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Dark streaks, everywhere! Many Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images of the middle latitudes of the northern and southern hemispheres of Mars show wild patterns of criss-crossing dark streaks. Many of these streaks are straight and narrow, others exhibit curly arcs, twists, and loops. They often cross over hills, run straight across dunes and ripples, and go through fields of house-sized boulders. The picture is illuminated by sunlight from the lower left. It shows an area approximately 3 km by 5 km in Promethei Terra at a latitude of 58°S.
For many months the MOC science team was seeing streaks such as these, but were uncertain how they formed. Now it is known that they result from the passage of dust devils. Each dust devil leaves a dark streak by removing bright dust from the terrain in its path, revealing a darker surface underneath. Several dust devils were caught in action! Click here for an example.