What are dust devils?
The dark, narrow, thread-like stripes that can be seen in the images are the traces of small whirlwinds – known as dust devils – which are caused by atmospheric turbulence. Dust devils on Mars form in a similar way to their counterparts on Earth – as the Martian soil is warmed by sunlight during the day, the heated air rises, creating an updraught. Under certain conditions, this updraught then begins to rotate, causing a vertical vortex. Differences in atmospheric pressure create a suction effect, lifting any loose material from the surface. On Mars, this loose material is dust; on Earth it may also come in the form of sand or snow. When a dust devil moves across the Martian surface, it lifts a thin layer of light-coloured sand from the ground, exposing the darker underlying material. These narrow dark tracks mark the paths taken by dust devils.