Question

Jupiter has sixteen satellites. What were the four largest ones discovered by Galileo?

Answer 1

In order of increasing distance from Jupiter: Io, Europa, Ganymede, Callisto.

Explanation:

Each of these Galilean moons (https://en.wikipedia.org/wiki/Galilean_moons) is an interesting world in its own right. Io, the most volcanically active body in the Solar System, has a unique yellowish surface from the sulfur emitted by the volcanoes that then condenses on the cold surface. The other three Galilean moons are all ice-covered but show evidence of liquid water beneath. The three icy Galilean moons are all considered candidates for life, especially Europa.