Metis (moon)

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Metis Template:IPAc-en, also known as Template:Nowrap, is the innermost known moon of Jupiter. It was discovered in 1979 in images taken by Voyager 1, and was named in 1983 after the Titaness Metis, the first wife of Zeus and the mother of Athena. Additional observations made between early 1996 and September 2003 by the Galileo spacecraft allowed its surface to be imaged.

Metis is tidally locked to Jupiter, and its shape is strongly asymmetrical, with the largest diameter being almost twice as large as the smallest one. It is also one of the two moons known to orbit Jupiter in less than the length of Jupiter's day, the other being Adrastea. It orbits within the main ring of Jupiter, and is thought to be a major contributor of ring material.

Discovery and observationsEdit

File:Metis ontdekking.gif

Voyager 1 discovery image of Metis on 4 March 1979, showing the moon's tiny silhouette against the backdrop of Jupiter's clouds

Metis was discovered in 1979 by Stephen P. Synnott in images taken by the Voyager 1 probe and was provisionally designated as Template:Nowrap.Template:Sfn Template:Sfn In 1983, it was officially named after the mythological Metis, a Titaness who was the first wife of Zeus (the Greek prototype for the Roman god Jupiter) who between her and Zeus bore a daughter Athena.Template:Sfn 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 by 1998.Template:Sfn

Although the Juno orbiter, which arrived at Jupiter in 2016, has a camera called JunoCam, it is almost entirely focused on observations of Jupiter itself. During close observations of Jupiter, it may capture some distant images of the innermost moons Metis and Adrastea.<ref>Template:Cite journal</ref>

Physical characteristicsEdit

File:Metis moon.jpg

Metis imaged by Galileo on 4 January 2000

Metis has an irregular shape and measures Template:Val across, which makes it the second smallest of the four inner satellites of Jupiter.Template:Sfn Therefore, a very rough estimate of its surface area could be placed between 5,800 and 11,600 square kilometers (approx. 8,700).Template:Cn The bulk composition and mass of Metis are not known, but it is likely that its mean density is 1.5 g/cm³ or higher,Template:Sfn and its mass can therefore be estimated as ~6.4×10¹⁶ kg or higher.

The surface of Metis is heavily cratered, dark, and appears to be reddish in colorTemplate:Failed verification. There is a substantial asymmetry between the 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 excavates a bright material (presumably ice) from its interior.Template:Sfn

Orbit and rotationEdit

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 Jupiter's main ring. Metis's orbit has very small eccentricity (~0.0002) and inclination (~ 0.06°) relative to the equator of Jupiter.Template:Sfn Template:Sfn

Due to tidal locking, Metis rotates synchronously with its orbital period (about 7 hours), with its longest axis aligned towards Jupiter.Template:Sfn Template:Sfn Jupiter casts a shadow on all of Metis for 68 minutes each Metian day.Template:Efn

Metis lies inside Jupiter's synchronous orbit radius (as does Adrastea), and as a result, tidal forces slowly cause its orbit to decay. If its density is similar to Amalthea's, Metis's orbit lies within the fluid Roche limit; however, because it has not broken up, it must lie outside its rigid Roche limit.Template:Sfn

Relationship with Jupiter's ringsEdit

File:PIA09921 Shepherd Moons.gif

Metis orbiting at the edge of Jupiter's Main Ring, as imaged by the New Horizons spacecraft on 24 February 2007

Metis's orbit lies ~1,000 km within the main ring of Jupiter. It orbits within a ~500 km wide "gap" or "notch" in the ring.Template:Sfn Template:Sfn 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.Template:Sfn 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.Template:Sfn