90 Antiope

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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.

One seen stellar occultation by Antiope has been reported, on June 11, 1980.

Double asteroid[change | edit source]

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.[1] 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).[2] Every several years, a period of mutual occultations occurs when the asteroid is viewed from Earth.[3] 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°)[4] with 2 degrees uncertainty.[4] This is tilted about 63° to the circumsolar orbit of the system.

S/2000 (90) 1
Discovery[1] and designation
Discovered by W. J. Merline, L. M. Close,
J. C. Shelton, C. Dumas,
F. Menard, C. R. Chapman,
and D. C. Slater
Discovery time August 10, 2000
Group Main belt (Themis family)
Longest distance from the center of its orbital path
("semi-major axis")
171 ± 1 km
How egg-shaped its orbit is
0.01 ± 0.02
How long it takes to complete an orbit 0.687713 ± 0.00004 d (16.5051 ± 0.0001 h)
Average speed 18.0 m/s
What it orbits Binary with 90 Antiope
Size and Other Qualities
Measures 86±1 km[4]
Mass ~ 8.1−8.5 ×1017 kg[4]
Slowest speed able to escape into space
("escape velocity")
variable; ~ 35−40 m/s
How long it takes to turn around one time 0.687 d (16.50 h)[3]
True brightness
("absolute magnitude")
90 Antiope
The Antiope Doublet - Eso0718b.png
Antiope Douplet by VLT
Discovery [1] and designation
Discovered by Robert Luther
Discovery time October 1, 1866
Other names 1952 BK2 [2]
Group Main belt
 (Themis family)
Orbit [3]
Reference date August 18, 2005
(JD 2453600.5)
Longest distance from the Sun 545.753 Gm
3.648 AU
Shortest distance from the Sun 398.502 Gm
2.664 AU
Longest distance from the center of its orbital path
("semi-major axis")
472.128 Gm
3.156 AU
How egg-shaped its orbit is
How long it takes to complete an orbit 2047.856 d (5.61 a)
Average speed 16.66 km/s
Mean anomaly 348.378°
Angle above the reference plane
Longitude of where it comes up through the reference plane 70.235°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
Size and Other Qualities
Measures 86±1 km
(each component)[4]

8.3×1017 kg
(whole system)[2]

~ 4.1−4.2 ×1017 kg (components)
Average density 1.25 ± 0.05 g/cm³ (each)[4]
Gravity at its surface variable; ~ 0.03−0.04 m/s²
Slowest speed able to escape into space
("escape velocity")
variable; ~ 35−40 m/s
How long it takes to turn around one time 0.687 d (16.50 h).[3]
How much light it reflects 0.060[5]
Surface temp. Min. Avg. Max.
Kelvin ~158 K 244 K
Celsius -115 C -29°
Light-band group
("spectral type")
True brightness
("absolute magnitude")
8.27 (together)
9.02 (each component)

Other websites[change | edit source]

References[change | edit source]

  1. 1.0 1.1 IAUC 7503
  2. 2.0 2.1 2.2 90 Antiope A & B, online data sheet, F. Marchis
  3. 3.0 3.1 3.2 "T. Michałowski et al. (2004). "Eclipsing binary asteroid 90 Antiope". Astronomy & Astrophysics 423: 1159.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 Descamps et al., 2007, Icarus article published in April 2007
  5. Supplemental IRAS Minor Planet Survey
  6. PDS spectral class data