Color

Mars displays a reddish-orange color to the naked eye, but detailed observations show a range in color. The high-albedo surface regions (exclusive of the polar caps) appear reddish-ochre in color while the lower-albedo regions appear grayish. Color views of the planet (Figure 4.2) reveal three discrete units: bright red-ochre, dark gray, and intermediate. The intermediate units appear to be a mixture of the material comprising the bright and dark regions. Color contrast can be enhanced by ratioing the reflectivities obtained using different color filters (James et al., 1996; Bell et al., 1997). These color ratios indicate that the darker units can be subdivided into redder (red/ violet ratio ~ 3) and less red (red/violet ratio ~ 2) units. Redder dark units include the Tharsis volcanic region and the southern hemisphere highland plateau regions, while less red dark units are correlated with the intermediate-aged ridged plains (Soderblom, 1992). These color variations result from differences in both composition and grain size. The brighter regions are generally correlated with dust deposits while the darker regions correspond to basaltic-rich materials.

Figure 4.1 Mars displays variations in albedo across its surface, as revealed by MGS TES (Christensen et al., 2001a). (NASA/Arizona State University (ASU).)

Figure 4.2 Mars displays slight variations in color, as demonstrated in this MOC image taken at LS = 211° (northern autumn/southern spring) in May 2005. The bright south polar cap is visible at the bottom of the image. The dark feature in the center is the volcanic province Syrtis Major Planum and the brighter circular feature below Syrtis Major is the Hellas impact basin. (MOC Release MOC2-1094; NASA/MSSS.) See also color plate.

Figure 4.2 Mars displays slight variations in color, as demonstrated in this MOC image taken at LS = 211° (northern autumn/southern spring) in May 2005. The bright south polar cap is visible at the bottom of the image. The dark feature in the center is the volcanic province Syrtis Major Planum and the brighter circular feature below Syrtis Major is the Hellas impact basin. (MOC Release MOC2-1094; NASA/MSSS.) See also color plate.

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