9 Metis
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A three-dimensional model of 9 Metis based on its light curve.
|
|
| Discovery | |
|---|---|
| Discovered by | A. Graham |
| Discovery date | 25 April 1848 |
| Designations | |
| Pronunciation | /ˈmiːtᵻs/ |
|
Named after
|
Mētis |
| 1974 QU2 | |
| Main belt | |
| Adjectives | Metidian /mɛˈtɪdiən/ |
| Orbital characteristics | |
| Epoch 14 July 2004 (JD 2453200.5) | |
| Aphelion | 400.548 Gm (2.678 AU) |
| Perihelion | 313.556 Gm (2.096 AU) |
| 357.052 Gm (2.387 AU) | |
| Eccentricity | 0.122 |
| 1346.815 d (3.69 a) | |
|
Average orbital speed
|
19.21 km/s |
| 274.183° | |
| Inclination | 5.576° |
| 68.982° | |
| 5.489° | |
| Proper orbital elements | |
|
Proper semi-major axis
|
2.3864354 AU |
|
Proper eccentricity
|
0.1271833 |
|
Proper inclination
|
4.6853629° |
|
Proper mean motion
|
97.638314 deg / yr |
|
Proper orbital period
|
3.68708 yr (1346.705 d) |
|
Precession of perihelion
|
38.754973 arcsec / yr |
|
Precession of the ascending node
|
−41.998090 arcsec / yr |
| Physical characteristics | |
| Dimensions | 222×182×130 km 235×195×140 km 190 km (Dunham) |
| Mass | (1.47±0.20)×1019 kg |
|
Mean density
|
4.12±1.33 g/cm³ |
| ~0.070 m/s² | |
| ~0.11 km/s | |
| 0.2116 d (5.079 h) | |
| Albedo | 0.118 (geometric) |
| Temperature | ~173 K max: 282 K (+9 °C) |
|
Spectral type
|
S-type |
| 8.1 to 11.83 | |
| 6.28 | |
| 0.23" to 0.071" | |
9 Metis is one of the larger 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. Metis is estimated to contain just under half a percent of the total mass of the asteroid belt.
Metis was discovered by Andrew Graham on 25 April 1848, at Markree Observatory in Ireland; it was his only asteroid discovery. It also has been the only asteroid to have been discovered as a result of observations from Ireland until 7 October 2008, when, 160 years later, Dave McDonald from observatory J65 discovered 2008 TM9. Its name comes from the mythological Metis, a Titaness and Oceanid, daughter of Tethys and Oceanus. The name Thetis was also considered and rejected (it would later devolve to 17 Thetis).
Metis' direction of rotation is unknown at present, due to ambiguous data. Lightcurve analysis indicates that the Metidian pole points towards either ecliptic coordinates (β, λ) = (23°, 181°) or (9°, 359°) with a 10° uncertainty. 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 and lightcurve analyses are in agreement that Metis has an irregular elongated shape with one pointed and one broad end. Radar observations suggest the presence of a significant flat area, in agreement with the shape model from lightcurves.
The Metidian surface composition has been estimated as 30–40% metal-bearing olivine and 60–70% Ni-Fe metal.
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