90 Antiope

90 Antiope is an asteroid found on October 1, 1866 by Robert Luther. The 90th asteroid to be found, it is named after Antiope from Greek mythology, though it is disputed as to whether the namesake is Antiope the Amazon or Antiope the mother of Amphion and Zethus. Antiope orbits in the farther 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 that it is made of carbonaceous chondrite. There have been 9 occultations observed since 1988, many of which are multichord occultations. Double asteroid The most remarkable feature of Antiope is that it has two asteroids of almost equal size (the difference in mass is less than 2.5%), making it a truly "double" asteroid. Its binary nature was found on 10 August, 2000 by a group of astronomers using adaptive optics at the Keck Telescope on Mauna Kea. The "secondary" is designated S/2000 (90) 1. 90 Antiope occulted the star LQ Aquarii on July 19, 2011 in western USA. 46 stations observed a positive occultation Each asteroid is about 86±1 km across, with their centers separated by only about 170 kilometers. This means that the space separating the two halves is only 60 km, or so. The two bodies orbit around the same center of mass which lies in the space between them. The orbital period is about 16.50 hours, the eccentricity below 0.03 (best estimate 0.01 ± 0.02). 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 asteroids can be derived from the orbital period and asteroid sizes. The axis of the mutual orbit of the two asteroids points towards ecliptic coordinates (β, λ) = (200°, 38°) with 2 degrees uncertainty. This is tilted about 63° to the circumsolar orbit of the system. S/2000 (90) 1 Discovery 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 Designations Minor planet category Main belt (Themis family) Orbital characteristics 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 Physical characteristics Dimensions 86±1 km Mass ~ 8.1−8.5 ×1017 kg Equatorial escape velocity variable; ~ 35−40 m/s Rotation period 0.687 d (16.50 h) Absolute magnitude (H) 9.02

90 Antiope Antiope Douplet by VLT Discovery [1] Discovered by Robert Luther Discovery date October 1, 1866 Designations Alternative designations 1952 BK2 [2] Minor planet category Main belt  (Themis family) Orbital characteristics [3] Epoch August 18, 2005 (JD 2453600.5) Aphelion 545.753 Gm 3.648 AU Perihelion 398.502 Gm 2.664 AU Semi-major axis 472.128 Gm 3.156 AU 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° Physical characteristics Dimensions 86±1 km (each component) Mass 8.3×1017 kg (whole system) ~ 4.1−4.2 ×1017 kg (components) Mean density 1.25 ± 0.05 g/cm³ (each) 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). Geometric albedo 0.060 Surface temp. min mean max Kelvin ~158 K 244 K Celsius -115 C -29° Spectral type C Absolute magnitude (H) 8.27 (together) 9.02 (each component)

90 Antiope Media

• Antiope asteroidal occultation - LQ_Aquarii_occultation_20110719

Other websites

• 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 Archived April 3, 2007, at the Wayback Machine The Impossible Siblings
• UC-Berkeley Press-Release published on May 29, 2007 Binary asteroid revealed as twin rubble piles
• Antiope, a true binary asteroid Archived 2007-06-06 at the Wayback Machine, The Planetary Society weblog, E. Lakdawalla, 11 Apr, 2007.