... Explanation: This composite image features classic portraits of members of one of the Solar System's most prominent families - Jupiter and its four large "Galilean" moons. Starting from the top the moons are Io , Europa , Ganymede , and Callisto . ... The smallest of the lot, Europa, is the size of Earth's moon while Ganymede is the largest moon in the Solar System. ... The other portraits were taken by the Galileo spacecraft which began exploring the Jovian system in 1995. ... 1995 1996 . ...