Color Variations
Rocks and soils on the surface are thought to be composed of minerals
similar to those found on earth's surface. One of the most important tools for recognizing
these minerals is the spectrum of sunlight reflected by them. At the visible and
near-infrared light wavelengths measured by the Imager for Mars Pathfinder (IMP), the most
important coloring materials in the martian surface are iron minerals. There are two broad
classes of iron minerals. Minerals which occur in igneous rocks (such as pyroxene) have a
relatively flat spectrum and they reflect only a small amount of light; they are said to
have a low reflectance. Ferric iron minerals, which occur as weathering products, reflect
longer-wavelength light and absorb short-wavelength light, hence their very red color. The
relative brightnesses of Martian surface materials in IMP's different wavelength filter is
a powerful tool for recognizing the iron minerals present.