90 Antiope

90 Antiope (pronEng|ænˈtaɪəpi "an-tye'-ə-pee") is an asteroid discovered on October 1, 1866 by Robert Luther. The 90th asteroid to be discovered, it is named after Antiope from Greek mythology, though it is disputed as to whether this is Antiope the Amazon or Antiope the mother of Amphion and Zethus.

Antiope orbits in the outer 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 a carbonaceous composition. The low density (1.3±0.2 g/cm³) of its components (see below) suggests a significant porosity (>30%), indicating a rubble pile asteroid composed of debris that accumulated in the aftermath of a previous asteroid collision (possibly the one that formed the Themis family).

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

Double asteroid

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%cite journal|author=F. Marchis, F. Descamps, P. Hestroffer, and I. de Pater|title="Fine Analysis of 121 Hermione, 45 Eugenia, and 90 Antiope Binary Asteroid Systems With AO Observations"|year=2004|journal=Bulletin of the American Astronomical Society|volume=36|pages=1180|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004DPS....36.4602M&db_key=AST&data_type=HTML&format=&high=444b66a47d22122] ), 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. [http://cfa-www.harvard.edu/iauc/07500/07503.html#Item3 IAUC 7503] ] The "secondary" is designated S/2000 (90) 1.

Each component is about 86±1 km across, with their centers separated by only about 170 kilometers. This means that the gap separating the two halves is a mere 60 km, or so. 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, 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 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°) [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2007Icar..187..482D&db_key=AST&data_type=HTML&format=&high=3fd1d1211521078 Descamps et al., 2007, Icarus article published in April 2007] ] with 2 degrees uncertainty. This is tilted about 63° to the circumsolar orbit of the system.

The complementary observations using adaptive optic observations on 8-10m class telescopes and mutual events photometric lightcurve over several months have served as input quantities for a derivation of a whole set of other physical parameters (shapes of the components, surface scattering, bulk density, and internal properties). The shape model is consistent with a slightly non-spherical components, having a size ratio of 0.95 (with an average radius of 42.9 km), and exhibiting equilibrium figures for homogeneous rotating bodies. A comparison with grazing occultation event lightcurves taken in 2003 suggests that the real shape of the components do not depart much from Roche equilibrium figures (by more than 10%).

Infobox Planet
name=S/2000 (90) 1
width=24em
discovery=yes
physical_characteristics = yes
bgcolour=#A0FFA0
minorplanet=yes


caption=Adaptive optics image of Antiope
discovery_ref = [http://cfa-www.harvard.edu/iauc/07500/07503.html#Item3 IAUC 7503] ]
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)
orbit_ref=
semimajor= 171 ± 1 km
eccentricity= 0.01 ± 0.02
period=0.687713 ± 0.00004 d (16.5051 ± 0.0001 h)
avg_speed=18.0 m/s
satellite_of = Binary with 90 Antiope
dimensions=89.4×82.8×79.6 km
mass=~ 8.1−8.5 e|17 kg
escape_velocity=variable; ~ 35−40 m/s
rotation = 0.687 d (16.50 h)
abs_magnitude=9.02

Infobox Planet
minorplanet = yes
discovery=yes
discovery_ref = [http://cfa-www.harvard.edu/iau/lists/NumberedMPs.html]
physical_characteristics = yes
bgcolour=#FFFFC0
name=90 Antiope
discoverer=Robert Luther
discovered=October 1, 1866
alt_names=1952 BK₂ [http://cfa-www.harvard.edu/iau/MPDes.html]
mp_category=Main belt
(Themis family)
orbit_ref = [http://asteroid.lowell.edu]
epoch=August 18, 2005
(JD 2453600.5)
semimajor=472.128 Gm
3.156 AU
perihelion=398.502 Gm
2.664 AU
aphelion=545.753 Gm
3.648 AU
eccentricity=0.156
period=2047.856 d (5.61 a)
inclination=2.220°
asc_node=70.235°
arg_peri=242.480°
mean_anomaly=348.378°
avg_speed=16.66 km/s
dimensions=93.0×87.0×83.6 km
mass=8.3×10¹⁷ kg
(whole system) [http://astro.berkeley.edu/~fmarchis/Science/Asteroids/Antiope.html 90 Antiope A & B] , online data sheet, F. Marchis]
~ 4.1−4.2 e|17 kg (components)
density=1.25 ± 0.05 g/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).cite journal|author="T. Michałowski "et al."|title="Eclipsing binary asteroid 90 Antiope"|year=2004|journal=Astronomy & Astrophysics|volume=423|pages=1159|doi=10.1051/0004-6361:20040449]
spectral_type=C [http://www.psi.edu/pds/resource/taxonomy.html PDS spectral class data] ]
abs_magnitude=8.27 (together)
9.02 (each component)
albedo=0.060 [http://www.psi.edu/pds/resource/imps.html Supplemental IRAS Minor Planet Survey] ]
temperatures=yes
temp_name1 = Kelvin
min_temp_1 =
mean_temp_1 = ~158 K
max_temp_1 = 244 K
temp_name2 = Celsius
min_temp_2 =
mean_temp_2 = -115 C
max_temp_2 = -29°

References

External links

* [http://www.boulder.swri.edu/merline/press/index.html "Discovery of Companions to Asteroids 762 Pulcova and 90 Antiope"] SWrI Press Release.
* [http://www.johnstonsarchive.net/astro/astmoons/am-00090.html Data on (90) Antiope from Johnston's archive] (maintained by W. R. Johnston)
* [http://astron.berkeley.edu/~fmarchis/Science/Asteroids/#Antiope online data on the Antiope system] maintained by F. Marchis; includes images and simulated occultation movies.
* [http://www.eso.org/outreach/press-rel/pr-2007/pr-18-07.html ESO Press-Release published on May 29, 2007] The Impossible Siblings
* [http://www.berkeley.edu/news/media/releases/2007/03/29_antiope.shtml UC-Berkeley Press-Release published on May 29, 2007] Binary asteroid revealed as twin rubble piles
* [http://planetary.org/blog/article/00000942/ Antiope, a true binary asteroid] , The Planetary Society weblog, E. Lakdawalla, 11 Apr, 2007.
*JPL Small Body