Io, which is slightly larger than Earth's moon, is the most colourful. Deposits from active volcanoes and volcanic vents, which are visible as small dark spots, cover its surface.

The bright white and bluish parts of Europa's surface are composed almost completely of ice. In contrast, the brownish mottled regions on the right may be covered by salts (such as hydrated magnesium sulphate) and an unknown red component. The yellowish mottled terrain on the left is caused by some other, unknown contaminant.

Ganymede, larger than Mercury, is the largest Jovian satellite. Its distinctive surface is characterised by patches of dark and light terrain. Bright frost is visible at the north and south poles. The very bright icy impact crater, Tros, is near the centre of the image in a region known as Phrygia Sulcus. The dark area to the northwest of Tros is Perrine Regio; the dark terrain to the south and southeast is Nicholson Regio.

Callisto's dark surface has numerous bright impact craters. The large Valhalla multi-ring structure (visible near the centre of the image) has a diameter of about 4,000 kilometres, making it one of the largest impact features in the solar system. Although many crater rims exhibit bright icy 'bedrock' material, a dark layer composed of hydrated minerals and organic components (tholins) is seen inside many craters and in other low-lying areas. Evidence of tectonic and volcanic activity, seen on the other Galilean satellites, appears to be absent on Callisto.