Tracks on Mars

Like others, I am getting used to pictures from the robotic explorers Spirit and Opportunity as they explore Mars. I was very struck though by this picture when I first saw it on Astronomy Picture of the Day.

I think I am struck because of seeing something that is so mundane in an Earthly context - wheel tracks - left on the pristine Martian surface. Sometimes the mundane becomes fascinating when it is encountered out of its usual context. (By now the Martian winds will have erased these tracks.)