Now go outside and look at the sky.
Just found this via the always great Bad Astronomy blog:
You have to click through for the larger version!
What you see here is the result of dust devils removing the red surface dust in graceful arcs, with the grey sand in this particular crater on Mars shining through. Now how cool is that?
Of course it could also be Martians doing donuts in their offroad vehicles, but for now we'll go with the other theory. :-)