Metis (moon)

''For the asteroid, see 9 Metis.


Metis

Image of Metis was taken by Galileo's solid state imaging system between November 1996 and June 1997.
Discovery
Discovered by:S. Synnott
Discovery date:March 4, 1979
Orbital characteristics
Periapsis:127,974 km[1]
Apoapsis:128,026 km[1]
Mean radius of orbit:128,000 km (1.792 RJ)[2][3]
Eccentricity:0.0002[2][3]
Orbital period:0.294780 d (7 h 4.5 min)[2][3]
Avg. orbital speed:31.501 km/s[1]
Inclination:0.06° (to Jupiter's equator)[2][3]
Satellite of:Jupiter
Physical characteristics
Dimensions:60×40×34 km3[3]
Mean radius:21.5 ± 2.0 km[3]
Volume:~42,700 km3
Mass:3.6 1016 kg[1]
Mean density:0.86 g/cm3 (assumed)
Equatorial surface gravity:0.005 m/s2 (0.0005 g)[1]
Escape velocity:0.012 km/s[1]
Rotation period:synchronous
Axial tilt:zero[3]
Albedo:0.061 ± 0.003[5]
Temperature:~123 K
Metis (mee'-təs, IPA: /ˈmiːtɨs/, Greek Μήτις) or Jupiter XVI, is Jupiter's innermost moon.

Metis was discovered in 1979 by Stephen P. Synnott in images taken by the Voyager 1 probe.[5] Its provisional designation was S/1979 J 3.[6][5] In 1983 it was officially named after the mythological Metis, a Titaness who was the first wife of Zeus (the Greek equivalent of Jupiter).[8]

Physical characteristics

Metis has an irregular shape and measures 60×40×34 km across.[3] The bulk composition and mass of Metis are not known, but assuming that its mean density is like that of Amalthea (~0.86 g/cm3),[9] its mass can be estimated as ~7×1016 kg. Amalthea's density implies that that moon is composed of water ice with a porosity of 10-15%, and Adrastea may be similar.[9]

The surface of Metis is heavily cratered. It is dark and appears to be reddish in color. There is a substantial asymmetry between leading and trailing hemispheres: the leading hemisphere is 1.3 times brighter than the trailing one. The asymmetry is probably caused by the higher velocity and frequency of impacts on the leading hemisphere, which excavate a bright material (presumably ice) from the interior of the moon.[5]

Orbit

Metis is the innermost of Jupiter's four small inner moons. It orbits Jupiter at a distance of ~128,000 km (1.79 Jupiter radii) within the planet's Main Ring. Its orbit has very small eccentricity (~0.0002) and inclination (~ 0.06°) relative to the equator of Jupiter.[2][3]

Due to tidal locking, Metis rotates synchronously with its orbital period, keeping one face always looking toward the planet. Its long axis is aligned towards Jupiter, this being the lowest energy configuration.[3][3]

The orbit of Metis lies inside Jupiter's synchronous orbit radius (as does Adrastea's), and as a result, tidal forces are slowly causing its orbit to decay, so that it will one day impact into Jupiter. If its density is similar to Amalthea's then its orbit would actually lie within the fluid Roche limit. In any case, however, since it is not breaking up, it must still lie outside its rigid Roche limit.[3]

Relationship with Jupiter's rings

Metis's orbit lies ~1000km within the main ring of Jupiter. It orbits within a ~500km wide 'gap' or 'notch' in the ring.[10][3] The gap is clearly somehow related to the moon but the origin of this connection has not been established. Metis supplies a significant part of the Main Ring’s dust.[11] This material appears to consist primarily of material that is ejected from the surfaces of Jupiter's four small inner satellites by meteorite impacts. It is easy for the impact ejecta to be lost from the satellites into space because the satellites' surfaces lie fairly close to the edge of their Roche spheres due to their low density.[3]

Exploration

The photographs taken by Voyager 1 showed Metis only as a dot, and hence knowledge about Metis was very limited until the arrival of the Galileo spacecraft. Galileo imaged almost all of the surface of Metis and put constraints on its composition.[3]

See also

References

1. ^ Calculated on the basis of other parameters
2. ^ Evans, M.W.; Porco, C.C.; Hamilton, D.P. (2002). "The Orbits of Metis and Adrastea: The Origin and Significance of their Inclinations". Bulletin of the American Astronomical Society 34: 883. 
3. ^ Burns, J.A.; D.P. Simonelli & M.R. Showalter et al. (2004), "Jupiter’s Ring-Moon System", in Bagenal, F.; Dowling, T. E.; McKinnon, W. B., Jupiter: The planet, Satellites and Magnetosphere, Cambridge University Press
4. ^ Thomas, P.C.; Burns, J.A.; Rossier, L.; et.al. (1998). "The Small Inner Satellites of Jupiter". ICARUS 135: 360–371. DOI:10.1006/icar.1998.5976. 
5. ^ Simonelli, D.P.; Rossiery, L.; Thomas, P.C.; et.al. (2000). "Leading/Trailing Albedo Asymmetries of Thebe, Amalthea, and Metis". ICARUS 147: 353–365. DOI:10.1006/icar.2000.6474. 
6. ^ IAUC 3507: Satellites of Jupiter 1980 August 26 (discovery)
7. ^ Synnott, S.P. (1981). "1979J3: Discovery of a Previously Unknown Satellite of Jupiter". Science 212 (4501): 1392. 
8. ^ IAUC 3872: Satellites of Jupiter and Saturn 1983 September 30 (naming the moon)
9. ^ Anderson, J.D.; Johnson, T.V.; Shubert, G.; et.al. (2005). "Amalthea’s Density Is Less Than That of Water". Science 308: 1291–1293. DOI:10.1126/science.1110422. 
10. ^ Ockert-Bel, M.E.; Burns, J.A.; Daubar, I.J.; et.al. (1999). "The Structure of Jupiter’s Ring System as Revealed by the Galileo Imaging Experiment". ICARUS 138: 188–213. DOI:10.1006/icar.1998.6072. 
11. ^ Burns, J.A.; Showalter, M.R.; Hamilton, D.P.; et.al. (1999). "The Formation of Jupiter's Faint Rings". Science 284: 1146-1150. DOI:10.1126/science.284.5417.1146. 

External links

Metis Profile by NASA's Solar System Exploration


(Jupiter) | Metis | Adrastea | ...


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9 Metis  
Discovery
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Discovery date: April 25, 1848
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1 kilometre =
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0 m 0106 mm
US customary / Imperial units
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1 kilometre =
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