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.
In their earliest histories, every planet & moon was hit with the leftover material from their start. If a planet's surface does not show many craters it is younger because it was not around while the planet was being hit. If the planet's surface still shows many craters, they are left over from it's beginning, and the surface is very old.
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