Metis (moon)

Metis, also known as Jupiter XVI, 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. This small moon orbits very close to Jupiter and is tidally locked to the planet, meaning it always shows the same face to Jupiter.

Metis has a unique shape that is not perfectly round; its largest diameter is almost twice as large as its smallest one. It is one of only two moons that orbit Jupiter faster than Jupiter rotates on its axis, the other being Adrastea. Metis travels within the main ring of Jupiter and is believed to play a big role in supplying material to this ring. Scientists were able to see its surface when the Galileo spacecraft made observations between 1996 and 2003.

Discovery and observations

Metis was discovered in 1979 by Stephen P. Synnott using images from the Voyager 1 probe. It was given a temporary name, S/1979 J 3, before being officially named in 1983 after Metis, a mythological Titaness. Metis was the first wife of Zeus, the Greek god who is also known as the Roman god Jupiter.

At first, images from Voyager 1 only showed Metis as a small dot, so not much was known about it. Later, the Galileo spacecraft provided much better pictures of Metis, allowing scientists to see almost its whole surface.

Physical characteristics

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

The surface of Metis is covered in many craters and looks dark and reddish. One interesting feature is that the front part of Metis (the part that faces forward as it orbits Jupiter) looks brighter than the back part. This difference in brightness is likely 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 or notch 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