90 Antiope Facts for Kids

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.

Quick facts for kids
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