Astronomy:90 Antiope
| Discovery [1] | |
|---|---|
| Discovered by | Robert Luther |
| Discovery date | October 1, 1866 |
| Designations | |
| (90) Antiope | |
| Pronunciation | /ænˈtaɪəpiː/[2] |
| 1952 BK2[1] | |
| Minor planet category | Main belt[1] (Themis family) |
| Adjectives | Antiopean |
| Orbital characteristics[1] | |
| Epoch July 23, 2010 (JD 2455400.5) | |
| |{{{apsis}}}|helion}} | 545.94 Gm 3.6494 AU |
| |{{{apsis}}}|helion}} | 398.02 Gm 2.6606 AU |
| 471.19 Gm 3.1550 AU | |
| Eccentricity | 0.15670 |
| Orbital period | 2046.9 d (5.60 yr) |
| Average Orbital speed | 16.66 km/s |
| Mean anomaly | 304.12° |
| Inclination | 2.2195° |
| Longitude of ascending node | 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) |
| Mean density | 1.25 ± 0.05 g/cm3 (each)[5] |
| Rotation period | 0.687 d (16.50 h)[6] (synchronous) |
| Geometric albedo | 0.060[7] |
| C[8] | |
| Absolute magnitude (H) | 8.27 (together)[1] 9.02 (each component) |
 | |
| Discovery[10] | |
|---|---|
| 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[9] |
| Designations | |
| Minor planet category | Main belt (Themis family) |
| Orbital characteristics[4] | |
| 171 ± 1 km | |
| Eccentricity | <0.006 |
| 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 |
| Physical characteristics | |
| Dimensions | 89.4×82.8×79.6 km[3] |
| Mean diameter | 83.8 ± 1.0 km[3] |
| Mass | ~ 8.1−8.5 ×1017 kg[5] |
Equatorial escape velocity | variable; ~ 35−40 m/s |
| Rotation period | 0.687 d (16.50 h)[6] (synchronous) |
| Absolute magnitude (H) | 9.02 |
Antiope (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.[11]
Naming
The asteroid's proper name comes from Greek mythology, but it is disputed whether this is Antiope the Amazon or Antiope the mother of Amphion and Zethus.
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.
Properties
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%[12]), 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.[10] Before this, IRAS observations had suggested that the asteroid was 120 km in diameter.[1]
Orbital
Antiope orbits in the outer third of the core region of the asteroid belt, and is a member of the Themis family.[13]
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 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.[4] Every several years, a period of mutual occultations occurs when the asteroid is viewed from Earth.[6] 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°)[5] with 2 degrees uncertainty.[5] This is tilted about 63° to the circumsolar orbit of the system.
Physical
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.[citation needed]
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%).[citation needed]
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 that broke proto-Antiope into two equisized bodies.[14] The impactor is calculated to have been more than 17 km in diameter.[15] The crater can not be resolved using the W.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.[16]
Occultations
There have been 9 occultations observed since 1988,[17] many of which are multichord occultations.
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. 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.[18][19]
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File:LQ Aquarii occultation 20110719-001.webm
References
- ↑ 1.0 1.1 1.2 1.3 1.4 "JPL Small-Body Database Browser: 90 Antiope". https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=90.
- ↑ Noah Webster (1884) A Practical Dictionary of the English Language
- ↑ 3.0 3.1 3.2 3.3 Wm. Robert Johnston (2008-11-23). "(90) Antiope and S/2000 (90) 1". Johnston's Archive. http://www.johnstonsarchive.net/astro/astmoons/am-00090.html.
- ↑ 4.0 4.1 4.2 4.3 90 Antiope A & B , online data sheet, F. Marchis
- ↑ 5.0 5.1 5.2 5.3 Descamps et al., 2007, Icarus article published in April 2007
- ↑ 6.0 6.1 6.2 "T. Michałowski et al. (2004). "Eclipsing binary asteroid 90 Antiope". Astronomy & Astrophysics 423 (3): 1159. doi:10.1051/0004-6361:20040449. Bibcode: 2004A&A...423.1159M.
- ↑ Supplemental IRAS Minor Planet Survey
- ↑ PDS spectral class data
- ↑ "90 Antiope: Raw Keck Image". SWrI Press Release. August 2000. http://www.boulder.swri.edu/merline/press/fig1.html.
- ↑ 10.0 10.1 IAUC 7503
- ↑ Moore, Patrick; Rees, Robin, eds. (2011), Patrick Moore's Data Book of Astronomy (2nd ed.), Cambridge University Press, p. 165, ISBN 9781139495226, https://books.google.com/books?id=2FNfjWKBZx8C&pg=PA165.
- ↑ 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.
- ↑ Florczak, M. et al. (February 1999). "A spectroscopic study of the THEMIS family". Astronomy and Astrophysics Supplement 134: 463–471. doi:10.1051/aas:1999150. Bibcode: 1999A&AS..134..463F.
- ↑ 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. doi:10.1016/j.icarus.2009.04.022. Bibcode: 2009Icar..203..102D.
- ↑ Marchis, F.; Enriquez, J.E.; Emery, J.P.; Berthier, J.; Descamps, P.; Vachier, F. (2011). "The origin of (90) Antiope from component-resolved near-infrared spectroscopy". Icarus 213 (1): 252–264. doi:10.1016/j.icarus.2011.02.011. Bibcode: 2011Icar..213..252M.
- ↑ "Asteroid Data Sets". https://sbn.psi.edu/pds/resource/occ.html.
- ↑ Antiope Occultation Yields Double Bonanza . Sky & Telescope
- ↑ Franck Marchis (July 21, 2011). "An Occultation by the double asteroid (90) Antiope seen in California". NASA blog (Cosmic Diary). http://cosmicdiary.org/fmarchis/2011/07/21/an-occultation-by-the-double-asteroid-90-antiope-seen-in-california/.
External links
- 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 (September 9, 2011). "Antiope Occultation Yields Double Bonanza". Sky and Telescope. http://www.skyandtelescope.com/community/skyblog/observingblog/129541438.html.
- 90 Antiope at AstDyS-2, Asteroids—Dynamic Site
- 90 Antiope at the JPL Small-Body Database
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