ 4.1−4.2 × 1017 kg (components) |
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| Mean density | 1.25 ± 0.05 g/cm³ (each)[2] | |||||||||
| Equatorial surface gravity | variable; ~ 0.03−0.04 m/s² | |||||||||
| Equatorial escape velocity | variable; ~ 35−40 m/s | |||||||||
| Rotation period | 0.687 d (16.50 h).[3] | |||||||||
| Geometric albedo | 0.060[4] | |||||||||
| Surface temp. Kelvin Celsius |
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| Spectral type | C[5] | |||||||||
| Absolute magnitude (H) | 8.27 (together) 9.02 (each component) |
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90 Antiope (pronounced /ænˈtaɪ.əpiː/ an-TYE-ə-pee) is an asteroid discovered on October 1, 1866 by Robert Luther. The 90th asteroid to be discovered, it is named after Antiope from Greek mythology, though it is disputed as to whether this is Antiope the Amazon or Antiope the mother of Amphion and Zethus.
Antiope orbits in the outer third of the core region of the main belt, and is a member of the Themis family of asteroids. Like most bodies in this region, it is of the dark C spectral type, indicating a carbonaceous composition. The low density (1.3±0.2 g/cm³) of its components (see below) suggests a significant porosity (>30%), indicating a rubble pile asteroid composed of debris that accumulated in the aftermath of a previous asteroid collision (possibly the one that formed the Themis family).
One of the components appears to have a 68-km bowl-shaped impact crater that may be the result of a violent collision of proto-Antiope into two equisized bodies.[6]
One observed stellar occultation by Antiope has been reported, on June 11, 1980.
Double asteroid
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Discovery[8] and designation
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| Discovered by | W. J. Merline, L. M. Close, J. C. Shelton, C. Dumas, F. Menard, C. R. Chapman, and D. C. Slater |
| Discovery date | August 10, 2000[7] |
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Designations
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| Minor planet category |
Main belt (Themis family) |
| Semi-major axis | 171 ± 1 km |
| Eccentricity | 0.01 ± 0.02 |
| Orbital period | 0.687713 ± 0.00004 d (16.5051 ± 0.0001 h) |
| Average orbital speed | 18.0 m/s |
| Satellite of | Binary with 90 Antiope |
| Dimensions | 89.4×82.8×79.6 km |
| Mass | ~ 8.1−8.5 × 1017 kg[2] |
| Equatorial escape velocity | variable; ~ 35−40 m/s |
| Rotation period | 0.687 d (16.50 h)[3] |
| Absolute magnitude (H) | 9.02 |
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%[9]), making it a truly "double" asteroid.[10] Its binary nature was discovered on 10 August 2000 by a group of astronomers using adaptive optics at the Keck Telescope on Mauna Kea.[8] The "secondary" is designated S/2000 (90) 1.
Each component is about 86±1 km across, with their centers separated by only about 170 kilometers. This means that the gap separating the two halves is a mere 60 km, or so. The two bodies orbit around the common center of mass which lies in the space between them. The orbital period is approximately 16.50 hours, the eccentricity below 0.03 (best estimate 0.01 ± 0.02).[1] Every several years, a period of mutual occultations occurs when the asteroid is viewed from Earth.[3] Using Kepler's third 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 towards ecliptic coordinates (β, λ) = (200°, 38°)[2] with 2 degrees uncertainty.[2] This is tilted about 63° to the circumsolar orbit of the system.
The complementary observations using adaptive optic observations on 8-10m 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 a 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 from Roche equilibrium figures (by more than 10%).
References
- ^ a b c 90 Antiope A & B, online data sheet, F. Marchis
- ^ a b c d Descamps et al., 2007, Icarus article published in April 2007
- ^ a b c "T. Michałowski et al. (2004). "Eclipsing binary asteroid 90 Antiope". Astronomy & Astrophysics 423: 1159. doi:.
- ^ Supplemental IRAS Minor Planet Survey
- ^ PDS spectral class data
- ^ Marchis, Franck; Enriquez, J. E.; Emery, J. P.; Berthier, J.; Descamps, P. (2009). "The Origin of the Double Main Belt Asteroid (90) Antiope by Component-Resolved Spectroscopy". DPS meeting #41. American Astronomical Society. http://adsabs.harvard.edu/abs/2009DPS....41.5610M. Retrieved 2009-11-08.
- ^ "90 Antiope: Raw Keck Image". SWrI Press Release. August 2000. http://www.boulder.swri.edu/merline/press/fig1.html. Retrieved 2009-10-20.
- ^ a b IAUC 7503
- ^ F. Marchis, F. Descamps, P. Hestroffer, and I. de Pater (2004). "Fine Analysis of 121 Hermione, 45 Eugenia, and 90 Antiope Binary Asteroid Systems With AO Observations". Bulletin of the American Astronomical Society 36: 1180. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004DPS....36.4602M&db_key=AST&data_type=HTML&format=&high=444b66a47d22122.
- ^ "Satellites and Companions of Minor Planets". IAU / Minor Planet Center. 2009-09-17. http://www.cfa.harvard.edu/iau/minorsats.html. Retrieved 2009-10-14.
External links
- Discovery of Companions to Asteroids 762 Pulcova and 90 Antiope SWrI Press Release.
- Data on (90) Antiope from Johnston's archive (maintained by W. R. Johnston)
- online data on the Antiope system maintained by F. Marchis; includes images and simulated occultation movies.
- ESO Press-Release published on May 29, 2007 The Impossible Siblings
- UC-Berkeley Press-Release published on May 29, 2007 Binary asteroid revealed as twin rubble piles
- Antiope, a true binary asteroid, The Planetary Society weblog, E. Lakdawalla, 11 April 2007.
- NASA JPL Small-Body Database Browser on 90 Antiope
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