All of these satellites are tidally locked to their parent planet and therefore rotate with a period equal to the period of their revolution. From cosmochemical considerations it can be argued that silicate minerals should be present on the surfaces of these objects. Infrared spectra at wavelengths of 3 um and longer suggest that, indeed, silicate minerals such as olivine may be present on the surfaces of Callisto and Ganymede. All the icy satellites exhibit a strong absorption at ultraviolet wavelengths that is not attributable to water ice. Several possible sources for this absorption have been proposed including silicate minerals and iron-bearing minerals, but not firm identification has been made.
Environmental factors play an important role in altering the composition of satellite surfaces.
The principle consequence of this irradiation appears to be the buildup of oxygen in the surface ice which is manifested in a number of observables including UV and IR absorption by sulfur dioxide ice on Europa and Callisto, molecular oxygen and ozone trapped in the surface ice of Ganymede, possible IR absorption by carbon dioxide ice in Jupiter's satellites, indirect evidence for molecular oxygen atmospheres around Europa and Ganymede, and UV absorption by ozone trapped in the surface ice of Rhea and Dione. Micrometeorite gardening of the surface may also play a role particularly for Iapetus and Callisto. The most conspicuous inhomgeneity in either satellite system, the hemispheric dichotomy present on Iapetus, remains unexplained despite many attempts to do so.