Nili Fossae in natural color and across the spectrum

This image of the Nili Fossae region was taken by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at 06:43 UTC on June 21, 2007 near 21.15° north latitude, 74.24° east longitude.

CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 20 meters (66 feet) across. The region covered is just over 10 kilometers (6.2 miles) wide at its narrowest point, and is one of several dozen that CRISM has taken to map the minerals present at candidate landing sites for the Mars Science Laboratory (MSL) mission, which will launch in 2010.
The Nili Fossae region is critical to understanding the history of water on Mars and whether water ever formed environments suitable for life, because the region is underlain by a layer of phyllosilicate (clay) minerals. This type of mineralogy formed where water was in contact with Mars' crustal rocks for very long periods, altering the silicates in volcanic rocks. In addition, phyllosilicates have the capability to encapsulate and preserve organic chemicals associated with life if life ever got started. Its rock record of an ancient wet environment makes Nili Fossae a top contender among the more than thirty landing sites currently being considered for MSL, whose objectives include measuring the chemistry preserved in an ancient wet environment.

This series of four different versions of the same 544-color image illustrates the mineral-mapping capability that comes from moving beyond the wavelength range of the human eye, and into infrared wavelengths where different minerals leave distinct "fingerprints" in reflected sunlight. In the version at the upper left, over three dozen of the distinct wavelengths measured by CRISM were combined to mimic the way the human eye would perceive the image.

The subtlety of the shading is because the Sun was high in Mars' sky when the image was taken, creating few shadows. The bland, butterscotch color comes from the dust coating nearly all of Mars' surface to some degree. In the version at the upper right, three infrared wavelengths (2.53, 1.50, and 1.08 micrometers) are used instead for the red, green, and blue image planes. These wavelengths are less sensitive to dust, and begin to show the spectral variations in the underlying rocks.

The two bottom versions combine different wavelengths to show strengths of absorptions due to the different minerals that are present, providing indications of the minerals' presence and distribution. The lower left version combines measurements of the strength of iron mineral absorptions at 0.53, 0.86, and 1.0 microns in the red, green, and blue image planes. Bluer areas have more of the mineral pyroxene, found in volcanic basaltic rock, whereas reddish and especially orange areas have more oxidized iron minerals. The lower right version combines measurements of mineral absorptions at 1.0, 1.9 and 2.3 microns in the red, green, and blue image planes. Redder areas are richer in pyroxene, and green and blue areas have greater contents of phyllosilicate minerals. The combination of basaltic rocks and highly altered phyllosilicates in close proximity would allow MSL to make detailed measurements of rocks formed in two distinct environments.

Source: Johns Hopkins University Applied Physics Laboratory
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