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**.

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.

## 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  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 Apr, 2007.

## Infobox (planet)

- **name**: S/2000 (90) 1
- **bgcolour**: #A0FFA0
- **minorplanet**: yes
- **discoverer**: W. J. Merline, L. M. Close,
J. C. Shelton, C. Dumas,
F. Menard, C. R. Chapman,
and D. C. Slater
- **discovered**: August 10, 2000
- **mp category**: Main belt (Themis family)
- **semimajor**: 171 ± 1 kilometer, km
- **eccentricity**: 0.01 ± 0.02
- **period**: 0.687713 ± 0.00004 day, d (16.5051 ± 0.0001 hour, h)
- **avg speed**: 18.0 m/s
- **satellite of**: Binary with 90 Antiope
- **dimensions**: 86±1 km
- **mass**: ~ 8.1−8.5  kg
- **escape velocity**: variable; ~ 35−40 m/s
- **rotation**: 0.687 d (16.50 h)
- **abs magnitude**: 9.02


## Infobox (planet)

- **minorplanet**: yes
- **discovery ref**:  [http://cfa-www.harvard.edu/iau/lists/NumberedMPs.html]
- **bgcolour**: #FFFFC0
- **name**: 90 Antiope
- **discoverer**: Karl Theodor Robert Luther, Robert Luther
- **discovered**: October 1, 1866
- **image**: The Antiope Doublet - Eso0718b.png
- **caption**: Antiope Douplet by VLT
- **alt names**: 1952 BK<sub>2</sub> [http://cfa-www.harvard.edu/iau/MPDes.html]
- **mp category**: Main belt
 (Themis family)
- **orbit ref**:  [http://asteroid.lowell.edu]
- **epoch**: August 18, 2005
(Julian day, JD 2453600.5)
- **semimajor**: 472.128 Giga, Gmetre, m
3.156 Astronomical unit, AU
- **perihelion**: 398.502 Gm
2.664 AU
- **aphelion**: 545.753 Gm
3.648 AU
- **eccentricity**: 0.156
- **period**: 2047.856 day, d (5.61 Julian year (astronomy), a)
- **inclination**: 2.220degree (angle), °
- **asc node**: 70.235°
- **arg peri**: 242.480°
- **mean anomaly**: 348.378°
- **avg speed**: 16.66 km/second, s
- **dimensions**: 86±1 km
(each component)
- **mass**: 8.3×10<sup>17</sup> kilogram, kg
(whole system)

~ 4.1−4.2  kg (components)
- **density**: 1.25 ± 0.05 g/cubic centimetre, cm³ (each)
- **surface grav**: variable; ~ 0.03−0.04 m/s²
- **escape velocity**: variable; ~ 35−40 m/s
- **rotation**: 0.687 d (16.50 h).
- **spectral type**: C-type asteroid, C
- **abs magnitude**: 8.27 (together)
 9.02 (each component)
- **albedo**: 0.060
- **temp name1**: Kelvin
- **mean temp 1**: ~158 kelvin, K
- **max temp 1**: 244 K
- **temp name2**: Celsius
- **mean temp 2**: -115 celsius, C
- **max temp 2**: -29°