This is an image of the Martian dunefields.
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What causes a Planet's surface to change?
Over the course of time there are many things which can cause the surface of a planet to change its appearance.
- winds can slowly wear erode a planet's surface.
- The surface of Mars is affected by wind.
- Monument Valley on Earth is an example
- weather & water cause more dramatic erosion.
- volcanism, which pours out a new surface
- The maria on the Moon are examples.
- plate tectonics, or continental drift
- slow forces of uplift & deformation similar to those which cause mountains to form.
- relaxation of craters, mountains and volcanoes.
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 show many 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 the many craters left over from it's formation, then that same surface was present during the ancient bombardment, and has not been changed by any activity.
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