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9 Metis

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For the moon of Jupiter, see Metis (moon).
9 Metis Astronomical symbol for 9 Metis
Discovered byA. Graham
Discovery timeApril 25, 1848
Other names1974 QU2
GroupMain belt
Reference date July 14, 2004 (JD 2453200.5)
Longest distance from the Sun400.548 Gm (2.678 AU)
Shortest distance from the Sun313.556 Gm (2.096 AU)
Longest distance from the center of its orbital path
("semi-major axis")
357.052 Gm (2.387 AU)
How egg-shaped its orbit is
How long it takes to complete an orbit1346.815 d (3.69 a)
Average speed19.21 km/s
Mean anomaly274.183°
Angle above the reference plane
Longitude of where it comes up through the reference plane68.982°
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
Measures235×195×140 km[1][2]
Mass~9×1018 kg
Average density~2.7 g/cm³[3]
Gravity at its surface~0.070 m/s²
Slowest speed able to escape into space
("escape velocity")
~0.11 km/s
How long it takes to turn around one time0.2116 d (5.078 h)[4]
How much light it reflects0.243 (geometric)[5]
Avg. surface temp.~173 K
max: 282 K (+9° C)[6]
Light-band group
("spectral type")
Seeming brightness
("apparent magnitude")
8.1[8] to 11.83
True brightness
("absolute magnitude")
Seeming size
("angular diameter")
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]

Discovery and naming

The first 10 asteroids profiled against Earth's Moon. 9 Metis is second from right.

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]


  1. 1.0 1.1 1.2 J. Torppa et al., Shapes and rotational properties of thirty asteroids from photometric data, Icarus Vol. 164, p. 346 (2003).
  2. 2.0 2.1 A. D. Storrs et al., A closer look at main belt asteroids 1: WF/PC images, Icarus Vol. 173, p. 409 (2005).
  3. G. A. Krasinsky et al., Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).
  4. PDS lightcurve data
  5. MSX Infrared minor planet survey (at PDS)
  6. 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).
  7. asteroid lightcurve data file (March 2001)
  8. Donald H. Menzel and Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd edition ed.). Boston, MA: Houghton Mifflin. pp. p. 391. ISBN 0-395-34835-8 . 
  9. 9.0 9.1 M. S. Kelley and M. J. Gaffey, 9 Metis and 113 Amalthea: A Genetic Asteroid Pair, Icarus Vol. 144, p. 27 (2000).
  10. Graham, A.; New Planet, Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 6 (dated April 14, 1848!), p. 146 (signed April 29, 1848; the discovery was first announced on April 27)
  11. Graham, A.; Metis, Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 7 (dated May 12, 1848), pp. 147 – 150)
  12. 12.0 12.1 12.2 Hubble Space Telescope observations
  13. 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).
  14. research at IMCCE (in French)
  15. "other" reports of asteroid companions
  16. 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).

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