The red polar caps of Io

An excellent series of Jupiter photographs obtained on August 9, 1973 showed Io to have red-brown polar caps, with the South Cap substantially larger than the North Cap. Reproductions are shown in the color Plate. The polar caps stand out by the color contrast against a white-bluish zone of Jupiter. When projected against a brown belt, only the truncated brighter equatorial region of the satellite is seen. Some 1968 images of Io also show the color of the polar caps directly.