Metis , also known as , is the innermost known moon of Jupiter. It was discovered in 1979 in images taken by ''

Voyager 1 ''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and the interstellar medium, interstellar space beyond the Sun's heliosphere. It was launched 16 days afte ...

'', and was named in 1983 after the Titaness Metis, the first wife of

Zeus Zeus (, ) is the chief deity of the List of Greek deities, Greek pantheon. He is a sky father, sky and thunder god in ancient Greek religion and Greek mythology, mythology, who rules as king of the gods on Mount Olympus. Zeus is the child ...

and the mother of

Athena Athena or Athene, often given the epithet Pallas, is an ancient Greek religion, ancient Greek goddess associated with wisdom, warfare, and handicraft who was later syncretism, syncretized with the Roman goddess Minerva. Athena was regarde ...

. 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 Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

, 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 observations

Metis was discovered in 1979 by Stephen P. Synnott in images taken by the ''

'' probe and was provisionally designated as . In 1983, it was officially named after the mythological Metis, a Titaness who was the first wife of

(the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

prototype for the

Roman god Roman mythology is the body of myths of ancient Rome as represented in the Latin literature, literature and Roman art, visual arts of the Romans, and is a form of Roman folklore. "Roman mythology" may also refer to the modern study of these ...

) who between her and Zeus bore a daughter

. 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. Although the '' Juno'' orbiter, which arrived at Jupiter in 2016, has a camera called

JunoCam JunoCam (or JCM) is the visible-light camera/telescope onboard NASA, NASA's Juno (spacecraft), ''Juno'' spacecraft that entered orbit around Jupiter in 2016. The camera is operated by the JunoCam Digital Electronics Assembly (JDEA). Both the camer ...

, 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.

Physical characteristics

Metis has an irregular shape and measures across, which makes it the second smallest of the four inner satellites of Jupiter. Therefore, a very rough estimate of its surface area could be placed between 5,800 and 11,600 square kilometers (approx. 8,700). 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, 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 color. 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.

Orbit and rotation

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 Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

(~0.0002) and

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

(~ 0.06°) relative to the equator of Jupiter. Due to

tidal locking Tidal locking between a pair of co-orbiting astronomical body, astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where ...

, Metis rotates synchronously with its orbital period (about 7 hours), with its longest axis aligned towards Jupiter. Jupiter casts a shadow on all of Metis for 68 minutes each Metian day. Metis lies inside Jupiter's

synchronous orbit A synchronous orbit is an orbit in which an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body. Simplified meani ...

radius (as does Adrastea), and as a result,

tidal force The tidal force or tide-generating force is the difference in gravitational attraction between different points in a gravitational field, causing bodies to be pulled unevenly and as a result are being stretched towards the attraction. It is the ...

s slowly cause its orbit to decay. If its density is similar to Amalthea's, Metis's orbit lies within the fluid

Roche limit In celestial mechanics, the Roche limit, also called Roche radius, is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal force ...

; however, because it has not broken up, it must lie outside its rigid Roche limit.

Relationship with Jupiter's rings

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. 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. 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.

Notes

References

Citations

Sources

* * * * * (discovery) * (naming the moon) * * * *

External links

Metis Profile
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NASA's Solar System Exploration
{{DEFAULTSORT:Metis (Moon) Moons of Jupiter 19790304 Discoveries by Stephen P. Synnott Moons with a prograde orbit