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9 Metis

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For the moon of Jupiter, see Metis (moon).
9 Metis
Discovery
Discovered byA. Graham
Discovery date25 April 1848
Designations
Named after
Metis
1974 QU2
Main belt
AdjectivesMetidian
Symbol
Orbital characteristics[1]
Epoch 14 July 2004 (JD 2453200.5)
Aphelion400.548 Gm (2.678 AU)
Perihelion313.556 Gm (2.096 AU)
357.052 Gm (2.387 AU)
Eccentricity0.122
1346.815 d (3.69 a)
19.21 km/s
274.183°
Inclination5.576°
68.982°
5.489°
Physical characteristics
Dimensions222×182×130 km[2]
235×195×140 km[3][4][5]
190 km (Dunham)[1]
Mass1.13×1019 kg[2]
Mean density
4.12±1.33 g/cm³[2]
~0.070 m/s²
~0.11 km/s
0.2116 d (5.079 h)[1]
Albedo0.118 (geometric)[1]
Temperature~173 K
max: 282 K (+9° C)[6]
Spectral type
S-type[7]
8.1[8] to 11.83
6.28[1]
0.23" to 0.071"

9 Metis (Template:Pron-en MEE-tiss, [Μήτις] Error: {{Lang-xx}}: text has italic markup (help)) 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.[9] Metis is estimated to contain just under half a percent of the total mass of the asteroid belt.[2]

Discovery and naming

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

Metis was discovered by Andrew Graham on 25 April 1848; it was his only asteroid discovery.[10] 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.[11] Its name comes from the mythological Metis, a Titaness and Oceanid, daughter of Tethys and Oceanus.[12] The name Thetis was also considered and rejected (it would later devolve to 17 Thetis).

Characteristics

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.[4] 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.[citation needed]

Hubble space telescope images[5][13] and lightcurve analyses[4] are in agreement that Metis has an irregular elongated shape with one pointed and one broad end.[4][13] Radar observations suggest the presence of a significant flat area,[14] 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.[9]

Light curve data on Metis led to an assumption that it could have a satellite. However, subsequent observations failed to confirm this.[15][16] Later searches with the Hubble Space Telescope in 1993 found no satellites.[13]

Mass

In 2007, Bear and Chesley estimated Metis to have a mass of 1.6-to-2.5×1019 kg.[3] This would give this stony asteroid a density of about 6 (3.3 to 8.9) g/cm³.[3] A more recent estimate by Baer suggests it has a mass of 1.13×1019 kg.[2] Metis appears to be more dense than most other asteroids with a diameter close to 200km. This may support the theory that Metis is the core remnant of a large evolved asteroid for which 90% of the original mass has been lost.[9]

Metis passed within 0.034AU (5 million kilometres) of Vesta on 19 August 2004.[17]

Family relationships

Metis was once considered to be a member of an asteroid family known as the Metis family,[18] 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) and differentiated.[9] Metis would be the relatively intact core remnant, and Amalthea a fragment of the mantle.[9] Coincidentally, both Metis and Amalthea have namesakes among Jupiter's inner moons.

Occultations

In 1984 an occultation of a star produced seven chords that Kristensen used to derive an ellipsoidal profile of 210x170km.[19] On 6 August 1989, Metis occulted a magnitude 8.7 star producing five chords suggesting a diameter of 173.5 km.[19] Observations of an occultation on 11 February 2006, produced only two chords indicating a minimum diameter 156 km.[20] All three of these occultations fit the ellipsoid 222×182×130 km suggested by Baer.[2]

References

  1. ^ a b c d e "JPL Small-Body Database Browser: 9 Metis". 9 September 2008 last obs. Retrieved 10 November 2008. {{cite web}}: Check date values in: |date= (help)
  2. ^ a b c d e f Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. Retrieved 29 November 2008.
  3. ^ a b c Baer, James (2007). "Astrometric masses of 21 asteroids, and an integrated asteroid ephemeris" (PDF). Celestial Mechanics and Dynamical Astronomy. 100 (2008). Springer Science+Business Media B.V. 2007: 27–42. doi:10.1007/s10569-007-9103-8. Retrieved 10 November 2008. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ a b c d J. Torppa et al., Shapes and rotational properties of thirty asteroids from photometric data, Icarus Vol. 164, p. 346 (2003).
  5. ^ a b A. D. Storrs et al., A closer look at main belt asteroids 1: WF/PC images, Icarus Vol. 173, p. 409 (2005).
  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 ed.). Boston, MA: Houghton Mifflin. p. 391. ISBN 0395348358.
  9. ^ a b c d e Kelley, Michael S (2000). "9 Metis and 113 Amalthea: A Genetic Asteroid Pair". Icarus. 144 (1): 27–38. doi:10.1006/icar.1999.6266. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ Graham, A.; New Planet, Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 6 (dated 14 April 1848!), p. 146 (signed 29 April 1848; the discovery was first announced on 27 April)
  11. ^ "Amateur Astronomer Becomes Second Ever to Discover Asteroid from Ireland, After 160 Years". International Year of Astronomy in Ireland. 10 October 2008. Retrieved 2 March 2009.
  12. ^ Graham, A.; Metis, Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 7 (dated 12 May 1848), pp. 147–150
  13. ^ a b c Hubble Space Telescope observations
  14. ^ 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).
  15. ^ research at IMCCE (in French)
  16. ^ "other" reports of asteroid companions
  17. ^ "JPL Close-Approach Data: 9 Metis". 15 March 2009 last obs. Retrieved 6 May 2009. {{cite web}}: Check date values in: |date= (help)
  18. ^ J. G. Williams, Asteroid Families - An Initial Search, Icarus Vol. 96, p. 251 (1992).
  19. ^ a b Kissling, W.M (1991). "The Diameter of 9 Metis from the Occultation of SAO:190531". Proceedings of the Astronomical Society of Australia. 9: 150. Retrieved 6 December 2008. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ "Occultation of TYC 0862-00695-1 by (9) Metis 2006 February 11". Royal Astronomical Society of New Zealand. Retrieved 6 December 2008. (Chords)

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