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Because Ganymede lacks a substantial atmosphere, its surface is exposed to the harsh space environment in the Jovian magnetosphere. Generally speaking, the space environment interacts with and alters the surface of any airless icy moon via four processes:

1. Sputtering and radiolysis by particle irradiation

2. Thermal sublimation

3. Micrometeoroid impacts

4. Photo-stimulated desorption

These interaction processes are important both for the surface itself and as sources for the neutral atmosphere and the ionosphere of Ganymede. The latter two will be covered in detailin chapters 16 (atmosphere) and 17 (ionosphere). The focus of this chapter lies on the surface interaction processes themselves.