Wind is the main process shaping the surface of the planet Mars today. Wind on Mars was suspected even before spacecraft explored the surface. Astronomers observed changes in the brightness of the planet over time and suspected that wind-borne dust clouded the atmosphere. The presence of winds was overwhelmingly confirmed when Mariner 9 arrived at Mars in the middle of a huge dust storm. The Mariner and Viking spacecraft also revealed surface features that were obviously wind-formed (aeolian), including various types of dunes and windstreaks.

Windstreaks are formed by the interaction of wind with surface features, such as the craters in this image. Notice the bright streaks and dark streaks, each extending in opposite directions. Windstreaks form downwind from the crater, either from deposition or erosion of fine debris. Windstreaks can therefore serve as a type of wind vane, indicating the prevailing wind direction when the streaks were formed. Windstreaks also change over time and can be used to gauge seasonal or long-term changes in surface wind direction.

Dunes

Dunes are widespread on Mars and are very similar in appearance to dunes on Earth. Like windstreaks, active dunes change over time and can indicate prevailing wind directions.

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Viking Orbiter image #VO-575B60

Dunes that lie inside craters, like this image of dunes in crater Kaiser, are known as intracrater dunes.