Jupiter’s Moons

Jupiter has at least 67 moons. Most are very small. The first 4 moons of Jupiter were discovered by Galileo and are thus called the Galilean moons. They are large, about the size of the Earth’s Moon. These and four more smaller moons all orbit over the equator and in the same direction as Jupiter spins. These 8 moons all probably formed with Jupiter like a Solar System in miniature.

Four more small moons orbit farther out, orbiting in the opposite direction were discovered before 1970, bringing the total to 12. In 1979 the Voyager space probe discovered 4 small irregularly shaped moons orbiting close to Jupiter. They are probably the source of the material for Jupiter’s rings. Since 1999 51 more smaller moons were discovered orbiting far from Jupiter and are either captured asteroids or the result of collisions.

Galilean Moons The Galilean moons come in two types: The Inner ones, Io and Europa are rocky like the inner planets. The outer ones, Ganymede and Callisto are made of lighter Icy materials. This is consistent with the mini-solar system formation theory

IO Io is the Galilean moon closest to Jupiter. It is just a little larger than Earth’s Moon. The Gravity of Jupiter and Europa play tug-o-war with Io heating its interior. This makes Io the most volcanically active object in the solar system. Volcanoes have even been observed erupting! Its surface is pocked with volcanoes and colored black, white, blue, yellow, orange and red sulfur compounds from the eruptions

The largest volcano is taller than Mount Everest and larger than New Jersey! Io orbits in Jupiter’s magnetic field generating up to 2 trillion watts of electricity in the Io flux Tube to Jupiter, and further heating IO’s interior.

Europa Like Io Europa’s interior structure is similar to Earth’s The tug-a-war between the Gravity of Jupiter and Ganymede heats its interior. Its surface is water ice that has cracked, built pressure ridges. This is evidence of a an ocean of water beneath the surface kept liquid by the internal heat In which there may be life!

Geysers of water ice…like water volcanoes have coated the surface with white “snow” Plans have been made to pierce the surface ice with an impact probe causing a Geyser so that the water beneath can be analyzed. More ambitious is a plan to pierce the surface and launch a submersible! Europa is just a little smaller than Earth’s moon.

Ganymede Ganymede is the largest of Jupiter’s Moons is also the largest in the Solar System Larger than Mercury! It is an icy version of our Moon. Its craters look white like when you poke a chunk of ice with an ice pick Ganymede has a thin atmosphere and is the only moon known to have a magnetic field. In 2015 Aurora were seen on Ganymede in such a way as to prove an ocean of water exists under the icy surface

Callisto Callisto is smaller icier version of Ganymede about the size of Mercury. It is the third largest Moon in the Solar System. It is covered in white ice craters. It is covered in ice that may have liquid water beneath it.