9 Metis
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 Convex hull model of 9 Metis |
|
| Discovery | |
|---|---|
| Discovered by: | A. Graham |
| Discovery date: | April 25, 1848 |
| Alternative names: | 1974 QU2 |
| Minor planet category: | Main belt |
| Orbital characteristics | |
| Epoch July 14, 2004 (JD 2453200.5) | |
| Aphelion distance: | 400.548 Gm (2.678 AU) |
| Perihelion distance: | 313.556 Gm (2.096 AU) |
| Semi-major axis: | 357.052 Gm (2.387 AU) |
| Eccentricity: | 0.122 |
| Orbital period: | 1346.815 d (3.69 a) |
| Avg. orbital speed: | 19.21 km/s |
| Mean anomaly: | 274.183° |
| Inclination: | 5.576° |
| Longitude of ascending node: | 68.982° |
| Argument of perihelion: | 5.489° |
| Physical characteristics | |
| Dimensions: | 235×195×140 km[1][2] |
| Mass: | ~9×1018 kg |
| Mean density: | ~2.7 g/cm³[3] |
| Equatorial surface gravity: | ~0.070 m/s² |
| Escape velocity: | ~0.11 km/s |
| Rotation period: | 0.2116 d (5.078 h)[4] |
| Albedo: | 0.243[6] |
| Temperature: | ~173 K max: 282 K (+9° C)[7] |
| Spectral type: | S-type[5] |
| Absolute magnitude: | 6.28 |
9 Metis (IPA: [ˈmiɾɪs]) is one of the largest Main belt asteroids. It is composed of silicates and metallic nickel-iron, and may be the core remnant of a large asteroid that was destroyed by an ancient collision.[8]
Contents |
[edit] Discovery and naming
Metis was discovered by Andrew Graham on April 25, 1848; his only asteroid discovery. It is also the only asteroid to have been discovered as a result of observations from Ireland. Its name comes from the mythological Metis, a Titaness, daughter of Tethys and Oceanus (and thus an Oceanid), who was the first wife of Zeus and the mother of Athena. Zeus devoured her lest she bear a child more powerful than he.
[edit] Characteristics
Metis' direction of rotation is unknown at present, due to ambiguous data. Lightcurve analysis indicates that Metis' pole points towards either ecliptic coordinates (β, λ) = (23°, 181°) or (9°, 359°) with a 10° uncertainty.[1] The equivalent equatorial coordinates are (α, δ) = (12.7 h, 21°) or (23.7 h, 8°). This gives an axial tilt of 72° or 76°, respectively.
Hubble space telescope images[2][9] and lightcurve analyses[1] are in agreement that Metis has an irregular elongated shape with one pointed and one broad end.[1][9] Radar observations suggest the presence of a significant flat area,[10] in agreement with the shape model from lightcurves.
The surface composition has been estimated as 30-40% metal-bearing olivine and 60-70% Ni-Fe metal.[8]
Light curve data on Metis led to an assumption that it could have a satellite. However, subsequent observations failed to confirm this.[11][12] Later searches with the Hubble Space Telescope in 1993 found no satellites.[9]
[edit] Family relationships
Metis was once considered to be a member of an asteroid family (the Metis family),[13] but more recent searches for prominent families did not recognize any such group, nor is a clump evident in the vicinity of Metis by visual inspection of proper orbital element diagrams.
However, a spectroscopic analysis found strong spectral similarities between Metis and 113 Amalthea, and it is suggested that these asteroids may be remnants of a very old (at least ~1 Ga) dynamical family whose smaller members have been pulverised by collisions or perturbed away from the vicinity. The putative parent body is estimated to have been 300 to 600 km in diameter (Vesta-sized), differentiated, and Metis would be the relatively intact core remnant, while Amalthea a fragment of the mantle.[8] It is an ironic coincidence that both Metis and Amalthea have namesakes among Jupiter's moons.
[edit] Occultations
Metis has been observed occulting a star no less than 5 times.[14]
[edit] References
- ^ a b c d J. Torppa et al., Shapes and rotational properties of thirty asteroids from photometric data, Icarus Vol. 164, p. 346 (2003).
- ^ a b A. D. Storrs et al., A closer look at main belt asteroids 1: WF/PC images, Icarus Vol. 173, p. 409 (2005).
- ^ G. A. Krasinsky et al., Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).
- ^ PDS lightcurve data
- ^ asteroid lightcurve data file (March 2001)
- ^ MSX Infrared minor planet survey (at PDS)
- ^ L. F. Lim et al., Thermal infrared (8–13 µm) spectra of 29 asteroids: the Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) Survey, Icarus Vol. 173, p. 385 (2005).
- ^ a b c M. S. Kelley and M. J. Gaffey, 9 Metis and 113 Amalthea: A Genetic Asteroid Pair, Icarus Vol. 144, p. 27 (2000).
- ^ a b c Hubble Space Telescope observations
- ^ D. L. Mitchell et al., Radar Observations of Asteroids 7 Iris, 9 Metis, 12 Victoria, 216 Kleopatra, and 654 Zelinda, Icarus Vol. 118, p. 105 (1995).
- ^ research at IMCCE (in French)
- ^ "other" reports of asteroid companions
- ^ J. G. Williams, Asteroid Families - An Initial Search, Icarus Vol. 96, p. 251 (1992).
- ^ W. M. Kissling et al., The diameter of (9) Metis from the Occultation of SAO 190531, Proceedings of the Astronomical Society of Australia Vol 9, p. 150 (1991).
[edit] External links
- shape model deduced from lightcurve
- "Notice of discovery of Metis", MNRAS 8 (1848) 146
- Irish Astronomical History: Markree Castle Observatory and The Discovery of the Asteroid Metis
- Yeomans, Donald K.. Horizons system. NASA JPL. Retrieved on 2007-03-20. — Horizons can be used to obtain a current ephemeris.
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For other objects and regions, see Asteroid groups and families, Binary asteroids, Asteroid moons and the Solar System.
For a complete listing, see List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.
