Discovery | |
---|---|
Discovered by | A. Graham |
Discovery date | April 25, 1848 |
Designations | |
1974 QU2 | |
Main belt | |
Orbital characteristics | |
Epoch July 14, 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° | |
Physical characteristics | |
Dimensions | 235×195×140 km[1][2] |
Mass | ~9×1018 kg |
Mean density | ~2.7 g/cm³[3] |
~0.070 m/s² | |
~0.11 km/s | |
0.2116 d (5.078 h)[4] | |
Albedo | 0.243 (geometric)[5] |
Temperature | ~173 K max: 282 K (+9° C)[6] |
Spectral type | S-type[7] |
8.1[8] to 11.83 | |
6.28 | |
0.23" to 0.071" | |
9 Metis is one of the biggest main belt asteroids. It is made of silicates and metallic nickel-iron, and may be the core remnant of a big asteroid that was destroyed by an ancient collision.[9]
Metis was found by Andrew Graham on April 25, 1848; it was his only asteroid discovery.[10] It is also the only asteroid to have been found as a result of observations from Ireland. Its name comes from the mythological Metis, a Titaness and Oceanid, daughter of Tethys and Oceanus.[11] The name Thetis was also considered and rejected (it would later devolve to 17 Thetis).
Metis' direction of rotation is unknown at present.
Hubble space telescope images[2][12] and lightcurve analyses[1] are in agreement that Metis has a non-spherical stretched shape with one pointed and one broad end.[1][12] Radar observations suggest the presence of a significant flat area,[13] in agreement with the shape model from lightcurves.
What the surface is made of has been estimated as 30-40% metal-bearing olivine and 60-70% Ni-Fe metal.[9]
Light curve data on Metis led to an assumption that it could have a moon. However, subsequent observations failed to confirm this.[14][15] Later searches with the Hubble Space Telescope in 1993 found no moons.[12]
Metis has been seen to occult stars no less than 5 times.[16]