Io, Europa, Ganymede, and Callisto

In March 1979, as Voyager 1 cruised by Jupiter, the spacecraft captured photos of the planet's four largest moons: Io, Europa, Ganymede, and Callisto.

Although Jupiter has 63 moons in all, these four large Galilean satellites are the largest, with diameters of around 3,000 to 5,000 kilometers, and were discovered in 1610 by Galileo Galilei.

The moons, shown in relative size to each other, were the first objects found to orbit a body other than the Earth or sun.