Exposures taken through separate red, green, and blue filters and used to create a color image of Mars (lower right). The red filter shows the best surface detail. Because Mars' atmosphere scatters blue light (as on Earth) Martian surface detail is obscured in the blue filter exposure. The blue filter exposure does allow for clouds to be easily seen. A polar hood of clouds over Mars' north pole is evident, and a thin sheet of morning clouds is evident on the western limb (bottom).