  We study the morphological evolution of surfaces during ion sputtering and we
compare their dynamical roughening with aeolian ripple formation in sandy
deserts. We show that, although the two phenomena are physically different,
they must obey to similar geometrical constraints and therefore can be
described within the same theoretical framework. The present theory distinguish
between atoms that stay bounded in the bulk and others that are mobile on the
surface. We describe the excavation mechanisms, the adsorption and the surface
mobility by means of a continuous equation derived from the study of dune
formation on sand. This approach can explain the different dynamical behaviors
experimentally observed in metals or in semiconductors and amorphous systems.
We also show that this novel approach can describe the occurrence of ripple
rotation in the $(x,y)$ plane induced by changes in the sputtering incidence
angle.
