Over the course of time there are many things which can cause the surface of a planet to change its appearance.
- winds, as shown in the example The Great Dune of Pyla, a dune is a hill of sand built by wind (The surface of Mars is affected by wind,Monument Valley on Earth is an example)
- weather & water, which cause erosion
- volcanism, which pours out a new surface (The maria on Moon is an example)
- plate tectonics, or continental drift
- slow forces of deformation like those which cause mountains to form (The crust of Ganymede is an example)
- slumping of craters, mountains and volcanoes (The surface of Callisto is an example).
In their earliest histories, every planet & moon was bombarded with the remains of the material which formed them. If a planet’s surface does not showmany craters, it means that the surface is new, and the planet has been resurfaced, perhaps by one of the processes above. If the planet’s surface still shows themany craters left over from it’s formation, then that surface is very old, and has not been changed by any activityThe Great Dune of Pyla is the largest dune in Europe. source: windows to the universe