In December 1999, scientists had their first solid evidence, a picture of a dust devil caught like a graffiti artist in the act of etching the surface of Mars. We've captured them in the midst of sweeping up dust and leaving behind a dark streak. This is the 'smoking gun' that explains the wild, sometimes twisted 'spaghetti' of dark streaks and trails we have been seeing. I get the feeling when I look at these pictures that something is 'moving'. These things send shivers down my spine.
Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars.
They form when the ground heats up during the day, warming the air immediately above the surface. As the warmed air nearest the surface begins to rise, it spins. The spinning column begins to move across the surface and picks up loose dust. On Earth, dust devils typically last for only a few minutes and the same is probably true for Mars. What is exciting about this dust devil finding is that we are witness to one of the processes that help explain cause of some of the seasonal variations in the bright and dark surfaces on Mars.