Metis, also known as Jupiter XVI, is the first moon of Jupiter in order of distance from the planet. It was discovered on March 4th, 1979 in images taken by the Voyager 2 spacecraft.
Discovery and observations[]
Metis was discovered in 1979 by Stephen P. Synnott in images taken by the Voyager 2 probe. Metis was originally cataloged as S/1979 J 3 until In 1983 it was officially named Metis. Metis gets its name from mythological Metis, a Titaness who was the first wife of Zeus (the Greek equivalent of Jupiter). The photographs taken by Voyager 2 showed Metis only as a dot so very little information was known about Metis at the time. Then the Galileo spacecraft arrived at the Jovian system in 1995. Galileo imaged almost all of the surface of Metis and put constraints on its composition by 1998. Another spacecraft called Juno arrived at the Jovian system in 2016. This mission is mainly targeted at Jupiter itself not so much its moons. However, Metis could still appear in some of Juno's images against the clouds of Jupiter.
Orbit and rotation[]
Metis is the innermost moon of Jupiter. It orbits Jupiter at a distance of about 128,000 km (79535 mi) within Jupiter's main ring. Metis's orbit has very small eccentricity (~0.0002) and inclination (~ 0.06°) relative to the equator of Jupiter. Due to tidal locking, Metis rotates synchronously with its orbital period (about 7 hours), with its longest axis aligned towards Jupiter.
Metis lies inside Jupiter's synchronous orbit radius , 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.
Jupiter casts a shadow on all of Metis for 68 minutes each Metian day.
Relationship with Jupiter's rings[]
Metis's orbit lies about 1000 km within the main ring of Jupiter. It orbits within a 500 km wide gap or in the ring. The gap is clearly somehow related to the moon but the origin of this correlation is still unknown. Metis supplies a significant part of the main ring's material. 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 debris to be lost from the moons into space because the satellites' surfaces lie fairly close to the edge of their Roche spheres due to their low density.
Color Image of Metis by Galileo