Jupiter, Io, and Ganymede's Shadow
Jupiter , the solar system 's largest planet, is seen here next to Io , its closest Galilean moon. On the cloud tops of Jupiter near the left edge of the picture can be seen a dark circular spot which is caused by the shadow of Jupiter 's largest moon Ganymede . Jupiter 's cloud tops show light bands and dark belts. The clouds are primarily composed of hydrogen and helium , but their intense colors are probably caused by very small amounts of heavier elements such as sulfur or organic (carbon-containing) compounds.