What conclusions were reached about the nature of the four Galilean satellites in orbit around Jupiter when images were first sent back from exploring spacecraft?

Question

Quizplus · Accepted Answer

The Galilean satellites (Io, Europa, Ganymede, and Callisto) are indeed fundamentally different from each other and from anything previously seen. Io is volcanically active, Europa has a surface of ice that may cover an ocean of water, Ganymede is the largest moon in the solar system with its own magnetic field, and Callisto is heavily cratered. This diversity was unexpected and showed the complexity of celestial bodies in our solar system.

What Conclusions Were Reached About the Nature of the Four