Astronomy:90 Antiope

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90 Antiope
Discovery [1]
Discovered byRobert Luther
Discovery date1 October 1866
Designations
(90) Antiope
Pronunciation/ænˈtaɪəpiː/[2]
1952 BK2[1]
Minor planet categoryMain belt[1]
(Themis family)
AdjectivesAntiopean
Orbital characteristics[1]
Epoch 23 July 2010
(JD 2455400.5)
|{{{apsis}}}|helion}}3.6494 AU
|{{{apsis}}}|helion}}2.6606 AU
3.1550 AU
Eccentricity0.15670
Orbital period2046.9 d (5.60 yr)
Average Orbital speed16.66 km/s
Mean anomaly304.12°
Inclination2.2195°
Longitude of ascending node70.21°
242.96°
Physical characteristics
Dimensions93.0×87.0×83.6 km[3]
87.8 ± 1.0 km[3]
Mass8.3×1017 kg
(whole system)[4]
~ 4.1−4.2 ×1017 kg (components)
Mean density1.25 ± 0.05 g/cm3 (each)[5]
Rotation period0.687 d (16.50 h)[6] (synchronous)
Geometric albedo0.060[7]
C[8]
Absolute magnitude (H)8.27 (together)[1]
9.02 (each component)


Companion
Discovery[10]
Discovered byW. J. Merline, L. M. Close,
J. C. Shelton, C. Dumas,
F. Menard, C. R. Chapman,
and D. C. Slater
Discovery date10 August 2000[9]
Designations
Minor planet categoryMain belt (Themis family)
Orbital characteristics[4]
171 ± 1 km
Eccentricity<0.006
Orbital period0.687713 ± 0.00004 d (16.5051 ± 0.0001 h)
Average Orbital speed18.0 m/s
Satellite ofBinary with 90 Antiope
Physical characteristics
Dimensions89.4×82.8×79.6 km[3]
Mean diameter83.8 ± 1.0 km[3]
Mass~ 8.1−8.5 ×1017 kg[5]
Equatorial escape velocity
variable; ~ 35−40 m/s
Rotation period0.687 d (16.50 h)[6] (synchronous)
Absolute magnitude (H)9.02


90 Antiope is a double asteroid in the outer asteroid belt. It was discovered on 1 October 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 unclear whether it refers to Antiope the Amazon or Antiope 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) designation S/2000 (90) 1.[13] However, the name "Antiope" is also used to refer to the binary system as a whole.[where?]

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%[14]), 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.[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 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 companion 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.

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.[16] The impactor is calculated to have been more than 17 km in diameter.[17] 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.[18]

Occultations

There have been 9 occultations observed since 1988,[19] many of which are multichord 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]

90 Antiope occulted the star LQ Aquarii on July 19, 2011, in western USA. 46 stations observed a positive, 11 stations observed a miss and others were clouded out. Many stations were pre-pointed and left unattended.

File:LQ Aquarii occultation 20110719-001.webm

References

  1. ↑ 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. 
  2. ↑ Noah Webster (1884) A Practical Dictionary of the English Language
  3. ↑ 3.0 3.1 3.2 3.3 Wm. Robert Johnston (2008-11-23). "(90) Antiope and its companion". Johnston's Archive. http://www.johnstonsarchive.net/astro/astmoons/am-00090.html. 
  4. ↑ 4.0 4.1 4.2 4.3 90 Antiope A & B , online data sheet, F. Marchis
  5. ↑ 5.0 5.1 5.2 5.3 Descamps et al., 2007, Icarus article published in April 2007
  6. ↑ 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. 
  7. ↑ Supplemental IRAS Minor Planet Survey
  8. ↑ PDS spectral class data
  9. ↑ "90 Antiope: Raw Keck Image". SWrI Press Release. August 2000. http://www.boulder.swri.edu/merline/press/fig1.html. 
  10. ↑ 10.0 10.1 IAUC 7503
  11. ↑ 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. 
  12. ↑ Schmadel, Lutz D. (2012). "(90) Antiope". Dictionary of Minor Planet Names – (90) Antiope. Springer Berlin Heidelberg. p. 21. doi:10.1007/978-3-642-29718-26. ISBN 978-3-642-29717-5. 
  13. ↑ "OCCULTATIONS BY (90) ANTIOPE AND BY S/2000 (90) 1". Central Bureau for Astronomical Telegrams. International Astronomical Union. 17 February 2008. http://www.cbat.eps.harvard.edu/iau/cbet/001200/CBET001263.txt. 
  14. ↑ 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. 
  15. ↑ Florczak, M. et al. (February 1999). "A spectroscopic study of the THEMIS family". Astronomy and Astrophysics Supplement 134 (3): 463–471. doi:10.1051/aas:1999150. Bibcode: 1999A&AS..134..463F. 
  16. ↑ 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. 
  17. ↑ 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. 
  18. ↑ 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. 
  19. ↑ "Asteroid Data Sets". https://sbn.psi.edu/pds/resource/occ.html. 
  20. ↑ Antiope Occultation Yields Double Bonanza . Sky & Telescope
  21. ↑ 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/. 



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