The four great satellites of Jupiter, shown here at the same size in four color observations from the Galileo orbiter. They are shown in order from outermost to innermost. The Callisto portrait was taken during Galileo's 31st orbit (I31), on August 5, 2001. Ganymede is from the C9 flyby on June 26, 1997. Europa is from E14 on March 29, 1998. Io is from C9 on June 28, 1997.