The satellites discovered by Galileo with his small telescope form a small, `mini' solar system around Jupiter. They each have special characteristics related to their formation process, but have the following traits in common:
1) all orbit Jupiter
2) they all are tidally locked to Jupiter
3) they all have radii larger than our Moon
4) the inner moons have densities higher than outer moons (implies that Jupiter was much warmer in the past, such that the moons formed near Jupiter have less of the volatile elements such as CO2 and H2O)
Io is the innermost world, closest to Jupiter and can be classified as one of the most unusual moons in our solar system. Its unique properties include:
A hot spots associated with a volcanic features measure about 17 C (60 F). Scientists believe the hot spots may be lava lakes, although the temperature indicates the surface is not molten.
Europa is the next world out from Io and is considered a strong candidate to find primitive life. Its characteristics are:
Ganymede is much less dense than Europa or Io. Its interesting characteristics are:
Callisto is the outermost of the 4 primary satellites:
Summary of Galilean Moons:
Titan is the largest satellite of Saturn, unique in its methane atmosphere:
Above is a moasic of three frames taken by the lander as it entered Titans atmoshere. It shows detail of a high ridge area including the flow down a major river channel (liquid methane river) into what appears to be a "wet" plain.
The above image shows the boundary between lighter-colored uplifted terrain and drainage channels into the darker lower areas. This picture was taken from an altitude of 8 kilometers.
Above is a color image from the surface of Titan. Rocks near the bottom are pebble-sized, objects in the middle of the frame are meters in size. The surface is darker than expected, consisting of a mixture of water and hydrocarbon ice. There is evidence of erosion indicating fluid activity in the recent past.