Metis (moon)

Metis, also known as Jupiter XVI, is the closest known moon of Jupiter. It was found in 1979 in pictures taken by Voyager 1 and was named in 1983 after the Titaness Metis, the first wife of Zeus and the mother of Athena. This small moon orbits very close to Jupiter and is tidally locked to the planet. This means it always shows the same face to Jupiter.

Metis has a special shape that is not perfectly round; its largest part is almost twice as big as its smallest part. It is one of only two moons that orbit Jupiter faster than Jupiter spins, the other being Adrastea. Metis travels inside the main ring of Jupiter and is thought to help fill this ring with material. Scientists saw its surface when the Galileo spacecraft observed it between 1996 and 2003.

Discovery and observations

Metis was found in 1979 by Stephen P. Synnott using pictures from the Voyager 1 probe. It was first called S/1979 J 3 and later named after Metis, a mythological Titaness. Metis was the first wife of Zeus, the Greek god who is also called the Roman god Jupiter.

At first, the pictures from Voyager 1 only showed Metis as a tiny dot, so scientists knew very little about it. Later, the Galileo spacecraft took better pictures of Metis, letting scientists see almost all of its surface.

Physical characteristics

Metis has an uneven shape, about 60 km × 40 km × 34 km across. It is the second smallest of the four inner satellites of Jupiter. Scientists think it might be denser than water, but we do not know much about its composition and mass.

The surface of Metis is covered in many craters and looks dark and reddish. One interesting fact is that the front part of Metis (the part that faces forward as it travels around Jupiter) looks brighter than the back part. This may be because the front part experiences more impacts, which brings up brighter materials, possibly ice, from inside Metis.

Orbit and rotation

Metis is the closest of Jupiter's four small inner moons. It orbits Jupiter at a distance of about 128,000 km, very close to the planet. Its path around Jupiter is almost perfect, with very little stretching or tilting.

Metis always shows the same face to Jupiter because it is tidally locked. Each day, Jupiter's shadow covers Metis for about 68 minutes. Because Metis is so close to Jupiter, its orbit is slowly getting smaller over time.

Relationship with Jupiter's rings

Metis orbits very close to Jupiter, about 1,000 km inside the planet's main ring. Its path creates a gap in the ring, though scientists are still unsure why this happens. Metis helps supply dust to Jupiter's main ring. This dust comes from pieces thrown off the surfaces of Jupiter's small inner moons when meteorites hit them. Because these moons are close to the edge of their Roche spheres, the thrown material easily escapes into space.

Main article: Jupiter's four small inner satellites