Infrared spectra imply dark rock fragments.
Gas giants are also very much larger than terrestrial planets.
This color-enhanced image of Jupiter was taken by Voyager 1. Jovian System Voyager 1 took this photo of Jupiter and two of its satellites, Io on the left and Europa on the right. Although both satellites have about the same brightness, Io's color is different from Europa's. Io's equatorial region shows two shades of red, possibly indicating different surface materials. The colorful, wavy cloud pattern to the left of the Red Spot is a region of extraordinarily complex wave motion.