MARS - THREE COLOR COMPOSITE                      STSCI-PRC91-11
Wide Field/Planetary Camera

Exposures taken through separate red, green and blue filters are used
to create a color image of Mars.  The red filter shows the best surface
detail.  Mars' atmosphere scatters blue light, much like that of Earth,
thus Martian surface detail is obscured in the blue filter exposure
which permits clouds to be seen easily.  A polar hood of clouds over
Mars' north pole is evident and a thin sheet of morning clouds can be
seen on the western limb.