Antiope (// ann-TY-ə-pee; minor planet designation: 90 Antiope) is a double asteroid in the outer asteroid belt. It was discovered on October 1, 1866, by Robert 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 largest asteroids. Antiope is a member of the Themis family of asteroids that share similar orbital elements.
Adaptive-optics image of Antiope
|Discovered by||Robert Luther|
|Discovery date||October 1, 1866|
|MPC designation||(90) Antiope|
|Epoch July 23, 2010|
|2046.9 d (5.60 yr)|
Average orbital speed
87.8 ± 1.0 km
~ 4.1−4.2 ×1017 kg (components)
|1.25 ± 0.05 g/cm³ (each)|
|0.687 d (16.50 h) (synchronous)|
9.02 (each component)
|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|
|Main belt (Themis family)|
|171 ± 1 km|
|0.687713 ± 0.00004 d (16.5051 ± 0.0001 h)|
Average orbital speed
|Satellite of||Binary with 90 Antiope|
|83.8 ± 1.0 km|
|Mass||~ 8.1−8.5 ×1017 kg|
Equatorial escape velocity
|variable; ~ 35−40 m/s|
|0.687 d (16.50 h) (synchronous)|
Since the discovery of Antiope's binary nature, the name "Antiope" technically refers to the slightly larger of the two components, with the smaller component bearing the provisional designation S/2000 (90) 1. However, the name "Antiope" is also used to refer to the binary system as a whole.
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%), making it a truly "double" asteroid. Its binary nature was discovered on 10 August 2000 by a group of astronomers using adaptive optics at the Keck Telescope on Mauna Kea. Before this, IRAS observations had suggested that the asteroid was 120 km in diameter.
Since each component is about 86±1 km across, with their centers separated by only about 171 kilometers, 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 common center of mass which lies in the space between them. The orbital period is approximately 16.50 hours, and the eccentricity below 0.006. Every several years, a period of mutual occultations occurs when the asteroid is viewed from Earth. 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°) with 2 degrees uncertainty. This is tilted about 63° to the circumsolar orbit of the system.
Antiope itself has an average diameter of about 88 km, while its twin, S/2000 (90) 1, has an average diameter of 84 km. Like most bodies in this region, the components of the Antiope system are 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 rubble-pile asteroids composed of debris that accumulated in the aftermath of a previous asteroid collision, possibly the one that formed the Themis family.
Complementary observations using adaptive 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 from Roche equilibrium figures (by more than 10%).
Observations from the VLT-UT4 telescope equipped with an adaptive optics system in 2007 and lightcurve 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 of proto-Antiope into two equisized bodies. The impactor is calculated to have been more than 17 km in diameter. The crater can not be resolved using the W.M. Keck II telescope.
The best is the July 19, 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. Alas, many planned stations were clouded. Many stations were so-called Mighty-Mini or Mighty-Maxi consisting of a binocular objective (homemade using binoculars + hacksaw + plumbing fittings) as well as 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.
- "JPL Small-Body Database Browser: 90 Antiope" (2010-06-13 last obs). Retrieved 8 July 2010.
- Wm. Robert Johnston (23 November 2008). "(90) Antiope and S/2000 (90) 1". Johnston's Archive. Retrieved 23 January 2008.
- 90 Antiope A & B Archived 2008-08-28 at the Wayback Machine, online data sheet, F. Marchis
- Descamps et al., 2007, Icarus article published in April 2007
- "T. Michałowski, et al. (2004). "Eclipsing binary asteroid 90 Antiope". Astronomy & Astrophysics. 423 (3): 1159. Bibcode:2004A&A...423.1159M. doi:10.1051/0004-6361:20040449.
- Supplemental IRAS Minor Planet Survey Archived 2009-08-17 at the Wayback Machine
- PDS spectral class data Archived 2009-08-05 at the Wayback Machine
- "90 Antiope: Raw Keck Image". SWrI Press Release. August 2000. Retrieved 20 October 2009.
- IAUC 7503
- Moore, Patrick; Rees, Robin, eds. (2011), Patrick Moore's Data Book of Astronomy (2nd ed.), Cambridge University Press, p. 165.
- F. Marchis; F. Descamps; P. Hestroffer; Berthier, J. & 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. Bibcode:2004DPS....36.4602M.
- 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. Bibcode:2009DPS....41.5610M.
- Descamps, P.; Marchis; Michalowski; Berthier; Pollock; Wiggins; Birlan; Colas; et al. (2009). "A giant crater on 90 Antiope?". Icarus. 203 (1): 102–111. arXiv:0905.0631. Bibcode:2009Icar..203..102D. doi:10.1016/j.icarus.2009.04.022.
- "Asteroid Data Sets". sbn.psi.edu. Retrieved 28 April 2018.
- Antiope Occultation Yields Double Bonanza. Sky & Telescope
- Franck Marchis (21 July 2011). "An Occultation by the double asteroid (90) Antiope seen in California". NASA blog (Cosmic Diary). Retrieved 28 January 2012.
- Discovery of Companions to Asteroids 762 Pulcova and 90 Antiope SWrI Press Release.
- (90) Antiope, datasheet, johnstonsarchive.net
- Asteroids with Satellites, Robert Johnston, johnstonsarchive.net
- 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.
- An Occultation by the double asteroid (90) Antiope seen in California (Franck Marchis)
- Beatty, Kelly (9 September 2011). "Antiope Occultation Yields Double Bonanza". Sky and Telescope. Retrieved 13 September 2011.
- 90 Antiope at AstDyS-2, Asteroids—Dynamic Site
- 90 Antiope at the JPL Small-Body Database