Jupiter is the largest planet in the solar system. In fact, if you took the mass of all the other planets combined, they would not add up to the mass of Jupiter. Jupiter is a bright object when viewed from Earth. As in the case of Venus, this is because of the atmosphere is reflecting a large percentage of the sunlight striking it. When viewed through a telescope, the atmosphere of Jupiter shows stripes, dark and light bands across its surface. The stripes run parallel to the equator of Jupiter. In addition, a large spot is often seen on the surface of Jupiter. The "Great Red Spot" was seen by Galileo hundreds of years ago. It is still visible today.

Satellites have given us a better view of Jupiter and allowed us to see things we did not know existed. The cloud patterns on the Jovian surface show remarkable patterns of turbulence. These are due to the various wind directions in the Jovian atmosphere. They are especially interesting around the great red spot. Satellites have shown us that the great red spot is a storm much like a hurricane, which has lasted at least since the time of Galileo.

Analysis of Jupiter has shown us that it is mostly hydrogen and helium gas. Small amounts of other gases also appear and are likely the reason for the various Jovian colors. The structure of Jupiter, and indeed all Jovian planets, is layered. The central layer is a solid core. But this core is a small percentage of Jupiter's radius. Surrounding the core is a mantle of liquid metallic hydrogen. Outside this mantle is a layer of hydrogen and helium gas.

The liquid metallic hydrogen layer is critical to the magnetic field of Jupiter. Because of its metallic nature this layer of hydrogen conducts electricity. The electrical currents create the magnetic field of Jupiter. Combined with the rapid rotation of Jupiter, approximately 10 hours, and the huge layer of liquid metallic hydrogen, the magnetic field of Jupiter is 14 times stronger than the magnetic field here on Earth.

In general Jovian planets have multiple moons in their systems, and Jupiter is no exception. But four of Jupiter's moons stand out. These were the four moons first seen by Galileo almost 400 years ago. With Jupiter as a central body, these four moons and the rest of Jupiter's moons form a miniature solar system. From the smallest radial orbit out, these four moons are Io, Europa, Ganymede, and Callisto.

These four moons show characteristics very similar to the planets in orbit around the sun. The inner two moons, Io and Europa, have higher densities than the outer two moons. This gives them a characteristic similar to the terrestrial planets. The outer two moons, Ganymede and Callisto, have smaller densities and also show indications of a large liquid mantle underneath their exterior. They are larger than the inner two moons and seemed to show characteristics similar to the Jovian planets.

The innermost Moon is Io. Io is characterized by a very new (geologically) surface. The surface contains a multitude of volcanoes. The source of these volcanoes on the surface of Io is the gravitational force between Jupiter, Io, and the other moons of Jupiter. Since Io is near Jupiter, the gravitational force on the near side of Io is significantly different than the gravitational force on the far side of Io. These differences are referred to as tidal forces. The tidal forces stretch Io and warm it up much like an artist pounds on clay to soften it.

The second Moon is Europa. Much like Io, Europa suffers the tidal forces of Jupiter. However, since Europa is farther away the tidal forces have a smaller effect. The effect to Europa is that the icy surface of Europa is cracked. Europa therefore resembles a cue ball with tiny scratches on its surface filled with dirt. Europa is the smallest of the four Galilean satellites.

The third Moon of Jupiter is Ganymede. Ganymede of the largest Moon in the solar system. In fact Ganymede is larger than Pluto and Mercury. Being farther from Jupiter than Io or Europa, Ganymede is not as affected by Jupiter's tidal forces as the inner two moons. Ganymede does show signs of tectonic activity. But the surface is also covered by craters, indicating any tectonic activity was long ago.

The last of the Galilean satellites is Callisto. Callisto is pockmarked with craters indicating little to no tectonic activity now or in the past. The surface of Callisto also very dark, therefore reflecting very little of the light from the sun.

Finally in discussing the Jovian system, we find that Jupiter has a ring. This ring is much thinner than the ring system surrounding Saturn, but it does exist. This ring system was discovered by Voyager 1 during its fly by Jupiter. This ring system is temporary and has not always been around Jupiter. Therefore we theorize that the ring material is re-supplied by passing comets or small moonlets. The picture below was taken in the IR portion of the spectrum.

This page was last updated on 06/13/01.