Images of a lava flow (left), and two volcanic plumes. The volcanic eruptions appear blue against the background of space and red when seen against Io itself.
Io: Galileo's close flybys of Jupiter's moon Io gave our world a close view of its volcanic vistas.
Io is the most volcanic world in the solar system and Galileo has given us all an incredible front row seat to the action. Galileo passed just 300 miles over the moon on its October 10th closest approach. It came even closer on November 25 (Thanksgiving Day), 1999. On February 22, 2000 it passed just 124 miles from Io!
Io is the only solid body in the solar system that has no known impact craters. Essentially all of the features seen upon its surface are due to its volcanic activity making far more active than our Earth.
A color image of the eruption of Tvashtar Catena (above) taken on November 25, 1999 can be found HERE.
A second color image of Tvashtar Catena was taken by Galileo on February 22, 2000. You can find it HERE
The trip to Io is filled with peril however. Galileo passed through high levels of radiation which is quite hard on the spacecraft. Galileo has received funding for the mission continue durnig 2000. Galileo did survive its February encounter with Io and it is hoped that it will be able to do joint observations with Cassini when it passes Jupiter in December, 2000.
Jupiter's moon Europa may be the only place in the solar system, besides our own Earth, with an ocean of liquid water. It is thought that the ocean lies underneath its exterior of water ice. Just how thick the icy crust is nobody knows. However, the speculation of the existence of Europa's ocean has led many to consider that Europa may be the most likely place in the solar system, asside from our Earth, to look for life.
Ganymede is the largest moon in the solar system and is even bigger than the planet Mercury. It displays some of the most fantastic features in the solar system. Its surface of rock and ice clearly has gone through periods of intense geologic activity. Notice the wide range of colorations in the image at left. The bright white spots are relatively recent impact craters. The number of impact craters suggest that all of Ganymede's activity has ended.
With a diameter of over 2,985 miles, Callisto (at right) is the third largest satellite in the solar system and is almost as big as the planet Mercury. Its surface of rock and ice shows the scars of billions of years of impacts which suggest that this world has never been active. Despite this, Galileo evidence suggests that it may have an ocean deep under its frozen surface.
Jupiter's rings are a far cry from those of Saturn. They are thin and difficult to see unless you happen to be at Jupiter. Apparently the only reason that they are there at all is because of Jupiter's small moons. The constant barrage of micrometeorites that impact into these moons kicks dust into orbit about Jupiter forming its rings.
It is important to remember that Jupiter is all atmosphere! It displays incredibly dynamic weather systems of very long life. The energy that powers weather here on Earth comes from the Sun. Jupiter is just over five times farther from the Sun than we are and so it gets much less solar energy. The energy source that powers Jupiter's atmosphere is Jupiter itself! Being a gaseous planet, Jupiter is slowly being squeezed from its own gravitational pull. This creates internal heat which powers its fantastic system of storms.
At right are some large white oval storms which were first observed in the 1930's. The leftmost of the ovals shown here is 5,592 miles across! This image was taken in 1997, the ovals later merged in 1998.
The most famous of Jupiter's weather systems is the Great Red Spot.
The Great Red Spot (GRS) has been known to exist for over 300 years. It spins in the counter-clockwise direction with a period of 6 days. Being a weather feature of Jupiter's southern hemisphere, this means that the GRS is a vast high pressure region. Recently it was determined that the spot itself, which is larger than our Earth, is ringed by Jovian thunderstorms.
Other Resources: