Wind is the main geological process shaping the Mars' surface today. Wind-formed (aeolian) features include dunes and wind streaks.
At left: sand dunes photographed by Mars Rover, Opportunity.
On Earth, wind often develops in areas where thermal inertia suddenly changes, for example between sea and land. Without seas, the winds on Mars form where the thermal inertia of soil changes during the day (as the sun heats it up). Mars has morning and afternoon winds that sometimes create 'dust devils'.
'Dust devils' were photographed by the Mars Rovers, which explained the mysterious 'markings' photographed by Mars satellites - they were 'dust devil' trails. (see image above)
A rare photograph snapped by a satellite shows a dust devil 'creating' a trail.
Surface wind speeds on Mars were recorded by the Viking landers at 111 km per hour, though dust storm speeds are expected to reach between 200 and 400 km per hour.
The Rover's meteorological station includes an instrument to measure wind speed and direction - a 'tell-tale'.
'Dust devils' were responsible for the sudden increase in performance of the Mars Rover, Opportunity's solar panels - they were 'cleaned' of dust by a passing dust devil. (see image above)